BOAC de Havilland Comet 1 , en route to Johannesburg from London, breaks its journey at Entebbe Airport, Uganda. 1952
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). Unlike the picture above it had riveted windows, square, and was one of the reasons for the splitting of the Aluminium fuselage.
The Comet had its roots in the British government’s wartime planning for the post war world – as early as 1942, the Air Ministry established a committee led by aviation pioneer and government minister John Moore-Brabazon, 1st Baron Brabazon of Tara, to consider how to meet future civilian aircraft needs.
Brabazon’s Committee recommended that six types of civilian aircraft be developed, ranging from a large, luxurious airliner capable of serving the transatlantic market to a ten seat plane for low volume domestic routes. The resulting designs were a mixed bunch. The large Bristol Brabazon was a flop – only one prototype was built. The economics of a plane the size of a Boeing 767 but with just 100 seats were as weak as the design was over-ambitious.
By 1942, the RAF had ordered what became the de Havilland Vampire as one of two prototype fighters using the new technology – and its success gave Brabazon committee member Geoffrey de Havilland the confidence to push the committee to include a specification for a 100 seat pressurised jet powered airliner, aiming for a cruising speed of 400 mph (640 km/h).
Picture from Flightglobal.com
De Havilland was convinced his company could produce a plane meeting the resulting specification, and, determined to get ahead of his competitors, stuck to his guns. And, in February 1945, the British government duly gave de Havilland the contract to develop what became the Comet; by December the state owned British Overseas Airways Corporation (BOAC) had ordered 10, and a design team began work in 1946 – all without any publicity.
Colin Williams Photography
The design was all de Havilland’s, led by Ronald Bishop (1903 – 1989), a 25 year de Havilland veteran and also chief designer of the Mosquito.
The Real Story of the Comet Disaster (De Havilland Comet - Structural Fatigue)
It also discusses the jet airliners that would compete against the Comet in the late 50's, the American built Boeing 707 and Douglas DC-8.
Frank Halford's Ghost engines were in the prototype 1 or Comet 1 until they were replaced by Rolls Royce Avons from series 2 onwards. Comet variants 2,3 and 4 were longer and carried more passengers. Unlike the Ghosts, which used centrifugal flow, the Rolls-Royce Avon employed an axial-flow design, which shot air directly through the engine, a more efficient arrangement. Airlines from around the world lined up to purchase the Avon-powered craft.
Even though The Comet was groundbreaking in passenger jet travel, being faster and more comfortable, the crashes of The Comet early series of planes is what is remembered now when the name is mentioned. This subsequently means that there is a mass of material of studies about the subject.
'Engineers from both Boeing and Douglas are reported to have told de Havilland privately that they also had no idea about the fatigue and pressurisation problems, and may well have made the same mistake if it hadn’t been for the Comet. Design problems were also magnified by the manufacturing process. Rivets attaching the windows were punched instead of drilled, creating more stress than expected by the designers — who had planned for drilled rivets. Wherever the blame is laid, the aviation industry benefited from the intensive analysis and resulting learnings about pressurisation and metal fatigue.'
From : Tech wrecks: Lessons from some of the biggest hardware ...by David Cardinal on May 25, 2012
According to de Havilland's chief test pilot John Cunningham, who had flown the prototype's first flight, representatives from American manufacturers such as Boeing and Douglas privately disclosed that if de Havilland had not experienced the Comet's pressurisation problems first, it would have happened to them.
P72, Faith, Nicholas. Black Box: Why Air Safety is no Accident, The Book Every Air Traveller Should Read. London: Boxtree, 1996. ISBN 0-7522-2118-3.
Huge amounts of data led to not only air safety being improved it also impacted on the development of the processing of aerospace material plus manufacture of the aircraft.*
*Fracture processes of aerospace materials://www.sciencedirect.com/science/article/pii/B9781855739468500182
This great article by Jonathan Glancey gives the facts on aeroplane safety and its development in aviation. Written April 2014 Extract from : The tragedies that were part of a long and fraught process that has helped make flying as safe as it is today.Link to external siteBefore engines could lift heavier-than-air machines convincingly off the ground, any attempt at flight had been dangerous, and yet for hundreds of years, adventurers strapped wings to their arms, and leapt off hilltops and towers in the vain hope of flying. Even when a part of the science of flight had been understood, men like Otto Lilienthal, a 19th Century German pioneer who experimented with gliders, were doomed, their contraptions too heavy and too unresponsive to allow their brave pilots to chase birds or even to get much above ground.Sacrifices were made in great numbers in the early days of powered flight. Aeroplanes suffered a catalogue of catastrophic construction and engineering failures compounded by bad weather and pilot error. These tragedies were part of a long and fraught process that helped make flying as safe as it is today.Today, the Rolls-Royce logo on the engines of an airliner is taken as a guarantee of smooth-spinning and reliable power; yet, 32-year-old Charles Rolls himself was killed at Bournemouth in July 1910 when the tail of his Wright Flyer fell off. He was the first to die in a British air accident. Roy Chadwick, the designer who gave us the legendary Rolls-Royce Merlin-powered Lancaster and the striking Vulcan V-bomber died in August 1947 when his prototype Avro Tudor airliner crashed in the Lake District, the result of a maintenance error.Chadwick crashed and died at the very time a new post-war aviation industry was taking flight. Before the Second World War, civil aviation was strictly the realm of the wealthy, adventurers, government officials and lucky journalists. Airliners had been small, if charmingly fitted out at their best like first class ship’s cabins or Pullman railway carriages. Now, the industry was to expand rapidly, its future looking towards carrying untold numbers of passengers and prodigious amounts of freight worldwide. This new chapter was to be told by jet airliners, by those who designed and tested them, and those fare-paying passengers who took to the air in these new and unproven machines. The development of fast jet flight led to the death of legions of test pilots, notoriously during the 1950s. But these accidents led to technical improvements and changes in operations and legislation that were to make civil aviation increasingly safe.Among the most shocking were the three occasions, within a year, when brand new de Havilland Comet airliners broke up in flight. Launched into service with BOAC in 1952, the Comet was the world’s first jet airliner. It was a beauty. It could cross the Atlantic in style and, for a moment, it looked as Britain might truly lead the Jet Age. And, yet, because the nature of metal fatigue, new construction techniques and repeated re-pressurisation of airliner cabins was little understood, early Comets were to fail in spectacularly fatal fashion. In 1953 and 1954, three Comets broke up soon after taking off killing all on board, two over the Mediterranean as they climbed in January and April that year from Rome’s Ciampino airport, and a third caught in a thunder squall on the Calcutta to Delhi leg of a BOAC flight from Singapore to London. Comet flights were suspended, and production of the British jet was halted.The investigation that followed broke new ground in aviation safety. Led by Sir Arnold Hall, director of the Royal Aircraft Establishment, Farnborough, a team of engineers and scientists rebuilt recovered wrecks and, subjecting one of the aircraft hulls to pressurisation tests in a giant water tank, discovered what had gone so very wrong. Cracks had developed in the fuselages of the ill-fated Comets, around doors and window apertures as the aircraft were subject to repeated pressurisation cycles - where the fuselage is pressurised for passenger comfort at the start of each flight and depressurised when the engines shut down - and as the particular form of riveted construction couldn’t contain the stretching forces at work on the aircraft’s stressed hull. The Comets had blown apart at the seams.Improved construction techniques, the fitting of rounded rather than square windows (these, too, caused cracks) and other improvements ensured that later Comets were safe. Indeed, the final development of the jet – the air-reconnaissance Nimrod – was in service with the RAF until June 2011, more than 60 years after the maiden flight of the Comet 1 in 1949. After the Comet suffered a series of accidents, airliners switched to the Boeing 707 for long-distance flights.Engineers in the United States, however, took note of the RAE’s findings and were able to incorporate these into the hugely successful jetliners made by Boeing and Douglas that were to dominate not just transatlantic but global long-distance services. Effectively, fare-paying Comet passengers had been used as research and development guinea pigs, a horrible thought. Sad, too, was the fact that Comet and other British jet sales never really took off after these early accidents. Even BOAC, Britain’s international airline and first champion of the Comet, was quick to swap to the Boeing 707 for long-distance flights. If only de Havilland had got things right in 1952, we might have seen 800-seat Comet 2000s under construction today. Meanwhile, the deep-sea aircraft salvage, reconstruction and investigation techniques developed by the RAE at Farnborough are still very much in use, as are specific lessons learned from fatal air accidents since then. A collision over the Grand Canyon in June 1956, for example, between a TWA Super Constellation and a United Airlines DC-7 – the first commercial crash numbering more than a hundred deaths – led to upgraded forms of air traffic control.The major change came in 1958 with the formation of the Federal Aviation Agency (FAA). This new body was given total authority over American airspace, including military flights, ensuring that all were mapped and charted. At the same time, the latest radar and radio technology meant there were no “dead” areas over regular flight paths where contact with crews could be lost, a frequent occurrence into the mid-1950s. Radio transponders were soon tracing aircraft in flight, while collision warning systems and, finally in the 1970s, GPS (Global Positioning System] helped to make aviation so much safer. In the past half century, and with 30,000 flights made each day, no airliners have collided over the US. A Japanese Airlines Boeing 747 crash in 1985 highlighted the importance of knowing the exact structural state of a specific aircraft.Other notable accidents led to such helpful developments as Cockpit Resource Management (crews working as a cross-checking team at all times), smoke detectors and automatic fire extinguishers in lavatories and cargo-holds, wind-shear detectors, transponders and flame-retardant materials. Even then, airlines have pushed reliable jets too far on occasions expecting such winged workhorses as the Boeing 737 (8,000 built) to fly around the clock.In April 1988, part of the fuselage of an Aloha 737 flying from Hilo to Honolulu failed at 24,000ft. One flight attendant was swept overboard, while everyone else survived, despite passengers flying with nothing between them, their safety belts, and thin air. It was found that the hard-pressed Boeing had undergone a total of 89,000 re-pressurisations – the first Comets had failed at between just 900 and 3,060 re-pressurisations.As a result, the FAA set up its National Ageing Aircraft Research Program, employing its new full scale Aircraft Structural Test Evaluation and Research Facility in New Jersey; this allowed for predictive testing for structural fatigue, corrosion and many aspects of the operation of aircraft to increase the long-term safety of civil airliners not just in the US, but worldwide.The vital importance of knowing the exact structural state of a specific aircraft was highlighted in August 1985, when a Japanese Airlines Boeing 747 flying from Tokyo to Osaka lost all cabin pressure, along with its hydraulic fluids and its vertical stabiliser. The crew struggled valiantly to find a way to bring the stricken aircraft down to land, yet in the event it crashed, killing 520 of those on board; there were – rather miraculously – four survivors. Concorde’s accident in July 2000 led to its retirement three years later.The Jumbo had always seemed such a safe aircraft, yet on this occasion a bodged repair made several years earlier, and very much not to Boeing specifications, to the rear pressure bulkhead - separating the passenger cabin from the tail – broke apart much as the fuselages of those early Comets had done.There has always been something new to learn, and ever-tighter safety standards to be upheld. A Swissair MD-11, for instance, caught fire and exploded, killing all 229 on board, on a flight from New York to Geneva in September 1998. The cause was a fire in the aircraft’s entertainment system. New flameproof materials were introduced.In July 2000, a loose piece of metal dropped on the runway from a Continental Airlines DC-10 cut one of the tyres of a Concorde taking off at the Charles de Gaulle airport near Paris. The debris caused a pressure wave that ruptured a fuel tank, its contents ignited, most probably, by a severed electrical cable. The plane caught fire and crashed into a hotel, killing all 100 passengers, nine crew and four hotel employees. It was the first fatal accident in the Mach 2 aircraft’s super-safe history; and, although, fuel tanks and tyres were upgraded, it was also the blow that triggered Concorde’s retirement three years later.
15th April 2014 for BBC FUTURE
Before and during the Comet era the aircraft design philosophy was predominantly SAFE-LIFE, which means that the structure was designed to sustain the required fatigue life with no initial damage and no accumulation of damage during service e.g. cracking.The Comet accidents showed that around stress concentration cracks would initiate and propagate much earlier than expected, such that safety could not be universally guaranteed in the SAFE-LIFE approach without uneconomically short aircraft service lives.
For this reason the FAIL-SAFE design philosophy was developed in the late 1950’s. All materials are assumed to contain a finite initial defect size before entering service that may grow due to fatigue loading in-service. The aircraft structure is thus designed to sustain structural damage without compromising safety up to a critical damage size that can be easily detected by visual inspection between flights. All inspections are coupled with crack propagation calculations that guarantee that an observed crack is not susceptible to grow to the critical size between two inspection cycles, in which case adequate repair is performed. Furthermore, the structure is designed to be damage tolerant with multiple load paths and built-in redundancies that impart residual strength to the aircraft in case the primary structure is compromised in-service.
1. R.J.H Wanhill (2002). Milestone Case Histories in Aircraft Structural Design. National Aerospace Laboratory. NLR-TP-2002-521 from : https://aerospaceengineeringblog.com/dehavilland-comet-crash/
Putting it simply
The fail-safe approach relies on the fact that the failure of a member in a redundant structure does not necessarily lead to the collapse of the complete structure, provided the remaining members are able to carry the load shed by the failed member and can withstand further repeated loads until the presence of the failed member is discovered. Such a structure is called a fail-safe structure or a damage tolerant structure.
Generally, it is more economical to design some parts of the structure to be fail-safe rather than to have a long safe life, since such components can be lighter. When failure is detected, either through a routine inspection or by some malfunction, such as fuel leakage from a wing crack, the particular aircraft may be taken out of service and repaired. However, the structure must be designed and the inspection intervals arranged such that a failure, for example, a crack, too small to be noticed at one inspection must not increase to a catastrophic size before the next.
Chapter 14 on Fatigue by T.H.G. Megson, in Introduction to Aircraft Structural Analysis (Third Edition), 2018
Civil Aircraft Accident: Report of the Court of Inquiry Into the Accidents to Comet
'The Comet 4 (including 4B/4C) was the most successful. 77 were built, twice as many as all the other series put together, and they flew a total of 1.7 million hours. It was in commercial service from October 1958 to November 1980, and XS-235 continued to fly for the MoD until 1997.
The structure was completely revised, with heavier gauge skin, oval windows, and reinforcement around apertures and butt straps. A new pressure testing tank was built in which an entire aircraft could be submitted to torture, simultaneously loading the fuselage by pressurisation while hydraulic rams acted on the wings. The whole process was accelerated so one “flight” occurred every 4 minutes. This enabled the Comet 4 to be certified for 30,000 hours use. Test airframe 6402 was tested to 100,000 hours.'
In 1951 the poor financial state of three airlines (Etaireía, Technical and Aeronautical Exploitations,Greek Air Transport) led to a decision by the Greek state to merge them into a single operator, TAE Greek National Airlines (TAE).
The new airline operated a fleet of twin-engine Douglas DC-3 airliners on domestic Greek routes until the last example was disposed of in May 1970. A four-engine Douglas DC-4 was acquired in 1950 and this was operated on a route to London. The new airline faced financial problems so the government closed it down in 1955.
There was no buyers for the airline so the Greek State bought the company back. In July 1956 the Greek State reached an agreement with Greek shipping magnate Aristotle Onassis for Onassis to purchase the airline. The company flew under the T.A.E. name until the end of the year and for the first few months of 1957. On 6 April 1957 the company was renamed Olympic Airways (Ολυμπιακή Αεροπορία/Olympiaki Aeroporia).
Olympic Airways operated ten Douglas DC-6Bs between 1958 and 1972 serving the longer domestic and European routes. 
Olympic Airways first jet aircraft type, the de Havilland Comet at Manchester Airport in 1966. The BEA codeshare logo can be partially seen on the fuselage, in red.
The new company developed rapidly. To allay the distrust of air transport by Greeks, Onassis developed the "aviation days of '57" scheme, providing short, free flights in a DC-3 to demonstrate the reliability of air travel. Onassis always wanted to be in the cutting-edge of the technology, so in 1959 he signed a deal to buy four de Havilland Comet 4B that in 1960 was Olympic's first jet aircraft, that entered service.
Olympic and British European Airways created the first codeshare flights; later the companies expanded their cooperation. When Greek crews had to spend a night in London, British crews would fly the Olympic Comets to BEA destinations, and the same with Greek crews and BEA Comets.
On all BEA and OA Comets, there would be a "BEA-OLYMPIC" sign. In 1962 Olympic set a record flying a DH Comet 4B from London to Athens in just two hours and 51 minutes.
2. p260 Roach, J and Eastwood A.B., Piston Engined Airliner Production List, 2007, The Aviation Hobby Shop, ISBN none.
3. ^^ Roach p300-303
4. Our World (supplement)", USA Today, p. 9, 15 February 2007
5. Destiny Prevails: My life with Aristotle, Alexander, Christina Onassis and her daughter, Athina, Paul J. Ioannidis, Livani Publishing, 2013
Olympic Airways first jet aircraft type, the de Havilland Comet at Manchester Airport in 1966. The BEA codeshare logo can be partially seen on the fuselage, in red.
By RuthAS - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=6120000