What happened
On January 19, 2017, a Beech 99A, registration N326CA, was performing a Part 135 cargo flight from Glendova, Montana, to Sidney, Montana, when the pilot experienced a landing gear malfunction. Shortly after departing Dawson Community Airport, the pilot retracted the landing gear and heard a thud. Following this sound, the landing gear "unsafe" light illuminated, and the left main landing gear light remained green, indicating the gear was still extended despite the handle being in the retracted position.
After a low pass over the runway at Sidney to allow for a visual inspection by maintenance personnel, which revealed the nose gear was in a trail position, the pilot diverted to Billings Logan International Airport. During the landing on runway 28R, the right main landing gear collapsed upon touchdown. The pilot was not injured, but the aircraft sustained substantial damage to the right aileron and right-wing spar.
The investigation
Post-accident examination of the left landing gear actuator revealed a fracture that allowed hydraulic fluid to pass freely, preventing the hydraulic system from maintaining pressure to control the gear position. A metallurgical examination of the piston rod performed by Textron Aviation found that the rod had failed in the threaded region due to fatigue cracking across approximately 60% of the cross-section.
Further analysis by the NTSB Materials Laboratory identified contact wear on the piston rod shoulder, the piston head, and the retaining nut. These findings were consistent with the retaining nut not being sufficiently tight, which allowed the piston head to slide relative to the rod and nut. The investigation noted that the left actuator had been last overhauled in November 2001 and had accumulated 7,445.2 hours of service since that time.