Tuesday, May 4, 2010
Analyzing Pilot Performance
The NTSB’s findings on the Colgan Air crash
At 10:12:18, the approach controller cleared the flight down to 2,300 feet. The captain and first officer performed flight-related tasks, but also continued a conversation that was unrelated to their flying duties. At 10:12:44, the approach controller cleared them to a heading of 330 degrees. The captain called for the descent and approach checklists, and the approach controller told them to turn left to 310 degrees. The autopilot’s altitude hold mode became active one second later, as the airplane was approaching the preselected altitude of 2,300 feet. The airspeed was 180 knots at the time. The captain called for five degrees of flaps, and the CVR recorded a sound similar to flap handle movement. Afterward, the approach controller cleared the flight to turn left to 260 degrees and maintain 2,300 feet until established on the localizer for the ILS approach to runway 23. The first officer acknowledged the clearance. The captain began to slow the airplane less than three miles from the outer marker to establish the appropriate airspeed before landing. According to the flight data recorder (FDR), the engine power levers were pulled back, and both engines reached minimum thrust at 10:16:02. The approach controller then instructed the flight to contact the tower, and the first officer acknowledged. This was the last communication between the flight and ATC. The CVR recorded sounds similar to landing-gear handle deployment and landing-gear movement, and the FDR showed that the propeller condition levers had been moved forward to maximum rpm and that nose-up pitch trim had been applied by the autopilot.
The first officer said the gear was down. At that time, the airspeed was about 145 knots. The autopilot added additional nose-up pitch trim, and an “ice detected” message appeared on a cockpit display. At the same time, the captain called for 15 degrees of flaps and for the before-landing checklist. The CVR then recorded a sound similar to flap handle movement, and FDR data showed that the flaps had been selected to 10 degrees. FDR data also showed that the airspeed at the time was 135 knots. The CVR recorded the stall-warning stick shaker and a sound similar to the autopilot disconnect horn, which repeated until the end of the recording. When the autopilot disengaged, the airplane was at 131 knots. FDR data also showed that the control columns moved aft, and the engine power levers were advanced one second later.
While engine power was increasing, the plane pitched up, rolled to the left and reached 45 degrees left wing down, then rolled to the right. As the airplane rolled to the right through wings level, the stick pusher activated. The stick pusher applies a nose-down control column input to decrease the wing’s angle of attack after an aerodynamic stall. At 10:16:37, the first officer told the captain that she had put the flaps up. FDR data confirmed that the flaps had begun to retract by 10:16:38; at that time, the airplane’s airspeed was about 100 knots. FDR data also showed that the roll angle reached 105 degrees right wing down before the airplane began to roll back to the left, and the stick pusher activated a second time. Despite the stick pusher trying to lower the nose, the airplane’s nose was only one degree down, not low enough for stall recovery.
At 10:16:42, the CVR recorded the captain making a grunting sound. FDR data showed that the roll angle had reached about 35 degrees left wing down before the airplane began to roll again to the right. The first officer asked whether she should put the landing gear up, and the captain said, “gear up,” followed by an expletive. The airplane’s pitch and roll angles had reached about 25 degrees nose down and 100 degrees right wing down when the airplane entered a steep descent. The stick pusher activated a third time. FDR data showed that the flaps were fully retracted at 10:16:52. About the same time, the CVR recorded the captain stating, “we’re down,” along with the sound of a thump.
The investigation revealed that during training, the captain was shown a video produced by NASA, which dealt with tailplane icing and showed that if an airplane’s tail stalls due to ice, the recovery procedure involves pulling back on the yoke rather than pushing it forward. However, investigators concluded that it’s unlikely the captain was attempting a tailplane stall recovery, and that there was no evidence the DHC-8-400 was susceptible to tailplane icing. The Safety Board found that the captain’s improper control inputs for stall recovery were consistent with being startled and confused.
Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other NTSB news. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, NY 10602-0831.
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