Investigation Summary
The flight, operated for Police Scotland, was returning to base after tasks in Midlothian and Glasgow. The EC135 fuel system consists of a main tank and two supply tanks. Fuel must be actively transferred from the main tank to the supply tanks by two fuel transfer pumps. During the return flight, the pilot received five separate low fuel warnings over a period of several minutes. The investigation found that both transfer pump switches were in the 'OFF' position at the time of the crash. This prevented the remaining 76kg of fuel in the main tank from reaching the engines. The pilot did not declare an emergency and continued the flight for approximately 12 minutes after the first warning, beyond the 10-minute limit where a landing was required by the emergency checklist. As the supply tanks emptied, the right engine flamed out first, followed shortly by the left engine. The helicopter descended rapidly and struck the roof of the Clutha Vaults pub, which was occupied by approximately 120 people at the time.
Final Conclusions
The AAIB final report concluded the cause was fuel starvation due to the fuel transfer pumps being switched off for unknown reasons. The pilot failed to comply with the 'Land Immediately' instruction following the activation of low fuel warnings. Contributory factors included the flameout of the second engine causing a loss of electrical power to the Radio Altimeter (RADALT) and the steerable landing light, which reduced the pilot's height information and visual cues during the attempted autorotation. The aircraft was not equipped with a flight data recorder or cockpit voice recorder, which limited the ability to determine why the pumps were off or why the pilot did not follow emergency procedures.
Video Analysis
No video analysis linked for this case file yet.
Crew Experience
Captain
Former RAF Chinook instructor with 20 years of military experience.
Systems & Failure Modes
Fuel Transfer System
Consists of two transfer pumps that move fuel from the main tank to two supply tanks which directly feed the engines. Both pumps were found switched off.
Low Fuel Warning System
Triggers visual and audible alerts when supply tank levels drop below a certain threshold, requiring the pilot to land within a specific timeframe.
FADEC
The Full Authority Digital Engine Control units were analyzed by the NTSB to determine engine performance and the sequence of the flameouts.
Interesting Facts
- 01The helicopter struck the building with a high rate of descent and negligible forward speed.
- 02There was no evidence of engine or gearbox failure prior to the fuel starvation.
- 03Approximately 95 litres (76kg) of fuel remained in the main tank, but the supply tanks were empty.
- 04The aircraft was not fitted with a flight data recorder (FDR) or cockpit voice recorder (CVR).
- 05The pub roof was of complex construction, which complicated the search and rescue operation.
Safety Actions & Advisories
Flight Recorder Requirements
Source ↗The AAIB recommended that the Civil Aviation Authority require all police helicopters to be equipped with flight data and cockpit voice recorders, regardless of their weight, to aid future accident investigations.
Fuel System Management Training
Source ↗Recommendations were made to improve pilot training and procedures regarding the management of the EC135 fuel system to prevent situations where usable fuel remains in the main tank while supply tanks are depleted.