A preliminary report into the fatal crash of Coast Guard Rescue Helicopter 116 has found that an onboard warning system on the aircraft did not include data relating to Blackrock Island.
The helicopter crashed into the island off the coast of Co Mayo on 14 March, with the loss of all four crew members on board.
The bodies of Captain Dara Fitzpatrick and Captain Mark Duffy have been recovered but two others, winch operator Paul Ormsby and winch man Ciarán Smith, remain lost at sea.
In the report, the Air Accident Investigation Unit says that its initial inquiries have found that an Enhanced Ground Positioning Warning System did not have the "lighthouse obstacle" included in an obstacle database and that "the terrain of the island" was not listed on a terrain database.
The report finds "the helicopter pitched up rapidly, impacted with terrain at the western end of Black Rock and departed from controlled flight."
The report has recommended that CHC Ireland, which operates Coast Guard Helicopters, should immediately review all route guides on Search and Rescue aircraft to enhance the information provided on obstacles and terrain.
Preliminary report on fatal Rescue 116 crash finds onboard warning system did not include data relating to Blackrock Island pic.twitter.com/yc2GM8fSZ8— RTÉ News (@rtenews) April 13, 2017
It is also recommending that the effective operation of locator beacons on Mk44 life jackets needs to be reviewed.
While initial inquiries suggest these beacons and the corresponding GPS antenna were packed in line with an explanatory note, the AAIU points out that there should be at least 30cm between the two devices to ensure effective operation.
The report also contains data from the voice recorder from R116.
In the seconds before the helicopter impacted with Blackrock Island, crew members are heard to discuss "an island directly in front of us" before advice to "come right" is issued.
Three seconds later, the last recorded communication took place.
The AAIU says the inquiry is ongoing and a final report into the accident will be published in due course.
They also noted that this preliminary report contains information as known at this time, and does not contain analysis or conclusions.
As a result, the information is subject to change and may contain errors which will be corrected in the final report.
As well as a carrying out a detailed analysis of the flight recorders, the wreckage of R116 will be inspected at the unit's facility in Gormanston, Co Meath.
Mechanical anomalies on the helicopter have already been ruled out contributory factors and the AAIU focus is now understood to be on operational aspects of the flight.
These take in several headings but will include human behaviour, navigational controls and procedural issues.