What happened
On 1 July 2012, a Navion NAV 4, registration F-BAVZ, was conducting a private flight from Dunkeswell Airfield in Devon, destined for Rouen, France. Shortly after takeoff, the pilot observed oil streaming from the engine compartment. This was caused by the engine oil filler cap having been left off the engine.
Due to the oil obscuring his vision, the pilot elected to return to Dunkeswell. During the approach, the pilot attempted to extend the landing gear, but only the two green lights for the main gear illuminated. The nose landing gear failed to lock in the down position. The pilot attempted to deploy the nose gear via freefall, but this was unsuccessful. Following instructions from Air Traffic Control, the pilot performed a landing on the grass area adjacent to Runway 14, resulting in a successful gear-up landing.
The investigation
Investigators examined the aircraft following the incident. While the pilot had no injuries and there were no fatalities, the aircraft sustained damage to the propeller and the underside of the airframe. Upon lifting the aircraft, it was noted that the nose landing gear leg could be locked down under gravity with minimal effort.
Findings
- The primary cause of the engine oil leak was the oil filler cap being inadvertently left off the engine.
- The failure of the nose landing gear to lock down was caused by a fractured aluminium hydraulic pipe.
- The hydraulic pipe failure was attributed to improper manual fabrication, which had introduced residual stresses into the component, causing it to spring several inches from its installed profile after the fracture.