David Learmount/London

North Sea oil-support companies have grounded voluntarily about 50 Eurocopter AS 332L1 Super Pumas following the crash off the Norwegian coast of a Helikopter Service helicopter on 8 September, when all 12 people on board were killed.

The cause of the crash was unknown as Flight International went to press, but Helikopter Service says that the incident must have been "catastrophic", as there was no advice of difficulty nor an emergency call when the helicopter disappeared in good weather 160km (85nm) off the Scandinavian country's south-west coast.

The main body of wreckage had still not been located by 12 September, but two days after the event a main rotor-blade was found floating. Helikopter Service consequently grounded its four L1 Super Pumas, even though it was not known at the time whether blade-separation was the cause or a secondary effect of the crash. Other variants of the helicopter continue in service. Norsk Helikopter's single AS 332L1 is also grounded.

The UK's three major North Sea oil-support helicopter operators - Bond Helicopters, British International and Bristow - then decided to ground their 40 Super Pumas. The companies say that there is still no indication of a problem in any of their Puma fleets.

British International's managing director Paul Conway says: "We are ready for a prolonged [grounding] period." The company is down to about 60% of its theoretical capacity with the grounding of eight helicopters, says Conway, but by using more fully the capacity of its 13 Sikorsky S-61s he hopes to "meet [British International's] obligations". Helikopter Service has suffered a similar capacity loss.

Meanwhile, the Norwegian civil-aviation authority confirms that Norwegian metallurgy specialist Veritas is studying the separated rotor-blade in association with the manufacturer.

Improved lightning-protection for composite-material helicopter blades should be researched and implemented, according to the UK Air Accident Investigation Branch report of the 19 January 1995 North Sea ditching by a Bristow Helicopter Aerospatiale AS332L following destruction of its tail-rotor system by lightning.

Source: Flight International