Police helicopter crashes onto Glasgow pub: final AAIB report

[MightyGem]

I can answer that, YES. When flying with plenty / full tanks!

Err...no. With both pumps off in the cruise, the contents of the Supply Tanks start reducing with approximately 250kgs left in the Main Tank, rendering that unusable unless you raise the nose to spill it through the overflow channels.

[kevin_mayes]

Thats an interesting snippet in the report, page 58 section 1.16.7 concerning the warning unit taking too much current (how much), it implies that a capacitor wasn't spec'd with a high enough working voltage during manufacture, could a situation arise where the current drawn by the failing capacitor tripped a circuit breaker shutting off other systems (i.e fuel sensor) or the extra current drawn pulled the voltage down allowing false readings, some of the wires can be of a small cross sectional area, drawing a lot of current would easily produce a voltage drop, has anybody taken a look at the wiring diagram to see what other systems are connected to the warning panel supply at the same time...?

Never had a tantalum capacitor pack up due to mechanical stress here on things I make, its always due to over voltage, mainly due to fitting the wrong voltage type...

Just my observation.

Kev.

[chopjock]

Err...no. With both pumps off in the cruise, the contents of the Supply Tanks start reducing with approximately 250kgs left in the Main Tank, rendering that unusable unless you raise the nose to spill it through the overflow channels.

Yes, but when main tank is full or nearly full(ok I said plenty), the fuel in the main tank overflows into supply tanks, so transfer pumps are not needed, so they could be switched off. That's what I meant to say.

[skyrangerpro]

a couple more takeaways from the report

A couple more notes I made from the report.

Suppose we take the scenario where everything is supposedly functioning correctly and this is a 100% pilot error incident. Well doesn't that mean that just before the first engine starts sucking air the situation in the cockpit is that 3 people are staring at a CAD that has counted down inexorably to showing fuel of something like 2/77/0 in the fuel display, the primer cautions are allegedly on, we have LOW FUEL 1 and LOW FUEL 2 red captions warnings on the WU and the FUEL caution is also on in the CAD. We know that was the real fuel situation (2/77/0) approximately according to the report, but was it really displaying that? I don't buy it.

Neither do I find it odd that the xfer pumps are off at this stage, given the total amount of fuel on board, it would have been normal for them to be switched off anyway at this stage in the sortie as all the remaining fuel (79 odd) should have been in the supply tanks. So xfer pumps off would not have been a particularly odd configuration, it's most unfortunate that the caption is not triggered when a pump becomes immersed again if it was turned off after running dry.

P23: "When the manufacturer tested the fuel sensors that were returned from the worldwide fleet, for repair, it found about 70% had no fault."

Well helloooo. Did nobody think to question that? Isn't that a bit odd, your customers send in alleged faulty components and 7/10 have no fault! Footprints in the snow, ice that has melted then evaporated are the analogies that come to mind. The evidence has long since left the scene. I would be thinking, 'well unless my customers are crazy, there is something intangible going on here, that warrants further investigation in the field."

The AAIB have executed their remit, but it is solely data gathering and analysis, it is for us to read between the lines. They aren't infallible and neither are the authorities. No doubt they read this forum. They corrected the misspelling of Uddingston in the report (that I pointed out last year) on p6 but didn't correct it on p73. As someone has already pointed out, the new GCH is 1.5nm WEST of Stobcross not East as stated on p28. And there's been a bit of a backflip on the whole primer switch thing when a photo revealed that they weren't in the same position (ON) that they found them in later, assumed and publicised. If that photo hadn't come to light the whole primer/xfer switch pilot mix up bandwagon would probably never have got derailed. Small things but having had nearly 2 years to compile the report and umpteen people proof reading it, I'm surprised considering their exacting standards.

There was also the ghastly revelation in the post mortem that one of the victims was still alive under the heli for up to 17 hours but the scene could not be moved as someone had decided to lock it down for Health & Safety reasons.

[Pozidrive]

Skyranger,


What is the source of information for your last paragraph?


None of the protocols I've ever read prohibit recovery of casualties, even if that means disturbing wreckage/evidence.

[SilsoeSid]

The low fuel action is to land within 10 minutes.
At that stage the low fuel warnings would have both be on at about 22:09 hrs, with the fuel readings being 20/76/17. (36 kgs) This is the time at which they were about to commence a job, they then did another, followed by the start of the trip back to base.

Why would they do all this while being presented with;

LOW FUEL 1...................LOW FUEL 2


PRIME PUMP...................PRIME PUMP
......................FUEL
..................F PUMP AFT
..................F PUMP FWD


......20…….........76…….........17



(Possibly not the prime pumps but maybe)


Interesting to note that on three occasions when the low fuel one warnings were acknowledged, the caption also cleared.

After the normal start-up sequence warnings had cleared, the next recorded snapshot showed that a low fuel 1 warning (caption and audio) was triggered, relating to the level of fuel in the supply tank cell supplying the left engine.
The audio attention-getter was acknowledged and then the caption cleared. The low fuel 1 warning was triggered again, the audio attention-getter was acknowledged once more and the warning then cleared for the second time.
The next warning was low fuel 2, relating to the level of fuel in the supply tank cell supplying the right engine. The audio attention-getter was acknowledged and the caption on the WU remained for the rest of the flight.
This was followed by another sequence of a low fuel 1 warning, the audio attention-getter being acknowledged and the caption clearing. A further, final onset of this warning was followed by the audio attention-getter being acknowledged and the warning caption remaining for the rest of the flight.

But everything was working and indicating ok .... wasn't it !

page 95.
No significant pre-impact technical defect was identified in any part of the aircraft or its systems.

[Mechta]

Skyrangerpro wrote:

P23: "When the manufacturer tested the fuel sensors that were returned from the worldwide fleet, for repair, it found about 70% had no fault."

Well hello. Did nobody think to question that? Isn't that a bit odd, your customers send in alleged faulty components and 7/10 have no fault! Footprints in the snow, ice that has evaporated are the analogies that come to mind. The evidence has long since left the scene. I would be thinking, 'well unless my customers are crazy' there is something intangible going on here, that warrants further investigation in the field.

I'm glad you noticed that too. As I recall Eurocopter (as they were at the time) said,

The issue, discovered by Bond Air Services, appears to be that the probes are indicating a fuel level higher than actual. Investigations showed that the incorrect signals that the probes transmit to the indicator may also inhibit the amber “fuel caution” light. Tests confirmed the problem starts with water contamination. As of December 23 (2013), 264 sensors had been tested. Of those, 12 needed to be cleaned but were fully functional afterward, while two failed and needed to be replaced. Meanwhile, the “low fuel” warning system is independent and remains reliable, Eurocopter said.

EC135 Faces Fuel Sensor Fault | Business Aviation News: Aviation International News

That means twelve sensors which should have been working were not, because they were contaminated with something.

Pozidrive,

None of the protocols I've ever read prohibit recovery of casualties, even if that means disturbing wreckage/evidence.

My interpretation of the report was that the accident scene was so unstable due to the danger of the wreckage collapsing into the Clutha basement, that it was not safe to extract the injured person until the basement ceiling had been shored up.

[G0ULI]

Health and Safety and scene preservation have nothing to do with the recovery of victims. Sometimes the risks are too great to proceed without specialist equipment or shoring, which takes time to arrange. Just diving in will end up with more casualties among the rescuers as debris shifts and collapses and will almost certainly hasten the demise of any victim(s).

The fuel sensor issues and possible misleading display of fuel levels are to some extent a red herring. Fuel gauges in all aircraft are notoriously trouble prone and are only an indication that some fuel is probably in the tanks. I was taught to manually dip the tanks to check fuel levels before every flight and calculate maximum endurance accordingly and subtract 30 minutes. That was the point I should be back on the ground, no matter what.

Even if the fuel had been in the supply tanks and not the main tank, the helicopter would have landed back at base well below the mandated minimum fuel load. What excuse would have been used to explain that? What sanctions would have been taken against the pilot, if any? Could the severity of any penalties for breaching minimum landing fuel have been preying on the pilot's mind? That would certainly be a distraction especially with doubts already being raised about fuel gauge accuracy in the EC135.

Maybe accepting the last tasking was simply resignation that the helicopter was below minimum fuel anyway, and it was only a couple of miles back to base. Might as well get hung for a sheep as a lamb.

[skyrangerpro]

Families hope FAI will finally give answers over Clutha crash | News | The National

“An FAI should give me answers as to why my father was left under that helicopter alive and according to the post mortem report he was alive for over 17 hours after the crash.

“I believe my dad could have been saved and I want to know why he wasn’t freed while he was still alive.

[DrinkGirls]

Since the accident, a lot more has been learned about the 135 fuel system. Some of you experienced operators commenting here don't realise yet that what you thought was correct is in fact not true. Until recently, I would have agreed with you.
The main fact is about spillage between the main and supply tanks if you pitch the aircraft. Whilst there can be some transfer, the tanks are not like the diagrams, they have gaps between them. Any transfer is a trickle only and is not significant. Therefore pumps need to be on, even if the main is full.

Second, when the supply tanks are full to the brim, they hold more than the gauged 90kg. The excess fuel is added to the main tank indication. The 90kg amount is basically for certification (ish). This affects in 2 ways.
First, when the actual main tank is empty, there will be a small amount of fuel showing on the main gauge.
Second, when carrying out the supply tank drain ground run, after you turn the transfer pumps off, the main tank continues to show a reduction for a few minutes. Then the supply tanks start to reduce. This is that little bit of fuel 'above' the supply tanks burning off. Initially, pilots thought that fuel was still transferring.
This is not my opinion, this is fact

[skyrangerpro]

Even if the fuel had been in the supply tanks and not the main tank, the helicopter would have landed back at base well below the mandated minimum fuel load.

From the report the fuel policy that was in place at the time was:

"2.1.3 Fuel policy

The PAOM Part 1 provides guidance for fuel planning, advising that fuel for
30 minutes at endurance speed (burning 170 kg/hr) should be included for a
flight over a non-hostile environment at night, in addition to fuel for start, run-up and taxi allowance, as appropriate, and the duration of the task.

At the time of the accident, the operator’s Operations Manual stated that the
Final Reserve Fuel IFR was 85 kg, with a Minimum Land on Allowance (MLA)
of 40 kg, and that:

‘Company policy is that the aircraft should not land with less than
60kg of fuel in the tanks.

If it appears to the aircraft Commander that the Final Reserve Fuel
may be required, a PAN call should be made. If the Final Reserve
fuel is then subsequently reached, this should be upgraded to a
MAYDAY.’

Since the helicopter had 76 kg of fuel on board at the time of the accident, the pilot might have been expected to make a PAN call, upgrading it to a MAYDAY on reaching the Final Reserve Fuel IFR, if he was aware of the fuel state. Again, due to the lack of evidence that might otherwise have been provided by cockpit voice and flight data recorders, the investigation was unable to determine the reasons for this apparent omission."



No surprise that with three different numbers in the mix there, that these policies were updated shortly after the incident to clarify:

"Following the accident, the operator amended their Operations Manual
procedure on fuel calculations, replacing the Minimum Land on Allowance
(MLA) with Final Reserve Fuel (FRF), and increasing the VFR and IFR/night
FRFs to 90 kg."

Now it's easy to sit in an armchair with a calculator and see that it is tight starting with 400kg and running for 1hr 40 (Both 3kg/min and 3.3kg/min have been used as quoted consumption figures, dependant on task type). But IF the display was stuck at 45/x/49 where x is some number, then it is not clear to me that the pilot would think that he is 'well below' any of those levels. What measure does he have other than the CAD display over rough mental arithmetic in his head to cross check?

[ShyTorque]

(Both 3kg/s and 3.3kg/s sec have been used as quoted consumption figures, dependant on task type).

I would check those figures again, if I were you.

[SilsoeSid]

Drinkgirls;

Since the accident, a lot more has been learned about the 135 fuel system. Some of you experienced operators commenting here don't realise yet that what you thought was correct is in fact not true. Until recently, I would have agreed with you.

First, when the actual main tank is empty, there will be a small amount of fuel showing on the main gauge.

This is not my opinion, this is fact

[DrinkGirls]

Badly explained by me Sid. What I am trying to say is that when the last drop of fuel is pumped from the main tank itself, the display still shows a few kg of fuel in the main tank display. This is because a small amount of fuel ABOVE the supply tank is actually displayed as main tank contents.
This then is used until we reach your picture.
Really, this is true and not Pprune guff, it's from Airbus

You have assumed that when I said "when the main tank is empty", I meant empty on the gauges

[DrinkGirls]

In your picture, it implies that once the main tank is above the "fence" fuel spills into the supplies, it doesn't. The tanks are separated with overflows back to the main. Airbus have issued an updated schematic in which it all makes sense. This is where we had it explained about the metered fuel. The supply tank actually holds more than 90kg, it is DISPLAYED as 47/43 (ish) and a bit is added to the main contents as well.
Really, it IS fact

[SilsoeSid]

You have assumed that when I said "when the main tank is empty", I meant empty on the gauges

How could I possibly assume that? You were quite clear in that you were saying that when the actual main tank is empty, the gauges will still indicate a quantity.


More seriously though, what you are suggesting Drinkgirls is that the tests that were completed on the manufacturers EC135 Articulated Fuel System Test Rig, from page 54 in the report, were incorrect.

"The supply tank actually holds more than 90kg, it is DISPLAYED as 47/43 (ish) and a bit is added to the main contents as well.
Really, it IS fact"

page 59;

One test point replicated the orbit at Dalkeith, as much as possible. The orbit was flown at 30 kt, with an indicated nose-up attitude of 5-7°, in level flight. The fuel on board at the start of this test consisted of 47 kg and 43 kg in the left and right supply tank cells respectively, with 97 kg in the main tank. After four minutes, the indicated fuel in the left and right supply tank cells remained the same and the amount in the main tank had reduced to 82 kg.

(Main tank started with 97 kgs, 4 minutes later had 82, consistent with a 3.5 kg/min burn rate.)

[DrinkGirls]

Originally Posted by SilsoeSid

Drinkgirls;


Page B-3

Thank you, that diagram is the one. It explains what I meant far better than I could.

[SilsoeSid]

If only you could have described what you meant better

Mmm, where's that gone? Pic is on page B-3
https://assets.digital.cabinet-offic...015_G-SPAO.pdf

[DrinkGirls]

I know, I know! I'm a divvie. But what I was trying to say is in agreement with you, people are commenting and have no idea on reality. It is frustrating, just like a certain chinook thread.

[SilsoeSid]

Just to highlight what the pilot sees when the Prime Pumps are switched on;



Best seen on the youtube site in full screen, in a darkened room
https://www.youtube.com/watch?v=8_KvlaIYyIo