What happened
The aircraft was operating as part of a flight from Flin Flon Airport in Manitoba, Canada, with a destination of Mason City, Iowa. The pilot had made an intermediate stop at Grand Forks, North Dakota, to refuel and clear customs procedures. While taxiing on the ramp for departure, the airplane encountered a one-inch concrete lip. This impact caused the right main landing gear to collapse.
The investigation
Post-accident examination of the aircraft revealed significant mechanical issues with the landing gear system. The actuator rod end was found to be bent. Additionally, one of the four springs on the overcenter cam device had detached from its proper attachment point and was excessively stretched.
When the aircraft was placed on jacks, the spring was reattached, allowing the gear to extend. However, this process trapped the spring between the downlock switch and the downlock overcenter mechanism. Tests showed that applying firm upward pressure to the overcenter device while weight was applied to the landing gear allowed the right main gear to retract.
Further testing revealed critical design or maintenance flaws. The landing gear selector handle did not always catch the safety latch when placed in the neutral position. It was possible for the selector to move from the down to the up position without triggering the latch, allowing unintended retraction.
Findings
The primary mechanical failure involved the bent actuator rod end and the detached spring on the overcenter cam device. The investigation determined that the landing gear system allowed for inadvertent retraction because the selector handle failed to engage the safety latch reliably in the neutral position.