Pilot Debrief

Lancair LEGACY RG near Gainesville, GA — 2018-11-17

Final reportERA19FA049
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Date
2018-11-17
Location
Gainesville, GA, USA
Airport
GVL
Aircraft
Lancair LEGACY RG
Registration
N8448J
Category
Airplane
Highest injury
Fatal
Fatalities
1
Phase of flight
Approach

Probable cause

The pilots’ failure to execute a go-around when the nighttime autopilot-coupled approach became unstable, which resulted in a loss of control and subsequent impact with terrain. Also causal was the flight instructor's inadequate supervision of the pilot and his failure to perform remedial action. Contributing to the accident was the inadvertent application of pressure to the pitch control while the autopilot was engaged, which caused an out-of-trim condition that was not identified by either pilot and resulted in control difficulty when the autopilot was disengaged.

Contributing factors

Contributing to the accident was the inadvertent application of pressure to the pitch control while the autopilot was engaged, which caused an out-of-trim condition that was not identified by either pilot and resulted in control difficulty when the autopilot was disengaged.

NTSB narrative

The pilot/owner and flight instructor were returning from a cross-country flight and arrived in the vicinity of the airport after dark in visual meteorological conditions. The flight instructor requested (to the air traffic controller) and was cleared for a practice GPS approach to the runway, which was equipped with precision approach path indicator (PAPI) lighting. Flight data indicated the approach was flown using the autopilot. Just after the airplane passed the final approach fix, the flaps were partially extended, the pitch attitude decreased, and the airplane descended below the glidepath. The autopilot commanded nose up elevator and the airplane returned to slightly above the glidepath where it remained stable for about 16 seconds, before drifting to nearly a full-scale course deviation above the glidepath. The autopilot commanded the elevator to nose down, and the electric pitch trim to near the full nose-down position. The autopilot was then disconnected. Although the autopilot can automatically disengage in the event of a system failure, no failures were observed in the recorded data. Therefore, it was likely that the autopilot was manually disengaged. About 15 seconds later, the flaps were extended to full and then fully retracted. The descent rate increased, and the airplane descended below the glidepath, until the recorded data ended when the airplane was about 0.3 mile from the runway. The airplane then struck trees, crossed over a road, and impacted the left side of a localizer antenna platform before coming to rest in the grass short of the runway. Examination of the wreckage and the recorded flight data did not reveal any preimpact electrical or mechanical anomalies that would have precluded normal operation. The pilot's guide for the autopilot system warned that with the autopilot engaged, a small amount of force on the pitch controls can result in the autopilot automatic trim entering an out-of-trim condition. As the airplane drifted above the glidepath, the autopilot attempted to command nose-down elevator, and the elevator servo met with some resistance, as evidenced by the increase in elevator servo torque, which was sufficient to activate the electric pitch trim. Given that there were no indications of a flight control malfunction, it is likely that one of the pilots was applying pressure to the elevator control in the cockpit, and the autopilot applied elevator trim to counteract that pressure, in its attempt to return to the glidepath. At the time the autopilot was disengaged, the pitch trim was full nose down, which likely resulted in an unexpected increase in the (forward) force the pilot felt on the control stick, making it more difficult to control the airplane. The airplane's nose-down tendency would have increased further when the flaps were subsequently extended to full. This would have resulted in an even greater forward force on the control stick. It is likely that the pilot decided to then retract the flaps fully, due to the increased nose-down force on the control stick. However, the flap retraction resulted in an increased descent rate, and the airplane descended farther below the glidepath. A witness and the flight instructor reported that the airplane rolled inverted before impact. The recorded flight data, which ended when the airplane was on the extended runway centerline about 0.3 mile from the runway and about 50 ft above the runway elevation, did not indicate that the airplane had rolled inverted. The struck trees were also located on the extended runway centerline, about 0.1 mile from the end of the runway. Therefore, it is unlikely that the airplane experienced any significant lateral course deviation or roll, between the end of the recorded data and the struck trees. It is likely that the roll occurred after the airplane struck the trees and before it impacted the localizer antenna platform. The flight instructor had limited memory of the accident flight. He recalled that the pilot/owner was flying the airplane during the approach; however, the investigation was unable to determine which pilot was manipulating the controls at the time of the accident.

Analysis

Primary failure mode
Automation / mode confusion
First missed decision gate
Proper preflight checks of elevator trim and autopilot system were not performed.

NTSB coding

Evidence available

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  • 22 docket documents
View NTSB final reportView NTSB docket

Docket documents22

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