OSLO (Reuters) - Norwegian investigators looking into the cause of a fatal North Sea helicopter crash have sent a recommendation to European air safety authorities about a possible safety issue with the model's gearbox, they said on Wednesday.
An Airbus H225 Super Puma helicopter ferrying passengers from a Norwegian oil platform operated by Statoil went down on April 29, killing all 13 people on board.
Since then the helicopter model, a workhorse of the oil industry, has been grounded for commercial flights in Norway and Britain. Investigators have ruled out human error, saying that the crash was caused by a technical fault.
On Wednesday, the Accident Investigation Board Norway said it had made findings recently that justified issuing an immediate safety recommendation to the European Aviation Safety Agency.
"Recent metallurgical findings have revealed features strongly consistent with fatigue in the outer race of a second stage planet gear in the epicyclic module of the (main gear box)," the Accident Investigation Board Norway said in a report published on its website.
"It cannot be ruled out that this signifies a possible safety issue that can affect other (main gear boxes) of the same type. The AIBN therefore recommends that EASA (European Aviation Safety Agency) take immediate action to ensure the safety of the Airbus Helicopters H225 main gearbox."
The head of the investigation board told Reuters that investigators were still looking at other reasons for the accident.
"We are still investigating and keeping options open," said William Bertheussen, general director of the investigation board. "This is an important discovery and is part of the possible scenarios we have."
"We wanted to make known (that) this is an important finding ... We have issued this immediate recommendation so that the European Safety Aviation Agency should follow up."
Another accident investigation board official said signs of fatigue found on mechanical parts are seldom related to maintenance.
"It is very seldom maintenance-related with a fatigue issue," Kaare Halvorsen, director of the aviation department at the board, told Reuters.
Design and production are the responsibility of Airbus Helicopters, while maintenance is handled by the operator, CHC Helicopter.
"We are analyzing the document with great attention," said an Airbus Helicopters spokesman.
CHC Helicopter was in the process of reviewing the report, a company spokesman said.
The European Aviation Safety Agency was not immediately available for comment.
(Reporting by Gwladys Fouche in Oslo, Cyril Altmeyer in Paris and Victoria Bryan in Dublin; Editing by Mark Heinrich, Larry King)