Investigators have found no initial evidence of engine or gearbox failure in their probe into the police helicopter crash in Glasgow which claimed nine lives.
In a special bulletin, the Air Accidents Investigation Branch (AAIB) said "all significant components were present" at the time the two-engined Eurocopter EC135 helicopter crashed through the roof of The Clutha Bar on the night of 29 November.
The remains of the helicopter being removed from the roof of the Clutha Bar
The report went on: "Initial assessment provided no evidence of major mechanical disruption of either engine and indicated that the main rotor gearbox was capable of providing drive from the No 2 engine turbine to the main rotor and to the fenestron drive shaft."
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 inside the pub.
The AAIB report on Monday said that the helicopter had left Glasgow City Heliport at 8.45pm on the Friday of the crash and had flown, to start with, to a location on the south side of Glasgow city centre, staying there for about 30 minutes at a height of 1,000ft above sea level.
In had then gone about 40 miles east to Dalkeith in Midlothian, staying there for a further 10 minutes before returning to Glasgow.
At 10.18pm the pilot had requested clearance from air traffic controllers to re-enter the Glasgow control zone and return to the heliport. This had been approved and no further radio transmissions from the pilot were received.
The AAIB added that radar contact with the helicopter was lost at 10.22pm.
The report went on: "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.
"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 three occupants of the helicopter and six people in, or adjacent to, the bar were fatally injured. Thirty two other people suffered injuries, 12 seriously."
The AAIB said the weather just after the helicopter took off and also at the time of the crash was described, in aviation jargon, as CAVOK - meaning that visibility was good. Winds were light at around 7-8 knots.
The report said that initial evidence indicated that the helicopter struck the flat roof of the pub "with a high rate of descent and low/negligible forward speed".
The AAIB went on: "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.
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Glasgow helicopter crash
"The impact forces caused the roof of the bar to collapse and helicopter entered the building, its forward section coming to rest on and amongst building debris.
"Very extensive damage and disruption of the helicopter structure and components resulted from the impact forces and from contact with the collapsing building. The helicopter did, however, remain approximately upright."
The AAB said its team, working closely with the emergency services and the authorities in Glasgow, had conducted a preliminary examination of the aircraft within the collapsed area of the pub.
After that, the damaged sections of the building were shored up and made safe, "enabling closer examination to be carried out".
The special bulletin added that the building debris was progressively removed allowing additional access to be gained.
But the state of the building limited the extent to which examination of the helicopter was possible at the scene, the AAIB added.
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The report continued: "After further debris removal and cutting off the main rotor blade, it was determined that the helicopter structure remained sufficiently robust for it to be lifted clear of the building by means of a crane, using strops attached to the main rotor head.
"Once removed from the building, approximately 95 litres of fuel were drained from the fuel tank system."
The AAIB said the helicopter was transferred to its headquarters at Farnborough in Hampshire.
The investigation team said detailed examination of the helicopter continued. The bulletin added that the aircraft was not required to have, and was not fitted with, flight recorders, not did its systems "provide a continuous recording of helicopter parameters".
But the AAIB said that some systems record fault codes as they occur, in memory that is not crash-protected. The report went on: "Those, and systems that can record camera images and audio, will be examined and analysed."
The bulletin also said that radar data covering the flight had been recovered and was being analysed, along with radio communications as well as closed-circuit TV recordings.
The AAIB promised to report any significant developments as the investigation progressed.
The pilots' union Balpa 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. The AAIB must be given the time to complete its thorough investigation and we have faith in their ability to do so."