Bond Air Services has grounded its EC135 helicopter fleet in the wake of a November 29 accident in which one of the aircraft it operates for local police crashed into a pub in Glasgow, Scotland, killing nine people and injuring 32 others. The operator took the decision to suspend operations of its 38 EC135s after the UK Air Accident Investigation Branch (AAIB) released a special bulletin on December 10.

Around 10:20 p.m. local time that night, just after the pilot’s last contact with Glasgow ATC, a witness described hearing a noise like a loud misfiring car followed by silence. He also saw the helicopter descending at a high vertical rate.

The AAIB report said neither the main nor the tail rotor was turning when the helicopter hit the roof of the building. “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 number-two engine power turbine to the main rotor and to the drive shaft,” said the AAIB bulletin.

The rotors appear to have simply stopped turning and the helicopter fell.