What happened
On the night of 22 June 2004, a Piper PA-28R-201T Turbo Cherokee Arrow, registration G-DNCS, was performing solo stop-and-go circuits at Liverpool Airport as part of a night qualification exercise. The pilot had previously completed a successful instructional flight earlier that evening and had been cleared to fly solo following a briefing and refuelling.
During the second solo circuit, the pilot performed standard downwind checks, confirming the landing gear was down and locked via the three green cockpit indicators. After receiving clearance for a stop-and $\text{go}$ maneuver, the pilot continued the approach. The aircraft crossed the runway threshold at approximately 75 knots and flared for landing. However, upon touchdown, the landing gear collapsed. Air traffic control observed sparks emanating from the aircraft as it moved along the runway. The impact caused damage to the engine, propeller, and the underside of the fuselage. The pilot was able to exit the aircraft unassisted, and there were no injuries.
The investigation
Investigators examined the aircraft's retractable tricycle landing gear system, which utilizes an electrically powered hydraulic pump. This system includes a backup extender designed to automatically lower the gear at low airspeeds and low power settings.
Upon inspection at a maintenance facility, the landing gear selector was found in the DOWN position, and the backup override lever was in the NORMAL position. Physical evidence, including the state of the nose gear doors and abrasion on the left main wheel hub, suggested that the gear extension process had only just begun immediately before the aircraft touched the runway. When the aircraft was powered up on the ground, the gear moved to the locked position without manual intervention.
Findings
- The investigation established that the backup extender's actuating diaphragm was leaking, which prevented the system from automatically lowering the gear at the required airspeeds.
- The landing gear warning horn failed to function correctly under normal operating conditions, as it only sounded if the throttle lever was held in an unnatural position.
- A leaking diaphragm in the backup extender system prevented the automatic deployment of the gear.
- There was no evidence of any pre-existing mechanical failure that would have blocked the gear from extending had the pilot had selected it down earlier in the approach.