Investigators believe the Rescue 116 helicopter came into contact with rocks at Black Rock Island off the Mayo coast.
In a statement, the Air Accident Investigation Unit (AAIU) said it has recovered tail wreckage in the area around the lighthouse.
The AAIU's chief inspector Jurgen Whyte, in consultation with the appointed investigator-in-charge Paul Farrell, said: "A significant amount of wreckage has been recovered from the sea and this has been logged and will be brought to the AAIU wreckage facility in Gormanston, Co Meath, for detailed examination.
"Furthermore, the AAIU has visited Black Rock Light House, on the approaches to Blacksod Bay, which is close to the last recorded position of the helicopter.
"Some helicopter wreckage has been recovered from the general area of Black Rock Light House.
"This wreckage is primarily from the tail area of the helicopter.
"At this early stage in the investigation it is not possible to be definitive about the exact nature of damage to the recovered wreckage or indeed the circumstances of the accident.
"However, there appears to be marks on some of the recovered wreckage which are consistent with the tail of the aircraft contacting rocky surfaces on the western end of Black Rock.
"The investigation has not yet definitively identified the initial point of impact."
The AAIU is also says it is "anxious" to recover and examine as much wreckage as possible, and in particular the voice and flight data recorder, known as the 'black box'.
It is a week to the day the helicopter came down with four crew on board.
Captain Dara Fitzpatrick has since been laid to rest, and the search for her three colleagues continues.
Manager of the Irish Coastguard is Declan Geoghegan.
"As far as the Coast Guard are concerned it is a body recovery search for our colleagues at this time.
"It's clear that there was contact from that statement.
"However it doesn't change the parameters of the search - that's more or less in relation to the case of the accident that the Accident Investigation Unit will be looking at".
