Clutha Fatal Accident Inquiry

The following is a summary of the Determination of Sheriff Principal Craig Turnbull, following a Fatal Accident Inquiry held at Glasgow into the deaths of the ten people who died as a result of the accident in which a helicopter, then carrying out duties on behalf of Police Scotland, crashed in to the Clutha Vaults public house on 29 November 2013.

The cause of the accident resulting in the deaths was that (a) the engines of the Eurocopter Deutschland EC135 T2+ helicopter, with registration G-SPAO, owned and operated by Bond Air Services Limited, then carrying out operations on behalf of Police Scotland, flamed out sequentially while the helicopter was airborne, as a result of fuel starvation, due to depletion of the contents of the supply tank; and (b) the pilot of the helicopter, Captain David Traill was unable to successfully perform an autorotation and landing of the helicopter (Finding F4.1).

The contents of the supply tanks depleted due to the failure of Captain Traill to ensure that at least one of the helicopter’s fuel transfer pump switches was set to ON (Finding F4.2).

The central issue in the inquiry was why Captain Traill allowed the contents of the supply tank of the helicopter to deplete to the point it did when there was more than sufficient usable fuel available to him in the main tank to allow the helicopter to return safely to its base. The inquiry concluded that the accident was caused by Captain Traill’s failure to ensure that at least one of the fuel transfer pump switches was set to ON [145].

In normal operation, one or both of the helicopter’s fuel transfer pumps should be running constantly, to deliver fuel from the main tank to the supply tank [157].

In flight, as the depth of the fuel in the main tank reduces and the pitch attitude of the helicopter changes, one or other of the fuel transfer pump inlets can become uncovered, causing the associated pump to run dry. The dry running is detected by the helicopter’s fuel control and indication system software, which produces an F PUMP AFT or F PUMP FWD caution caption on the helicopter’s caution and advisory display (CAD). The appearance of this caution caption prompts a procedure in the Pilot’s Checklist (which is reproduced in Appendix 4 to the determination) [159]. That procedure requires a dry running pump to be switched off.

At separate points in the helicopter’s final flight, circumstances existed that caused Captain Traill to switch off both fuel transfer pumps; and where each pump was properly switched off by Captain Traill. When switching off the second (i.e. the aft) fuel transfer pump, Captain Traill appears to have overlooked the fact that he had previously switched off the forward fuel transfer pump approximately 11 minutes earlier [224].

At the point in time when Captain Traill switched off the aft fuel transfer pump, the CAD displayed cautions to the effect that both fuel transfer pumps were switched off. On switching off the aft fuel transfer pump, there would have been flashing bars on the CAD and the helicopter’s master caution would have illuminated. They would have continued to display until such time as Captain Traill acknowledged the aft fuel transfer pump caution, by way of the reset button on the cyclic control [345].

The LOW FUEL warnings were generated by thermistors, which are attached to the outside of the fuel sensor capacitance tubes in the supply tank cells. As part of their investigation, the Air Accidents Investigation Branch (AAIB) tested the helicopter’s thermistors (which were undamaged by the crash). They were found to work correctly [231].

The sheriff principal has found that (a) the thermistors on the helicopter were working correctly; (b) that the LOW FUEL warnings were triggered before the helicopter reached Bothwell; and (c) that Captain Traill was aware of, and acknowledged, the LOW FUEL warnings. The helicopter crashed 16 minutes after it had reached Bothwell. There was sufficient fuel on board the helicopter to have permitted it to land within the ten minute period mandated by the Pilot’s Checklist, had that been necessary [243].

Both the fuel transfer pumps switches were in the OFF position at the point in time the LOW FUEL warnings were triggered. Had one or both of them been switched back on by Captain Traill at that point in time the helicopter would not have crashed. The fuel transfer pumps were not switched back on by Captain Traill [248].

There was sufficient time between the first and second engine flame outs for Captain Traill to have switched on the fuel transfer pumps. When the first engine flamed out, Captain Traill failed to identify that both transfer pumps had been switched off [330]. The helicopter should never have reached the stage of flying with one engine operative, far less suffering a double engine flameout [406].

The sheriff principal has found that there were two reasonable precautions which could have been taken and, had they been taken, might realistically have resulted in the deaths being avoided (see Findings F5.1 and F5.2). These are:

1.         for Captain Trail, to have followed the procedure set down in the Pilot’s Checklist – Emergency and Malfunction Procedures in respect of the LOW FUEL 1 and / or LOW FUEL 2 warnings; and

2.         for Airbus Helicopters Deutschland GmBH to have included within the fuel contents indication system a warning and associated aural attention-getter which activated where both fuel transfer pumps had been switched OFF.

The sheriff principal has determined that there is no defect in any system of work. No aspect of the training of pilots contributed to the accident [410].

In light of the safety recommendations made by the AAIB, no recommendations are made. The two reasonable precautions identified do not, of themselves, justify the making of related recommendations [446]. All affected aircraft being operated for or on behalf of Police Scotland and other emergency services in Scotland now have flight recorders fitted [423].

By January 2013 the potential risk of the CAD displaying a higher fuel quantity compared to the actual quantity of fuel on-board had been identified; and pilots, including Captain Traill, had been made aware of that potential risk [280].

The sheriff principal has determined that the following fact is also relevant to the circumstances of the deaths, namely, that it is more likely than not that the quantities of fuel displayed on the fuel quantity indication system of the helicopter contradicted the LOW FUEL warnings (see Finding 7.1). There are, however, two points that must be stressed in relation to this finding.

Firstly, the contradictory fuel display is only of relevance until the illumination of the LOW FUEL warnings. At that point the actions set out in the Pilot’s Checklist should have been performed by Captain Traill. By not carrying out the actions set out in the Pilot’s Checklist, Captain Traill consciously took a risk in proceeding on the basis that the LOW FUEL warnings were in some way erroneous (when they were not). That decision had fatal consequences. There was no logical basis for preferring the (possibly erroneous) figures displayed on the CAD to the accurate LOW FUEL warnings, particularly in circumstances where the fuel transfer pumps were both switched off [312].

Secondly, whilst this fact is relevant to the circumstances of the deaths, it neither caused nor contributed to them. The contents of the helicopter’s supply tank depleted due to the failure of Captain Traill to ensure that at least one of the fuel transfer pump switches was set to ON [313].

The sheriff principal has concluded that the circumstances of the accident are so unusual that it is improbable they will be repeated, even without the introduction of the safety actions taken since the accident. Until the accident, the EC135 had accumulated more than three million flying hours, over a period of twenty years, without there previously being a reported instance of fuel starvation [448].

The fact that it took more than two years from the publication of the AAIB Report to the decision that there were to be no criminal proceedings is surprising, notwithstanding the extensive work carried out by Police Scotland and the Crown in the intervening period. It took far too long to lodge a notice of an inquiry in this case, although the inquiry itself was conducted with great efficiency for which all those responsible for its preparation and conduct are to be commended [509]. The Crown was not sufficiently resourced to enable the inquiry to start far sooner than it did [510].

References in square brackets are to paragraphs of the determination.

NOTE

This summary is provided to assist understanding of the court’s determination. It does not form part of the reasons for the decision. The full determination is the only authoritative document. Determinations in fatal accident inquiries are published on the SCTS website