Lincoln Muni Airport
Aircraft Accident/Incident Report

Lincoln, Nebraska 68524
Thursday, May 4, 2006 18:00 CDT

The airplane departed controlled flight as the flight crew conducted an intentional stall maneuver. The flight crew stated that the airplane rolled off to the right about 11 knots above the expected stick shaker speed. The pilot-in-command (PIC) stated that "as the airplane slowed through [approximately] 126 knots [indicated airspeed], it abruptly rolled off / dropped the right wing and the nose fell rapidly." He noted that, although the autopilot was on as required by the test procedure, he was holding the control wheel and felt "no vibration or abnormal indication" prior to the event. He reported that the airplane rolled 5 to 7 times, both to the right and the left. The second-in-command (SIC) stated that the right wing dropped and characterized it as a steady roll to the right, not a violent roll. He commented that the wing dropped "as though it was a root stall." He reported that he moved to push forward on the controls in order to unload the wing; however, the PIC instructed him to stay off the controls. He stated that the PIC did not unload the wing and the aircraft kept rolling. The aircraft subsequently rolled several times before it was recovered to controlled flight. The flight crew executed a no-flap landing without further incident. The SIC pilot reported that one of the mechanics had come forward during the flight and informed him some frost was present on the wings near the root. However, the SIC reported he did not observe any ice form on the aircraft nor did he observe the icing advisory light during the flight. Outside air temperatures were not below freezing. He added that from the pilot's seat approximately the outboard one-half of the wings are visible. In his post incident statement, one of the mechanics on the flight reported that a small amount of ice had accumulated on the wings during the initial tests, prior to the stall. He subsequently noticed that the ice was dissipating. He thought that this was due to warmer temperatures or the aircraft deice system. Post incident inspection of the airframe did not reveal any anomalies consistent with a premature stall and loss of control. Subsequent flight testing did not reveal any adverse stall characteristics. The Airplane Flight Manual required that all external airframe surfaces must be free of ice when performing intentional stalls.

The pilot-in-command's failure to maintain control during the initial roll at onset of the stall due to his improper remedial action related to the stall recovery. A contributing factor was initiation of an intentional stall with residual wing ice contamination, resulting in the stall occurring at a higher than anticipated airspeed. An additional factor was the flight crew's failure to ensure all external surfaces were free of contamination prior the stall as required by the airplane flight manual.