View source for Engineering:De Havilland Comet

{{Short description|First commercial jet airliner}}
{{DISPLAYTITLE:de Havilland Comet}}
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{|{{Infobox aircraft begin
 |name = DH.106 Comet
 |image = File:BEA de Havilland DH-106 Comet 4B Berlin.jpg
 |caption = British European Airways (BEA) Comet 4B arriving at Berlin Tempelhof Airport in 1969
}}{{Infobox aircraft type
 |type = [[Engineering:Narrow-body aircraft|Narrow-body]] jet airliner
 |manufacturer = de Havilland
 |national origin = United Kingdom
 |first flight = 27 July 1949
 |introduced = 2 May 1952 with BOAC
 |retired = 14 March 1997 (Comet 4C XS235)<ref name=walker169/>
 |status = Retired
 |primary user = BOAC
 |more users = {{plainlist|
*British European Airways
*Dan-Air
*{{wipe|Royal Air Force}}}}
 |produced = 1949–1964
 |number built = 114 (including prototypes)<ref name=bao>Lo Bao 1996, pp. 36–47.</ref>{{refn|Total of Comets in production: 114,<ref name =bao/> or 136 (when including refitting of original airframes and conversions).<ref>Walker 2000, pp. 185–190.</ref>|group=N}}
 |variants with their own articles = 
 |developed into = [[Engineering:Hawker Siddeley Nimrod|Hawker Siddeley Nimrod]]
}}
|}

The '''de Havilland DH.106 Comet''' is the world's first commercial jet airliner. Developed and manufactured by de Havilland in the United Kingdom, the Comet 1 prototype first flew in 1949. It features an aerodynamically clean design with four [[Engineering:De Havilland Ghost|de Havilland Ghost]] [[Engineering:Turbojet|turbojet]] engines buried in the wing roots, a [[Engineering:Cabin pressurization|pressurised cabin]], and large windows. For the era, it offered a relatively quiet, comfortable passenger cabin and was commercially promising at its debut in 1952.

Within a year of the airliner's entry into service, three Comets were lost in highly publicized accidents after suffering catastrophic mishaps mid-flight. Two of these were found to be caused by structural failure resulting from metal fatigue in the [[Engineering:Airframe|airframe]], a phenomenon not fully understood at the time; the other was due to overstressing of the airframe during flight through severe weather. The Comet was withdrawn from service and extensively tested. Design and construction flaws, including improper [[Engineering:Rivet|rivet]]ing and dangerous [[Physics:Stress concentration|stress concentration]]s around square cut-outs for the ADF (automatic direction finder) antennas were ultimately identified. As a result, the Comet was extensively redesigned, with structural reinforcements and other changes. Rival manufacturers heeded the lessons learned from the Comet when developing their own aircraft.

Although sales never fully recovered, the improved Comet&nbsp;2 and the prototype Comet&nbsp;3 culminated in the redesigned Comet&nbsp;4 series which debuted in 1958 and remained in commercial service until 1981. The Comet was also adapted for a variety of military roles such as VIP, medical and passenger transport, as well as surveillance; the last Comet 4, used as a research platform, made its final flight in 1997. The most extensive modification resulted in a specialised maritime patrol derivative, the [[Engineering:Hawker Siddeley Nimrod|Hawker Siddeley Nimrod]], which remained in service with the {{wipe|Royal Air Force}} until 2011, over 60 years after the Comet's first flight.

==Development==

===Origins===
[[File:Design Studies for the DH 106 Comet.jpg|thumb|upright=1.7|Design studies for the DH.106 Comet 1944–1947 (artist's impression)]]

On 11 March 1943, the Cabinet of the United Kingdom formed the Brabazon Committee, which was tasked with determining the UK's airliner needs after the conclusion of the Second World War.<ref name=TH88>Trischler and Helmuth 2003, p. 88.</ref> One of its recommendations was for the development and production of a pressurised, transatlantic mailplane that could carry {{cvt|1|LT|lb kg}} of payload at a cruising speed of {{cvt|400|mph}} non-stop.<ref name=Birtles124>Birtles 1970, p. 124.</ref> Aviation company de Havilland was interested in this requirement, but chose to challenge the then widely held view that [[Engineering:Jet engine|jet engine]]s were too fuel-hungry and unreliable for such a role.{{refn|During the same era, both Lockheed with their [[Engineering:Lockheed L-188 Electra|Lockheed L-188 Electra]] and Vickers with the ground-breaking [[Engineering:Vickers Viscount|Vickers Viscount]] discounted the advantages of "pure" jet power to develop [[Engineering:Turboprop|turboprop]]-powered airliners.<ref>Kodera et al. 2010, p. 16.</ref>|group=N}} As a result, committee member Sir Geoffrey de Havilland, head of the de Havilland company, used his personal influence and his company's expertise to champion the development of a jet-propelled aircraft; proposing a specification for a pure [[Engineering:Turbojet|turbojet]]-powered design.<ref name=TH88/>

The committee accepted the proposal, calling it the "Type IV" (of five designs),{{refn|The "Type IV" Specifications issued on 3 February 1943 provided for a "high-speed mail-carrying airliner, gas-turbine powered."<ref name=Jones60>Jones 2010, p. 60.</ref>|group=N}} and in 1945 awarded a development and production contract to de Havilland under the designation ''Type 106''. The type and design were to be so advanced that de Havilland had to undertake the design and development of ''both'' the airframe and the engines. This was because in 1945 no turbojet engine manufacturer in the world was drawing-up a design specification for an engine with the thrust and specific fuel consumption that could power an aircraft at the proposed cruising altitude ({{cvt|40000|ft}}), speed, and transatlantic range as was called for by the Type 106.<ref>Jackson 1988, p. 453.</ref> First-phase development of the DH.106 focused on short- and intermediate-range mailplanes with small passenger compartments and as few as six seats, before being redefined as a long-range airliner with a capacity of 24 seats.<ref name=Birtles124/> Out of all the Brabazon designs, the DH.106 was seen as the riskiest: both in terms of introducing untried design elements and for the financial commitment involved.<ref name=TH88/> Nevertheless, the British Overseas Airways Corporation (BOAC) found the Type IV's specifications attractive, and initially proposed a purchase of 25 aircraft; in December 1945, when a firm contract was created, the order total was revised to 10.<ref name=Jones62>Jones 2010, p. 62.</ref>

{{Quote box|align=left|width=21%|quote="During the next few years, the UK has an opportunity, which may not recur, of developing aircraft manufacture as one of our main export industries. On whether we grasp this opportunity and so establish firmly an industry of the utmost strategic and economic importance, our future as a great nation may depend."|source=<small>Duncan Sandys, Minister of Supply, 1952.<ref name=TH90/></small>}}
A design team was formed in 1946 under the leadership of chief designer Ronald Bishop, who had been responsible for the [[Engineering:De Havilland Mosquito|Mosquito]] fighter-bomber.<ref name=Jones62/> Several unorthodox configurations were considered, ranging from [[Engineering:Canard (aeronautics)|canard]] to [[Engineering:Tailless aircraft|tailless]] designs;{{refn|From 1944 to 1946, the design group prepared submissions on a three-engined twin-boom design, a three-engined canard design with engines mounted in the rear, and a tailless design that featured a [[Engineering:Swept wing|swept wing]] and four "[[Engineering:Podded engine|podded]]" engines.<ref name=Jones62/>|group=N}} All were rejected. The Ministry of Supply was interested in the most radical of the proposed designs, and ordered two experimental tailless [[Engineering:De Havilland DH 108|DH 108]]s{{refn|The Ministry of Supply's order for DH 108s was listed as Operational Requirement OR207 to Specification E.18/45.<ref name=watkins39/>|group=N}} to serve as [[Proof of concept|proof of concept]] aircraft for testing swept-wing configurations in both low-speed and high-speed flight.<ref name=Birtles124/><ref name=watkins39>Watkins 1996, p. 39.</ref> During flight tests, the DH 108 gained a reputation for being accident-prone and unstable, leading de Havilland and BOAC to gravitate to conventional configurations and, necessarily, designs with less technical risk.<ref>Darling 2001, p. 11.</ref> The DH 108s were later modified to test the DH.106's power controls.<ref name=Birtles125/>

In September 1946, before completion of the DH 108s, BOAC requests necessitated a redesign of the DH.106 from its previous 24-seat configuration to a larger 36-seat version.<ref name=Birtles124/>{{refn|BOAC's requested capacity increase was known as Specification 22/46.<ref name=Birtles124/>|group=N}} With no time to develop the technology necessary for a proposed tailless configuration, Bishop opted for a more conventional 20-degree swept-wing design{{refn|The wing was drastically redesigned from a 40˚ sweep.<ref name=Jones62–63/>|group=N}} with unswept tail surfaces, married to an enlarged fuselage accommodating 36 passengers in a four-abreast arrangement with a central aisle.<ref name=Winchester109/> Replacing previously specified [[Engineering:De Havilland Goblin|Halford H.1 Goblin]] engines, four new, more-powerful [[Engineering:Rolls-Royce Avon|Rolls-Royce Avon]]s were to be incorporated in pairs buried in the wing roots; [[Engineering:De Havilland Ghost|Halford H.2 Ghost]] engines were eventually applied as an interim solution while the Avons cleared certification. The redesigned aircraft was named the DH.106 ''Comet'' in December 1947.{{refn|The name "Comet", previously used by the de Havilland DH.88 racing aircraft, was revived.<ref>Jackson 1988, p. 356.</ref>|group=N}} Revised first orders from BOAC and British South American Airways{{refn|British South American Airways merged with BOAC in 1949.<ref name=Birtles124/>|group=N}} totalled 14 aircraft, with delivery projected for 1952.<ref name=Jones62–63>Jones 2010, pp. 62–63.</ref>

===Testing and prototypes===
As the Comet represented a new category of passenger aircraft, more rigorous testing was a development priority.<ref name=d17/> From 1947 to 1948, de Havilland conducted an extensive research and development phase, including the use of several stress test rigs at Hatfield Aerodrome for small components and large assemblies alike. Sections of pressurised fuselage were subjected to high-altitude flight conditions via a large [[Physics:Pressure vessel|decompression chamber]] on-site {{refn|The fuselage sections and nose simulated a flight up to {{cvt|70000|ft}} at a temperature of {{cvt|−70|°C|°F}}, with {{cvt|2000|lb}} pressure applications at {{cvt|9|psi}}.<ref name=Birtles125>Birtles 1970, p. 125.</ref>|group=N}} and tested to failure.<ref name=d18/> Tracing fuselage failure points proved difficult with this method,<ref name=d18/> and de Havilland ultimately switched to conducting structural tests with a water tank that could be safely configured to increase pressures gradually.<ref name=Birtles125/><ref name=d18/><ref>{{citation |url=http://www.flightglobal.com/pdfarchive/view/1955/1955%20-%201835.html |title=Tank Test Mk 2. |work=Flight |publisher=Iliffe |date=30 December 1955 |pages=958–959 |access-date=26 April 2012 |archive-url=https://web.archive.org/web/20190131201738/https://www.flightglobal.com/pdfarchive/view/1955/1955%20-%201835.html |archive-date=31 January 2019}}</ref> The entire forward fuselage section was tested for metal fatigue by repeatedly pressurising to {{convert|2.75|psi|kPa}} overpressure and depressurising through more than 16,000 cycles, equivalent to about 40,000 hours of airline service.<ref name=DaviesandBirtles>Davies and Birtles 1999, p. 30.</ref> The windows were also tested under a pressure of {{cvt|12|psi|kPa}}, {{cvt|4.75|psi|kPa}} above expected pressures at the normal service ceiling of {{cvt|36000|ft}}.<ref name=DaviesandBirtles/> One window frame survived {{cvt|100|psi|kPa}},<ref>{{citation|url=https://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200556.html |title=Comet Engineering |publisher=Iliffe |via=FlightGlobal Archive |work=Flight |date=1 May 1953 |access-date=23 March 2019 |page=552 |archive-url=https://web.archive.org/web/20170202030058/https://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200556.html |archive-date=2 February 2017}}</ref> about 1,250 per cent over the maximum pressure it was expected to encounter in service.<ref name=DaviesandBirtles/>

[[File:Comet Prototype at Hatfield.jpg|thumb|left|Comet 1 prototype (with square windows) at Hatfield Aerodrome in October 1949]]

The first prototype DH.106 Comet (carrying [[Engineering:United Kingdom aircraft test serials|Class B markings]] G-5-1) was completed in 1949 and was initially used to conduct ground tests and brief early flights.<ref name=d18>Darling 2001, p. 18.</ref> The prototype's maiden flight, out of Hatfield Aerodrome, took place on 27 July 1949 and lasted 31 minutes.<ref>Dick and Patterson 2010, pp. 134–137.</ref><ref name=green174>Green and Swanborough April 1977, p. 174.</ref> At the controls was de Havilland chief test pilot John "Cats Eyes" Cunningham, a famous night-fighter pilot of the Second World War, along with co-pilot Harold "Tubby" Waters, engineers John Wilson (electrics) and Frank Reynolds (hydraulics), and flight test observer [[Biography:Tony Fairbrother|Tony Fairbrother]].<ref>Prins 1998, p. 43.</ref>

The prototype was [[Engineering:United Kingdom aircraft registration|registered]] G-ALVG just before it was publicly displayed at the 1949 Farnborough Airshow before the start of flight trials. A year later, the second prototype G-5-2 made its maiden flight. The second prototype was registered G-ALZK in July 1950 and it was used by the BOAC Comet Unit at Hurn from April 1951 to carry out 500 flying hours of crew training and route-proving.<ref>Swanborough 1962, p. 45.</ref> Australian airline [[Company:Qantas|Qantas]] also sent its own technical experts to observe the performance of the prototypes, seeking to quell internal uncertainty about its prospective Comet purchase.<ref>Gunn 1987, p. 268.</ref> Both prototypes could be externally distinguished from later Comets by the large single-wheeled main landing gear, which was replaced on production models starting with G-ALYP by four-wheeled [[Engineering:Bogie#Bogie (aircraft)|bogies]].<ref name=Walker25/>
{{Clear}}

==Design==

===Overview===
[[File:Museum of Flight DH Comet interior.jpg|thumb|upright|Dan-Air Comet 4C cabin at the National Museum of Flight]]
The Comet was an all-metal low-wing cantilever monoplane powered by four jet engines; it had a four-place cockpit occupied by two pilots, a flight engineer, and a navigator.<ref name=francis99/> The clean, low-drag design of the aircraft featured many design elements that were fairly uncommon at the time, including a swept-wing leading edge, integral wing fuel tanks, and four-wheel bogie main undercarriage units designed by de Havilland.<ref name=francis99>Francis 1950, p. 99.</ref> Two pairs of turbojet engines (on the Comet 1s, Halford H.2 Ghosts, subsequently known as de Havilland Ghost 50 Mk1s) were buried into the wings.<ref name=francis100-101>Francis 1950, pp. 100–101.</ref>

The original Comet was the approximate length of, but not as wide as, the later [[Engineering:Boeing 737|Boeing 737-100]], and carried fewer people in a significantly more-spacious environment. BOAC installed 36 reclining "slumberseats" with {{cvt|45|in|mm}} centres on its first Comets, allowing for greater leg room in front and behind;<ref>Hill 2002, p. 27.</ref> Air France had 11 rows of seats with four seats to a row installed on its Comets.<ref name=popmech149>Cookman, Aubery O. Jr. [https://books.google.com/books?id=6NkDAAAAMBAJ&pg=PA149 "Commute by Jet."] ''Popular Mechanics'', 93(4), April 1950, pp. 149–152.</ref> Large picture window views and table seating accommodations for a row of passengers afforded a feeling of comfort and luxury unusual for transportation of the period.<ref>Smith 2010. 30(4), pp. 489, 506.</ref> Amenities included a [[Engineering:Galley (kitchen)|galley]] that could serve hot and cold food and drinks, a bar, and separate men's and women's toilets.<ref name=francis98>Francis 1950, p. 98.</ref> Provisions for emergency situations included several life rafts stored in the wings near the engines, and individual [[Engineering:Personal flotation device|life vest]]s were stowed under each seat.<ref name=francis99/>

One of the most striking aspects of Comet travel was the quiet, "vibration-free flying" as touted by BOAC.<ref name=walker69>Walker 2000, p. 69.</ref>{{refn|BOAC flight crew revelled in standing a pen on end and pointing that out to passengers; invariably, the pen remained upright throughout the entire flight.<ref>Windsor-Liscombe, Rhodri. [http://pi.library.yorku.ca/ojs/index.php/topia/article/view/2680/1885 "Usual Culture: The Jet."] ''Topia: Canadian Journal of Cultural Studies (Toronto: York University)'', Number 11, Spring 2004. Retrieved 26 April 2012.</ref> |group=N}} For passengers used to propeller-driven airliners, smooth and quiet jet flight was a novel experience.<ref name=francis100>Francis 1950, p. 100.</ref>

===Avionics and systems===
For ease of training and fleet conversion, de Havilland designed the Comet's flight deck layout with a degree of similarity to the [[Engineering:Lockheed Constellation|Lockheed Constellation]], an aircraft that was popular at the time with key customers such as BOAC.<ref name=d18/> The cockpit included full dual-controls for the captain and first officer, and a flight engineer controlled several key systems, including fuel, air conditioning and electrical systems.<ref>Darling 2001, pp. 35–36.</ref> The navigator occupied a dedicated station, with a table across from the flight engineer.<ref name=d36>Darling 2001, p. 36.</ref>

[[File:De Havilland DH106 Comet 4 G-APDB Cockpit.JPG|left|thumb|The flight deck of a Comet 4]]
Several of the Comet's avionics systems were new to civil aviation. One such feature was irreversible, powered flight controls, which increased the pilot's ease of control and the safety of the aircraft by preventing aerodynamic forces from changing the directed positions and placement of the aircraft's control surfaces.<ref>Abzug and Larrabee 2002, pp. 80–81.</ref> Many of the control surfaces, such as the elevators, were equipped with a complex gearing system as a safeguard against accidentally over-stressing the surfaces or airframe at higher speed ranges.<ref>Darling 2001, p. 2.</ref>

The Comet had a total of four hydraulic systems: two primaries, one secondary, and a final emergency system for basic functions such as lowering the undercarriage.<ref>Darling 2001, pp. 16–17.</ref> The undercarriage could also be lowered by a combination of gravity and a hand-pump.<ref>Darling 2001, p. 40.</ref> Power was syphoned from all four engines for the hydraulics, cabin [[Physics:Air conditioning|air conditioning]], and the de-icing system; these systems had operational [[Engineering:Redundancy (engineering)|redundancy]] in that they could keep working even if only a single engine was active.<ref name=d17>Darling 2001, p. 17.</ref> The majority of hydraulic components were centred in a single avionics bay.<ref>Darling 2001, p. 45.</ref> A pressurised refuelling system, developed by Flight Refuelling Ltd, allowed the Comet's fuel tanks to be refuelled at a far greater rate than by other methods.<ref>[http://www.flightglobal.com/pdfarchive/view/1951/1951%20-%200887.html "F.R. equipment speeds refuelling."] ''Flight,'' 11 May 1951. Retrieved 26 April 2012.</ref>

[[File:DeHavillandCometCockpit.jpg|thumb|The Comet 4 navigator's station]]
The cockpit was significantly altered for the Comet 4's introduction, on which an improved layout focusing on the onboard navigational suite was introduced.<ref name=d40>Darling 2001, pp. 40–41.</ref> An EKCO E160 [[Engineering:Radar|radar]] unit was installed in the Comet 4's [[Engineering:Nose cone|nose cone]], providing search functions as well as ground and cloud-mapping capabilities,<ref name=d36/> and a radar interface was built into the Comet 4 cockpit along with redesigned instruments.<ref name=d40/>

Sud-Est's design bureau, while working on the [[Engineering:Sud Aviation Caravelle|Sud Aviation Caravelle]] in 1953, licensed several design features from de Havilland, building on previous collaborations on earlier licensed designs, including the [[Engineering:De Havilland Vampire|DH 100 Vampire]];{{refn|The Sud-Est SE 530/532/535 Mistral (FB 53) was a single-seat fighter-bomber version of the de Havilland Vampire jet fighter, used by ''{{wipe|French Air Force}}''.<ref>Watkins 1996, pp. 181–182.</ref>|group=N}} the nose and cockpit layout of the Comet 1 was grafted onto the Caravelle.<ref>Motem 1990, p. 143.</ref> In 1969, when the Comet 4's design was modified by Hawker Siddeley to become the basis for the Nimrod, the cockpit layout was completely redesigned and bore little resemblance to its predecessors except for the control yoke.<ref>Darling 2001, p. 96.</ref>

===Fuselage===
Diverse geographic destinations and cabin pressurisation alike on the Comet demanded the use of a high proportion of alloys, plastics, and other materials new to civil aviation across the aircraft to meet certification requirements.<ref name=engineering>[http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200555.html "Comet Engineering: The Performance of Airframe, Engines, and Equipment in Operational Service."] ''Flight International,'' 1 May 1953, p. 551. Retrieved 26 April 2012.</ref> The Comet's high cabin pressure and fast operating speeds were unprecedented in commercial aviation, making its fuselage design an experimental process.<ref name=engineering/> At its introduction, Comet airframes would be subjected to an intense, high-speed operating schedule which included simultaneous extreme heat from desert airfields and frosty cold from the kerosene-filled fuel tanks, still cold from cruising at high altitude.<ref name=engineering/>

[[File:De Havilland Comet RAF Museum Cosford (1).jpg|thumb|left|A Comet 1's fuselage and de Havilland Ghost engine intakes]]
The Comet's thin metal skin was composed of advanced new alloys{{refn|Fuselage alloys detailed in Directorate of Technical Development 564/L.73 and DTD 746C/L90.|group=N}} and was both riveted and chemically bonded, which saved weight and reduced the risk of fatigue cracks spreading from the rivets.<ref>[http://www.rafmuseum.org.uk/online-exhibitions/comet/comet2.cfm "Comet Enters Service."] {{webarchive |url=https://web.archive.org/web/20090922200849/http://www.rafmuseum.org.uk/online-exhibitions/comet/comet2.cfm |date=22 September 2009}} ''{{wipe|Royal Air Force Museum Cosford}}''. Retrieved 1 November 2010.</ref> The chemical bonding process was accomplished using a new [[Chemistry:Adhesive|adhesive]], [[Physics:Redux (adhesive)|Redux]], which was liberally used in the construction of the wings and the fuselage of the Comet; it also had the advantage of simplifying the manufacturing process.<ref>Moss, C. J. [http://www.flightglobal.com/pdfarchive/view/1951/1951%20-%200269.html "Metal to Metal Bonding – For Aircraft Structures: Claims of the Redux Process."] ''Flight International'', 8 February 1951, p. 169. Retrieved 26 April 2012.</ref>

When several of the fuselage alloys were discovered to be vulnerable to weakening via metal fatigue, a detailed routine inspection process was introduced. As well as thorough visual inspections of the outer skin, mandatory structural sampling was routinely conducted by both civil and military Comet operators. The need to inspect areas not easily viewable by the naked eye led to the introduction of widespread [[Physics:Radiography|radiography]] examination in aviation; this also had the advantage of detecting cracks and flaws too small to be seen otherwise.<ref>Jefford 2001, pp. 123–125.</ref>

Operationally, the design of the cargo holds led to considerable difficulty for the ground crew, especially baggage handlers at the airports. The cargo hold had its doors located directly underneath the aircraft, so each item of baggage or cargo had to be loaded vertically upward from the top of the baggage truck, then slid along the hold floor to be stacked inside. The individual pieces of luggage and cargo also had to be retrieved in a similarly slow manner at the arriving airport.<ref>Birtles 1970, p. 132.</ref><ref>Jones 2010, p. 67.</ref>

{{Anchor|Engines}}
===Propulsion===

The Comet was powered by two pairs of turbojet engines buried in the wings close to the fuselage. Chief designer Bishop chose the Comet's embedded-engine configuration because it avoided the drag of [[Engineering:Podded engine|podded engine]]s and allowed for a smaller fin and rudder since the hazards of asymmetric thrust were reduced.<ref name=francis101-102>Francis 1950, pp. 101–102.</ref> The engines were outfitted with [[Physics:Sound baffle|baffle]]s to reduce noise emissions, and extensive [[Physics:Soundproofing|soundproofing]] was also implemented to improve passenger conditions.<ref>Darling 2001, pp. 35, 46.</ref>

[[File:De Havilland Comet pic 1 REJS.jpg|thumb|The Comet 4's enlarged Rolls-Royce Avon engine intakes]]
Placing the engines within the wings had the advantage of a reduction in the risk of foreign object damage, which could seriously damage jet engines. The low-mounted engines and good placement of service panels also made aircraft maintenance easier to perform.<ref name=Withuhn88/> The Comet's buried-engine configuration increased its structural weight and complexity. Armour had to be placed around the engine cells to contain debris from any serious engine failures; also, placing the engines inside the wing required a more complicated wing structure.<ref name=francis103>Francis 1950, p. 103.</ref>

The Comet 1 featured {{cvt|5050|lbf|kN}} de Havilland Ghost 50 Mk1 turbojet engines.<ref name=francis100-101/><ref>[http://www.rafmuseum.org.uk/online-exhibitions/comet/comet3.cfm "Ghost engine."] {{webarchive|url=https://web.archive.org/web/20100204110840/http://www.rafmuseum.org.uk/online-exhibitions/comet/comet3.cfm |date=4 February 2010}} ''Royal Air Force Museum Cosford''. Retrieved 1 November 2010.</ref> Two [[Chemistry:Hydrogen peroxide|hydrogen peroxide]]-powered de Havilland Sprite booster rockets were originally intended to be installed to boost [[Engineering:Takeoff|takeoff]] under [[Engineering:Hot and high|hot and high]] altitude conditions from airports such as Khartoum and Nairobi.<ref name=popmech149/><ref name=francis98-102>Francis 1950, pp. 98–102.</ref> These were tested on 30 flights, but the Ghosts alone were considered powerful enough and some airlines concluded that rocket motors were impractical.<ref name=Birtles125/> Sprite fittings were retained on production aircraft.<ref>Gunn 1987, p. 269.</ref> Comet 1s subsequently received more powerful {{cvt|5700|lbf|kN}} Ghost DGT3 series engines.<ref name=walker190/>

From the Comet 2 onward, the Ghost engines were replaced by the newer and more powerful {{cvt|7000|lbf|kN}} Rolls-Royce Avon AJ.65 engines. To achieve optimum efficiency with the new powerplants, the air intakes were enlarged to increase mass air flow.<ref name=d33/> Upgraded Avon engines were introduced on the Comet 3,<ref name=d33/> and the Avon-powered Comet 4 was highly praised for its takeoff performance from high-altitude locations such as Mexico City where it was operated by Mexicana de Aviacion, a major scheduled passenger air carrier.<ref>[https://www.timetableimages.com/ttimages/mx/mx60/mx60-5.jpg En route] Time Table Images</ref><ref>[https://books.google.com/books?id=qiEDAAAAMBAJ&pg=RA1-PA52 "Comet Gets Stronger Engines."] ''Popular Science'', 160(6), June 1952, p. 142.</ref>

==Operational history==

===Introduction===
The earliest production aircraft, registered G-ALYP ("Yoke Peter"), first flew on 9 January 1951 and was subsequently lent to BOAC for development flying by its Comet Unit.<ref name=DaviesandBirtles31>Davies and Birtles 1999, p. 31.</ref> On 22 January 1952, the fifth production aircraft, registered G-ALYS, received the first Certificate of Airworthiness awarded to a Comet, six months ahead of schedule.<ref name=DaviesandBirtles34>Davies and Birtles 1999, p. 34.</ref> On 2 May 1952, as part of BOAC's route-proving trials, G-ALYP took off on the world's first jetliner{{refn|The [[Engineering:Avro Canada C102 Jetliner|Avro Canada C102 Jetliner]], for which it was coined, first used the term; "jetliner" later became a generic term for all jet airliners.<ref>Floyd 1986, p. 88.</ref>|group=N}} flight with fare-paying passengers and inaugurated scheduled service from London to Johannesburg.<ref name=McNeil2002,39>McNeil 2002, p. 39.</ref><ref name=bbc>[http://news.bbc.co.uk/onthisday/hi/dates/stories/may/2/newsid_2480000/2480339.stm "On This Day: Comet inaugurates the jet age."] ''BBC News,'' 2 May 1952. Retrieved 26 April 2012.</ref><ref name=cookman195207>Cookman, Aubrey O. Jr. [https://books.google.com/books?id=WNwDAAAAMBAJ&pg=PA90 "I Rode The First Jet Airliner."] ''Popular Mechanics'', July 1952, pp. 90–94. Retrieved 26 April 2012.</ref> The final Comet from BOAC's initial order, registered G-ALYZ, began flying in September 1952 and carried cargo along South American routes while simulating passenger schedules.<ref>Jackson 1988, pp. 173–174.</ref>

[[File:BOAC Comet 1952 Entebbe.jpg|thumb|left|BOAC Comet 1 at Entebbe Airport, Uganda in 1952]]

Prince Philip returned from the Helsinki Olympic Games with G-ALYS on 4 August 1952. Queen Elizabeth, the Queen Mother and Princess Margaret were guests on a special flight of the Comet on 30 June 1953 hosted by Sir Geoffrey and Lady de Havilland.<ref>Lane 1979, p. 205.</ref> Flights on the Comet were about 50 per cent faster compared to advanced piston-engined aircraft such as the [[Engineering:Douglas DC-6|Douglas DC-6]] ({{cvt|490|mph}})
vs {{cvt|315|mph}}, respectively), and a faster rate of climb further cut flight times. In August 1953 BOAC scheduled the nine-stop London to Tokyo flights by Comet for 36 hours, compared to 86 hours and 35 minutes on its [[Engineering:Canadair North Star|Argonaut]] (a DC-4 variant) piston airliner. (Pan Am's DC-6B was scheduled for 46 hours 45 minutes.) The five-stop flight from London to Johannesburg was scheduled for 21 hr 20 min.<ref>{{cite magazine |magazine=Flight |title=Jet Air-Routes |url=http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200551.html |archive-url=https://web.archive.org/web/20160305070326/http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200551.html |archive-date=5 March 2016 |date=1 May 1953 |page=547}}</ref>

In their first year, Comets carried 30,000 passengers. As the aircraft could be profitable with a load factor as low as 43 per cent, commercial success was expected.<ref name=Walker25>Walker 2000, p. 25.</ref> The Ghost engines allowed the Comet to fly above weather that competitors had to fly through. They ran smoothly and were less noisy than piston engines, had low maintenance costs <!--lower for parts, lower for labour, & also faster turnaround times--> and were fuel-efficient above {{cvt|30000|ft}}.{{refn|Depending on weight and temperature, cruise fuel consumption was {{cvt|6|to|10|kg}} per nautical mile (1.2 miles; 1.9 km), the higher figure being at the lower altitude needed at high weight.{{citation needed|date=April 2021}}|group=N}} In summer 1953, eight BOAC Comets left London each week: three to Johannesburg, two to Tokyo, two to Singapore and one to Colombo.<ref>Davies and Birtles 1999, p. 22 (Route map illustration).</ref>

In 1953, the Comet appeared to have achieved success for de Havilland.<ref>Schnaars 2002, p. 71.</ref> ''Popular Mechanics'' wrote that Britain had a lead of three to five years on the rest of the world in jetliners.<ref name=cookman195207/> As well as the sales to BOAC, two French airlines, Union Aéromaritime de Transport and Air France, each acquired three Comet 1As, an upgraded variant with greater fuel capacity, for flights to West Africa and the Middle East.<ref name=1A>Schnaars 2002, p. 70.</ref><ref>{{cite magazine |url=http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%201135.html |title=Preludes and Overtures: de Havilland Comet 1 |magazine=Flight |date=4 September 1953 |access-date=30 May 2012 |url-status=dead |archive-date=14 January 2015 |archive-url=https://web.archive.org/web/20150114231808/http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%201135.html}}</ref>{{page needed|date=April 2023}} A slightly longer version of the Comet 1 with more powerful engines, the Comet 2, was being developed,<ref>Darling 2001, p. 20.</ref> and orders were placed by Air India,<ref>Cacutt 1989, p. 146.</ref> [[Biology:British Commonwealth Pacific Airlines|British Commonwealth Pacific Airlines]],<ref name=darling119/> Japan Air Lines,<ref name=JAPL/> Linea Aeropostal Venezolana,<ref name=JAPL/> and Panair do Brasil.<ref name=JAPL/> American carriers Capital Airlines, National Airlines and Pan Am placed orders for the planned Comet 3, an even-larger, longer-range version for transatlantic operations.<ref name=darling128>Darling 2005, p. 128.</ref><ref>Proctor et al. 2010, p. 23.</ref> Qantas was interested in the Comet 1 but concluded that a version with more range and better takeoff performance was needed for the London to Canberra route.<ref>Gunn 1987, pp. 268–270.</ref>

===Early hull losses===

On 26 October 1952, the Comet suffered its first hull loss when a BOAC flight departing Rome's Ciampino airport failed to become airborne and ran into rough ground at the end of the runway. Two passengers sustained minor injuries, but the aircraft, G-ALYZ, was a write-off. On 3 March 1953, a new Canadian Pacific Airlines Comet 1A, registered CF-CUN and named ''Empress of Hawaii,'' failed to become airborne while attempting a night takeoff from Karachi, Pakistan, on a delivery flight to Australia. The aircraft plunged into a dry drainage canal and collided with an embankment, killing all five crew and six passengers on board.<ref>[http://aviation-safety.net/database/record.php?id=19530303-1 "Comet Accident Record."] ''Aviation Safety Network.'' Retrieved: 22 September 2010.</ref><ref>[http://www.edcoatescollection.com/ac4/CF-CUN.html "CF-CUN"] ''Ed Coates' Civil Aircraft Photograph Collection.'' Retrieved: 18 February 2011.</ref> The accident was the first fatal jetliner crash.<ref name=JAPL/> In response, Canadian Pacific cancelled its remaining order for a second Comet 1A and never operated the type in commercial service.<ref name=JAPL/>

[[File:De Havilland Comet 1 BOAC Heathrow G-ALYX 1953.jpg|thumb|BOAC Comet 1 ''G-ALYX'' (Yoke X-Ray) at London Heathrow Airport in 1953 prior to a scheduled flight]]

Both early accidents were originally attributed to pilot error, as overrotation had led to a loss of lift from the [[Engineering:Leading edge|leading edge]] of the aircraft's wings. It was later determined that the Comet's wing profile experienced a loss of lift at a high [[Physics:Angle of attack|angle of attack]], and its engine inlets also suffered a lack of pressure recovery in the same conditions. As a result, de Havilland re-profiled the wings' leading edge with a pronounced "droop",<ref name=Withuhn85>Withuhn 1976, p. 85.</ref> and [[Engineering:Wing fence|wing fence]]s were added to control spanwise flow.<ref name=Birtles127>Birtles 1970, p. 127.</ref> A fictionalised investigation into the Comet's takeoff accidents was the subject of the novel ''Cone of Silence'' (1959) by Arthur David Beaty, a former BOAC captain. ''Cone of Silence'' was made into a film in 1960, and Beaty also recounted the story of the Comet's takeoff accidents in a chapter of his non-fiction work, ''Strange Encounters: Mysteries of the Air'' (1984).<ref>Beaty 1984, pp. 113–114.</ref>

The Comet's second fatal accident occurred on 2 May 1953, when BOAC Flight 783, a Comet 1, registered G-ALYV, crashed in a severe [[Earth:Squall|thundersquall]] six minutes after taking off from Calcutta-Dum Dum (now Netaji Subhash Chandra Bose International Airport), India,<ref>Darling 2005, p. 36.</ref> killing all 43 on board. Witnesses observed the wingless Comet on fire plunging into the village of Jagalgori,<ref name=lokurNS>{{cite web |last1=Lokur |first1=N. S. |title=Report of the court investigation on the accident to COMET G-ALYV |url=http://lessonslearned.faa.gov/Comet1/G-ALYV_Report.pdf |website=Lessons Learned |publisher=Federal Aviation Administration |access-date=23 February 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150415121817/http://lessonslearned.faa.gov/Comet1/G-ALYV_Report.pdf |archive-date=15 April 2015}}</ref> leading investigators to suspect structural failure.<ref name=Walker37/>

====India Court of Inquiry====
After the loss of G-ALYV, the Government of India convened a court of inquiry<ref name=lokurNS/> to examine the cause of the accident.{{refn|The court acted under the provisions of Rule 75 of the Indian Aircraft Rules 1937.<ref name=Walker37>Walker 2000, p. 37.</ref>|group=N}} Professor Natesan Srinivasan joined the inquiry as the main technical expert. A large portion of the aircraft was recovered and reassembled at Farnborough,<ref name=Walker37/> during which the break-up was found to have begun with a left elevator spar failure in the horizontal stabilizer. The inquiry concluded that the aircraft had encountered extreme negative [[Physics:G-force|g-force]]s during takeoff; severe turbulence generated by adverse weather was determined to have induced down-loading, leading to the loss of the wings. Examination of the cockpit controls suggested that the pilot may have inadvertently over-stressed the aircraft when pulling out of a steep dive by over-manipulation of the fully powered flight controls. Investigators did not consider metal fatigue as a contributory cause.<ref name=LoBao7>Lo Bao 1996, p. 7.</ref>

The inquiry's recommendations revolved around the enforcement of stricter speed limits during turbulence, and two significant design changes also resulted: all Comets were equipped with [[Earth:Weather radar|weather radar]] and the "Q feel" system was introduced, which ensured that control column forces (invariably called stick forces) would be proportional to control loads. This artificial feel was the first of its kind to be introduced in any aircraft.<ref name=Walker37/> The Comet 1 and 1A had been criticised for a lack of "[[Feedback|feel]]" in their controls,<ref>Job 1996, p. 14.</ref> and investigators suggested that this might have contributed to the pilot's alleged over-stressing of the aircraft;<ref>Darling 2001, p. 26.</ref> Comet chief test pilot John Cunningham contended that the jetliner flew smoothly and was highly responsive in a manner consistent with other de Havilland aircraft.<ref name=Faith>Faith 1996, pp. 63–64.</ref>{{refn|Cunningham: "[the Comet] flew extremely smoothly and responded to the controls in the best way de Havilland aircraft usually did."<ref name=Faith/>|group=N}}

===Comet disasters of 1954===
[[File:Fuselage of de Havilland Comet Airliner G-ALYP.JPG|thumb|Fuselage fragment of G-ALYP at the Science Museum in London]]

Just over a year later, Rome's Ciampino airport, the site of the first Comet hull loss, was the origin of a more-disastrous Comet flight. On 10 January 1954, 20&nbsp;minutes after taking off from Ciampino, the first production Comet, G-ALYP, broke up in mid-air while operating BOAC Flight 781 and crashed into the Mediterranean off the Italian island of Elba with the loss of all 35 on board.<ref name=witheyfatigue>{{citation |title=Fatigue Failure of the de Havilland Comet I |journal=Engineering Failure Analysis |volume=4 |issue=2 |page=147 |year=1997 |last1=Withey |first1=P.A. |doi=10.1016/S1350-6307(97)00005-8}}</ref><ref>[http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%200130.html "B.O.A.C. Comet Lost: Services Suspended."] ''Flight,'' January 1954, p. 58. Retrieved 26 April 2012.</ref> With no witnesses to the disaster and only partial radio transmissions as incomplete evidence, no obvious reason for the crash could be deduced. Engineers at de Havilland immediately recommended 60 modifications aimed at any possible design flaw, while the Abell Committee met to determine potential causes of the crash.<ref>Faith 1996, p. 66.</ref>{{refn|The Abell Committee, named after chairman C. Abell, Deputy Operations Director (Engineering) of BOAC, consisted of representatives of the Allegation Review Board (A.R.B.), BOAC, and de Havilland.<ref>Keith 1997, p. 288.</ref>|group=N}} BOAC also voluntarily grounded its Comet fleet pending investigation into the causes of the accident.<ref name=d29>Darling 2001, pp. 28–30.</ref>

====Abell Committee Court of Inquiry====
Media attention centred on potential sabotage;<ref name=Withuhn85/> other speculation ranged from [[Physics:Clear-air turbulence|clear-air turbulence]] to an explosion of vapour in an empty fuel tank. The Abell Committee focused on six potential aerodynamic and mechanical causes: control flutter (which had led to the loss of DH 108 prototypes), structural failure due to high loads or [[Fatigue (material)|metal fatigue]] of the wing structure, failure of the powered flight controls, failure of the window panels leading to explosive decompression, or fire and other engine problems. The committee concluded that fire was the most likely cause of the problem, and changes were made to the aircraft to protect the engines and wings from damage that might lead to another fire.<ref>[https://web.archive.org/web/20080703165044/http://www.geocities.com/CapeCanaveral/Lab/8803/comgalyp.htm "Report of the Public Inquiry into the causes and circumstances of the accident which occurred on the 10 January 1954, to the Comet aircraft G-ALYP, Part IX (d)."] ''geocities.com.'' Retrieved: 3 September 2010.</ref>

{{Quote box|align=left|width=20%|quote="The cost of solving the Comet mystery must be reckoned neither in money nor in manpower."|source=<small>Prime Minister Winston Churchill, 1954.<ref>Job 1996, p. 11.</ref></small>}}
During the investigation, the Royal Navy conducted recovery operations.<ref>[http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%200224.html "Elba Accident Developments."] ''Flight,'' January 1954, p. 108. Retrieved 26 April 2012.</ref> The first pieces of wreckage were discovered on 12 February 1954<ref>[https://web.archive.org/web/20080703165044/http://www.geocities.com/CapeCanaveral/Lab/8803/comgalyp.htm "Report of the Public Inquiry into the causes and circumstances of the accident which occurred on the 10 January 1954, to the Comet aircraft G-ALYP, Part IX (c): Action taken after the accident and prior to the accident to Comet G-ALYY: Naval search for wreckage."] ''geocities.com.'' Retrieved: 3 September 2010.</ref> and the search continued until September 1954, by which time 70 per cent by weight of the main structure, 80 per cent of the power section, and 50 per cent of the aircraft's systems and equipment had been recovered.<ref>[http://www.rafmuseum.org.uk/online-exhibitions/comet/comet5.cfm "Comet Failure."] {{webarchive|url=https://web.archive.org/web/20090923173849/http://www.rafmuseum.org.uk/online-exhibitions/comet/comet5.cfm |date=23 September 2009}} ''Royal Air Force Museum Cosford''. Retrieved 1 November 2010.</ref><ref name=flight54p652>''Flight'' 29 October 1954, p. 652.</ref> The forensic reconstruction effort had just begun when the Abell Committee reported its findings. No apparent fault in the aircraft was found,{{refn|On 4 April, Lord Brabazon wrote to the Minister of Transport, "Although no definite reason for the accident has been established, modifications are being embodied to cover every possibility that imagination has suggested as a likely cause of the disaster. When these modifications are completed and have been satisfactorily flight-tested, the Board sees no reason why passenger services should not be resumed."<ref name=d29/>|group=N}} and the British government decided against opening a further public inquiry into the accident.<ref name=d29/> The prestigious nature of the Comet project, particularly for the British aerospace industry, and the financial impact of the aircraft's grounding on BOAC's operations both served to pressure the inquiry to end without further investigation.<ref name=d29/> Comet flights resumed on 23 March 1954.<ref name=Birtlespp.128–129>Birtles 1970, pp. 128–129.</ref>

On 8 April 1954, Comet G-ALYY ("Yoke Yoke"), on charter to South African Airways, was on a leg from Rome to Cairo (of a longer route, SA Flight 201 from London to Johannesburg), when it crashed in the Mediterranean near Naples with the loss of all 21 passengers and crew on board.<ref name=witheyfatigue/> The Comet fleet was immediately grounded once again and a large investigation board was formed under the direction of the Royal Aircraft Establishment (RAE).<ref name=witheyfatigue/> Prime Minister Winston Churchill tasked the Royal Navy with helping to locate and retrieve the wreckage so that the cause of the accident could be determined.<ref name=DaviesandBirtles30–31/> The Comet's Certificate of Airworthiness was revoked, and Comet 1 line production was suspended at the Hatfield factory while the BOAC fleet was permanently grounded, [[Engineering:Cocooning (aircraft)|cocooned]] and stored.<ref name=Withuhn85/>

====Cohen Committee Court of Inquiry====
[[File:DH.106 Comet 1 G-ALYW BOAC LAP (2) 12.09.54 edited-3.jpg|thumb|BOAC Comet 1 cocooned and stored in the maintenance area at London Heathrow Airport in September 1954]]

On 19 October 1954, the Cohen Committee was established to examine the causes of the Comet crashes.<ref name=Jones68/> Chaired by Lord Cohen, the committee tasked an investigation team led by Sir Arnold Hall, Director of the RAE at Farnborough, to perform a more-detailed investigation. Hall's team began considering fatigue as the most likely cause of both accidents and initiated further research into measurable strain on the aircraft's skin.<ref name=witheyfatigue/> With the recovery of large sections of G-ALYP from the Elba crash and BOAC's donation of an identical airframe, G-ALYU, for further examination, an extensive "water torture" test eventually provided conclusive results.<ref name=Groh-comet-crash>{{cite web |last1=Groh |first1=Rainer |title=The DeHavilland Comet Crash |url=https://aerospaceengineeringblog.com/dehavilland-comet-crash/ |website=Aerospace Engineering Blog |access-date=31 July 2022 |date=9 June 2012 |archive-date=10 September 2022 |archive-url=https://web.archive.org/web/20220910013234/http://aerospaceengineeringblog.com/dehavilland-comet-crash/ |url-status=dead }}</ref> This time, the entire fuselage was tested in a dedicated water tank that was built specifically at Farnborough to accommodate its full length.<ref name=d29/>

[[File:Comet G-ALYU escape hatch failure.png|thumb|Image from the Cohen Inquiry Report showing fuselage failure under water pressure test of Comet 1 G-ALYU. Note intact escape hatch window frame]]
In water-tank testing, engineers subjected G-ALYU to repeated repressurisation and over-pressurisation, and on 24 June 1954, after 3,057 flight cycles (1,221 actual and 1,836 simulated),<ref name=rafwebarchive>[https://web.archive.org/web/20061002072008/http://www.rafmuseum.org.uk/london/exhibitions/comet/comet5.cfm "Comet."] ''RAF Museum''. Retrieved 3 September 2010.</ref> G-ALYU burst open. Hall, Geoffrey de Havilland and Bishop were immediately called to the scene, where the water tank was drained to reveal that the fuselage had ripped open at a bolt hole, forward of the forward left escape hatch cut out. The failure then occurred longitudinally along a fuselage stringer at the widest point of the fuselage and through a cut out for an escape hatch. The skin thickness was discovered to be insufficient to distribute the load across the structure, leading to overloading of fuselage frames adjacent to fuselage cut outs. (Cohen Inquiry accident report Fig 7).<ref>Cohen Inquiry Report P 31</ref> The fuselage frames did not have sufficient strength to prevent the crack from propagating. Although the fuselage failed after a number of cycles that represented three times the life of G-ALYP at the time of the accident, it was still much earlier than expected.<ref>Cohen Inquiry Report p 27</ref> A further test reproduced the same results.<ref name=Withuhn87>Withuhn 1976, p. 87.</ref> Based on these findings, Comet 1 structural failures could be expected at anywhere from 1,000 to 9,000 cycles. Before the Elba accident, G-ALYP had made 1,290 pressurised flights, while G-ALYY had made 900 pressurised flights before crashing. Dr P. B. Walker, Head of the Structures Department at the RAE, said he was not surprised by this, noting that the difference was about three to one, and previous experience with metal fatigue suggested a total range of nine to one between experiment and outcome in the field could result in failure.<ref name=rafwebarchive/>

The RAE also reconstructed about two-thirds of G-ALYP at Farnborough and found fatigue crack growth from a rivet hole at the low-drag fibreglass forward [[Astronomy:Aperture|aperture]] around the Automatic Direction Finder, which had caused a catastrophic break-up of the aircraft in high-altitude flight.<ref>"Summary: Aircraft Investigation." ''Aircraft Engineering'', 37, 1965, p. 38.</ref> The exact origin of the fatigue failure could not be identified but was localised to the ADF antenna cut out. A countersunk bolt hole and manufacturing damage that had been repaired at the time of construction using methods that were common, but were likely insufficient allowing for the stresses involved, were both located along the failure crack.<ref>Cohen Inquiry Report P 28 Para 131-136</ref> Once the crack initiated the skin failed from the point of the ADF cut out and propagated downward and rearward along a stringer resulting in an explosive decompression.<ref>Cohen report P 20 para 77-79</ref>

[[File:Comet G-ALYP ADF windows.png|thumb|Image (Fig 12) from the Cohen Inquiry showing the location of the ADF antenna cut out 'windows' in the roof above the cockpit of Comet 1 G-ALYP]]

It was also found that the punch-rivet construction technique employed in the Comet's design had exacerbated its structural fatigue problems;<ref name=witheyfatigue/> the aircraft's windows had been engineered to be glued and riveted, but had been punch-riveted only. Unlike drill riveting, the imperfect nature of the hole created by punch-riveting could cause fatigue cracks to start developing around the rivet. Principal investigator Hall accepted the RAE's conclusion of design and construction flaws as the likely explanation for G-ALYU's structural failure after 3,060 pressurisation cycles.{{refn|Hall: "In the light of known properties of the aluminium alloy D.T.D. 546 or 746 of which the skin was made and in accordance with the advice I received from my Assessors, I accept the conclusion of RAE that this is a sufficient explanation of the failure of the cabin skin of Yoke Uncle by fatigue after a small number, namely, 3,060 cycles of pressurisation."<ref>Cohen Inquiry Report, Part XI (a. 69)</ref>|group=N}}

====Earlier structural indications====

The issue of the lightness of Comet 1 construction (in order to not tax the relatively low thrust de Havilland Ghost engines), had been noted by de Havilland test pilot John Wilson, while flying the prototype during a Farnborough flypast in 1949. On the flight, he was accompanied by Chris Beaumont, Chief Test Pilot of the de Havilland Engine Company who stood in the entrance to the cockpit behind the Flight Engineer. He stated "Every time we pulled 2 1/2-3G to go around the corner, Chris found that the floor on which he was standing, bulging up and there was a loud bang at that speed from the nose of the aircraft where the skin 'panted' (flexed), so when we heard this bang we knew without checking the airspeed indicator, that we were doing 340 knots. In later years we realised that these were the indications of how flimsy the structure really was."<ref>{{cite book |title=Empire of the Clouds |first=James |last=Hamilton-Paterson |pages=39–40 |publisher=Faber and Faber |date=2010}}</ref>

====Square window myths====
[[File:Comet 1 windows.png|thumb|Surviving DeHavilland Comet 1 showing rectangular windows with rounded corners not 'square' as commonly described.]]

Despite findings of the Cohen Inquiry, a number of myths have evolved around the cause of the Comet 1's accidents. Most commonly quoted are the 'square' passenger windows. While the report noted that stress around fuselage cut-outs, emergency exits and windows was found to be much higher than expected due to DeHavilland's assumptions and testing methods<ref>Cohen Report P 26 – para 118-123</ref> the passenger windows shape has been commonly misunderstood and cited as a cause of the fuselage failure. In fact the mention of 'windows' in the Cohen report's conclusion, refers specifically to the origin point of failure in the ADF Antenna cut-out 'windows', located above the cockpit, not passenger windows.<ref>Report of the Court of Inquiry into the Accidents to Comet G-ALYP on 10th January 1954 and Comet G-ALYY on 8th April 1954-HM Stationery Office 1955-p 20 – para 78-79</ref> The shape of the passenger windows were not indicated in any failure mode detailed in the accident report and were not viewed as a contributing factor. A number of other pressurised airliners of the period including the Boeing 377 Stratocruiser, Douglas DC-7, and DC-8 had larger more 'square' windows than the Comet 1 and experienced no such failures.<ref name=autogenerated1>The DeHavilland Comet Disaster – Aerospace Engineering – Paul Withey Professor of Casting at the University of Birmingham School of Metallurgy – Video presentation retrieved 30NOV22</ref> In fact, the Comet 1's window general shape resembles a slightly larger Boeing 737 window mounted horizontally. They are rectangular ''not square'', have rounded corners and are within 5% of the radius of the Boeing 737 windows and virtually identical to modern airliners.<ref name=autogenerated1/> Paul Withey, Professor of Casting at the University of Birmingham School of Metallurgy states in a video presentation delivered in 2019, analysing all available data that: "The fact that DeHavilland put oval windows into later marks, is not because of any 'squareness' of the windows that caused failure."<ref>The deHavilland Comet Disaster – Aerospace Engineering - Paul Withey Professor of Casting at the University of Birmingham School of Metallurgy – Video presentation retrieved 30NOV22 Time stamp 42:07</ref> "DeHavilland went to oval windows on the subsequent Marks because it was easier to Redux them in (use adhesive) – nothing to do with the [[Physics:Stress concentration|stress concentration]] and it's purely to remove rivets." (from the structure)<ref>The DeHavilland Comet Disaster – Aerospace Engineering – Paul Withey, Professor of Casting at the University of Birmingham School of Metallurgy – Video presentation retrieved 30NOV22 Time stamp 58:27</ref>

Surviving Comet 1s can be seen on view at the RAF Museum Cosford and the DeHavilland Museum at Salisbury Hall, London Colney.

====Response====
In responding to the report de Havilland stated: "Now that the danger of high level fatigue in pressure cabins has been generally appreciated, de Havillands will take adequate measures to deal with this problem. To this end we propose to use thicker gauge materials in the pressure cabin area and to strengthen and redesign windows and cut outs and so lower the general stress to a level at which local stress concentrations either at rivets and bolt holes or as such may occur by reason of cracks caused accidentally during manufacture or subsequently, will not constitute a danger."<ref>Cohen Inquiry Report p 42</ref>

The Cohen inquiry closed on 24 November 1954, having "found that the basic design of the Comet was sound",<ref name=Jones68/> and made no observations or recommendations regarding the shape of the windows. De Havilland nonetheless began a refit programme to strengthen the fuselage and wing structure, employing thicker-gauge skin and replacing the rectangular windows and panels with rounded versions, although this was not related to the erroneous 'square' window claim, as can be seen by the fact that the fuselage escape hatch cut-outs (the source of the failure in test aircraft G-ALYU) retained their rectangular shape.<ref name=DaviesandBirtles30–31>Davies and Birtles 1999, pp. 30–31.</ref><ref>{{cite web |title=XS235 – De Havilland DH-106 Comet 4C – United Kingdom – Royal Air Force (RAF) – David Oates |website=JetPhotos |url=https://www.jetphotos.com/photo/7193453 |access-date=22 March 2019}}</ref>

Following the Comet enquiry, aircraft were designed to "[[Fail-safe|fail-safe]]" or safe-life standards,<ref>{{cite web |url=https://www.researchgate.net/publication/287199920 |title=Milestones in Aircraft Structural Integrity |website=[[Company:ResearchGate|ResearchGate]] |access-date=22 March 2019}}</ref> though several subsequent catastrophic fatigue failures, such as Aloha Airlines Flight 243 of April 28, 1988 have occurred.<ref>{{cite web |url=https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR8903.pdf |title=Aircraft Accident Report AAR8903: Aloha Airlines, Flight 243, Boeing 737-200, N73711 |publisher=NTSB |date=14 June 1989}}</ref>

===Resumption of service===
[[File:MSA Comet Groves.jpg|thumb|Malaysia-Singapore Airlines Comet 4 at Kai Tak Airport in 1966]]

With the discovery of the structural problems of the early series, all remaining Comets were withdrawn from service, while de Havilland launched a major effort to build a new version that would be both larger and stronger. All outstanding orders for the Comet 2 were cancelled by airline customers.<ref name=d33>Darling 2001, p. 33.</ref> All production Comet 2s were also modified with thicker gauge skin to better distribute loads and alleviate the fatigue problems (most of these served with the {{wipe|Royal Air Force}} as the Comet C2); a programme to produce a Comet 2 with more powerful Avons was delayed. The prototype Comet 3 first flew in July 1954 and was tested in an unpressurised state pending completion of the Cohen inquiry.<ref name=d33/> Comet commercial flights would not resume until 1958.<ref>Swanborough 1962, pp. 47–48.</ref>

Development flying and route proving with the Comet 3 allowed accelerated certification of what was destined to be the most successful variant of the type, the Comet 4. All airline customers for the Comet 3 subsequently cancelled their orders and switched to the Comet 4,<ref name=d33/> which was based on the Comet 3 but with improved fuel capacity. BOAC ordered 19 Comet 4s in March 1955, and American operator Capital Airlines ordered 14 Comets in July 1956.<ref>"Capital Comet." ''Canadian Aviation'', 29(9–12), 1956, p. 51.</ref> Capital's order included 10 Comet 4As, a variant modified for short-range operations with a stretched fuselage and short wings, lacking the pinion (outboard wing) fuel tanks of the Comet 4.<ref name=darling128/> Financial problems and a takeover by United Airlines meant that Capital would never operate the Comet.{{citation needed|date=October 2021}}

[[File:United Arab Airlines Comet Soderstrom.jpg|thumb|left|United Arab Airlines Comet 4C at Geneva Airport in 1968]]

The Comet 4 first flew on 27 April 1958 and received its Certificate of Airworthiness on 24 September 1958; the first was delivered to BOAC the next day.<ref name=bao11>Lo Bao 1996, p. 11.</ref><ref>Walker 2000, pp. 187–188.</ref> The base price of a new Comet 4 was roughly £1.14 million (£{{Inflation|UK-CAP|1.14|1958|r=2|fmt=c}} million in {{Inflation/year|UK-CAP}}).<ref>[http://www.flightglobal.com/pdfarchive/view/1960/1960%20-%202684.html "De Havilland."] ''Flightglobal.com,'' 18 November 1960. Retrieved 13 August 2012.</ref> The Comet 4 enabled BOAC to inaugurate the first regular jet-powered transatlantic services on 4 October 1958 between London and New York (albeit still requiring a fuel stop at Gander International Airport, Newfoundland, on westward North Atlantic crossings).<ref name=McNeil2002,39/> While BOAC gained publicity as the first to provide transatlantic jet service, by the end of the month rival Pan American World Airways was flying the [[Engineering:Boeing 707|Boeing 707]] on the New York-Paris route, with a fuel stop at Gander in both directions,<ref>[https://books.google.com/books?id=BZdQhOW-ys0C&pg=PA940 "The Comet's chance to shine."]{{Dead link|date=January 2024 |bot=InternetArchiveBot |fix-attempted=yes }} ''The New Scientist'', 4(98), 2 October 1958, p. 940. Retrieved 26 April 2012.</ref> and in 1960 began flying [[Engineering:Douglas DC-8|Douglas DC-8's]] on its transatlantic routes as well. The American jets were larger, faster, longer-ranged and more cost-effective than the Comet.<ref>Haddon-Cave 2009, p. 16.</ref> After analysing route structures for the Comet, BOAC reluctantly cast-about for a successor, and in 1956 entered into an agreement with Boeing to purchase the 707.<ref>Lo Bao 1996, p. 12.</ref>

[[File:DH.106 Comet 5H-AAF EAA LHR 10.05.64 edited-3.jpg|thumb|Comet 4 of East African Airways at London Heathrow in 1964]]

The Comet 4 was ordered by two other airlines: Aerolíneas Argentinas took delivery of six Comet 4s from 1959 to 1960, using them between Buenos Aires and Santiago, New York and Europe, and East African Airways received three new Comet 4s from 1960 to 1962 and operated them to the United Kingdom and to Kenya, Tanzania, and Uganda.<ref name=darling114>Darling 2005, p. 114.</ref> The Comet 4A ordered by Capital Airlines was instead built for BEA as the Comet 4B, with a further fuselage stretch of {{cvt|38|in}} and seating for 99 passengers. The first Comet 4B flew on 27 June 1959 and BEA began Tel Aviv to London-Heathrow services on 1 April 1960.<ref name=DaviesandBirtles62/> Olympic Airways was the only other customer to order the type.<ref name=Jacksondhp459>Jackson 1987, p. 459.</ref> The last Comet 4 variant, the Comet 4C, first flew on 31 October 1959 and entered service with Mexicana in 1960.<ref>[http://www.flightglobal.com/pdfarchive/view/1962/1962%20-%200749.html "Comet 4Cs for Mexicana."] ''Flight International'', 76, 6 November 1959, p. 491. Retrieved 26 April 2012.</ref> The Comet 4C had the Comet 4B's longer fuselage and the longer wings and extra fuel tanks of the original Comet 4, which gave it a longer range than the 4B. Ordered by Kuwait Airways, Middle East Airlines, Misrair (later Egyptair), and Sudan Airways, it was the most popular Comet variant.<ref name=JAPL/><ref>Howard, Paul. [https://abpic.co.uk/pictures/view/1101609/ "De Havilland DH.106 Comet 4C, OD-ADT, MEA – Middle East Airlines."] ''Air-Britain Photographic Images Collection''. Retrieved 19 November 2010.</ref>

===Later service===
[[File:Comet Canopus.jpg|thumb|Comet 4C ''Canopus'' on display at the Bruntingthorpe Aerodrome in Leicestershire, England]]

In 1959 BOAC began shifting its Comets from transatlantic routes{{refn|The Feb 1959 OAG shows eight transatlantic Comets a week out of London, plus 10 BOAC Britannias and 11 DC-7Cs. In April 1960, 13 Comets, 19 Britannias and 6 DC-7Cs. Comets quit flying the North Atlantic in October 1960 (but reportedly made a few flights in summer 1964).{{citation needed|date=April 2021}} |group=N}} and released the Comet to associate companies, making the Comet 4's ascendancy as a premier airliner brief. Besides the 707 and DC-8, the introduction of the [[Engineering:Vickers VC10|Vickers VC10]] allowed competing aircraft to assume the high-speed, long-range passenger service role pioneered by the Comet.<ref>Lo Bao 1996, p. 13.</ref> In 1960, as part of a government-backed consolidation of the British aerospace industry, de Havilland itself was acquired by Hawker Siddeley, within which it became a wholly owned division.<ref name=post>[http://www.rafmuseum.org.uk/online-exhibitions/dehavilland/post_war.cfm "De Havilland – Post War"] {{webarchive|url=https://web.archive.org/web/20110625135746/http://www.rafmuseum.org.uk/online-exhibitions/dehavilland/post_war.cfm |date=25 June 2011}}, ''rafmuseum.org.uk''. Retrieved 30 May 2012</ref>

In the 1960s, orders declined, a total of 76 Comet 4s being delivered from 1958 to 1964. In November 1965, BOAC retired its Comet 4s from revenue service; other operators continued commercial passenger flights with the Comet until 1981. Dan-Air played a significant role in the fleet's later history and, at one time, owned all 49 remaining airworthy civil Comets.<ref>Swanborough 1980, p. 35.</ref> On 14 March 1997 a Comet 4C serial ''XS235'' and named ''Canopus'',<ref name=d5/> which had been acquired by the British Ministry of Technology and used for radio, radar and avionics trials, made the last documented production Comet flight.<ref name=walker169>Walker 2000, p. 169.</ref>

==Legacy==
[[File:Dan-Air Comet.jpg|thumb|Dan-Air Comet 4C, G-BDIW exhibited at the ''Flugausstellung Hermeskeil'' in Germany]]

The Comet is widely regarded as both an adventurous step forward and a supreme tragedy; the aircraft's legacy includes advances in aircraft design and in accident investigations. The inquiries into the accidents that plagued the Comet 1 were perhaps some of the most extensive and revolutionary that have ever taken place, establishing precedents in accident investigation; many of the deep-sea salvage and aircraft reconstruction techniques employed have remained in use within the aviation industry.<ref>Bibel 2008, p. 68.</ref> In spite of the Comet being subjected to what was then the most rigorous testing of any contemporary airliner, pressurisation and the dynamic stresses involved were not thoroughly understood at the time of the aircraft's development, nor was the concept of metal fatigue. Though these lessons could be implemented on the drawing board for future aircraft, corrections could only be retroactively applied to the Comet.<ref>Bibel 2008, pp. 115–116.</ref>

According to de Havilland's chief test pilot John Cunningham, who had flown the prototype's first flight, representatives from American manufacturers such as [[Company:Boeing|Boeing]] and [[Company:Douglas Aircraft Company|Douglas]] privately disclosed that if de Havilland had not experienced the Comet's pressurisation problems first, it would have happened to them.<ref>Faith 1996, p. 72.</ref> Cunningham likened the Comet to the later [[Engineering:Concorde|Concorde]] and added that he had assumed that the aircraft would change aviation, which it subsequently did.<ref name=Faith/> Aviation author Bill Withuhn concluded that the Comet had pushed "'the state-of-the-art' beyond its limits."<ref name=Withuhn88>Withuhn 1976, p. 88.</ref>

{{Quote box|align=left|width=19%|quote="I don't think it is too much to say that the world changed from the moment the Comet's wheels left the ground."|source=[[Biography:Tony Fairbrother|Tony Fairbrother]], manager, upgraded Comet development.<ref name=Fairbrother>[http://www.timesonline.co.uk/tol/comment/obituaries/article506335.ece "Obituary: Tony Fairbrother."] ''The Times'', 26 January 2005.</ref><ref>{{citation |last=Ramsden |first=J.M. |title=Jet Transport's Next 40 Years |work=Flight International |date=29 July 1989 |page=146 |url=http://www.flightglobal.com/pdfarchive/view/1989/1989%20-%202331.html |access-date=2 May 2012 |url-status=dead |archive-url=https://web.archive.org/web/20190202095622/http://www.flightglobal.com/pdfarchive/view/1989/1989%20-%202331.html |archive-date=2 February 2019}}</ref>}}

Aeronautical-engineering firms were quick to respond to the Comet's commercial advantages and technical flaws alike; other aircraft manufacturers learned from, and profited by, the hard-earned lessons embodied by de Havilland's Comet.<ref name=TH90>Trischler and Helmuth 2003, p. 90.</ref><ref>Job 1996, p. 21.</ref> The Comet's buried engines were used on some other early jet airliners, such as the [[Engineering:Tupolev Tu-104|Tupolev Tu-104]],<ref>Stroud 1968, p. 201.</ref> but later aircraft, such as the Boeing 707 and Douglas DC-8, differed by employing podded engines held on pylons beneath the wings.<ref>Taylor 1996, p. 151.</ref> Boeing stated that podded engines were selected for their passenger airliners because buried engines carried a higher risk of catastrophic wing failure in the event of engine fire.<ref>Tegler 2000, p. 6.</ref> In response to the Comet tragedies, manufacturers also developed ways of pressurisation testing, often going so far as to explore rapid depressurisation; subsequent fuselage skins were of a greater thickness than the skin of the Comet.<ref>Dennies 2005, p. 27.</ref>
{{clear}}

==Variants==

===Comet 1===
[[File:Aeromaritime de Havilland Comet 1 Groves.jpg|thumb|Union Aéromaritime de Transport Comet 1A at Le Bourget Airport in 1952]]

The '''Comet 1''' was the first model produced, a total of 12 aircraft in service and test. Following closely the design features of the two prototypes, the only noticeable change was the adoption of four-wheel bogie main undercarriage units, replacing the single main wheels. Four Ghost 50 Mk 1 engines were fitted (later replaced by more powerful Ghost DGT3 series engines). The span was {{cvt|115|ft}}, and overall length {{cvt|93|ft}}; the [[Engineering:Maximum takeoff weight|maximum takeoff weight]] was over {{cvt|105000|lb}} and over 40 passengers could be carried.<ref name=walker190>Walker 2000, p. 190.</ref>

* An updated '''Comet 1A''' was offered with higher-allowed weight, greater fuel capacity,<ref name=1A/> and water-methanol injection; 10 were produced. In the wake of the 1954 disasters, all Comet 1s and 1As were brought back to Hatfield, placed in a protective cocoon and retained for testing.<ref>[https://www.rafmuseum.org.uk/research/archive-exhibitions/comet-the-worlds-first-jet-airliner/last-comet-1/ "Last Comet 1."] ''Royal Air Force Museum Cosford''. Retrieved 1 November 2010.</ref> All were substantially damaged in stress testing or were scrapped entirely.<ref name=Walker40/>
* '''Comet 1X''': Two RCAF Comet 1As were rebuilt with heavier-gauge skins to a Comet 2 standard for the fuselage, and renamed Comet 1X.<ref name=Jones68>Jones 2010, p. 68.</ref>
* '''Comet 1XB''': Four Comet 1As were upgraded to a 1XB standard with a reinforced fuselage structure and oval windows. Both 1X series were limited in number of pressurisation cycles.<ref name=Walker40>Walker 2000, p. 40.</ref>
* The '''DH 111 Comet Bomber''', a nuclear bomb-carrying variant developed to Air Ministry specification B35/46, was submitted to the Air Ministry on 27 May 1948. It had been originally proposed in 1948 as the "PR Comet", a high-altitude photo reconnaissance adaptation of the Comet 1. The Ghost DGT3-powered airframe featured a narrowed fuselage, a bulbous nose with H2S Mk IX radar, and a four-crewmember pressurised cockpit under a large bubble canopy. Fuel tanks carrying {{convert|2400|impgal|L}} were added to attain a range of {{convert|3350|mi}}. The proposed DH 111 received a negative evaluation from the Royal Aircraft Establishment over serious concerns regarding weapons storage; this, along with the redundant capability offered by the RAF's proposed V bomber trio, led de Havilland to abandon the project on 22 October 1948.<ref>Walker 2000, pp. 171–172.</ref>

===Comet 2===
[[File:De Havilland Comet CMk.2.jpg|thumb|Comet C2, XK671 ''Aquila'' at RAF Waterbeach, fitted with revised round windows]]

The '''Comet 2''' had a slightly larger wing, higher fuel capacity and more-powerful Rolls-Royce Avon engines, which all improved the aircraft's range and performance;<ref name=Jackson175/> its fuselage was {{cvt|3|ft|1|in}} longer than the Comet 1's.<ref name=ca1953/> Design changes had been made to make the aircraft more suitable for transatlantic operations.<ref name=Jackson175>Jackson 1980, p. 175.</ref> Following the Comet 1 disasters, these models were rebuilt with heavier-gauge skin and rounded windows, and the Avon engines featuring larger air intakes and outward-curving jet tailpipes.{{refn|Avon-powered Comets were distinguished by larger air intakes and curved tailpipes that reduced the thermal effect on the rear fuselage.<ref name=Munson155/>|group=N}}<ref name=Munson155>Munson 1967, p. 155.</ref> A total of 12 of the 44-seat Comet 2s were ordered by BOAC for the South Atlantic route.<ref name=Times52516>"Comet Service To South America Planned" (News). ''The Times'', Saturday, Issue 52516, 10 January 1953, col G, p. 3.</ref> The first production aircraft (G-AMXA) flew on 27 August 1953.<ref name=Jacksondhp456>Jackson 1987, p. 456.</ref> Although these aircraft performed well on test flights on the South Atlantic, their range was still not suitable for the North Atlantic. All but four Comet 2s were allocated to the RAF, deliveries beginning in 1955. Modifications to the interiors allowed the Comet 2s to be used in several roles. For VIP transport, the seating and accommodations were altered and provisions for carrying medical equipment including iron lungs were incorporated. Specialised [[Signals intelligence|signals intelligence]] and electronic surveillance capability was later added to some airframes.<ref name=Swanborough48/>
* '''Comet 2X''': Limited to a single Comet Mk 1 powered by four Rolls-Royce Avon 502 turbojet engines and used as a development aircraft for the Comet 2.<ref name=Jackson175/>
* '''Comet 2E''': Two Comet 2 airliners were fitted with Avon 504s in the inner nacelles and Avon 524s in the outer ones. These aircraft were used by BOAC for proving flights during 1957–1958.<ref name=Jackson175/>
* '''Comet T2''': The first two of 10 Comet 2s for the RAF were fitted out as crew trainers, the first aircraft (XK669) flying initially on 9 December 1955.<ref name=Swanborough48>Swanborough 1962, p. 48.</ref>
* '''Comet C2''': Eight Comet 2s originally destined for the civil market were completed for the RAF and assigned to No. 216 Squadron.<ref name=Swanborough48/>
* '''Comet 2R''': Three Comet 2s were modified for use in radar and electronic systems development, initially assigned to No. 90 Group (later Signals Command) for the RAF.<ref name=Swanborough48/> In service with No. 192 and No. 51 Squadrons, the 2R series was equipped to monitor [[Organization:Warsaw Pact|Warsaw Pact]] signal traffic and operated in this role from 1958.<ref name=Walker159/>{{refn|The 2R ELINT series was operational until 1974, when replaced by the Nimrod R1, the last Comet derivative in RAF service.<ref name=Walker159>Walker 2000, p. 159.</ref>|group=N}}

===Comet 3===
[[File:DH106 Comet 3 G-ANLO FAR 1954.jpg|thumb|left|Comet 3 G-ANLO in BOAC markings at Farnborough Airshow in September 1954]]

The '''Comet 3''', which flew for the first time on 19 July 1954, was a Comet 2 lengthened by {{cvt|15|ft|5|in}} and powered by Avon M502 engines developing {{cvt|10000|lbf|kN}}.<ref name=thenew/> The variant added wing pinion tanks, and offered greater capacity and range.<ref name=Jacksondhp457>Jackson 1987, p. 457.</ref> The Comet 3 was destined to remain a development series since it did not incorporate the fuselage-strengthening modifications of the later series aircraft, and was not able to be fully pressurised.<ref name=Birtles129>Birtles 1970, p. 129.</ref> Only two Comet 3s began construction; G-ANLO, the only airworthy Comet 3, was demonstrated at the Farnborough SBAC Show in September 1954. The other Comet 3 airframe was not completed to production standard and was used primarily for ground-based structural and technology testing during development of the similarly sized Comet 4. Another nine Comet 3 airframes were not completed and their construction was abandoned at Hatfield.<ref>Walker 2000, pp. 51–52.</ref> In BOAC colours, G-ANLO was flown by John Cunningham in a marathon round-the-world promotional tour in December 1955.<ref name=Jacksondhp457/> As a flying testbed, it was later modified with Avon RA29 engines fitted, as well as replacing the original long-span wings with reduced span wings as the '''Comet 3B''' and demonstrated in British European Airways (BEA) livery at the Farnborough Airshow in September 1958.<ref name=Birtles129/> Assigned in 1961 to the Blind Landing Experimental Unit (BLEU) at RAE Bedford, the final testbed role played by G–ANLO was in [[Engineering:Autoland|automatic landing system]] experiments. When retired in 1973, the airframe was used for foam-arrester trials before the fuselage was salvaged at BAE Woodford, to serve as the mock-up for the [[Engineering:Hawker Siddeley Nimrod|Nimrod]].<ref>Davies and Birtles 1999, p. 36.</ref>

===Comet 4===
[[File:BEA De Havilland DH-106 Comet 4B Tempelhof Manteufel.jpg|thumb|British European Airways Comet 4B at Berlin Tempelhof Airport in October 1968]]

The '''Comet 4''' was a further improvement on the stretched Comet 3 with even greater fuel capacity. The design had progressed significantly from the original Comet 1, growing by {{cvt|18|ft|6|in}} and typically seating 74 to 81 passengers compared to the Comet 1's 36 to 44 (119 passengers could be accommodated in a special charter seating package in the later 4C series).<ref name=Winchester109>Winchester 2004, p. 109.</ref> The Comet 4 was considered the definitive series, having a longer range, higher cruising speed and higher maximum takeoff weight. These improvements were possible largely because of Avon engines, with twice the thrust of the Comet 1's Ghosts.<ref name=DaviesandBirtles62>Davies and Birtles 1999, p. 62.</ref> Deliveries to BOAC began on 30 September 1958 with two 48-seat aircraft, which were used to initiate the first scheduled transatlantic services.

* '''Comet 4B''': Originally developed for Capital Airlines as the 4A, the 4B featured greater capacity through a 2m longer fuselage, and a shorter wingspan; 18 were produced.
* '''Comet 4C''': This variant featured the Comet 4's wings and the 4B's longer fuselage; 28 were produced.

The last two Comet 4C fuselages were used to build prototypes of the Hawker Siddeley Nimrod maritime patrol aircraft.<ref name=haddon/> A Comet 4C (SA-R-7) was ordered by Saudi Arabian Airlines with an eventual disposition to the {{wipe|Royal Saudi Air Force}} for the exclusive use of King Saud bin Abdul Aziz. Extensively modified at the factory, the aircraft included a VIP front cabin, a bed, special toilets with gold fittings and was distinguished by a green, gold and white colour scheme with polished wings and lower fuselage that was commissioned from aviation artist John Stroud. Following its first flight, the special order Comet 4C was described as "the world's first executive jet."<ref>Davies and Birtles 1999, p. 50.</ref>

===Comet 5 proposal===
The '''Comet 5''' was proposed as an improvement over previous models, including a wider fuselage with five-abreast seating, a wing with greater sweep and podded [[Engineering:Rolls-Royce Conway|Rolls-Royce Conway]] engines. Without support from the Ministry of Transport, the proposal languished as a hypothetical aircraft and was never realised.<ref name=Walker62/>{{refn|The MoT subsequently backed BOAC's order of Conway-powered Boeing 707s.<ref name=Walker62>Walker 2000, p. 62.</ref>|group=N}}

===Hawker Siddeley Nimrod===
{{Main|Engineering:Hawker Siddeley Nimrod}}

The last two Comet 4C aircraft produced were modified as prototypes (XV148 & XV147) to meet a British requirement for a maritime patrol aircraft for the Royal Air Force; initially named "Maritime Comet", the design was designated '''Type HS 801'''.<ref name=haddon>Haddon-Cave 2009, p. 17.</ref> This variant became the Hawker Siddeley Nimrod and production aircraft were built at the Hawker Siddeley factory at Woodford Aerodrome. Entering service in 1969, five Nimrod variants were produced.<ref>Haddon-Cave 2009, p. 19.</ref> The final Nimrod aircraft were retired in June 2011.<ref name=dmj-r1>[http://www.defencemanagement.com/news_story.asp?id=16738 "Nimrod R1 makes final flight"] {{webarchive |url=https://web.archive.org/web/20120325162031/http://www.defencemanagement.com/news_story.asp?id=16738 |date=25 March 2012}} ''Defence Management Journal'', 28 June 2011. Retrieved 28 June 2011.</ref>

==Operators==

[[File:Gatwick1976-mrh.jpg|thumb|Dan-Air Comet 4s and [[Engineering:BAC One-Eleven|BAC One-Eleven]]s at London Gatwick Airport in 1976]]

The original operators of the early Comet 1 and the Comet 1A were BOAC, Union Aéromaritime de Transport and Air France. All early Comets were withdrawn from service for accident inquiries, during which orders from British Commonwealth Pacific Airlines, Japan Air Lines, Linea Aeropostal Venezolana, National Airlines, Pan American World Airways and Panair do Brasil were cancelled.<ref name=darling119/><ref name=JAPL/> When the redesigned Comet 4 entered service, it was flown by customers BOAC, Aerolíneas Argentinas, and East African Airways,<ref name=d47-61>Darling 2001, pp. 47–61.</ref> while the Comet 4B variant was operated by customers BEA and Olympic Airways <ref name=d47-61/> and the Comet 4C model was flown by customers Kuwait Airways, Mexicana, Middle East Airlines, Misrair Airlines and Sudan Airways.<ref name=JAPL/>

Other operators used the Comet either through leasing arrangements or through second-hand acquisitions. BOAC's Comet 4s were leased out to Air Ceylon, Air India, AREA Ecuador, Central African Airways<ref>Simons, Graham M. "Comet! The World's First Jet Airliner" U.K. Pen and Sword, 2013 {{ISBN|1-7815-9279-9}}. p. 232</ref> and Qantas;<ref name=darling119>Darling 2005, p. 119.</ref><ref>Macfarlane, Ian. [https://abpic.co.uk/pictures/view/1003492/ "De Havilland DH.106 Comet 4, G-APDJ, Air Ceylon."] ''Air-Britain Photographic Images Collection''. Retrieved 19 November 2010.</ref> after 1965 they were sold to AREA Ecuador, Dan-Air, Mexicana, Malaysian Airways, and the Ministry of Defence.<ref name=JAPL/><ref name=d47-61/><ref name=MoF/> BEA's Comet 4Bs were chartered by Cyprus Airways, Malta Airways and Transportes Aéreos Portugueses.<ref name=darling117>Darling 2005, p. 117.</ref> Channel Airways obtained five Comet 4Bs from BEA in 1970 for inclusive tour charters.<ref name=darling138>Darling 2005, p. 138.</ref> Dan-Air bought all of the surviving flyable Comet 4s from the late 1960s into the 1970s; some were for spares reclamation, but most were operated on the carrier's inclusive-tour charters; a total of 48 Comets of all marks were acquired by the airline.<ref>Davies and Birtles 1999, p. 54.</ref>

In military service, the United Kingdom's Royal Air Force was the largest operator, with 51 Squadron (1958–1975; Comet C2, 2R), 192 Squadron (1957–1958; Comet C2, 2R), 216 Squadron (1956–1975; Comet C2 and C4), and the Royal Aircraft Establishment using the aircraft.<ref name=Jones68/><ref>Institution of Electrical Engineers 1978, p. 89.</ref> The {{wipe|Royal Canadian Air Force}} also operated Comet 1As (later retrofitted to 1XB) through its 412 Squadron from 1953 to 1963.<ref name=Walker40/>

==Accidents and incidents==
The Comet was involved in <!--28 [[Engineering:Aviation accidents and incidents|aviation occurrences]],<ref>[https://aviation-safety.net/database/dblist.php?Type=190 "de Havilland Comet incidents."] ''Aviation Safety Network.'' Retrieved: 28 May 2012.</ref> of which --> 25 hull-loss accidents, including 13 fatal crashes which resulted in 492 fatalities.<ref name=asn>[https://aviation-safety.net/database/dblist.php?field=typecode&var=190%&cat=%1&sorteer=datekey&page=1 "de Havilland Comet hull-losses."] ''Aviation Safety Network.'' Retrieved: 28 May 2012.</ref> Pilot error was blamed for the type's first fatal accident, which occurred during takeoff at Karachi, Pakistan, on 3 March 1953 and involved a Canadian Pacific Airlines Comet 1A.<ref name=JAPL>Roach and Eastwood 1992, pp. 331–335.</ref> Three fatal Comet 1 crashes were due to structural problems, specifically British Overseas Airways Corporation flight 783 on 2 May 1953, British Overseas Airways Corporation flight 781 on 10 January 1954, and South African Airways flight 201 on 8 April 1954, led to the grounding of the entire Comet fleet. After design modifications were implemented, Comet services resumed on October 4, 1958, with Comet 4s.<ref name=JAPL/><ref>{{cite web |title=Why are airplane windows rounded? |website=modernairliners.com |date=28 September 2016 |author=Pisquali |url=https://www.modernairliners.com/modern-airliner-posts/why-are-airplane-windows-rounded |access-date=22 January 2019 |quote=Whilst the Comet mark one never flew again and sales were severely affected for the following versions, it still went on to have a successful 30 years of life with rounded windows.}}</ref>

[[File:BOAC Comet Manteufel.jpg|thumb|left|Comet 4 G-APDN crashed in the Spanish Montseny range in July 1970 during a Dan-Air flight.<ref name=asn/>]]

Pilot error resulting in controlled flight into terrain was blamed for five fatal Comet 4 accidents: an Aerolíneas Argentinas crash near Asunción, Paraguay, on 27 August 1959, Aerolíneas Argentinas Flight 322 at Campinas near São Paulo, Brazil, on 23 November 1961, United Arab Airlines Flight 869 in Thailand's Khao Yai mountains on 19 July 1962, a Saudi Arabian Government crash in the Italian Alps on 20 March 1963, and United Arab Airlines Flight 844 in Tripoli, Libya, on 2 January 1971.<ref name=JAPL/> The Dan-Air de Havilland Comet crash in Spain's Montseny range on 3 July 1970 was attributed to navigational errors by [[Engineering:Air traffic control|air traffic control]] and pilots.<ref>[http://aviation-safety.net/database/record.php?id=19700703-0 "ASN Aircraft accident de Havilland DH-106 Comet 4 G-APDN Sierra del Montseny"] {{Webarchive|url=https://web.archive.org/web/20131020072629/http://aviation-safety.net/database/record.php?id=19700703-0 |date=20 October 2013}}. Aviation Safety Network, 28 May 2012. Retrieved 28 May 2012.</ref> Other fatal Comet 4 accidents included a British European Airways crash in Ankara, Turkey, following instrument failure on 21 December 1961, a United Arab Airlines Flight 869 crash during inclement weather near Bombay, India, on 28 July 1963, and the terrorist bombing of Cyprus Airways Flight 284 off the Turkish coast on 12 October 1967.<ref name=JAPL/>

Nine Comets, including Comet 1s operated by BOAC and Union Aeromaritime de Transport and Comet 4s flown by Aerolíneas Argentinas, Dan-Air, Malaysian Airlines and United Arab Airlines, were irreparably damaged during takeoff or landing accidents that were survived by all on board.<ref name=JAPL/><ref name=asn/> A hangar fire damaged a No. 192 Squadron RAF Comet 2R beyond repair on 13 September 1957, and three Middle East Airlines Comet 4Cs were destroyed by Israeli troops at Beirut, Lebanon, on 28 December 1968.<ref name=JAPL/>

==Aircraft on display==
[[File:De Havilland Comet RAF Museum Cosford.jpg|thumb|Comet 1 G-APAS at the RAF Museum Cosford in Shropshire]]

Since retirement, three early-generation Comet airframes have survived in museum collections. The only complete remaining Comet 1, a Comet 1XB with the registration G-APAS, the very last Comet 1 built, is displayed at the RAF Museum Cosford.<ref name=cosford/> Though painted in BOAC colours, it never flew for the airline, having been first delivered to Air France and then to the Ministry of Supply after conversion to 1XB standard;<ref name=cosford>[http://www.rafmuseum.org.uk/cosford/collections/aircraft/de-havilland-comet-1a.cfm "de Havilland Comet 1A."] {{webarchive |url=https://web.archive.org/web/20101206055821/http://www.rafmuseum.org.uk/cosford/collections/aircraft/de-havilland-comet-1a.cfm |date=6 December 2010}} ''Royal Air Force Museum Cosford''. Retrieved 1 November 2010.</ref> this aircraft also served with the RAF as XM823. The sole surviving Comet fuselage with the original square-shaped windows, part of a Comet 1A registered F-BGNX, has undergone restoration and is on display at the de Havilland Aircraft Museum in Hertfordshire, England.<ref>{{cite web |url=http://www.dehavillandmuseum.co.uk/aircraft/de-havilland-dh106-comet-1a/ |title=de Havilland DH106 Comet 1A – de Havilland Aircraft Museum |website=dehavillandmuseum.co.uk |access-date=25 April 2016}}</ref> A Comet C2 ''Sagittarius'' with serial ''XK699'', later maintenance serial 7971M, was formerly on display at the gate of RAF Lyneham in Wiltshire, England since 1987.<ref>Barratt, Tristan p. [https://www.flickr.com/photos/tristanbarratt/2044161326/ "Gate Guardian Comet C2 Sagittarius – XK699 – RAF Lyneham."] ''Flickr''. Retrieved 2 November 2010.</ref><ref name=XK699>Araujo, Ignacio. [http://www.publictenders.net/node/1664492 GB-High Wycombe: "Dismantlement and relocation of Gate Guardian Comet C2 XK699."] {{Webarchive|url=https://web.archive.org/web/20140202165754/http://www.publictenders.net/node/1664492 |date=2 February 2014}} ''Defence Equipment & Support''. Retrieved 31 May 2012.</ref> In 2012, with the planned closure of RAF Lyneham, the aircraft was slated to be dismantled and shipped to the RAF Museum Cosford where it was to be re-assembled for display. The move was cancelled due to the level of corrosion and the majority of the airframe was scrapped in 2013, the cockpit section going to the Boscombe Down Aviation Collection at Old Sarum Airfield.<ref>{{citation |date=5 November 2013 |title=Nose of RAF Lyneham's Comet Mk2 saved by volunteers |publisher=BBC |url=https://www.bbc.co.uk/news/uk-england-wiltshire-24940615}}</ref>

[[File:De Havilland Comet - Imperial War Museum Duxford.jpg|thumb|left|Comet 4 G-APDB outdoors at the Imperial War Museum Duxford in Cambridgeshire; this aircraft was later painted in BOAC's livery and placed inside the museum's AirSpace hall.]]

Six complete Comet 4s are housed in museum collections. The Imperial War Museum Duxford has a Comet 4 (G-APDB), originally in Dan-Air colours as part of its Flight Line Display, and later in BOAC livery at its AirSpace building.<ref>Oakey, Michael, ed. "Duxford's AirSpace opens". ''Aeroplane'', Vol. 35, No. 9, September 2007.</ref> A Comet 4B (G-APYD) is stored in a facility at the Science Museum at Wroughton in Wiltshire, England.<ref>[http://www.ssplprints.com/image.php?id=82768 "De Havilland Comet 4B airliner, serial no 6438, 1960."] ''Science & Society Picture Library''. Retrieved 2 November 2010.</ref> Comet 4Cs are exhibited at the ''Flugausstellung Peter Junior'' at Hermeskeil, Germany (G-BDIW),<ref>[http://www.luftfahrtmuseum.com/htmi/imr/dhj.htm "DeHavilland DH 106 Comet 4 C."] {{webarchive |url=https://web.archive.org/web/20120301022611/http://www.luftfahrtmuseum.com/htmi/imr/dhj.htm |date=1 March 2012}} ''luftfahrtmuseum.com''. Retrieved 2 November 2010.</ref> the Museum of Flight Restoration Center near Everett, Washington (N888WA),<ref name=MoF>[http://www.museumofflight.org/aircraft/de-havilland-dh-106-comet-mk-4c "de Havilland D.H. 106 Comet Mk. 4C."] ''Museum of Flight''. Retrieved 2 November 2010.</ref> and the National Museum of Flight near Edinburgh, Scotland (G-BDIX).<ref>"emdjt42." [https://www.flickr.com/photos/emdjt42/4063299981/ "De Havilland Comet 4C G-BDIX Interior View Scottish Museum of Flight."] ''[[Social:Flickr|Flickr]]''. Retrieved 2 November 2010</ref>

The last Comet to fly, Comet 4C ''Canopus'' (XS235),<ref name=walker169/> is kept in running condition at Bruntingthorpe Aerodrome, where fast taxi-runs are regularly conducted.<ref>[https://www.youtube.com/watch?v=fjTfg6CJb_w "DH106 Comet 'Canopus' 'Fast Taxi Run' – Bruntingthorpe Cold War Jets (May 2018)"] ''youtube.com''. Retrieved 28 July 2020.</ref> Since the 2000s, several parties have proposed restoring ''Canopus'', which is maintained by a staff of volunteers,<ref name=bruntingthorpe>{{cite web |url=https://www.bruntingthorpe.com/aviation/discover-explore/aviation-museum |title=Bruntingthorpe Aircraft Museum |publisher=Aviation Museum, Bruntingthorpe |access-date=22 March 2019 |archive-date=22 March 2019 |archive-url=https://web.archive.org/web/20190322213741/https://www.bruntingthorpe.com/aviation/discover-explore/aviation-museum |url-status=dead }}</ref> to airworthy, fully flight-capable condition.<ref name=d5>Darling 2001, p. 5.</ref> The Bruntingthorpe Aerodrome also displays a related Hawker Siddeley Nimrod MR2 aircraft.<ref name=bruntingthorpe/>

==Specifications==
{{multiple image
|align=left
|width1=175
|image1=De Havilland Comet 3-view line drawing.svg
|alt1=
|width2=250
|caption1=Comet 4B 3-view schematic (front, side, and dorsal views)
|image2=De Havilland Comet 1 silhouette.jpg
|alt2=
|caption2=Comet 1 3-view in silhouette (note differences in Comet 4 insert, reproduced in same scale)
}}
{{Clear}}
{| class="wikitable" style="text-align:center"
|-
! Variant<ref name=Jacksondhp464>Jackson 1987, p. 464.</ref>
! Comet 1 !! Comet 2 !! Comet 3 !! Comet 4
|-
![[Engineering:Cockpit|Cockpit]] crew
| colspan=4 | 4 (2 pilots, [[Engineering:Flight engineer|flight engineer]], and radio operator/navigator)<ref name=JAWA65p153-4>Taylor 1965, pp. 153–154.</ref>
|-
!Passengers
| colspan=2 | 36–44<ref name=Winchester109/><ref name=Times52516/>
| 58–76<ref name=thenew>{{citation |title=The New Comet |work=Flight |date=30 July 1954 |page=132 |url=http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%202137.html |access-date=1 May 2012}}</ref>
| 56–81<ref name=pax>''Flight'', 28 March 1958, pp. 422–423.</ref>{{dubious|reason=The Dan–Air Comet 4 that crashed in July 1970 was carrying over 100 passengers.|date=November 2021}}
|-
! Length
| {{cvt|93|ft}}<ref name=ca1953>[http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200296.html "Commercial Aircraft 1953: De Havilland Comet."] ''Flight'' 6 March 1953. Retrieved 1 May 2012. </ref>
|{{cvt|96|ft|1|in|lk=on}}<ref name=ca1953/>
| colspan="2" |{{cvt|111|ft|6|in}}<ref name=thenew/><ref name=more/>
|-
![[Engineering:Empennage|Tail]] height
|colspan="4"| {{cvt|29|ft|6|in}}<ref name=more>[http://www.flightglobal.com/pdfarchive/view/1957/1957%20-%201676.html "Comet 4C: More Payload on Medium Stages."] ''Flight'' 15 November 1957, p. 764. Retrieved 1 May 2012.</ref>
|-
![[Wingspan]]
|colspan="4"| {{cvt|115|ft}}<ref name=more/><ref name=trans1955/>
|-
![[Physics:Wing|Wing area]]
| colspan=3 | {{cvt|2015|sqft||lk=on}}<ref name=ca1953/>
|{{cvt|2121|sqft}}<ref name=more/>
|-
![[Engineering:Aspect ratio (aeronautics)|Aspect ratio]]
| colspan=3 | {{#expr:115/(2015/115)round2}} || {{#expr:115/(2121/115)round2}}
|-
!Airfoil
|colspan="4"| [[Physics:NACA airfoil|NACA 63A116 mod]] root, NACA 63A112 mod tip<ref>Lednicer, David. [http://www.ae.illinois.edu/m-selig/ads/aircraft.html "The Incomplete Guide to Airfoil Usage."] {{Webarchive|url=https://web.archive.org/web/20100420012244/http://www.ae.illinois.edu/m-selig/ads/aircraft.html |date=20 April 2010}} ''UIUC Applied Aerodynamics Group'', 15 September 2010. Retrieved 26 April 2012.</ref>
|-
! [[Engineering:Maximum takeoff weight|MTOW]]
|{{cvt|110000|lb|lk=on}}<ref name=ca1953/>
|{{cvt|120000|lb}}<ref name=ca1953/>
|{{cvt|150000|lb}}<ref name=ca1953/>
|{{cvt|156000|lb}}<ref name=more/>
|-
![[Engineering:Turbojet|Turbojet]]s (x 4)
|[[Engineering:De Havilland Ghost|Halford H.2 Ghost]] 50
|[[Engineering:Rolls-Royce Avon|R-R Avon]] Mk 503/504
|[[Engineering:Rolls-Royce Avon|R-R Avon]] Mk 502/521
|[[Engineering:Rolls-Royce Avon|R-R Avon]] Mk 524
|-
! Unit thrust
| {{cvt|5000|lbf|kN|lk=on}}<ref name=ca1953/>
| {{cvt|7000|lbf|kN}}<ref name=ca1953/>
| {{cvt|10000|lbf|kN}}<ref name=thenew/>
| {{cvt|10500|lbf|kN}}<ref name=ltd>{{citation |title=The De Havilland Aircraft Co., Ltd. |work=Flight |number=2536 |volume=72 |date=30 August 1957 |page=302 |url=http://www.flightglobal.com/pdfarchive/view/1957/1957%20-%201214.html |access-date=1 May 2012}}</ref>
|-
![[Astronomy:Range (aeronautics)|Range]]
|{{cvt|1500|mi|nmi km|disp=out|lk=on}}<ref name=bbc/>
|{{cvt|2600|mi|nmi km|disp=out}}<ref name=trans1955>{{citation |title=Transport Aircraft – 1955 |work=Flight |date=11 March 1955 |number=2407 |volume=67 |page=337 |url=http://www.flightglobal.com/pdfarchive/view/1955/1955%20-%200337.html |access-date=1 May 2012}}</ref>
|{{cvt|2700|mi|nmi km|disp=out}}<ref>Darling 2001, p. 35.</ref>
|{{cvt|3225|mi|nmi km|disp=out}}<ref name=JAWA65p153-4/>
|-
!Cruising [[Physics:Speed|speed]]
|{{cvt|740|kph|kn|order=flip|lk=on}}<ref name=ca1953/>
|{{cvt|790|kph|kn|order=flip}}<ref name=trans1955/>
| colspan=2 | {{cvt|840|kph|kn|order=flip}}<ref name=trans1955/><ref name=ltd/>
|-
!Cruise altitude
| colspan=2 | {{cvt|42000|ft}}<ref name=ca1953/><ref name=trans1955/>
| {{cvt|45000|ft}}<ref name=trans1955/>
| {{cvt|42000|ft}}<ref name=JAWA65p153-4/>
|}

==In popular culture==
<!--===============({{NoMoreCruft}})===============-->
<!-- Please READ Wikipedia:WikiProject Aircraft/page content#Popular culture and Wikipedia:WikiProject Military history/Style guide#Popular culture before adding any "Popular culture" items.

Please do not add the many minor appearances of the aircraft. This section is only for major cultural appearances where the aircraft plays a MAJOR part in the story line, or has an "especially notable" role in what is listed. A verifiable source proving the appearance's notability may be required. Random cruft, including ALL Ace Combat, Battlefield, and Metal Gear Solid appearances, and ALL anime/fiction lookalike speculation, WILL BE removed.

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==See also==
*Arnold Alexander Hall
*Seymour Collection, an aerophilately collection relating to the Comet in the British Library.

{{Aircontent
|related=
* [[Engineering:Hawker Siddeley Nimrod|Hawker Siddeley Nimrod]]
* [[Engineering:Hawker Siddeley Nimrod R1|Hawker Siddeley Nimrod R1]]
* [[Engineering:British Aerospace Nimrod AEW3|British Aerospace Nimrod AEW3]]
* [[Engineering:BAE Systems Nimrod MRA4|BAE Systems Nimrod MRA4]]
|similar aircraft=
* [[Engineering:Boeing 707|Boeing 707]]
* [[Engineering:Convair 880|Convair 880]]
* [[Engineering:Douglas DC-8|Douglas DC-8]]
* [[Engineering:Tupolev Tu-104|Tupolev Tu-104]]
* [[Engineering:Sud Aviation Caravelle|Sud Aviation Caravelle]]
|lists=
* [[Engineering:List of civil aircraft|List of civil aircraft]]
* [[Engineering:List of jet airliners|List of jet airliners]]
}}

==References==
;Notes
{{Reflist|45em|group=N}}

;Citations
{{Reflist}}

;Bibliography
{{Refbegin|}}
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* ''Antennas and Propagation, Part 1.'' London: Institution of Electrical Engineers, 1978. {{ISBN|0-85296-196-0|}}.
* Atkinson, R. J., W. J. Winkworth and G. M. Norris. [http://naca.central.cranfield.ac.uk/reports/arc/rm/3248.pdf "Behaviour of Skin Fatigue Cracks at the Corners of Windows in a ''Comet'' I Fuselage"] {{Webarchive|url=https://web.archive.org/web/20070614204718/http://naca.central.cranfield.ac.uk/reports/arc/rm/3248.pdf |date=14 June 2007 }}. Ministry of Aviation via Her Majesty's Stationery Office, 1962.
* Avrane, A. ''Sud Est Caravelle''. London: Jane's Publishing, 1981. {{ISBN|0-7106-0044-5|}}.
* Beaty, David. ''Strange Encounters: Mysteries of the Air''. London: Atheneum, 1984. {{ISBN|978-0-689-11447-2|}}.
* Bibel, George D. ''Beyond the Black Box: The Forensics of Airplane Crashes''. Baltimore, Maryland: JHU Press, 2008. {{ISBN|0-8018-8631-7|}}.
* Birtles, P.J. ''Classic Civil Aircraft 3: De Havilland Comet''. Shepperton, UK: Ian Allan, 1990. {{ISBN|0-7110-1947-9|}}.
* Birtles, P.J. "The de Havilland Comet Srs. 1–4." ''Aircraft in Profile, Volume 5.'' New York: Doubleday, 1970, first edition 1967.
* Bray, Robin. ''The Comet that Fell to Earth''. Cumbria, UK: Hayloft Publishing, 2015. {{ISBN|978-1-910237-01-4|}}.
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* [http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%202971.html "The Comet Accidents: History of Events: Sir Lionel Heald's Introductory Summary at the Enquiry"]. ''Flight'', 29 October 1954, pp.&nbsp;652–654.
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{{Refend}}

==External links==
* [https://www.baesystems.com/en/heritage/de-havilland-comet-1---2 De Havilland DH106 Comet 1 & 2] from BAE Systems site
* [http://www.flightglobal.com/pdfarchive/view/1949/1949%20-%201324.html "The Comet Emerges" a 1949 ''Flight'' article on the unveiling of the Comet prototype]
* [http://www.flightglobal.com/pdfarchive/view/1949/1949%20-%201356.html "Comet in the Sky" a 1949 ''Flight'' article on the Comet's maiden flight]
* [https://www.youtube.com/watch?v=242TXAq79I8 Film of BOAC De Havilland Comet 3 G-ANLO at Vancouver International Airport in December 1955 ]
* [https://web.archive.org/web/20101206071542/http://www.airforce.forces.gc.ca/v2/hst/page-eng.asp?id=621 The de Havilland Comet in RCAF Service]
* [http://www.flightglobal.com/pdfarchive/view/1951/1951%20-%200803.html "Comet Construction Methods"] a 1951 ''Flight'' article
* [http://www.flightglobal.com/pdfarchive/view/1952/1952%20-%201127.html "The Tale of the Comet" a 1952 ''Flight'' article on the design and development of the Comet]
* [http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200539.html "Conversion to Comets" a 1953 ''Flight'' article on the Comet's handling]
* [http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200555.html "Comet Engineering" a 1953 ''Flight'' article] by Bill Gunston
* [http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%202971.html "The Comet Accidents: History of Events" a 1954 ''Flight'' article of Sir Lionel Heald's summary of the enquiry]
* [http://www.flightglobal.com/pdfarchive/view/1955/1955%20-%200193.html "Report of the Comet Inquiry", a 1955 ''Flight'' article on the publishing of the enquiry into the Comet design]
* [https://web.archive.org/web/20121001190510/http://www.kbtc.org/page.php?id=795 Project Comet] Documentary produced by Full Focus
* [http://www.flightglobal.com/pdfarchive/view/1969/1969%20-%202527.html "The Comet is Twenty"] a 1969 ''Flight'' article
* [http://www.flightglobal.com/pdfarchive/view/1989/1989%20-%202330.html "Jet Transport's Next 40 Years"] a 1989 ''Flight'' article on the Comet's influence


[[Category:Low-wing aircraft]]
[[Category:Quadjets]]

{{Sourceattribution|De Havilland Comet}}