What happened
On 18 July 2006, a Skyranger 912(2), registration G-CCKF, was conducting a private flight near Eshott Airfield, Northumberland. The weather was clear and sunny with light winds. After a routine takeoff and climb to approximately 800 feet, the pilot began a right turn to enter the landing circuit. During this maneuver, the engine produced a clattering sound and the propeller ceased rotation.
Due to the low altitude, the pilot was forced to perform an immediate landing in a nearby field of cut crops. After contacting Newcastle radio to declare a MAYDAY, the aircraft landed long and struck a perimeter fence. The impact caused the nosewheel to detach and the aircraft to pitch upside down. The pilot, who was wearing a full harness, sustained minor injuries.
The investigation
The AAIB investigation focused on the sudden engine failure and the subsequent damage to the airframe. Investigators found that the engine had seized due to oil starvation. Evidence at the scene, including oil trails on the ground, indicated that the oil filter had detached from its mounting during engine operation.
Examination of the oil filter revealed that a 'FRAM' automotive filter had been used instead of the manufacturer-approved Rotax part. The investigation established that the pilot had replaced the filter the previous day. Because the FRAM filter was slightly larger in diameter and longer than the correct part, the pilot had experienced difficulty during installation. An acquaintance assisted with the installation, using a strap wrench to tighten the filter, which likely applied excessive load to the threads.
Findings
- The engine failed because the oil filter became detached from the mounting spigot, allowing oil to escape.
- The engine subsequently seized due to a lack of lubrication.
- The installed FRAM filter had a larger thread diameter and a different pitch than the approved Rotax filter.
- The filter was cross-threaded during installation, which severely damaged the threads.
- The use of a strap wrench to tighten the filter likely increased the static load on the compromised threads, leading to failure under engine pressure.
Safety action
- The Popular Flying Association was advised to remind owners of Rotax-powered aircraft that only manufacturer-specified oil filters are approved for use.
- The British Microlight Aircraft Association was also advised to issue similar reminders to its members.