![[ image: width=150]](/olmedia/510000/images/_511194_copter150.jpg)
Two main rotor blades on the Eurocopter AS332L were severely damaged and two others blades sustained less serious damage in the incident.
An Air Accidents Investigation Branch said damage was spread out in such a way that the crew was able to get the aircraft safely back to Sovereign Explorer Oil Rig in the North Sea.
The report into the incident at midday on 12 December 1997 said the crew and passengers reported "a bright flash and a loud bang".
The helicopter had taken off from the oil rig eight minutes earlier, was struck at a height of 3000ft.
Passengers were advised to secure their survival suits in preparation for landing.
However, the crew decided they had enough control to turn back and landed at the rig seven minutes after the strike.
The AAIB concluded the lighting strike was "well above the level to which the aircraft was originally certificated".
Its report said that, had the damage not been spread in the way it was, the vibrations caused would have damaged the structure of the helicopter so badly that the crew would have had to consider ditching.
'Isolated strike'
The AAIB added: "The damage appears to have inflicted by an isolated strike which was not proceeded by any other observed or detected activity in the immediate area."
A further report on a North Sea incident on 20 July last year said human error almost caused a helicopter to crash during a test flight from Aberdeen Airport.
It said the Bond Super Puma AS332L had just come off a maintenance check but engineers had not replaced the bolts linking one engine to the transmission system.
This caused it to fail but the pilots were able to land the aircraft without further damage, using the remaining engine.
The Air Accidents Investigation Branch said handover procedures during an engineering shift change were not properly carried out and have since been amended.
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