broke away and fuel from the wings set the debris on fire. To find out what caused the first failure, BOAC donated G-ALYU ("Yoke Uncle") for testing. The airframe was put in a large water tank, the tank was filled, and water was pumped into the plane to simulate flight conditions. The experiment was run 24 hours per day, 7 days per week. It could possibly have taken as long as five months. Official findings concerning BOAC Flight 781 and South African Airways Flight 201 were released jointly on 1 February 1955, in Civil Aircraft Accident: Report of the Court of Inquiry into the Accidents to Comet G-ALYP on 10 January 1954 and Comet G-ALYY on 8 April 1954. After the equivalent of 3,000 flights simulated with G-ALYU, investigators at the RAE were able to conclude that the crash of G-ALYP had been due to failure of the pressure cabin at the forward ADF window in the roof. This window was one of two apertures for the aerials of an electronic navigation system in which opaque fibreglass panels took the place of the window glass. The failure was a result of metal fatigue caused by the repeated pressurisation and de-pressurisation of the aircraft cabin. Another fact was that the supports around the windows were riveted, not glued, as the original specifications for the aircraft had called for. The problem was exacerbated by the punch rivet construction technique employed. Unlike drill riveting, the imperfect nature of the hole created by punch riveting caused manufacturing defect cracks, which may have caused fatigue cracks to start around the rivet. The investigators examined the final piece of wreckage with a microscope. Effects of the disaster and findings The Comet's pressure cabin had been designed to a safety factor comfortably in excess of that required by British Civil Airworthiness Requirements (BCAR)—the requirement was 1.33 times P with an ultimate load of 2 times P (where P is the cabin's "Proof" pressure), but the safety factor used in the Comet was 2.5 times P—hence the accident led to revised estimates for the safe loading strength requirements of airliner pressure cabins. In addition, it was discovered that the stresses around pressure cabin apertures were considerably higher than had been anticipated, particularly around sharp-cornered cut-outs, such as square windows. As a result, future jet airliners would feature windows with rounded corners, the purpose of the curve being to