History of the Flight
The pilot had flown several air experience flights in the aircraft. During the fourth sortie, a normal approach to Runway 16 was made in blustery conditions. After touchdown, the nose wheel was lowered and braking applied. As the aircraft decelerated, the nose wheel slowly collapsed, causing the aircraft to skid to a halt. Emergency services responded, and the pilot and passenger exited normally. No injuries were reported.
Aircraft and Nose Landing Gear Description
The aircraft was a Grob G115E (registration G-BYVZ) powered by one Lycoming AEIO-360-B1F engine. The nose landing leg is secured by a steel housing and consists of a tubular strut, sliding tube, gas spring strut, and flange mounted on the nose wheel fork assembly. The sliding tube is retained within the tubular strut at the top and secured by a bolt to the flange at the bottom. The gas spring strut is secured at the top to the steering actuator lever and screwed into a bottom fitting, which is bolted to the flange. The same bolt secures both the sliding tube and the gas spring strut bottom fitting to the flange.
Engineering Investigation
The maintenance organisation found that the bolt securing the sliding tube and gas spring strut bottom fitting to the flange had been incorrectly fitted. Only the bottom fitting was secured by the bolt; the sliding tube was not. When the aircraft landed, the weight on the nose wheel caused the bottom of the gas spring strut to fail, leading to collapse. The nose landing gear had last been refitted during a 150-hour maintenance activity, and the failure occurred 3.5 flying hours and 9 landings later.
Maintenance and Remedial Action
The maintenance organisation estimated that the subject bolt is disturbed approximately 60 times per year. A similar incident occurred in June 2002, after which a fleet check was conducted and a cautionary note added to the maintenance manual. Following this accident, the assembly of the nose leg was reclassified as a critical task, and a Vital/Duplicate inspection was introduced to confirm correct assembly prior to fitment of the nose wheel fork.