A police helicopter which crashed into a busy Glasgow pub killing 10 people suffered a double engine failure, air accident investigators have found.
The Air Accident Investigation Branch (AAIB) said both engines "flamed out" but its report does not pinpoint the cause. Some commentators have suggested a problem with the fuel supply.
Sorry; already posted by TF!
That seems improbable, given the separation of the two systems and the amount of fuel left in both. I would think that ingesting something is the most likely cause of a double engine failure.
Colin Bignell
"No evidence of damage caused by birdstrike or a foreign object..."
Tim
On the Radio 4 news they said, "Both engines ran out of petrol."
Bill
The AAIB do not agree:
"It was found that the main fuel tank contained 76 kg of fuel, whilst the No 1 supply tank (left) contained 0.4 kg of fuel and the No
2 supply tank (right) was empty.""Examination of all internal pipe work and transfer passages has not revealed any pre- or post-impact failure and all paths still permit uninterrupted fuel flow. It has been established that unrestricted flow was also available from each supply tank to the corresponding engine fuel control unit, through the relevant fuel shut-off valves which were found set to the open position."
"the fore and aft transfer pump (XFER F and A) switches were set to the OFF position"
Not the views of the AAIB:
Attitude change during the transition from high speed flight to a lower speed in in preparation for landing, plus failure to run the fore transfer pump earlier in the high speed flight and later failure to run the aft transfer pump due to possible calibration failure of fuel level transmitter and level alarms. the latter being suggested by the checks mandated by Eurocopter back in December
2013So possibly some pilot error maybe caused by an as yet unproven system failure.
There wasn't a drop of petrol found in the wreckage, that's true 'nuff...
That only rules out a particular type of ingestion. Anything that causes a loss of compression or that cools the combustion chamber can lead to a flame out and it is difficult to envisage anything else that would have the same effect on both engines.
Colin Bignell
The AAIB report issued very recently and linked to upthread says that at the time of impact there was no fuel in *either* of the tanks that directly feed the engines, but there was 76kg of fuel in the main tank. It also states that one engine flamed out, followed shortly afterwards by the other, in the sequence expected if fuel had not been transferred in the normal manner from the main tank to the running tanks. In effect, it ran out of usable fuel with plenty of fuel in the main tank. They're still trying to find out how and why this happened.
At this stage, the AAIB neither agree nor disagree. They never publish conclusions in an interim report.
You missed out the bit about the fuel tanks being being compressed in the accident with sufficient force to collapse the internal fuel quantity transmitters. While they are able to say that the fuel did not move while the helicopter was at rest in the building, they do not comment about any effect the compression may have had on the distribution of fuel during the impact.
Where have you taken that from?
At this stage, anything is possible. As the AAIB say:
'In particular, the investigation will seek to determine why a situation arose that led to both the helicopter?s engines flaming out when 76 kg of fuel remained in the fuel tank group, why no emergency radio transmission was received from the pilot and why, following the double engine failure, an autorotative descent and flare recovery was not achieved.'
Until they finish looking into that, we won't know what they think caused the accident.
Colin Bignell
Also confirmation that rotors were stationary at time of impact, no explanation of why no auto-rotation.
Hmm. They don't run on petrol.
You win tonight's star prize.
Bill
That is exactly what the BBC reported this afternoon, on Radio 4.
But that flies in the face of Colin's theory so can't be right. The lack of fuel in the filters and the fact that the transfer pumps were also switched off must also have been imagined.
Tim
Scroll down this page for a diagram of the helicopter's fuel system;
If the aircraft was in a nose-down position, fuel will not flow under gravity from the main tank to either supply tank. In order to keep the to supply tanks filled, one or both of the XFER F and A pumps must be set to ON. The AAIB found they were both OFF. I recall reading in the PPRUNE forum that this helicopter, in normal flight, needs the XFER pumps managed in order to fill the supply tanks, according to the flight speed and warning lights from the suppy tanks.
Although it isn't clear why, the XFER pumps should have been activated when the supply tanks warning lights came on. One scenario might be that the warning light for the first supply tank to empty malfunctioned, and the engine that it supplied stopped without warning. This should have given the pilot a few minutes to deal with the situation, but for some reason that didn't happen. Then the second engine ran out of fuel, even though there was ~75kg in the main tank.
The lack of rotation of the main rotors at impact suggests that the blades were set for normal flight, and the reversed airflow through them as the aircraft descended slowed them down. An emergency switch to engage a steerable landing light was secured in the NORMAL position, whereas procedure for a forced landing at night requires in to be set to ON. In addition, there were no radio calls.
IMV, these cumulative indications of lack of action could suggest some form of pilot incapacitation or major distraction to the normal operation of the aircraft, for example, if the pilot had been blinded by a laser at a critical point in the fuel management regime. This could have happened well away from the crash site and not be visible to the witnesses.
4* i presume
On 15/02/2014 07:21, Tim+ wrote: ...
Unlike some others on this newsgroup, I never claim infallibility. However, I much prefer a hypothesis (and at this stage all are simply hypotheses) that does not require a highly experienced pilot to have made a series of elementary errors.
Colin Bignell
Why not? The history of aviation is littered with the bodies of experienced pilots who made a series of elementary errors. Pilot error is still by far the most common cause of plane crashes.
Although it is becoming more common for the last words on the cockpit voice recorder to be along the lines of "Why the f**k did it do that?" Followed by "Oh, shit!"
I'm with you on that
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