The UK CAA is continuing its campaign to address the root causes of the accidents that have occurred during North Sea operations over the last two decades.

Since it cites pilot error as the biggest issue in operational accidents, the CAA sees flight data monitoring (FDM) as the primary tool. The authority has thus created a new helicopter sub-group in the FDM user group forum, according to research project manager David Howson.

Rotor and transmission failures account for 86 percent of accidents rooted in technical causes. The causes of these malfunctions remain under investigation, but the CAA nonetheless has leads for mitigation. For example, transmission Hums improvements are being implemented on the AgustaWestland AW139, Sikorsky S-92 and Airbus Helicopters EC225, Howson said. The CAA and AgustaWestland are looking at extending Hums to rotors.

Finally, for avoidance of lightning strikes (71 percent of external causes), the UK Meteorology Office is developing a lightning-strike forecast.

Spotlight on Survivability

However, accident prevention is not enough, Howson emphasized. “Although prevention is generally better than cure, in view of the complexity of the aircraft involved and the inherently hazardous environment in which they operate, it is considered unrealistic to expect to be able to prevent all offshore helicopter accidents,” he cautioned. A significant part of the CAA’s work therefore concentrates on passenger survivability.

The agency focuses much of its attention on passengers’ ability to escape from a capsized or sinking helicopter that is rapidly filling with water. The CAA had last year prohibited flights (except emergency response) over excessively rough seas. It has recently clarified the limit from “sea state 6” to “six meters significant wave height,” which is essentially equivalent. Using sea state for the definition was deemed “archaic and indeterminate,” and the agency has revised the limitation to apply to the whole journey, not just the destination.

The agency also requires arming emergency flotation systems (EFS) for all overwater departures and arrivals, not just in case of emergency. “A significant proportion of EFS ‘failures’ in survivable water impacts is to the result of the EFS being either not armed or not activated,” Howson said. In an August 2013 accident in which a CHC Super Puma landed in the water off the Shetland Islands, the EFS was not armed as the aircraft approached Sumburgh; it was armed at the last minute thanks to quick thinking by the copilot, possibly limiting the number of fatalities. The EASA is now considering automatic arming/disarming.

The new escape window size requirement has had major consequences for some helicopter types in service. The front and rear windows of the Sikorsky S-76 are too narrow, necessitating modification of the seating configuration. The rear windows of the Airbus Helicopters AS332L/L1 Super Puma are too narrow as well, forcing removal of that type from UK operations, Howson said.

On the AS332L2, exits meet the 22-inch minimum with the rubber seal removed. Airbus Helicopters is working to demonstrate that the rubber seal will detach on operation of the exit. An alternative solution would be to brief passengers to remove the rubber seal before egress, Howson suggested.

Passengers also need to be aware how compatible their physical size is with the available exit routes. o

Safety Statistics Stable in UK North Sea

The accident rate in the North Sea has been relatively stable over the 20 years between 1992 and 2012, according to analysis by the UK CAA. The accident rate is at 1.14 per year or 1.37 per 100,000 flight hours or 0.65 per 100,000 sectors. Approximately one quarter of these accidents were fatal. The main causal factors are, in order, operational (such as pilot error), technical (rotor and transmission failures) and external (lightning strikes).