THE door of a helicopter on which minister Martin Cullen was flying was accidentally opened by one of the passengers on board, Air Corps sources have said.

The source reported that one of the people on the aircraft had inadvertently pressed down on an emergency release handle. The door came loose and fell several hundred feet to the ground, where it was later recovered.

Defence Forces spokesman Gavin Young said: "The investigation into this incident is ongoing therefore it would be inappropriate to comment."

The Agusta Westland company which manufactured the helicopter involved in the accident said they had no records of any other incidents involving doors coming loose in flight.

Company spokesman Geoff Russell said: "There have not been any similar problems with the door on the AW139. This was the first occurrence."

The Defence Forces also said the helicopter, in which minister Cullen was flying, had not been needed for a military exercise at the time of the accident.

Air Corps sources said two of the €12m Agusta Westland AW139 choppers were supposed to have been involved in a training routine at Fort Davis in Co Cork on the day of the mishap.

However, only one of the choppers was made available in Cork and it too ended up being diverted to transport the minister after the first helicopter was grounded, the source said.

Young said only one aircraft was ever supposed to have been involved in the exercise. He said: "One AW139 was scheduled for the exercise in Fort Davis, Cork on 2 March. On completion of the planned training exercise it was sent to Killarney [to collect the minister]."

Young said an investigation into the door falling off the craft was "ongoing" and that such an incident had never happened before.

He said: "Based on the findings of the investigation, recommendations may be made to ensure another incident like this doesn't occur."

The Department of Defence said helicopters were used for transporting government ministers only when no other options were available.

They said: "Air Corps heli­copters are used from time to time for ministerial air transport in situations where, for operational reasons, fixed-wing aircraft may not be available; the point of destination may not be close to an airport and in circumstances where there is a requirement for greater flexibility than can be delivered by a fixed-wing aircraft.