What happened
On 20 May 2002, a Boeing 727-2H3, registration C-GYFA, was conducting a cargo flight from Copenhagen to East Midlands Airport. While approaching the airport, the crew encountered heavy rain and moderate turbulence caused by nearby thunderstorms. To comply with air traffic control instructions to descend and decelerate while intercepting the localiser, the handling pilot extended the speedbrakes.
During a 120-degree turn, the aircraft's stick shaker activated. In the ensuing attempt to recover, the crew increased engine thrust to go-around power; however, the aircraft continued to descend with a nose-down pitch of 7 degrees. The descent reached a minimum altitude of 1,100 feet QNH, triggering a Ground Proximity Warning System (GPWS) alert. During this period, the aircraft's speed increased to 235 kt. The descent was eventually arrested after the crew retracted the speedbrakes, allowing the aircraft to climb back to 3,000 feet and re-establish the approach for a safe landing.
The investigation
The investigation examined the flight data recorder, which showed the aircraft was subject to load factor oscillations between 0.75 g and 1.36 g due to turbulence. Investigators analyzed the aircraft's configuration, noting that the use of speedbrakes with flaps extended is prohibited on this model. It was established that the crew was managing high workloads due to weather avoidance and ATC instructions. The investigation also looked into the sequence of cockpit warnings, including the stick shaker, the speedbrake warning horn, and the GPWS alert.
Findings
- The activation of the stick shaker was triggered by a gust of wind that increased the angle of attack while the aircraft was already in a low-margin state due to the extended speedbrakes.
- The use of speedbrakes during a decelerating turn significantly reduced the margin to the stick shaker speed.
- High cockpit workload, driven by thunderstorm avoidance and simultaneous ATC instructions to descend and slow down, contributed to the crew overlooking the speedbrake configuration.
- The crew's initial attempt to recover via increased thrust was complicated by the aircraft's pitch characteristics and the simultaneous sounding of multiple warning devices.