US rotorcraft operator Era Group says a return to service for its fleet of nine Airbus Helicopters H225s is "improbable" after it was unable to develop a safety case for the move.

"We will not operate the H225 helicopters in our fleet unless and until we can develop a detailed safety case that demonstrates [it] can be operated safely," the company says in a full-year results filing.

"During the third quarter of 2017, we determined that we cannot develop such a case and that a broad-based return to service is improbable."

The decision is unsurprising – Era is already locked in a legal battle with the manufacturer over damages relating to its purchase of the H225s – and whether it is representative of sentiment in the wider market is unclear.

Nonetheless, it is an unwelcome reminder for Airbus Helicopters on how the 11t-class helicopter is still perceived by some customers.

"Even though H225s are no longer grounded by the regulatory authorities, our customers, their employees, and the unions to which our customers’ employees belong largely lack confidence in the H225 helicopter," says Era.

"As a result, we believe a full return to service for the H225 helicopter in offshore oil and gas operations is unlikely."

The H225 was grounded following a fatal crash off the west coast of Norway in April 2016 for which investigators have been unable to find a root cause.

Aviation regulators in Norway and the UK were the last to lift flight restrictions for the type, but the return to service has so far not materialised in the North Sea region.

Companies elsewhere have begun to operate the H225 again for offshore missions, with a pair recently contracted in Brazil to operate on behalf of oil giant Total.

But Era chief executive Chris Bradshaw, speaking on a call with analysts, described that deal as a "one-off situation", noting that the oil producer is a "large French company".

"And I think they are dealing with an operator there who was willing to put the aircraft back in service," he added. "In our case, and I think is the case for the majority of the Western helicopter operators, we don't believe that there is a detailed safety case that exists today that would justify a return to service for those aircraft."

Bradshaw points out that in tenders recently issued by state-controlled oil company Petrobras, the H225 was not listed as an eligible aircraft.