Pilot Debrief

WALLER CHARLES R RANS S12-XL near Gordon, AL — 2012-11-10

Final reportERA13LA052
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Date
2012-11-10
Location
Gordon, AL, USA
Aircraft
WALLER CHARLES R RANS S12-XL
Registration
N933CW
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Cruise

Probable cause

A fatigue failure of the elevator pitch trim cable, which resulted in aerodynamic flutter of the elevator in flight and the airplane’s subsequent nose-over during the resultant precautionary landing.

NTSB narrative

As the pilot leveled the airplane after departure and accelerated to cruise airspeed, the airplane's elevator suddenly began to flutter violently, shaking the airplane. The pilot reduced airspeed in an attempt to stop the elevator from fluttering, but the elevator continued to flutter. As a result of the flutter, the control column was moving rapidly forward and aft about 6 inches, which would correspond to an elevator up and down movement of about 20 degrees. The pilot decided to make an emergency landing in a cow pasture because he was worried about a structural failure. Upon touchdown on the cow pasture, the nosewheel dropped into a hole, and the airplane nosed over and came to rest inverted. Postaccident examination revealed that the fuselage was substantially damaged, and the trim push wire that actuated the elevator trim tab was fractured. Examination of the trim push wire revealed that it had been secured to the trim tab by a wire swivel/screw stop that was attached to the trim horn. Further examination revealed that the trim push wire was bent and had fractured just forward of the wire swivel/screw stop. The fracture face displayed corrosion and striations consistent with fatigue. Examination of the trim horn on which the wire swivel/screw stop was mounted also revealed wear, scratching, and gouging. The observed damage was consistent with the wire swivel/screw stop binding during operation and being unable to rotate under load. Airplane manufacturer personnel indicated that they observed a similar failure when spectators at an airshow leaned against a trim tab on an airplane that was on display, bending the trim push wire, which subsequently failed in flight.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Inspect trim push wire during pre-flight as per Operational Alert 173.

NTSB coding

Evidence available

  • Photos
  • 17 docket documents
View NTSB final reportView NTSB docket

Docket documents17

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