The Norwegian air accident investigation bureau (AIBN) has made progress in explaining the April 29 crash of a CHC-operated Airbus H225, and from this juncture the agency is considering only three possibilities. In an interim report released late last week, the bureau cites the three possible causes for in-flight separation of the main rotor as failure of the epicyclic module, a lift-strut attachment or the main gearbox conical housing.

Meanwhile, Airbus Helicopters said seven potential initial events have been considered. Of these, only one—failure of the lift-strut attachment—is deemed “probable.” The airframer pointed out that analysis of the helicopter’s maintenance history has just started.

The recordings on the CVFDR show that everything appeared to be normal until a sudden catastrophic failure developed over the course of one or two seconds, the AIBN said. The CVFDR recordings ended abruptly at the same time. However, the French BEA succeeded in downloading information from the flight data monitoring system that extends 13 seconds beyond the CVFDR data.

Detailed metallurgical examinations have been under way since May 19 but are said to be still at an early stage.