What happened
On 25 July 1998, an Enstrom F-28C-2-UK helicopter, registration G-BHAX, was conducting a private flight from Hereford toward a landing site in Neston on the Wirral. While flying approximately 2 nautical miles southeast of Pennyffordd, Flintshire, the pilot noticed smoke and a burning odor within the cockpit. Following permission from Liverpool Approach to enter the Control Zone, the pilot issued a 'Mayday' call and executed an emergency landing in a nearby field. The crew and two passengers evacuated the aircraft without injury. Although the police arrived at the scene, no further assistance was required, and the pilot later contacted Liverpool ATC to cancel the emergency declaration.
The investigation
Investigators examined the aircraft to determine the source of the smoke and burning smell. The inspection identified a small hole located in the exhaust pipe assembly, situated just upstream of the turbocharger unit. This hole was found within the bead of a weld that had been part of a previous repair. The investigation established that this defect allowed a jet of hot exhaust gas to strike a shroud-covered electrical wire used for the landing light. This concentrated heat caused the partial melting of the wire's shroud, which produced the smoke observed by the pilot.
Findings
- The primary cause of the incident was a leak of hot exhaust gases through a hole in a repaired section of the exhaust pipe assembly.
- The escaping gas was directed onto the landing light's electrical wire shroud, leading to its thermal degradation.
- The engine's last annual inspection had been completed approximately three months prior to the event.