What happened
On 4 October 2013, a Bell 2-06B Jet Ranger III, registration G-BPWI, was performing a private flight near Upper Edgebold, Shropshire. The pilot was returning to base following a visit to a maintenance facility. During the flight, the pilot observed the engine turbine temperature rising toward its maximum limit. In response, the pilot initiated a descent to perform a precautionary landing.
As the aircraft descended, the temperature readings returned to normal levels. Believing the issue had resolved, the pilot decided to abort the landing and continue to the destination. However, as the pilot increased power to climb, the turbine temperature spiked beyond the gauge's scale, and the engine began to fluctuate and lose power. The pilot was forced to enter an autorotation and declared a MAYDAY. During the forced landing, the helicopter rolled over and the tail boom struck the ground. The pilot sustained one minor injury and escaped the wreckage.
The investigation
The AAIB examination of the engine revealed significant internal damage. Investigators found metal debris in the main oil filter housing and the magnetic chip detectors. Specifically, the No 7 main bearing had completely disintegrated, showing evidence of extreme heat damage and metal splatter throughout the turbine casing.
Crucially, investigators discovered a foreign object within the check valve of the oil filter housing. This object was an O-ring, which appeared to be the same one missing from the oil filter spigot. This O-ring had become lodged in the valve, preventing it from functioning correctly. Additionally, the pilot had previously noted blue smoke from the exhaust following engine shutdowns, a symptom that investigators linked to the faulty valve.
Findings
- The engine failure was caused by the disintegration of the No 7 main bearing.
- This failure was most likely the result of oil starvation, which led to overheating of the bearing.
- An O-ring from the oil filter spigot had become lodged in the oil filter housing check valve.
- This obstruction restricted the flow of oil through the engine and prevented the check valve from closing properly during engine shutdown.
- The pilot's decision to continue the flight after the initial temperature spike contributed to the engine failing at a low altitude during a climb.