Case 1 De Havilland S Falling Comet Development Comet De Havilland Aircraft Company Great Q33300019

Case 1: de Havilland’s Falling Comet

The Development of the Comet

The de Havilland Aircraft Company of Great Britain had long beenrespected in the aircraft manufacturing industry for its innovativeand high-performance designs. Coming off its excellent work duringWorld War II, the company believed that it stood poised on thebrink of success in the commercial airframe industry. The deHavilland designers and executives accurately perceived that thenext generation of airplane would be jet-powered. Consequently,they decreed that their newest commercial airframe, tentativelycalled the Comet, would employ jet power and other leading-edgetechnology.

Jets offered a number of advantages over ­propeller-drivenairplanes, the most obvious of which was speed. Jets could cruiseat nearly 450 miles per hour compared with the 300 miles per hour apropeller could generate. For overseas flight, in particular, thisadvantage was important. It could reduce the length of long flightsfrom a mind-numbing two to three days to mere hours, encouragingmore and more businesspeople and tourists to use airplanes as theirprimary method for travel. Further, jets tended to be quieter thanpropeller-driven aircraft, giving a more comfortable interior soundlevel and ride to passengers.

De Havilland engineers sought to create a streamlined airplanethat could simultaneously carry up to 50 passengers in comfort,while maintaining aerodynamics and high speed. After working with anumber of design alternatives, the Comet began to take shape. Itsdesign was, indeed, distinctive: The four jet engines were embeddedin pairs in the wing roots, at the point where they joined thefuselage. From the front, the aircraft looked as though its wingswere literally held in place by the engines. The result of theseinnovative engineering designs was an aircraft that had remarkablestability in flight, was sleek in appearance, and was veryfast.

Another distinctive feature of the aircraft was the pressurizedcabin, intended to maintain passenger comfort at cruising altitudesof up to 30,000 feet. In its original testing for safety, deHavilland engineers had pressurized the airframe to more than fivetimes the recommended air density to ensure that there was a cleanseal. Consequently, they were confident that the pressurizationsystem would perform well at its lower, standardized settings.Finally, in an effort to add some flair to the design, each windowin the passenger cabin was square, rather than the small, round oroval shapes so commonly used.

Knowing that it was facing competition from Boeing Corporationto be first to market with a commercial jet, de Havilland’s goalwas to introduce its new aircraft as quickly as possible, in orderto establish the standard for the commercial airline industry. Atfirst, it appeared the company had succeeded: BOAC (BritishOverseas Airways Corporation) ordered several Comets, as did AirFrance and the British military. De Havilland also received somequeries from interested American airline companies, notably PanAmerican Airlines. It looked as though de Havilland’s strategy wasworking; the company was first to market with a radical new design,using a number of state-of-the-art technologies. BOAC’s first nineComet 1 s entered service with the airline on May 2, 1952. Thefuture looked bright.

Troubles

In early May of 1953, a brand new Comet operated by BOAC leftCalcutta, India, and flew off into the afternoon sky. Six minuteslater and only 22 miles from Calcutta’s Dum Dum Airport, theaircraft exploded and plunged to earth, killing all 43 passengersand crew on board. There had been no indication of problems and nowarning from the pilots of technical difficulties. Investigatorsfrom Great Britain and India tended to believe the crash came aboutdue to pilot error coupled with weather conditions. Evidence fromthe wreckage, including the tail section, seemed to indicate thatthe aircraft had been struck by something heavy, but without anyadditional information forthcoming, both the authorities and deHavilland engineers laid the blame on external causes.

January 10, 1954, was a mild, clear day in Rome as passengersboarded their BOAC aircraft for the final leg of their flight fromSingapore to London. When the airplane reached its cruisingaltitude and speed, it disintegrated over the Mediterranean Sea,near the island of Elba. Most of the airplane was lost at thebottom of the sea, but amid the flotsam 15 bodies of passengers andcrew were recovered. A local physician who examined the remainsnoted: “They showed no look of terror. Death must have come withoutwarning.” As a safety precaution, BOAC instituted a ban on the useof Comets until the airplanes had been thoroughly checked over.Technicians could find nothing wrong with the new aircraft and,following recertification, the airplanes were again brought backinto service.

Alas, it was too soon. On April 8, only 16 days after the Cometwas reintroduced into service, a third aircraft, operated by SouthAfrican Airways, departed from Rome’s Ciampino airport for Cairo,one of the legs of its regular flight from London to Johannesburg.Under perfect flying weather, the airplane rapidly gained itscruising altitude of 26,000 feet and its airspeed of almost 500miles an hour. Suddenly, the flight radio went silent and failed toanswer repeated calls. A search of the ocean off the island ofStromboli, Italy, turned up an oil slick and some debris. Becauseof the depth of the water and the time necessary to arrive at thecrash site, there was little to be found by search crews. Fivebodies were all that were recovered this time, though with an eeriesimilarity to the victims of the second disaster: Facialexpressions showed no fear, as though death had come upon themsuddenly.

What Went Wrong?

Investigators swarmed over the recovered wreckage of theaircraft and reexamined the pieces from the first Calcutta accidentwhile also conducting underwater searches at the sight of thesecond crash near the island of Elba. Guided by underwater cameras,investigators were able to collect sufficient aircraft fragments(in fact, they finally recovered nearly 70% of the airframe) tomake some startling discoveries. The foremost finding, from therecovery of the entire, intact tail section, was that the fuselageof the aircraft had exploded. Second, it appeared that enginefailure was not the cause of the accidents. Another finding wasequally important: The wings and fuselage showed unmistakable signsof metal fatigue, later shown to be the cause of failure in allthree aircraft. This point was important because it advanced thetheory that the problem was one of structural design rather thansimple part failure.

Britain’s Civil Aviation Board immediately grounded the entireComet fleet pending extensive reviews and airworthinesscertification. For the next five months, the CAB set out on anextensive series of tests to isolate the exact causes of themysterious crashes. Before testing was complete, one Comet had beentested literally to destruction, another had its fuel tanksruptured, more than 70 complete test flights were made in a third,and between 50 and 100 test models were broken up. The results ofthe extensive tests indicated a number of structural and designflaws.

Although the aircraft’s designers were convinced that thestructure would remain sound for 10,000 flight hours beforerequiring major structural overhauling, simulations showedunmistakable signs of metal fatigue after the equivalent of only3,000 flight hours. Experts argued that even when fatigue levelswere revised downward to less than 3,000 hours, Comets would not besafe beyond 1,000 flying hours, a ludicrously low figure in termsof the amount of use a commercial airliner is expected to receive.In addition, testing of the fuselage offered disturbing indicationsof the cause of failure. Specifically, cracks began developing inthe corners of the cabin windows, and these cracks were exacerbatedby repeated pressurization and depressurization of the cabin. Theinvestigators noted that this result was most pronounced along therivet lines near the fuselage windows.

Testing also demonstrated that the wings had a low resistance tofatigue. At a number of stages in the tests, serious cracksappeared, starting at the rivet holes near the wheel wells andfinally resulting in rivet heads in the top wing surface actuallyshearing off. Engineers and investigators were findingincontrovertible evidence in the pieces of recovered wreckage thatthe cause of the sudden disintegration of the aircraft could onlyhave been due to cabin pressure blowout. Engineers suspected thatthe critical failure of the aircraft occurred following suddendepressurization, when one or more windows were literally blown outof the aircraft. This led to a sudden “gyroscopic moment” as theaircraft nosed down and began its plunge to earth.

Although at the time no one would admit it, the handwriting wason the wall. After two years, in which Comets carried more than55,000 passengers over 7 million air miles, the Comet 1 was neverto fly again. De Havilland had indeed won the race to be first tomarket with a commercial jet—a race that it would have been betterto have never run at all.

Questions:

Comment on this statement: “Failure is the price we pay fortechnological advancement.”?