Prevailing Cultural / Organizational Factors

Miscommunication between Pratt & Whitney and British Airtours about the acceptability of repair types for combustor cans.

The repair carried out in 1983 used the direct-fusion weld method described in the British Airways engine overhaul manual. Solution heat treatment and optional post-weld stress relief, which formed part of the repair procedure in the Pratt & Whitney engine manual at that time, were not carried out. Omission of the above two heat treatments and a further process known as braze/reinforcement was permissible in accordance with the approval granted to British Airways/British Airways Engine Overhaul Ltd by the Civil Aviation Authority. Conflicting evidence was presented on the effectiveness of solution heat treatment; however, it is believed that it would not have had a significant effect on the fatigue life of the can. It was accepted, however, that its inclusion would have facilitated weld repair of the can. The Pratt & Whitney engine overhaul manual did not preclude direct-fusion weld repair of a circumferential crack of any length. Local areas of severe distortion and oxidation were not permitted to be weld repaired. A three-inch circumferential crack length limit had existed in the engine overhaul manual prior to 1977 at which time it was removed by Pratt & Whitney. British Airways was unaware of this preexisting limit, having started operation of the Model JT8D series engine in 1980. A small area of parallel cracking, possibly associated with thermally distressed material, was present on liner 3 of can No. 9 prior to repair and was addressed by fusion weld repair. The manufacturer had advised operators that direct-fusion weld-repaired cans have lower fatigue lives than ones repaired using material replacement techniques but had not quantified this reduction. British Airways interpreted this as applicable to cans with a much greater time in service than any they operated at the time.

Evolution of fuel tank access panel fabrication

Some fuel tank access panels, on some airplane models, were initially constructed from a type of nylon material. This type of construction offered a significant weight savings, using a non-metallic, non-electrically conductive material. However, in some post-crash fire events it was noted that these non-metallic panels to weren’t heat resistant, and could melt at temperatures significantly less than adjacent aluminum structure.

In order to address the concern relative to lack of heat resistance of non-aluminum panels, cast-aluminum panels were introduced into some airplane designs. This resulted in a panel manufactured that had stiffening webs integrally formed on the upper (internal) surface, but were later shown to be brittle. The panels were nominally non-stressed components so far as flight loads on the wing were concerned, and impact strength did not form a part of the design requirements for the access panel, nor were there any requirements for this capability. The cast aluminum material had an impact strength approximately one-quarter that of the lower wing for airplanes such as the 737.

Back to top