North Sea helicopter operators are scrabbling to acquire additional aircraft as they struggle to cope with the effective grounding of certain Eurocopter Super Puma types following a controlled ditching of an EC225 on 22 October.

Although a European Aviation Safety Authority emergency airworthiness directive states the aircraft are allowed to fly, providing data collected by vibration monitoring systems is downloaded with increased frequency, a ruling issued by the UK's Civil Aviation Agency on 25 October prohibits overwater flights of EC225s and AS332s fitted with a potentially faulty gearbox component.

CHC Scotia, which operated the helicopter (G-CHCN) involved in the incident, has nine UK-based aircraft out of service - five EC225s and four AS332 L2s. Bristow Helicopters, meanwhile, has grounded 11 EC225s from its UK fleet. The other large-scale operator in the region, Bond Offshore Helicopters, has also pulled four AS332s from service, along with three EC225s.

"We are trying to bring in helicopters where we can, but there's not a lot of them just lying about," says CHC Scotia.

Its comments are echoed by Bond: "The whole industry up there has been thrown up in the air. We are trying to bring in additional assets but there is a chronic shortage of airframes."

Bristow adds: "[Our] European fleet comprises 55 helicopters, of which at least 75% remain operational across the region. We are currently calling on additional support from other areas of the business to help us best match capacity with our customers' critical needs in the short to medium term."

The problem is not only affecting the UK. Bristow is not flying three EC225s in Australia, another EC225 in Norway, and an AS332 L2 in Nigeria, it says. CHC has grounded its EC225 and AS332 L1 and L2 fleets globally - a total of 64 airframes, including those in the UK.

For its part, Eurocopter has begun a detailed examination of G-CHCN's gearbox, which arrived at its factory in Marignane, France on 29 October. It is still trying to trace the root cause of the incident, which was triggered by the failure of the bevel gear vertical shaft in the main gearbox. A ditching in May involving an EC225 operated by Bond was downed by the same fault.

It is also testing the emergency lubrication system fitted to the EC225 using a test bench at a site belonging to engine supplier Turbomeca.

In the May ditching, the back-up system was functioning correctly but sensors indicated a system failure. Although Eurocopter says it is too early to definitively link the events, indications are that a sensor was again at fault.

Source: Flight International