Investigation Summary
Flight 201 was the final blow to the early jet age's first commercial success. The aircraft, G-ALYY (known as Yoke Yoke), had been returned to service only weeks earlier after a temporary grounding following the crash of BOAC Flight 781 (Yoke Peter) near Elba. Before its final departure from Rome, the aircraft was delayed for 25 hours. While engineers found 30 loose bolts on a wing panel, the primary driver of the delay was a faulty fuel gauge in the center tank, which required a replacement co-axial cable to be flown in from England. The flight finally departed at 18:32 GMT. As the aircraft reached its cruising altitude of 35,000 feet, the pressurized cabin failed. Because the Comet 1 was designed with relatively square windows and thin-gauge aluminum skin, the corners of the apertures acted as stress concentrators. Over repeated flight cycles, these stresses led to fatigue cracks that eventually reached a critical length, causing the fuselage to fail explosively. The wreckage of G-ALYY settled at a depth of approximately 3,300 feet, making recovery nearly impossible with 1950s technology. Consequently, investigators relied heavily on the concurrent salvage and testing of the Elba wreckage to confirm the cause.
Final Conclusions
The investigation concluded that the accident was caused by structural failure of the pressure cabin due to metal fatigue. The stress concentrations at the corners of the cabin windows led to the initiation of fatigue cracks, which eventually caused the fuselage to rupture under normal operating pressure. The similarity in flight profile and the suddenness of the event compared to the Elba accident led investigators to determine both were caused by the same design flaw. Following this crash, the Comet's Certificate of Airworthiness was withdrawn, and the type was grounded indefinitely. It would take four years for the Comet to conduct commercial airline flights again; this time as the Comet 4.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Captain William Mostert
First Officer
Systems & Failure Modes
Pressure Cabin
The fuselage was designed to be pressurized for high-altitude flight, but the use of square window cutouts created high stress concentrations at the corners.
Fuselage Skin
The thin-gauge aluminum skin was susceptible to metal fatigue, which initiated at stress points around windows and ADF aerial apertures.
Interesting Facts
- 01The aircraft was a de Havilland Comet 1 chartered by South African Airways from BOAC.
- 02The wreckage was located at a depth of approximately 3,300 feet, preventing full recovery.
- 03This was the third structural breakup of a Comet 1 in less than a year.
- 04The flight had been delayed in Rome to address 30 loose bolts on a wing panel and a fuel gauge issue.
- 05The accident led to the indefinite grounding of the entire Comet fleet and the withdrawal of its airworthiness certificate.
Safety Actions & Advisories
Indefinite Grounding
Immediately following the crash, the Certificate of Airworthiness was withdrawn from all Comet aircraft, grounding the fleet until a complete redesign could be implemented.
Structural Redesign
Future iterations of the Comet and all subsequent jet airliners adopted rounded or oval windows to eliminate the stress concentrations that caused the fatigue failures.