What happened
On 11 June 1999, a Cessna 182A, registration D-EEPY, was conducting a private flight from Galway to Londonderry Airfield. During the approach, the pilot reduced speed to 120 kt and attempted to extend the hydraulic landing gear. However, the green light indicating the nose wheel was down and locked failed to illuminate. After attempting to cycle the gear normally and subsequently performing a manual extension via the emergency hand pump, the nose wheel indication remained unchanged.
To verify the gear status, the pilot performed slow fly-pasts of the airfield. Due to continued uncertainty from tower personnel, an army helicopter flew alongside the aircraft to inspect the gear. The helicopter crew reported that the nose leg appeared to be correctly extended. Following clearance, the pilot landed the aircraft at a low speed, focusing on the main wheels. Despite applying maximum aft pressure on the control column, the nose continued to descend into a steep angle as the aircraft decelerable. There were no fatalities or injuries to the two occupants, though the aircraft sustained damage to the propeller and the nose-wheel area.
The investigation
Investigators examined the aircraft's nose-leg operating jack and discovered that the piston rod had been prevented from reaching full travel. The investigation established that the inner ends of the two lock pins, which the down-lock hooks engage with, had moved inboard within their mounting lugs. This movement caused the nut on the forward end of the piston rod to foul the protruding ends of the lock pins.
Further inspection revealed that both lock pins had fractured near the plane of their circumferential groove. The investigation also noted that a previous repair had utilized a different design for the bearing end, lock pins, and locating pins than the original manufacturer specifications. The new design used constant-diameter pins without the groove, which helped eliminate the stress concentrations present in the original grooved pins.