What happened
On 12 August 2012, a Jabiru UL-430, registration G-BYIM, was performing a private flight at Ince Airfield, Liverpool. Following a routine 20-minute flight, the pilot executed a normal approach and landing on Runway 29. The runway surface was grass and described as slightly soft, with calm wind conditions.
Shortly after the aircraft touched down, approximately 10 to 20 metres along the runway, the right main undercarriage collapsed. This failure was followed by the collapse of the nose leg. As the aircraft settled, the right wingtip and a propeller blade struck the ground. The incident resulted in no injuries to the pilot, but the aircraft sustained damage to the propeller, the right wing, and the nose and main undercarriage legs.
The investigation
The AAIB examined the wreckage and the aircraft's maintenance history. The investigation found that the aircraft was equipped with large wheels that weighed 15 kg more than the standard configuration. Additionally, the aircraft's empty weight had increased following a re-spray in 2010, which had been applied without removing the old paint. This caused the empty weight to reach 276.5 kg, exceeding the maximum permitted empty weight of 2ally 248 kg.
Technical analysis of the failed forward outboard attachment bolt revealed that the nut had been pulled off the bolt. While the bolt was made of a low alloy steel, the nut was manufactured from a softer steel alloy. Traces of a polymeric material were found in the bolt threads, suggesting the nut may have contained a nylon insert. The investigation also noted that the inside of the attachment clamp was highly polished, indicating relative movement between the spring leg and the bracket.
Findings
- The right main undercarriage collapsed because the nut pulled off the forward outboard attachment bolt.
- The nut was made of a softer steel than the bolt itself.
- The aircraft's empty weight exceeded the maximum limit due to an unrecorded weight increase from a new paint coating.
- There was evidence of movement within the undercarriage attachment, potentially caused by the nut becoming loose or the nut bottoming out on the bolt thread.
- The pilot was unaware that the aircraft's weight had increased beyond its certified limit following the re-spray.