THE investigation into the loss of Coast Guard Rescue 116 helicopter is currently focused on whether "electrical failure" on the helicopter caused the crash.
According to a report in The Irish Independent, investigators have also looked into the possibility the helicopter collided with the lighthouse at Blackrock, six miles off the coast of Mayo.
However, this theory is now discounted as there was no evidence of a collision with the rock and there was no wreckage around the lighthouse.
"There was no paint or debris on the lighthouse. There are 100 theories going around," a senior source involved in the investigation told the newspaper.
This morning, Newstalk Breakfast reported that the Defence Forces confirmed in a statement that they were initially asked to provide top cover for this mission.
However, the request was denied due to the fact it was outside normal hours and there was a lack of "experienced personnel" available.
The request was logged at 10.06 p.m. and the Air Corps was not able to carry out the mission as the fixed wing aircraft was unavailable.
The statement further added "plans are in place to deal with the shortages in personnel being experienced by the Air Corps."
The full-scale search is now homing in on an area near the lighthouse where the black box is now believed to be located.
The crash claimed the life of Captain Dara Fitzpatrick while her crew of three, Ciaran Smith, Mark Duffy and Paul Ormsby, are still missing.
Officials believe there was no mayday call because of a "catastrophic failure" on board.