What happened
On 18 July 2004, an Enstrom 280c, registration G-BRPO, was conducting a private VFR flight from Hawarden to Knutsford. During the flight, near the Oulton Park Racing Circuit in Cheshire, the pilot observed light smoke entering the cockpit, followed by a sensation of heat behind his back.
In response to these symptoms, the pilot initiated an emergency descent. While the pilot initially believed the engine had ceased functioning at approximately 600 feet, he later noted that there were no specific engine failure indications. During the attempt to land, the helicopter rolled over, resulting in substantial damage to the aircraft. There were no injuries to the pilot.
The investigation
The AAIB investigation focused on the cause of the smoke and heat, as well as the circumstances of the engine's performance. Post-accident inspections of the engine revealed that the engine turned normally and the drive train remained intact. While the engine contained very little oil, the presence of clean oil in the cylinders suggested no internal malfunction.
Investigators identified that the exhaust pipe from the turbocharger had become detached from the turbocharger itself. This detachment allowed exhaust gases to strike the aircraft skin, causing localized overheating. Furthermore, because this pipe was connected to a bypass system, the dislodged component allowed exhaust fumes to flow into the engine compartment and into the cockpit. The investigation determined that the fatigue fracture of a clamp was the primary cause of the pipe becoming dislodged.
Findings
- The pilot experienced smoke and heat due to exhaust gases entering the cabin.
- A clamp securing the turbocharger outlet pipe failed due to fatigue.
- The failure of this clamp allowed the exhaust pipe to detach, directing hot gases against the aircraft skin and into the cockpit.
- The pilot's decision to perform an immediate emergency landing was a necessary response to the smoke and heat, though the landing resulted in a rollover.