What happened
A Beech A100 King Air, registration not provided, was performing an instrument flight rules training mission from Ottawa to North Bay, Ontario, when an incident occurred during the return leg. After completing several touch-and-go and full-stop landings in North Bay, the crew returned to Ottawa. Upon selecting the landing gear down for arrival, the crew noticed an unsafe gear indication in the cockpit. Although ground observers could not see the gear extended, the crew performed the emergency extension procedure.
Despite the emergency efforts, the cockpit continued to show an unsafe position for the right main landing gear. The crew requested emergency services and proceeded to land on runway 25. During the landing roll, the right main landing gear collapsed, causing the aircraft to veer off the runway into a grass area. There were no injuries resulting from the event.
The investigation
The investigation focused on the failure of the landing gear to extend normally and the subsequent collapse. Investigators found that the aircraft had been modified via a supplemental type certificate to use a hydraulic landing gear system instead of the original electric version. The circuit breaker for the electric motor driving the hydraulic pump was located in a recessed area in the passenger cabin, making it inaccessible to the pilots during flight.
Examination of the aircraft revealed that the hydraulic system accumulator was defective, failing to maintain its nitrogen charge due to deteriorated O-rings. This defect caused the electric hydraulic pump motor to cycle much more frequently than intended. Additionally, the investigation found that the 60-amp circuit breaker for the pump motor had opened, which prevented the normal extension of the gear.
Findings
- The primary cause of the gear failure was the opening of the 60-amp circuit breaker for the hydraulic pump motor, likely due to overheating from excessive motor cycling.
- The frequent cycling of the motor was driven by a depleted nitrogen charge in the hydraulic system accumulator caused by leaking O-rings.
- The right main landing gear failed to lock in the down position following the manual emergency extension, leading to its collapse during the landing roll.
- The crew was fully qualified and the aircraft was maintained according to regulations.