A Boeing service bulletin (SB) issued in 2002 may provide clues to the engine power reductions that triggered the accident sequence for a West Caribbean Airways MD-82 that crashed in Venezuela last August. An initial report by the Venezuelan investigation agency CIAA confirms that the engines throttled back and speed decayed shortly after the aircraft reached its cruising level. The manufacturer’s SB deals with just such a performance pattern when the aircraft, on autopilot and autothrottle, levels out from a rapid climb.

The interim report says that, after reaching its cruise level at 33,000ft (10,000m) and accelerating to Mach 0.76, the power reduced and speed decayed to Mach 0.6, at which the autopilot tripped out and the aircraft began to descend (Flight International, 29 November–5 December 2005). The Boeing SB warns against selecting a rapid climb to level-out on autopilot, adding that upon reaching level flight the autothrottle might select a power setting that allows the speed to bleed off. Then, approaching the stall, the autopilot will trip out. This tallies with the CIAA account of what happened.

Within a minute of beginning its descent, the West Caribbean MD-82 appears to have entered a stall. The crew’s control inputs were opposite to those that would normally have been applied for stall recovery. The crew declared total power failure, but the CIAA says both engines were operating close to full power at impact. All 160 people on board were killed.

Source: Flight International