What happened
On 15 August 2004, a Puma Sprint microlight, registration G-MNFX, was performing a private flight from Egerton Green to Arclid. During the landing sequence on a dry, firm grass runway at Arclid Industrial Estate, the aircraft touched down on its rear wheels at a normal speed and approach height. As the pilot lowered the nose wheel, the assembly detached from the airframe. This caused the aircraft to pitch forward and roll over, resulting in two serious injuries (one to the pilot and one to the passenger). The aircraft sustained damage that was beyond economic repair.
The investigation
Investigators examined the wreckage and focused on the 'snoot', which is a forward extension of the keel tube. They found that the nose wheel assembly had separated from the microlight at the mounting location. Evidence on the ground showed that the remaining portion of the snoot scraped along the runway for about 5 metres before digging into the ground, which triggered the rollover.
Detailed inspection of the component revealed a fatigue crack that spanned roughly half the circumference of the snoot. This crack originated from a defect within the weld used to secure the nose wheel mounting bush to the snoot. While a small dent was noted on the lower surface of the snoot, there was no evidence of a heavy landing that would have caused such damage; investigators concluded the dent likely occurred during the rollover itself. The remaining material was found to be insufficient to withstand standard landing loads due to the extent of the fatigue crack.
Findings
- The nose wheel assembly detached because of a fatigue fracture in the snoot.
- The fracture originated from a defect in the weld connecting the mounting bush to the snoot.
- The fatigue crack had reached a critical length where the remaining metal could no longer support normal landing stresses.
- The crack was located in a position that would be difficult to detect during a standard pre-flight inspection.
Safety action
- Medway Microlights was advised to inspect the welds securing the nose wheel mounting bush to the snoot on Puma Sprint, Raven, and Raven X aircraft for signs of cracking.
- Medway Microlights was advised to review the maintenance, inspection protocols, and expected service life of the snoot assembly for these aircraft models.