A police helicopter that plunged into a packed Glasgow bar last year, causing 10 deaths, suffered a double engine failure.
The Air Accidents Investigation Branch (AAIB) said on Friday the right engine of the Eurocopter EC135 "flamed out" before the left engine did likewise shortly afterwards.
It is still unclear why the engines stopped when 76kg of fuel remained on board the helicopter belonging to Bond Air Services.
The AAIB said the continuing investigation would also want to find out why no emergency radio transmission was received from the pilot and why "an autorotative descent and flare recovery was not achieved".
All three people on board the helicopter were killed in the crash and six died in The Clutha pub, where around 120 people were watching a local ska band perform on November 29 last year.
A 10th victim died two weeks later from injuries sustained inside the bar. Eleven others were seriously hurt.
The flat roof of the single-story pub collapsed.
Bond briefly grounded its 22-strong fleet of EC135 models in December following an issue with the fuel indication system on one of its aircraft.
