Having been castigated for previous posts exploring scenarios where the supply tanks could run out in other than the prescribed fashion,it is with some trepidation that I enter the fray again!
However, the latest AAIB bulletin does raise several issues which would seem to corroborate a number of the scenarios which were previously dismissed. Posts since the latest bulletin have already picked up on some of these, but one which hasnt been picked up relates to whether the aircraft was afflicted with the fuel probe fault which was the subject of the subsequent Eurocopter service bulletin.
Having read the prescribed checks which had to be undertaken, it may not have been feasible to ascertain after the accident whether the probes were reading accurately on this aircraft, but it does seem clear that there was a major anomaly in relation to actual versus perceived fuel contents.
Had the transfer pumps been switched on, it would still be the case that the aircraft would have landed with fuel contents below MLA by an unhealthy margin. And yet on the return flight from Dalkeith, it seems to have diverted to not one but two non urgent tasks. If the pilot had any worries at all about fuel he would not have undertaken this tasking, not just because they were non urgent, but because they were so close to base that he could have RTB, refuelled, and relaunched in a short time.
Everything points, IMHO, to the fuel probe fault being present, misleading the pilot in relation to his actual fuel state.
The consequent late illumination of the yellow fuel warnings, followed too quickly by the (correctly functioning) red warnings would have been very confusing.
Also of relevance, again IMHO, is the fact that the total fuel on board was less than the total capacity of the supply tanks. In "normal" operations, at this stage should both transfer pumps not be switched off, as there would be nothing left in the main tank to transfer? Throw in the ability of fuel to spill assymetrically back into the main tank from the assymetric supply tanks, which could only be filled symetrically by the transfer pumps (had they been on) and you arrive at a situation where the supposed designed in delay between each supply tank emptying could be drastically reduced.
Still trying to join all the dots up, but keep coming back to the fuel probe fault as starting the sequence of events that caused this.

Art of flight, I can see what Arrab is getting at. Supposing something (e.g. water retaining bacteria - not unknown in fuel tanks) caused the capacitance gauge to indicate a higher reading than it should, and also delayed the drying out of the heated wire for the warning gong, the first thing warning the pilot might get is the gong, albeit later than it should be.

The capacitance probes were destroyed in the impact, so they couldn't easily be tested, and as the heated wire sensor would dry out over time if still powered up, the evidence would have been inconclusive by the time the accident investigators reached it. Eurocopter said that some faulty probes on other EC135s 'worked after cleaning', so one would hope the AAIB have been checking for traces of whatever was cleaned off the faulty ones, in the Glasgow helicopter's tanks.

I'm glad to read that. Whatever it means.... :confused:

Falcon, If the transfer pumps had been on, then there should have been towards 76 kg of fuel in the supply tanks as the aircraft was over the city centre, a couple of minutes from the heliport, and about 70kg left on shutdown.
Fair enough, that's less than the operator's reported reserve of 85kg, but it's still over 30 minutes.

I think you're right that the time difference between the engines running dry is an open question, and could depend on the amount of fuel flowing from the right to left supply tanks based on attitude and acceleration in the minutes before the accident.

Late, tired, busy, startled, confused, alone… the very best could end up in error.

I do agree there is merit in some of the conclusions the last few posts are drawing. Cladosporium resini (Fuel/water interface pink snot) could cause mis-sensing of the fuel probes, meaning a shortened time to alert the pilot if at all, that, along with this as yet un-declared display fault, gives room for things not appearing as they normally would be expected to in the cockpit. And this might also explain why there is no (released) evidence of anything untoward expressed to both ATC and the Police control room. Does not yet explain why the transfer pumps were selected to 'OFF' and the 'PRIME' pumps were selected on.

The aircraft came to rest pointing approx 60 degrees from the helipad down-river. The tail of the aircraft is pointing out over the river, not over the building attached to the pub. That's not to say that the aircraft wasn't rotating as it descended.

In fact an eye witness described it as rotating or 'tumbling' as it 'fell', so conclusions drawn from its final attitude on the bar roof might be well wide of the mark if using it as a basis for how it arrived there.

But eyewitnesses also reported it flying low along the river, and the AAIB report says it fell from 1000 feet.

If the rotors were stopped, it could in principle "tumble", but in the dark, can a single witness be trusted to say whether it was spinning around the rotor axis, "tumbling", changing in pitch or whatever? If it was tumbling, then it might be interesting, as that requires the rotor to have been stopped before that tumbling began.

The AAIB is clear that it suffered extreme deceleration/was upright on impact. I don't imagine that its orientation during this fast descent is very important for understanding the causes.

Reading the AAIB bulletin again, they say the low fuel 1 warning came on intermittently, then low fuel 2 illuminated permanently. If the supply tank contents were "as designed", low fuel 2 should have been the first to appear as it is the smaller tank, which would suggest that the actual safety margin between the two tank contents no longer existed, or indeed that there may have been more fuel in the smaller of the two tanks than was in the larger tank.
The appearance of these warnings in the "wrong" sequence, without the preceding amber warnings, and with his tank contents showing fuel present (erroneously) the pilot would certainly be confused, and would have been faced with the choice of believing his gauges or the warning lights.
As for the transfer pumps being off, because he had reached a point where the main tank had transferred all of its contents to the supply tanks, he would have had to switch them off. Thereafter they could only be used intermittently to return spillage to the supply tanks. If the supply tank contents were showing ok, turning the transfer pumps on may not have seemed an immediate priority.
As for the prime pumps, once fuel starvation set in ahead of flameout, with the fuel gauges still reading ok, switching on the prime pumps would not seem completely illogical.

Perhaps as pilots we have that compulsion to know every little detail of the timeline and sequence of events during this tragic crash. That's not a bad thing, but perhaps we might have to accept that much of these details will remain conjecture amongst us. The important things will come out from this investigation. Did any aircraft system or component fail to operate in the 'normal' manner? If it did, did the display and warning systems alert the pilot in a timely manner? If they did was there evidence that his reaction to the events could be described as reasonable given training/experience etc.

Sadly, we must realise that many interested parties will want to prove it wasn't their fault, the AAIB report says the engines could turn, though the media says they failed, so the engine manufacturer will want to refute that strongly and perhaps point the problem towards the fuel supply. The Fuel system manufacturer will want to say it all worked perfectly and that the transfer pumps should have been on and would have kept the engines turning if they had been. Though there is recent evidence of less than satisfactory fuel system reliability with the 135 fleet (after the fact). The operator will want to make it clear the pilot was properly trained and qualified, fit for duty etc. That very quickly ends up with someone having to try to prove the pilots actions and I don't know who's batting for him.

The AAIB's short recent report is clear that the right engine stopped first, although it doesn't explain the evidence for that. That's in the expected order from the sizes of the supply tanks.

The amber and red fuel warnings come from different sensor system, and so any crud living on the sensors shouldn't affect them both. A red warning should appear with at least ten minutes of possible flight, and 30kg of fuel in the supply tank, remaining.

I understand that the amber fuel warning appears whenever the supply tanks go below full. Depending on orientation and acceleration, I can imagine that happening at different times for the tanks 1 and 2 despite their slightly different capacities.

There are already questions about the status of display and perception of warnings, from a display fault, from any issues related to the bulletin about the sensors, and as mentioned just today, perhaps from issues of ergonomics with goggles.

There's some commentary from the manufacturer at
FAQ - Airbus Helicopters

All, as a non-helicopter professional, please feel free to PM/post if I am providing noise rather than signal or wearing out my welcome. I've been following the thread and events closely, and am intrigued by this strange investigation, but appreciate that I am a guest filling your inboxes.

Well said.

Which might be a good idea.

Which it isn't and the LOW FUEL lights will come on at approximately the same time as the sensors are the same distance vertically from the bottom of the tank. The No.2 SUPPLY TANK has less fuel remaining when the LOW FUEL activates as listed in the report.

Shy,

It means the same as in the report -

As per Vendee

Very well put Art of flight.

As professionals, we all hope that, should we not be around to defend ourselves, somebody, perhaps close friends in conjunction with family members, will have the financial wherewithall to defend our reputation. Without that, those interests with deep pockets can successfully avoid their own responsibilities.

This accident will undoubtedly be the subject of a Fatal Accident Inquiry. To access the 'truth', all parties should be equally well represented.

From very similar previous experience, I can recommend the finest man up there if anyone wishes to know. Provided he hasn't already been engaged.

AWB and others,

I'm not the Mod on here but in my opinion your input is as welcome as anyone else, sometimes we pilots can be too close to things, the link you have provided should be used by anyone who wants to know about the fuel system without asking often repeated questions on this thread so well done for providing it. I've just read it and whilst it does provide correct terminology of cautions and warnings which has caused confusion amongst posters here, it is very loose in other area's. Specifically the amber pump cautions do not alert the pilot to the fact the main tank is empty, that's just rubbish! they have nothing to do with the main tank at all apart from saying they have stopped working or have no fuel over them. The amber supply tank cautions alert the pilot to a specific content remaining in the respective supply tank. The Red warnings do not come on 'shortly' after the amber cautions. They are designed to come on at a specific fuel quantity remaining in the supply tanks! If the manufacturer thinks loose phaseology such this helps, thank goodness that pilots know the system a little better!
In summary, if the sensors don't work as advertised and the manufacturer can't accurately describe how the system works we're all in trouble before we take off.

Thanks TR and Vend.

As the mist clears with this accident investigation (and credit to the AAIB team for keeping the industry comprehensively informed at the earliest), whatever mechanical / design flaw developed that night, it appears the pilot may have found himself in unfamiliar territory:
Approximately 180 degrees out of wind, 400 feet AGL, one engine out, at night (possibly goggles) AND THEN the remaining engine fails!
I keep thinking about his background (Chinooks) and his present job (EC135): both NEVER practice total engine failure(s) to the ground.
(Possibly) decades of practical inexperience with EOL's - further aggravated by the spatial predicament he found himself in that evening. RiP.

I keep seeing comments about "Pilot Incapacitation"....yet we are confronted with evidence that shows the aircraft engines ran out of fuel and quit running.

If you think the Pilot was incapacitated at the same time the aircraft is running out fuel.....that would seem a huge coincidence indeed.

Stick to the facts and work from there.

Why did the Engines stop getting fuel?

Why did the Pilot fail to take effective action following the second engine failure?

Lowering the Collective Lever is not that difficult....is something we all know to do....but yet in this tragedy....it appears not to have happened.

Focus on that....as it was the last link in the chain but yet the most simple, most logical, and the single most important reaction to situation. Done properly, the outcome might have been a very bad landing....but at least one that would have provided for a better outcome than that which occurred.

All this discussion about pink paste, sequence of caution/warning lights is fine...but does not get to the basic issues.

A very qualified, experienced, well trained Pilot did not take the one action that everything hinged upon.....maintaining Rotor RPM.

That resulted in the Fatal Crash....everything else just set the chain of events into action to force the situation that required that action by the Pilot.

Since there was no CVR or other recordings of conversations in the aircraft....or Data Recorders to show control movements and other useful data....we shall never know exactly what happened. The AAIB will not be able to state with clarity what actually transpired in regard to the Pilot's actions or in-action and will in all likelihood state something like "Pilot failed to maintain Rotor RPM." as part of their Final Report.

We know that already....the physical evidence confirms that.

The "Incapacitation" I see is a failure to realize the aircraft was running out of fuel and a failure to properly react to the indications.....and upon the second engine quitting....a failure to carry out an EOL landing procedure.

I want to know "Why" the Pilot did not respond to what was clearly an Emergency Situation when the first Engine flamed out. When you are getting Low Fuel cautions and then an Engine quits....how much more "Waving Red Flags" does One need to understand the severity of the Situation?

Electricjohn, unless I misunderstand, the radar height reports will be from transponder returns from a big radar at Glasgow airport that sweeps every ten seconds or so. Recording a long string of 1000ft signals from the accident aircraft, followed by one from 400ft and then nothing would seem to be quite consistent with a sudden plummet in about 20s, where the 400ft signal just happens to come from the helicopter being caught mid crash in that single sweep.

Tandemrotor, while all the parties involved have their interests, including the victims' rather vocal lawyers, I would not expect the AAIB to be swayed in their statements based on various lawyers' views, would you?

Ultimately, justice will be handled after the final report is out, in a different forum; and as you suggest, those with the deepest pockets are most likely to get their views heard most clearly. However, in terms of causes and events, would you agree that we can trust the AAIB's statements to be neutral and unredacted?

Silsoe

I'm not aware of any aircraft that have had fuel probe issues, and there are many, have actually shown water contamination in the fuel. The issue seems to be with very small particles of water trapped in the probes.

awblain
I said nothing whatsoever to warrant such a condescending response.

I suspect I am at least as familiar as you with the precise role of the AAIB in such a case as this. Having listened to many days of their evidence at another Fatal Accident Inquiry into a high profile helicopter crash, in which there was similarly no evidence from CVR, FDR, or survivors.

The clear conclusions of the AAIB did little to prevent barristers for the operator and the equipment manufacturers from trying to shift the blame to anyone but themselves!