What happened
On February 11, 2017, a privately owned Beechcraft 35-C33A, registration JA3357, was performing a familiarization flight from Honda Airport to Oshima Airport. During the approach, the pilot encountered significant turbulence caused by wind gusts from the right side, with velocities reaching up to 22 knots.
After a smooth touchdown, the pilot maintained a higher engine RPM than usual to prevent rapid deceleration and avoid interfering with a following aircraft. While managing the aircraft amidst the gusty conditions, the pilot considered raising the flaps to stabilize the plane. During the landing roll, the aircraft's nose suddenly dropped, the propellers struck the runway, and the engine stopped. Upon inspection, the nose landing gear had fully retracted, and the left main landing gear was partially retracted.
The investigation
The JTSB investigation focused on the mechanical state of the landing gear system and the pilot's actions during the landing roll. Investigators examined the landing gear position switch, the safety detent mechanism, and the landing gear warning horn. The investigation confirmed that the safety switch, designed to prevent gear retraction on the ground by detecting strut compression, was functioning correctly.
Analysis of the runway surface revealed slash marks left by the propellers, which allowed investigators to estimate the aircraft's ground speed at approximately 48 knots. The investigation also looked into the physical layout of the cockpit, noting that the landing gear position switch and the flap position switch are located near each other and share a similar operational feel.
Findings
- The aircraft was subjected to varying wind gusts that caused the main landing gear strut to extend and compress intermittently.
- This movement likely caused the safety switch to alternately detect the aircraft as being on the ground or in flight.
- The pilot likely moved the landing gear position switch to the up position by mistake while attempting to adjust the flaps.
- Because the safety switch was intermittently detecting a mid-air state, the retraction circuit was not opened, allowing the gear mechanism to activate.
- The nose landing gear was eventually pushed into the wheel well by the weight of the aircraft as the mechanism attempted to reverse direction when the switch was moved back to the down position.
- The landing gear motor eventually tripped its circuit breaker due to the overload caused by the gear attempting to extend against the aircraft's weight.