What happened
On 9 March 1998, a Robinson R22 Beta, registration G-BUIW, was involved in an accident near Amport, Andover, Hampshire. While the initial investigation details were previously released, subsequent findings emerged following the identification of a similar mechanical issue in another helicopter, G-BOAM.
The investigation
Following the discovery of a defect in the sprag clutch assembly of aircraft G-BOAM, investigators performed a metallurgical examination on the clutch from G-BUIW. This analysis revealed that a sprag ear had failed in a manner nearly identical to the defect found in the other aircraft.
Technical analysis determined that the failure was driven by a high cycle fatigue mechanism, which originated from simple inward bending of the component. Investigators also found evidence suggesting that the failed ear, which was not recovered during the initial inspection, may have moved into the bearing raceway. This movement potentially caused a temporary locking of the rotational movement between the bearing races.
Findings
- The primary cause of the component failure was high cycle fatigue resulting from inward bending of the sprag ear.
- The failure of the sprag clutch assembly was part of a broader issue involving a defective batch of clutches.
- The manufacturer has since issued Service Bulletin 85 to address these specific clutch issues in R44 helicopters.