History of Jet Flight and the Issue of Metal Fatigue

History of Jet Flight and the Issue of Metal Fatigue


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History of Jet Flight and the Issue of Metal Fatigue


Today we fly wherever and whenever we want by use of turboprop aircraft and jet airliners as well as light jets both privately and by contract such as charter flights.  We take day trips to Miami and business trips to Houston.  We use charter flight services for vacations to Paris and for hauling computer equipment to our new facility in Palo Alto.  Air flight is so common that we often forget what it took to get us where we are today.

Jet flight arrived at a significant point in its short but rapid history in May 1952 when the British Overseas Airways Corporation (BOAC) introduced the world to jet transportation. The introduction of the new jet transport to commercial air routes was welcomed by the world with wide open arms. Civilians were going to be able to fly at speeds that were possible only hitherto by military aircraft. The plane that was used was the De Havilland Comet. For more than a year while the American aviation industry dragged aircraft engineers over the design boards the De Havilland Comet reigned as the only commercial jet transport available to the world.

This reign however was short lived when disaster struck on January 10th 1954. With 35 people on board (29 passengers and 6 crew members) a Comet crashed into the sea (in the vicinity of the Island of Elba) killing everybody on board. The incident stunned the world and BOAC immediately grounded all the Comets pending fact finding investigations into the reasons behind the crash.

The wreckage was salvaged from the deep watery grave and reconstructed in the hopes of shedding some light on what transpired an hour after its take off from Rome’s Ciampino Airport on that fateful morning.  After meticulous research and intense investigations and no answers as to why the jet plane crashed, BOAC resumed the commercial flights.

Almost, immediately after operations resumed a second incident under almost identical circumstances struck the jet liner only this time with 21 passengers onboard. En-route from Rome to Cairo, the plane made a routine check with Cairo approximately 30 minutes after takeoff and plunged into the Mediterranean Sea five minutes later. All on board perished and the wreckage could not be salvaged from the deep sea. The British Ministry of Transport and Civil Aviation responded immediately by withdrawing the Certificate of Airworthiness for the Comets operated by BOAC.

A second investigation was launched to establish the cause of the jet crash, only this time investigators had no ‘new material’ to work with. They decided to go back to the findings of the first incident and scour it for anything new that they could or might have missed in the initial investigation. The investigation of the accidents was lengthy and detailed this time as the ministry only released the report on the findings more than a year after the date of the first crash. The main passage of the report stated “The cause of the accident was the structural failure of the pressure cabin brought about by metal fatigue.”  Because the wreckage of the second plane was too deep in the Mediterranean sea to be salvaged, the report merely stated “consistent with the accident being due to the failure of the pressure cabin structure owing to metal fatigue.” A new realization dawned upon the world of aviation, something it had no bearing towards prior to the incidences: Metal fatigue.

Fatigue in a planes structural build is caused by repeated “stress” that is exerted upon the structure due to the constant pressurizing and depressurizing of the cabins. The cabins in planes flying at high altitudes are pressurized to simulate air pressure conditions at lower altitudes. The repeated exertion ‘modifies ‘the structural metal on a microscopic level. The increased ‘state of pressured condition within the cabin’ exerts an outward force on the fuselage skin which causes the ‘surfaces to expand and vice versa when pressure is reduced, causing the surfaces to contract. The repeated stress or modification cause cracks which, if left unattended augments into larger cracks.

This fact was not taken into consideration when the Comet was designed and built.  The metal fatigue was not only due to the pressure factor, but also due to lift, gravitational pull, drags, repeated landing impacts, thrust, turbulence, and sudden erratic maneuvers in mid-air which all contributed to metal fatigue. To make matters worse consider the fact that these ‘stress factors’ act upon a structure that weighs easily more than a hundred tons and travels at speeds exceeding 500 mph.

Maybe after reading this, the role of an aircraft designer can be better appreciated.  Today’s designers, place any new aircraft, jet or turboprop, large or small, through a series of wind-tunnel tests, stress tests, and structural tests.  Before any aircraft is ready for full production, flight tests include maneuvering and repeated pressurization and depressurization.  Indeed, a wonder of technology today is the modern aircraft for the failures of the past are seldom a concern.  Indeed, few of us today step into an aircraft with little concern for the safety and reliability because of the lessons learned though mistakes made in the history of air flight.

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