What happened
On 15 February 2000, an AS3im32L helicopter, registration G-TIGT, was performing an oil charter flight departing the Brent Bravo oil rig for Scatsta. During the climb to 2,000 feet, the aircraft encountered weather conditions consisting of rain and hail between two areas of radar returns. While passing through 1,500 feet, the crew experienced ADF fluctuations and radio static, followed by a flash, a bang, and a momentary heat pulse. Although the crew initially believed the aircraft had not been struck, the flight continued toward Scatsta and landed without further incident.
The investigation
An investigation by the AAIB established that the aircraft had indeed sustained a lightning strike. A physical examination of the AS332L revealed that all four main rotor blades had sustained lightning damage, characterized by local skin separations and ruptures in the bonding foil. One tip cap showed extensive burning and required replacement.
Investigators also reviewed the Cockpit Voice Recorder (CVR) and Flight Data Recorder (FDR). While the CVR confirmed the timing of the strike, the recording of navigational coordinates was non-functional due to an error in a recent modification intended to integrate new navigation equipment.
Findings
- The aircraft encountered rain and hail while transitioning between weather cells.
- The lightning strike caused damage to the skin and bonding foil of all four main rotor blades.
- The damage did not result in significant mass loss or changes to the aerodynamic profile, which prevented an increase in vibration during the flight.
- The structural integrity of the blades was not immediately compromised to a level that created an in-flight hazard.