What happened
The aircraft was on final approach when a circuit breaker caution light illuminated. The pilot in command failed to verify which specific circuit breaker had tripped and incorrectly assumed it was the gear control circuit breaker. Acting on this assumption, the pilot activated the emergency hydraulic system and manually lowered the landing gear.
After landing, the hydraulic selector valve was left in the emergency position. This configuration resulted in the toe brakes having only normal accumulator pressure available. The normal accumulator pressure was subsequently depleted, causing the aircraft to collide with a parked aircraft on the ramp. The pilot failed to apply the parking brake even though the parking brake emergency accumulator had sufficient hydraulic pressure. It was later determined that the initial tripped circuit breaker was for the landing gear warning system and not the gear control system.
The investigation
The investigation focused on the sequence of events following the illumination of the caution light. Examination of the aircraft systems revealed that the pilot's decision to activate the emergency hydraulic system was based on a misidentification of the fault. The failure to reset the hydraulic selector after landing left the normal braking system isolated from its primary pressure source.
Findings
The primary contributing factor was the pilot's incorrect assumption regarding the tripped circuit breaker. By not verifying the specific system affected, the pilot initiated an unnecessary emergency procedure. This action led to the depletion of the normal accumulator pressure, which was critical for stopping the aircraft on the ramp. The failure to apply the parking brake further exacerbated the situation, resulting in the collision with the parked aircraft.