What happened
On 16 May 1999, an Aerospatiale SA341G Gazelle 1, registration G-OGAZ, was conducting a private flight approximately 16 miles north of Edinburgh, Scotland. During the flight, the pilot encountered intense vibrations accompanied by a loud rumbling noise. Simultaneously, the aircraft began to yaw significantly, oscillating between 30 and 40 degrees from its original heading.
In response to these symptoms, the pilot shut down the Turbomeca Astazou 3A turboshaft engine and initiated an autorotation procedure. Due to concerns regarding a potential malfunction within the tail rotor system, the helicopter was brought down with a high run-on speed. There were no injuries to the single crew member or the three passengers on board, though the aircraft sustained damage to the underside of the fuselage.
The investigation
The investigation focused on the mechanical failure that triggered the vibration and yawing. Investigators examined the engine and transmission components to identify the source of the instability. The analysis centered on the mechanical integrity of the internal bearings and their operational history.
Findings
- The primary cause of the incident was the failure of a freewheel support bearing (part number 341A35-0176-20).
- The bearing in question had a required life limit of 1500 flying hours.
- At the time of the failure, the component had accumulated 1383.14 flying hours.