Island 'obstacle' was not on crew's warning system
The preliminary report into the fatal R116 crash found that the on-board warning system did not contain any data about Black Rock island or its lighthouse.
The Air Accident Investigation Unit's (AAIU) report into the crash - which occurred off the coast of Co Mayo at around 12.45am on March 14 - also questions why the locator beacons in the life jackets of the R116 crew did not emit any signal upon its crash landing.
The preliminary report - while not attributing blame or finding fault at this stage of the investigation - has made two interim safety recommendations relating to the on-board warning system and life jacket locator beacons.
It appears the R116 crew of Captain Dara Fitzpatrick (45), Captain Mark Duffy (51), winchman Paul Ormsby (53) and winch operator Ciarán Smith (38) - who flew out near Black Rock before making their planned scheduled fuel stop to Blacksod - were not aware of Black Rock island before it was too late.
They were flying using the 'Enhanced Ground Proximity Warning System' (EGPWS), which had data containing the obstacles and terrain of the entire island of Ireland fed into it. However, the preliminary report says information about Black Rock was missing from the data.
This meant the crew did not receive any warning signals and were unaware of the obstacle that was before them.
Senior AAIU investigator Graham Liddy told Newstalk Breakfast that there were general adverse weather conditions at the time of the crash, with strong high winds and poor visibility.
"The area in Black Sod may have even been a little worse than that," he said on Friday morning.
"The forecast doesn't tell you about the mist hanging over the whole island; the island was obscured".
In the report, under a section on EGPWS, it is stated that investigators have been in touch with the manufacturers, Honeywell, who confirmed that "the lighthouse obstacle is not in the obstacle database and the terrain of the island is not in our terrain database".
The AAIU said it will continue engaging with Honeywell and other parties/agencies to " reach a full understanding of this issue".
Read more: Full transcript of audio from Rescue 116
A source close to the investigation says this problem with the terrain database is just the "final link in the chain" and other circumstances around the crash are being investigated.
Following the crash, debris from R116 was found on Black Rock, in the sea and on the shorelines of counties Mayo and Donegal. The main wreckage was found some 40 metres away from the island thanks to it's acoustic beacon.
The investigation has identified another matter of concern being the installation of locator beacons in the lifejackets worn by crew.
The report says the lifejackets hold both GPS equipment and locator beacons - however, the beacons have to be some 30cm away from the GPS equipment in order to function. It is understood they did not function at the time of the crash and afterwards.
The AAIU has made two interim safety recommendations.
The first being that CHC - the company that provides Ireland's Search and Rescue (SAR) services of which R116 was part - should "review/re-evaluate all route guides used by SAR helicopters in Ireland, with a view to enhancing the information provided on obstacle heights and positions, terrain clearance, vertical profile, the positions of waypoints in relation to obstacles and EGPWS database terrain and obstacle limitations".
The second recommendation asks it to look closely at the lifejackets and locator beacons - reviewing the viability of the beacons in the lifejackets when taking into consideration the beacon manufacturer's recommendations for effective operation.