The Air Accident Investigation Unit has recommended that the company that runs the Coast Guard service in Ireland should review and re-evaluate all route guides used by search and rescue helicopters and the lifejacket manufacturer should review its instructions for locating beacons in jackets.

The recommendations are included in the AAIU's preliminary report into the crash of Coast Guard helicopter Rescue 116 on 14 March off the Co Mayo coast.

Coast Guard Captain Dara Fitzpatrick was taken from the sea following the crash but later died.  

Co-pilot Captain Mark Duffy's body was recovered from the wreckage of the helicopter late last month. Winch operator Paul Ormsby and winchman Ciarán Smith are still missing.

Dara Fitzpatrick and Mark Duffy were recovered after the crash, Paul Ormsby and Ciarán Smith are still missing

The first recommendation from the AAIU is that CHC - the company that runs the Irish Coast Guard helicopter service - should review and re-evaluate all route guides in use by its search and rescue helicopters in Ireland with a view to enhancing the information provided on obstacle heights and positions, terrain clearance, vertical profile, the position of waypoints and what is in the enhanced ground proximity warning system database.

The second recommendation relates to the location in lifejackets of beacons and the GPS antennae that operates them.

The locator beacons on the lifejackets of the crew of Rescue 116 were worn in the same pouch as the GPS antennae that operated them.

According to the manufacturer’s manual for the beacon, those two pieces of kit should be held 30cm apart.

The recommendation from the AAIU is that RFD Beaufort Ltd, the lifejacket manufacturers, should review the viability of the installation provisions and instructions for locator beacons on these lifejackets and if necessary amend or update these provisions and instructions taking into consideration the beacon manufacturer’s recommendations.

In a statement, the CHC said that it notes the safety recommendations made in the preliminary report, and a review "of a all route guides in use is well under way."

It also said that the initial report "does not identify the root cause" of the crash. It said that it will continue to support the AAIU in its ongoing investigation. 

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The 38-page preliminary report gives details on what happened on the night of the crash.

It states that Rescue 116 was tasked at 10.10pm on 13 March to assist in a medical emergency on board a fishing vessel that Sligo-based Rescue 118 was responding to.

Four minutes later the Rescue 116 crew was informed that the Air Corps had advised that no ‘top cover’ was available for the rescue mission.

The Rescue 116 crew decided to refuel at Blacksod on the Co Mayo coast after looking at their timings and their fuel.

The flight commander programmed an approach to Blacksod into the flight management system, this was confirmed as matching the operator’s route guide - separate to other navigational aids - essentially a map that sets out things like hazards, obstacles, co-ordinates and other general information.

This included an identification of the lighthouse at Blackrock giving its height as 310ft but crucially this information was not included on the enhanced ground proximity warning system on board the helicopter.

The aircraft began its descent at 12.34am on 14 March from a cruising altitude when it reached a point that indicated the arrival into Blacksod should commence.

At this point there was no reference on the voice recording to the lighthouse on the island.

The first indication of an obstacle comes 26 seconds before the initial impact when an automatic warning system gave a call-out "Altitude, altitude".

Thirteen seconds later one of the crew members in the back of the aircraft identified an island and advised the captain to veer right, away from the island.

In the final seconds the helicopter pitched up rapidly impacted with terrain at the western end of Blackrock and departed from controlled flight.

The last radar return for Rescue 116 was at 12.46am. The first indication that the helicopter may be missing was at 1.06am, when the helicopter crew did not answer radio calls to their call-sign.

The AAIU preliminary report includes transcripts of conversations between the four crew members of Rescue 116 from the cockpit voice recorder.

In the report there are references to discussions among the crew about how often they had landed at Blacksod in the past and the number of times they had been in the area.

It recorded the commander, Captain Dara Fitzpatrick, commenting to the other crew members on a number of occasions that it had been a substantial period of time since she had previously landed in Blacksod.

On one occasion the commander asked the co-pilot, Captain Mark Duffy, when he had last been into Blacksod and he indicated that he had not been there recently.

There is an appendix to the report that details the last one minute and 40 seconds on the cockpit voice recorder.

That recording opens with a contact from the rear crew channel. The winch operator or winchman, contacted Belmullet Coast Guard radio advising that the helicopter would be landing very soon at Blacksod and they would call again after refuelling.

Seconds later, the "Altitude" warning is heard. A speaker on the rear crew channel refers to an island "Directly ahead of us now guys", before advising the pilot and co-pilot "you want to come right".

That instruction was confirmed by the flight commander, followed by repeated messages from the rear crew: "come right now, come right, come right."

The last utterance on the voice recorder from the co-pilot was "we’re gone".

The rest of the data is comprised of messages and a series of noises before static and ultimately silence before the end of the recording.