What happened
On July 19, 2016, a Piper PA-32R-301, registration HB-PQN, was conducting a flight for the purpose of renewing a single-engine piston instrument rating. The flight originated from Geneva (LSGG) with a planned destination of Dôle (LFGJ). During the approach to the Dôle NDB, the crew attempted to extend the landing gear, but only the two main gear green lights illuminated; the nose gear indicator remained dark, triggering a cockpit warning light and horn.
Following the malfunction, the instructor initiated a go-around. The crew transitioned to visual flight rules (VFR) and proceeded to a specific area south of the airport to attempt emergency gear extension procedures. The crew performed multiple retraction and extension cycles, as well as the emergency extension checklist, but the nose gear failed to lock. During a subsequent normal command cycle, the three green lights finally illuminated and the warnings ceased. The crew decided to divert back to Geneva with the gear in the extended position. The aircraft landed at Geneva without further incident, and while there were no fatalities, one person sustained slight injuries.
The investigation
Technical examinations of the aircraft focused on the nose landing gear assembly. Investigators discovered that the rear attachment bolt for the hydraulic retraction cylinder had snapped, causing the cylinder to detach from its support. While the upper portion of the bolt remained in the support for metallurgical analysis, the lower portion was missing. The forward bolt was found to be bent, indicating it had been subjected to excessive force.
Findings
Metallurgical analysis confirmed that the bolt failure was caused by fatigue rupture resulting from excessive force applied during the activation of the hydraulic cylinder in both directions. The investigation identified two distinct fatigue crack initiations located 180 degrees apart on the analyzed bolt section.
Further inspection of the hydraulic system revealed that while the system pressure was within manual specifications, the hydraulic cylinder rigging was incorrect. Specifically, the cylinder length was found to be 3 to 4 millimeters greater than the limits prescribed in the aircraft maintenance manual. This excessive length created a constant spreading force between the two attachment bolts when the gear was extended and locked. Over repeated flight cycles, this continuous tension led to the fatigue and eventual failure of the rear bolt.