De Havilland Comet

Following entry is a record in the “Catalogue of Catastrophe” – a list of failed and troubled projects from around the world.

De Havilland Aircraft – UK
Project name : Comet
Project type : Commercial aircraft design and development
Date : 1949-1954 (filed under historical failures)
Cost :

Synopsis :

Comet 1 showing square windows

Comet 1 showing square windows
click for larger image

Developed in the late 1940’s, the de Havilland Comet was the first jet airliner to enter commercial service. A technological leap forward, the Comet ushered in the jet age, significantly reduced travel times and dramatically increased passenger comfort. Unfortunately the euphoria of the first flight was soon shattered after two aircraft broke up in mid-flight killing all aboard.

Following the incidents the fleet was grounded and an enquiry into the accidents conducted. The inquiry focused on a number of possible causes, but eventually concluded that onboard fires had been the cause of the crashes. Modifications were made to avoid the problem and the fleet was cleared to fly again. Sadly a few months later a third aircraft broke up in flight. Again the fleet was grounded and an enquiry launched.  This time it was found that the crash (and the two prior ones) had been caused by cracks in the metal airframe.

Unlike most prior commercial aircraft the Comet operated at altitudes where the aircraft cabin needed to be pressurized. The pressurization of the cabin resulted in stresses in the aircraft’s metal skin and the cycle of cabin pressurization and depressurization during each flight resulted in small cracks around the edge of the aircraft’s square passenger windows. Over time those cracks grew and on reaching a critical size, propagated catastrophically causing the breakup of the aircraft in mid-flight.

Comet 4 showing revised window design

Comet with revised window design
click for larger image

Although the designers knew about metal fatigue, they had not fully understood how stresses would accumulate at the corners of the square window frames they had included in the design. Following the discovery of the problem the remaining aircraft were modified with round windows. To this day commercial aircraft have rounded or elliptical windows rather than square ones because round shapes spread the stresses out rather than concentrating them in a single point.

Although the Comet did go on to some limited success, the crashes opened the door for the American Boeing 707 and DC-8 designs to dominate the market for commercial aircraft in the 1950’s. As a result, many people feel that the crashes contributed to the UK loosing its spot as a leading developer of commercial aircraft and as such the failure affected a complete industry rather than just a single project or organization.

Contributing factors as reported in the press:
Lack of technical knowledge available at the time (specifically incomplete understanding of how aircraft pressurization would induce metal fatigue). Pressure to get the aircraft flying again resulted in ineffective analysis by the initial enquiry.

Reference links :

  1. De Havilland Comet – Wikipedia page
  2. Aviation safety network – G-ALYP crash
  3. Aviation safety network – G-ALYY crash
  4. Aviation safety network – G-ALYV crash