The cause of the Glasgow helicopter tragedy that claimed nine lives is still unclear following an interim report by investigators.
The helicopter crashed onto the flat roof of the Clutha Vaults hotel on the night of November 29 with a high rate of descent and with low or negligible forward speed, an Air Accidents Investigation Branch (AAIB) bulletin revealed on Monday.
But the report also quoted a crash witness who heard a noise "like a loud misfiring car" before the helicopter plummeted.
The AAIB added that the weather was good, so far there was no evidence of engine or gearbox failure and "all significant components were present" at the time of impact.
When it crashed, the helicopter still had 95 litres of the 400 kilograms of fuel with which it had taken off.
The pilot of the helicopter, David Traill, 51, and his two passengers - police officers Kirsty Nelis, 36, and Tony Collins, 43 - were killed in the crash, as were six people in the pub.
The bulletin traced the events of the Friday night of the crash. Having left Glasgow City Heliport at 8.45pm, the pilot had requested and received clearance from air traffic controllers to re-enter the Glasgow control zone at 10.18pm.
Radar contact with the helicopter was lost at 10.22pm.
"Around this time, the helicopter was seen and heard by a witness who described hearing a noise like a loud 'misfiring car', followed by silence," the report said.
"He then saw the helicopter descend rapidly. It crashed through the roof of the Clutha Bar, a single-storey building on Stockwell Street in central Glasgow."
The report continued: "Preliminary examination showed that all main rotor blades were attached at the time of the impact but that neither the main rotor nor the fenestron tail rotor (a form of protected tail rotor) were rotating."
The report said initial assessment provided no evidence of major mechanical disruption of either engine.
Pilots union British Airline Pilots Association said: "The information published by the AAIB today is a helpful first assessment of the facts of the case and suggests there is no evidence of mechanical engine failure
"But, unfortunately, at this stage there is not much more to go on and the reasons behind the crash are, in truth, far from clear."