What happened
On 5 May 2008, a Spitfire Mk 26 (scale replica), registration G-CENI, was conducting its second flight following construction. The aircraft was operating on a private flight near Aboyne Airfield, Aberdeenshire. After a routine takeoff and climb to 2,000 ft, the pilot noted that the engine oil temperature had entered the caution range.
In response, the pilot initiated a precautionary return to the airfield. While descending, the pilot lowered the landing gear. Upon the gear locking into position, a loud bang was heard. During the subsequent base leg of the approach, the pilot discovered that the throttle movements were no longer affecting engine thrust and realized the propeller was missing. The pilot managed to execute a successful glide approach and landed the aircraft safely. There were no injuries to the pilot.
The investigation
An investigation by the AAIB examined the aircraft and the engine components. The inspection revealed that the propeller assembly, including the adaptor flange and the bolts connecting the adaptor flange to the crankshaft, had detached from the aircraft. The propeller assembly was not recovered from the site.
Examination of the engine showed that of the twelve threaded holes in the crankshaft flange, only two exhibited evidence of distressed threads. Investigators also found that a single application of 'Loctite' locking compound was present at the bottom of the threaded holes, but no compound was found in the upper threads. It was noted that once the propeller is mounted to the adaptor flange, the attachment bolts to the crankshaft cannot be visually inspected.
Findings
- The loss of the propeller was caused by the detachment of the propeller adaptor flange and its attachment bolts from the crankshaft.
- The presence of locking compound only at the bottom of the threaded holes suggests the bolts were not sufficiently secured.
- The physical configuration of the propeller assembly prevents a visual inspection of the security of the attachment bolts once the propeller is fitted.