INVESTIGATORS today said it is too early to pinpoint the exact cause of the helicopter crash.

Aviation experts believe that, based on eye-witness testimony, the crash at the Clutha pub, is thought to have been caused by mechanical failure.

Investigators from the Air Accidents Investigation Branch (AAIB) team who are responsible for determining the cause of the crash, have been working at the scene since Friday night.

A spokesman for the AAIB said yesterday that a statement about the basic events of the crash may be issued today.

But it could be some time before the exact cause of the accident is known and the AAIB is able to publish a full and detailed final report.

Yesterday, First Minister Alex Salmond sought to address concerns about the safety of other aircraft used by the emergency services.

"Over 1000 Eurocopters 135s have been in service, there are hundreds in service across the world at the present moment," he said.

"In terms of the other craft that we have got in our emergency services, they have been inspected.

"Our air ambulance is fully functional from this afternoon.

"The police have helicopter cover as required as well. So our emergency services continue with the appropriate cover.

"Any instructions that come out from the Civil Aviation Authority, based on advice from the Air Accidents Investigation Branch, of course these would be immediately followed."

Chief Constable Sir Steve House said yesterday that the helicopter was returning to its Glasgow base when it crashed.

Aviation experts said that, based on eye witness accounts, the rotorblades were not turning or were turning very slowly as it fell from the sky, which indicates mechanical failure.

Police Scotland said: "Following detailed inspection, in line with the latest airworthiness directive, no faults were identified and the force helicopter was available for operational deployment."

The procurator fiscal will decide in future, once the investigation by police is complete, if a prosecution is required, if for example, there had been any breach of health and safety law.

LUCY ADAMS