Accident Overview
On 24 May 2007 at 1543 UTC, a Grob G115E Tutor (registration G-BYWE) sustained damage when its nose landing gear collapsed during landing at Colerne Airfield in Wiltshire. The aircraft was on a training flight with two crew members aboard; no passengers were carried. Neither crew member was injured. The nose leg collapsed, the propeller struck the runway, and the engine was shock-loaded and stopped. The crew shut down the aircraft and exited normally.
Landing and Collapse
The flight had been uneventful until touchdown. As the nose was lowered to the ground, a slight judder and a 'clunk' noise were felt through the airframe. The handling pilot had intended to perform a touch-and-go but aborted due to the judder and slowed the aircraft. While applying right rudder to backtrack along the runway, the nose leg collapsed.
Nose Landing Gear Design
The nose leg of the Grob 115 consists of a steel housing secured to the airframe, into which a tubular shaft fits. Inside the shaft is a gas spring strut shock-absorber. The upper end of the strut attaches to the tubular shaft; the lower end screws into a bottom fitting. A sliding tube surrounds the spring strut and bottom fitting, secured at its bottom end by the same bolt that attaches the bottom fitting to a flange.
Examination Findings
Examination by the maintenance organisation revealed that the gas spring strut had fractured at its lower end where it screws into the bottom fitting. The sliding tube had been incorrectly assembled: it had not been secured to the flange, with the attaching bolt passing only through the flange and bottom fitting. This allowed the sliding tube to float freely, migrating upwards out of the lower flange and inducing high bending loads on the lower end of the strut, eventually leading to fracture and collapse of the nose leg.
Maintenance History
The last maintenance was a 50-hour inspection on 12 May 2007, during which the nosewheel bellows were replaced. This required dismantling the nose leg assembly, specifically removal of the sliding tube from the lower flange. The maintenance documentation for the bellows replacement did not show completion of a duplicate inspection.
Previous Occurrences
The AAIB had investigated two earlier similar nose leg failures on Grob 115 aircraft. The first occurred in February 2003 (G-BVHG, Bulletin 9/2003), after which the maintenance organisation added additional steps and warnings about correct installation. The second occurred in November 2006 (G-BYVZ, Bulletin 2/2006), after which the nose leg was reclassified as a critical task and a duplicate inspection requirement was introduced.
Discussion
The nose leg failed due to incorrect reassembly of the sliding tube following bellows maintenance. Procedures to prevent such failures, including duplicate inspection of work on the nose leg, had been established but were not carried out in this case. Once the leg was fully assembled and the bellows in place, it was not possible to verify correct securing of the sliding tube. The maintenance organisation has communicated the cause to relevant personnel, reinforced awareness and procedures, and requested that the aircraft manufacturer consider alternative bellows that do not require leg dismantling.