A key member of a team reviewing a report into the fatal R116 helicopter crash that occurred off the coast of Mayo in 2017 has resigned due to a conflict of interest, RTÉ Investigates has learned.

The resignation of Phillip Hanson, a senior manager at the UK Coastguard, and the technical expert on the two-man review team, is expected to significantly delay the review, which will ultimately delay the publication of the report into the causes of the accident.

RTÉ understands that Mr Hanson disclosed that he had a personal connection with a senior manager at the helicopter operator, CHC. That manager was due to give evidence on behalf of CHC to the review board.

CHC declined to comment to RTÉ, as did Mr Hanson. In a statement, the Department of Transport confirmed that Mr Hanson resigned from the review board on 21 September, but did not give any details about the reason for his resignation.

The resignation is the latest factor to delay the publication of the report by the Department of Transport's Air Accident Investigation Unit (AAIU) into an accident that claimed the lives of all four crew members of the helicopter: pilot Dara Fitzpatrick, co-pilot Mark Duffy, and rear crew Paul Ormsby and Ciarán Smith.

The search and rescue helicopter crashed into Blackrock Island off the coast of Co Mayo in the early hours of 14 March, 2017. The bodies of Mr Ormsby and Mr Smith have not been recovered. Their helicopter had been dispatched to provide assistance to another helicopter, Rescue 118, that was retrieving an injured fisherman from a trawler in the Atlantic.

The inquest into the deaths of the crew cannot be finalised until the AAIU report is published.

A draft report circulated by the AAIU to stakeholders late last year was expected to be published in January.

But publication was delayed after objections from a stakeholder, believed to be CHC, a US-based company which is hired by the State to operate search and rescue services.

Representatives of the families of some of the deceased crew are understood to have objected to Mr Hanson being on the review board once he disclosed his personal connection to the CHC manager. 

The review board is chaired by barrister Patrick McCann and Mr Hanson was the technical advisor. Mr McCann declined to comment for this article, stating that he is "bound by a statutory obligation of confidentiality".

In its statement, the Department of Transport said that "...the Review Board acts as an independent entity separate from the Minister and the Department. The re-examination by the Review Board is confidential and the timeframe... to carry out the re-examination is a matter for the Chairman".

It is understood sections of the draft AAIU report, which is the subject of the review, are highly technical and it will be difficult for the review board to make significant progress until a replacement aviation expert is appointed.

That appointment will be made by Transport Minister Eamon Ryan, whose predecessor Shane Ross established the review board last March.

"Minister Ryan is currently engaging with the Chair of the Review Board" on finding a replacement, the department said.

The Department of Transport now has "one big headache", said an aviation expert familiar with the situation who asked not to be named. He noted that because CHC is a significant operator in the UK and Ireland it would be difficult to find a high-level replacement who never had any connection with the company.

"Now they are going to have to find an expert who is completely and utterly independent," he told RTÉ. "How do you find an expert in search and rescue with all the gravitas needed and who has not come into contact with CHC?"

The law governing air accident investigations allows any person or organisation to seek a re-examination of "any findings and conclusions" that appear to "reflect adversely" on their reputation. However, this is the first time for an AAIU report to be referred to a review board in the AAIU's 25-year history, during which it has carried out nearly 1,000 investigations.

AAIU enquiries are protected by highly restrictive legislation that makes it a criminal offence to reveal details prior to official publication of an air accident investigation report. 

After the Rescue 116 accident, safety issues at helicopter operator CHC were highlighted by RTÉ's Prime Time, including an alleged failure to adequately deal with safety complaints. It also emerged that Blackrock Island was not included in a database designed to warn the crew they were in danger of hitting land.