Incident Description
A test flight involving an aircraft equipped with experimental 4-bladed propellers was conducted to determine handling characteristics following a throttle chop to idle power at 50 feet above ground level. The maneuver had been performed twice on the same flight without incident. On the third landing, the pilot reported that he retarded the throttles more briskly than on previous approaches. Observers both on the aircraft and on the ground witnessed a yaw and a wing drop. The right landing gear struck the runway first, followed by the left and nose gears. All three gears subsequently sheared off. The aircraft slid to a stop off the runway, 975 feet from the initial point of impact.
A postaccident teardown of the propellers revealed no preexisting misadjustments or abnormalities.
Probable Cause
The official investigation identified three occurrences and their findings:
- Occurrence #1: Abrupt maneuver (phase of operation: landing - flare/touchdown)
- Proper descent rate was not maintained by the pilot in command.
- Remedial action was delayed by the pilot in command.
- Occurrence #2: Hard landing (phase of operation: landing - flare/touchdown)
- Occurrence #3: Complete gear collapsed (phase of operation: landing - flare/touchdown)
- Design stress limits of the aircraft were exceeded by the pilot in command.