Fresh searches are to take place off Blackrock Island in Co Mayo this weekend, as the investigation into the crash of a Coast Guard rescue helicopter last March continues.

Garda divers will travel to the scene tomorrow to conduct more surveys of the area where Rescue 116 crashed, with the loss of all four crew members.

The bodies of two crewmen, Paul Ormsby and Ciarán Smith, have still not been found.

The Garda Superintendent leading the investigation into the crash, Tony Healy, said the searches were the latest stage in the ongoing investigation.

He said that more favourable sea conditions will allow for a fresh survey of the area around Blackrock.

It is expected that the investigators will trawl for any new evidential material.

One of the engines from the Sikorsky helicopter is still on the sea bed and this may be recovered this weekend.

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Small items of debris are still being gathered along the shoreline and are being processed by gardaí in Belmullet.

Detectives have been alerting the Air Accident Investigation Unit (AAIU) about any finds.

However, the volume of material being washed ashore has diminished in the months since the crash.

A piece of a stretcher board from the helicopter was recovered last week and this has been added to the store of debris already found.

Gardaí said that only small fragments of material are being found at this stage.

Rescue 116 did not have enough data to avoid collision

Retired Lieutenant Colonel Kevin Byrne has said Rescue 116 did not have enough data to avoid a collision.

Speaking on RTÉ’s News at One he said: "It was not a mechanical error, the aircraft was running normally and there was a problem, they struck a rock as there was no warning to alarm the pilot. It is not like normal flying."

From his own personal flying experience he said when coastal search and rescue services are flying late and [at] night and in bad weather conditions, there is a need to rely on radar and navigation.

He said he believes all the potential dangers of obstacles off the Irish coastline have now been addressed.

Separately, it has emerged that amateur associations representing sport and recreational pilots alerted the Irish Aviation Authority over the last year to numerous errors and omissions on aeronautical maps they use. 

Pilots became concerned following a light aircraft crash in the Blackstairs Mountain in 2015.

The AAIU report into that accident identified the absence of the 2,400 feet height of the mountain peak on the aeronautical charts available at the time. 

The aircraft crashed into the mountain in poor visibility, killing the pilot and his passenger. 

The report did not make any recommendation in relation to the mapping data. 

Meanwhile, the AAIU said it cannot comment on its probe into the circumstances surrounding the helicopter crash.

The AAIU issued a preliminary report into the accident last April and said it is working towards the completion of a draft final report. This is expected to take several months.

Investigators are still gathering evidence and compiling data into all aspects of the Rescue 116 mission on 14 March last.

There is an obligation to produce a full report on such incidents within 12 months. In the event that the work is not completed by then, a preliminary report would be issued, detailing progress to that point.

Until the draft report is completed, the AAIU said it will be making no further comment on the development of its inquiry.