Engine failure leads to obstacle collision during forced landing in Schleicher ASH 31 Mi

Casualties unknown • Mazères-sur-Nestes, FR

A motor glider experienced an engine failure and subsequent collision with an obstacle while attempting an emergency landing near Mazères-sur-Nestes.

What happened

On March 10, 2013, a Schleicher ASH 31 Mi motor glider, registration D-KWED, departed from Saint-Gaudens for a local flight. After climbing to approximately 2,300 meters, the pilot observed deteriorating weather conditions and decided to return toward the departure airfield. During the flight, the pilot determined that a gliding approach to the home airfield would be unfeasible due to the observed vertical descent rate and prepared for a potential engine failure by deploying the retractable engine.

At an altitude of roughly 900 meters, the pilot attempted to restart the engine multiple times, but the engine failed to ignite. While navigating through rain, the pilot identified an initial field for an emergency landing but subsequently abandoned it after discovering an undetected power line. While attempting to reach a second landing site, the pilot realized the aircraft was too low on the approach path. An attempt to retract the engine using the propeller realignment control was unsuccessful. Consequently, the right wing struck an obstacle prior to the field, causing the aircraft to pivot and crash on the opposite side of a railway track.

The investigation

The investigation focused on the mechanical state of the aircraft and the pilot's decision-making process. Investigators examined the wreckage and found that the propeller was stuck in a position that prevented the engine from being retracted into the fuselage. Although the pilot attempted to use the realignment control, the mechanism failed to engage. The investigation could not determine the specific cause of the initial engine malfunction, though the pilot noted having experienced similar issues during previous training exercises.

Technical analysis revealed that the aircraft's glide ratio had significantly degraded from a clean configuration of 55:1 to approximately 25:1 due to the extended, non-functioning engine. Weather conditions at the time included light rain and gusty winds.

Findings

  • The accident was caused by a failure to anticipate the significant increase in drag and loss of performance caused by flying with an unretracted, non-functioning engine in rainy conditions.
  • The pilot miscalculated the approach path required to reach the second chosen landing field.
  • The presence of rain further degraded the aircraft's aerodynamic performance during the descent.

Probable cause

The primary cause was the pilot's failure to account for the increased drag and reduced glide ratio resulting from the engine remaining in the extended position during flight in rainy weather, combined with an erroneous assessment of the approach path to the emergency landing site.

Frequently asked questions

What happened in the 2013-03-10 Schleicher ASH 31 Mi accident near Mazères-sur-Nestes, FR?

A motor glider experienced an engine failure and subsequent collision with an obstacle while attempting an emergency landing near Mazères-sur-Nestes.

What aircraft was involved and where did it happen?

The accident on 2013-03-10 involved a Schleicher ASH 31 Mi, registration D-KWED, at Mazères-sur-Nestes, FR.

What was the probable cause of the accident?

The primary cause was the pilot's failure to account for the increased drag and reduced glide ratio resulting from the engine remaining in the extended position during flight in rainy weather, combined with an erroneous assessment of the approach path to the emergency landing site.

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