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-   -   Police helicopter crashes onto Glasgow pub (https://www.pprune.org/rotorheads/528850-police-helicopter-crashes-onto-glasgow-pub.html)

skadi 15th Feb 2014 08:18


Fuel boost pumps (and not all machines have them) must be on all the time.
Not in the 135, the primepumps are normally on just for engine start.

skadi

Tailboom 15th Feb 2014 08:21

Surely when your low on fuel and especially if the low fuel light has already illuminated your main focus would be your hand on the collective, looking for a suitable landing spot and you'd be primed to react immediately.

Years ago I stupidly pushed on in a 206 with the low fuel light on, as I could see the airport a few minutes away ( haven't we all at some time ) I halved the book time, climbed to 1500ft and glued my hand over the collective and kept a constant look out for a suitable landing spot, should the worst happen it was the longest 2/3 minutes of my life unfortunately for me the engine flamed out but I managed a perfect EOL just inside the Airport in question all with 5 POB, I was really lucky and it taught me never to press on like that again.

I find it hard to believe that an experienced guy like this, flying in the dark a few minutes away from safety wouldn't have done the same, there must be other factors contributing to this tragedy, he would have been wound up like a spring ready to react, his mind would have been finely tuned to every sound or reaction of the machine, Surely his mind would also be on the outcome of surviving an EOL landing in the dark with no fuel being the cause! ie losing his job or prosecution. Poor bugger

SilsoeSid 15th Feb 2014 08:24

Should, Would, Could.
 
Sorry JT.


Now, to answer you, I don't 'mean' anything - my whole post is basically asking for a steer as to what might have happened to have caused him to not react quickly enough - surely my post is in plain enough language for anyone to understand that - I'm asking!!
Quite plainly, perhaps he simply didn't expect a double failure.


For instance is it possible that his hand wasn't on the collective for whatever reason or that the collective was locked with friction or the autopilot was engaged and it takes 1 second to disengage but the RRPM decays in under that time.
His hand could have possibly been doing something else as the first engine failed, but the collective shouldn't have been locked by collective friction to that degree. Input to the controls would override the autopilot and when the second engine went, the hand should have been on the collective in an instant.


In my machine, if my engine fails (god forbid) I get an engine out tone, I get un commanded yaw and I drop the lever quick. But my machine also allows me something like two seconds in which to do it. Does the EC135 allow such a time frame?
I believe the 206 has higher inertia blades, so I would imagine the timeframe is a lot shorter. For the 135, entering autorotation is an immediate action following a double failure.



However, if I had a passenger who panicked and grabbed my arm or I was switching my pitot heat on or changing frequency at the point my engine failed maybe those action could cause me to react more slowly and the RRPM might decay to an un-recoverable point. In this case whilst the manufacturer might consider in a calm cockpit with no other distraction there is traditionally sufficient time to lower the lever there are factors like those I've described that might cause there to be NOT sufficient time to react. It's not rocket science!
I would imagine that most helicopter pilots' motor systems should have developed enough to be able to get the hand back on the collective immediately, whatever it had been doing at the time.


If there were warning captions illuminated, aural tones, and procedures that he had to follow etc that distracted him, plus pax that might have been talking to him or were panicked causing him to not instantly realise that he'd had a double flame out then he may not have had sufficient (as in humanly possible) time to process the information that his brain was dealing with and consequently not lowered the lever quickly enough.
Mmm, doesn't this suggest that didn't react in time, rather than didn't have sufficient time. When the second engine failed, the time was always there and could have been used.


None of us were in that cockpit so no one knows what happened but I'm asking for a steer from someone like you who flies twins and understands the systems and processes that might have lead to that.
Quite true, but given the latest report, there are some pretty good leads as to what could have happened.


Finally, should the fuel transfer switches been on or off, because I don't think that's been answered.
Given that there was 76 kg in the main tank, the transfer pumps should have still been on, well at least one of them at any given time due to the ac attitude. The supply tanks should have had 47 & 43 kgs in them and the prime pumps should have been off. The only reason for the prime pumps to be on in flight, should be when you get a low fuel pressure warning.

At some point around 22:00 that night (Bothwell task?), when the supply tanks became the only fuel source, the configuration of all the fuel pumps was altered.

However, regardless of the switchology, this doesn't get us away from all the warnings and indications that should have been there and should have been actioned upon. I would have thought that the decrease of supply tank levels down to nothing, should have risen some back hairs and early action could have been taken . if indeed all the warnings and displays were there to take action on!

SilsoeSid 15th Feb 2014 08:27

Ranger One;

Your answers will be found here http://helicopterindia.com/yahoo_sit...2.24193407.pdf
It's not up to date as far as amendments go, but will sufficiently answer the questions you have asked :ok:


Robdean; Totally agree :ok:

skadi 15th Feb 2014 08:37

Given the timefacts from the report, I just roughly calculated the estimated fuelindication for the main tank.
They took off with around 300kg, after the 35 min first task and transfer to Dalkeith, the indication could have been around 100kg. So on the way westwards ( ~25 min ), the aft fuelpump fell dry and was switched off. When reaching Glasgow area, the trackcircles indicate the possibility of lowspeed/hover attitudes, which could have resulted in switching the fwd pump off, so the remaining 95ltr in the maintank now were unusable without switching the aft pump back on. And there is still the possibility of a false indication of the supplytank content.

skadi

Ranger One 15th Feb 2014 08:47

Post deleted

This is not the time to start asking questions which have been asked and answered over the past 6 weeks.

Read back through the thread and understand how the 135 fuel system works along with the auto characteristics and handling of the machine: it has all been well explained many, many times already by professional helicopter pilots who are current on type.

Senior Pilot

Art of flight 15th Feb 2014 09:05

Just to help clear up a few of the questions, misconceptions and speculations.

Some posters are jumping in with half knowledge or none on 135 type/helicopters/piloting/aviation experience at all.

A small handfull on here fly these aircraft night after night on police ops with thousands of hours on type, and no it doesn't make them or me infallible, but if those in the first category want answers to questions please don't then challenge in a personal manner the informed answer that those in the second category give.

The fuel system on the 135 has been explained in minute detail, with illustrations and text, please look back at the posts before before asking new questions that may confuse others and the press.

The overhead panel is laid out in a logical manner, NVS lighting does make it harder to read and the goggles certainly have to be lifted to the stowed position to read it and in that position with a taller pilot may in fact hinder the ability to identify the switches. In fact there is little clearance between the top of the helmet and the roof/panel structure at the best of times. Wearing spectacles for reading, with a helmet and goggles in that cockpit makes it very difficult to use the overhead panel.

A police aircraft cockpit is a real hotbed of noise and distraction. Those with private flying experience only will be very used to planning ahead, flying from A to land at B or perhaps even just flying around A many times before landing again. The Corporate pilots will be used to pretty much the same with the added pressure of satisfying the company and client. The airline pilots will be used to standard routes and someone else to load share. The military pilot will be used to a degree of planning and teamwork and regular training for the demanding roles and flying environment. The police pilot briefs such known factors as met /notams/ aircraft serviceability and fuel load at the start of the shift, after that it's take it as it comes, ie the TFO asks you to jump, you react straight away day or night, good or bad weather, you can be in flight with no planning at all within 2 minutes of someone answering the next phone call. You will have no advance knowledge of the destination or what lies between, the 3 of you need to exchange information with each other and the ground at very frequent and conflicting times. I've often taken off towards B, then whilst I'm asking ATC to give us clearance one of the TFOs is taking a higher priority task to C, whilst I the apologise to ATC and ask for clearance towards C, another radio asks us to drop everything and make our way towards D. This all has to be discussed, debated and prioritised in the cockpit whilst doing snap fuel calculations/weather apreciation and a huge dose CRM so that the 3 of you are still fuctioning as a team throughout the shift. Acrobat, diplomat, doormat is the police pilots motto for good reason. Having said that when asked how difficult it is to do the job I would answer, I use 5% of my military flying experience 95% of the time and was ready to use 95% of it 5% of the time.

Please don't condemn this pilot without absolute fact, the AAIB have said there was a fault with one of the displays, lets see how that pans out.

skyrangerpro 15th Feb 2014 09:05

Re how long does 4kg last
 
If both supply tanks had the same amount of fuel at a given reference time and both engines have a similar rate of fuel burn and useable fuel is the same as fuel remaining for both tanks, then both engines will flame out at approximately the same time. It is the useable fuel in both supply tanks at a certain reference point in time that matters, not the relative fuel tank sizes.

It is the left supply tank low fuel warning that will illuminate approx 2mins 25 seconds before the corresponding right hand one at 32kg and 28kg respectively, if they are working correctly, not one engine flaming out 2' 25 before the other.

What is niggling me is the multiple intermittent low fuel warnings issued by the left hand tank sensor. That doesn't seem normal behaviour to me. The right hand one illuminated later and illuminated permanently. Why were the two behaving differently?

Bertie Thruster 15th Feb 2014 09:06

Shy........looking up back and left for load shed, 2nd eng runs down .............

that certainly 'fits'.

Art of flight 15th Feb 2014 09:30

SkyRP,

If I'm reading your query right, my explanation is as follows.

Given that the Main tank transfer pump/s deliver fuel to the supply tanks at a rate greater than both engines at maximum power can suck it from both the supply tanks, the manufacturer believes and teaches that at the point where fuel transfer from the main tank ceases, the supply tanks will be full. From that starting point with engines sucking very similar flow rates from their respective supply tanks, the warnings will occur at different times, and the engines will flame out at different times. The supply tanks have the same manufactured capacity with the exception that one of them has a foam core inserted to take up the space that would otherwise be occuppied by fuel (4kg ish). It is my experience that this sequencial warning is what happens rather than simultaniously.

Just to summarise, the supply tanks should never have the same amount of fuel.

Digital flight deck 15th Feb 2014 09:38

Good to hear from you art.

Art of flight 15th Feb 2014 09:44

Thanks mate, tend to keep my powder dry these days because of the trolls. Safe flying.

SilsoeSid 15th Feb 2014 09:45

Bertie Thruster;

Shy........looking up back and left for load shed, 2nd eng runs down .............

that certainly 'fits'.
Would that be necessary?

Arrab 15th Feb 2014 09:59

A Theory
 
So how about this for a scenario

Both transfer pumps off as can happen during police scenarios due to transit and hover.

You would normally be made aware of this by supply tank contents reducing with fuel still in the main tank. Next thing you get is the yellow fuel caption, the eventually the red low fuel caption. You would have to ignore all these inputs to let the supply tanks run dry and the engine flameout.

What about if the first indication you get is the reflow fuel caption. You know you haven't had the yellow caption, which you should have had and both supply tanks are indicating full. Logical conclusion maybe that the low fuel caption is spurious as the gauges have always been extremely accurate.

Then an engine fails. You still have supply tanks indicating full and 78kg in the main. Natural reaction over a city at night maybe - ok, no need to panic. I have rotor rpm and fuel. Remain cal get into single engine speed and make a decision about continuing to the heliport or going to the airport. 30 secs latter the second engine fails. You are very poorly placed.

What's interesting is that the AAIB report does not mention the yellow fuel caption coming on.

Also interesting is that the current problem with EC135 fuel probes, only highlighted after the accident, is indicated by the yellow fuel caption not coming on and the supply tanks over reading (sometime indicating full)

I'd also like to comment on the lack of autorotation theory. The final route of the aircraft was 180 out from its final resting orientation. It came over a high building attached to the rear of the pub.

What if autorotation was successfully entered albeit with rrpm on the low side. From 1000 at night over a city, there is very little time and few options to choose from. What if at the final stages you are faced with a large building. Crash into it of flare and use some collective. Survival instinct would be that you flare. You've now used our one shot of collective but you fall with no rrpm over the other side of the building.

So maybe this guy didn't just ignore all the warnings that he should have had and maybe he did get into autorotation. Maybe he was faced with a very confusing situation over a city at night.

Just trying to balance some of the very black and white and sometimesl informed views on here.

Fact

From the AAIB
Transfer pumps were off - they should not have been and this Pedro the supply tanks emptying
The yellow fuel caption coming is not mentioned.

From airbus helicopters
Current EC135 fuel probe issue
Yellow fuel caption may not come on
Supply tanks indications may over read.

Art of flight 15th Feb 2014 10:17

Arrab,

tried to follow your thinking but a few phrases threw me off, by 'yellow fuel captions', do you mean amber low cautions? and by 'red fuel low caption', do you mean Red Fuel warning? This important, they are totally seperate systems, one cautions the pilot, the other warns with a gong. I say again, please re-read the previous excellent descriptions of the fuel system and then prepare a scenario. Also what is a reflow caption?

Ranger One 15th Feb 2014 10:45

Senior pilot, my apologies if you felt I was out of line; I haven't the time to wade through 107 pages at the moment. To be fair it's the first post I've had deleted in 15 years here. I'll butt out now.

SilsoeSid 15th Feb 2014 10:45

Arrab (first time caller!);

Ref the FUEL caption, there isn't any historical display information available from the CPDS, so we won't know if it or any captions came on or not.

As far as the fuel probe issue, you're nearly there,
They don't say, "Yellow fuel caption may not come on", they say;

"Tests have confirmed that the affected fuel content probes generate erroneously high signals if contamination with water occurs. In each case an incorrect frequency is being transmitted to the indicating system. That leads to an erroneously high indication of fuel quantity and prevents the amber FUEL caution light from operating."
http://www.airbushelicopters.com/sit...18-Rev0-EN.pdf

Surely that 0.4 litres of fuel remaining in the no2 supply tank would have indicated a water contamination issue, as would the 95 litres left in the main (where the supply fuel came from).
No contamination issues are mentioned in the report, nor are the twist grip positions.

Scuffers 15th Feb 2014 10:53

given all of the above info...

from the report, we are told he contacted ATC at 22:18 for clearance, and fell off radar at 22:22.19 (at 400ft).

given that from low fuel warnings you have at least 10 mins of flight time (or have I got this wrong?), he must have been looking at low fuel warnings before he contacted ATC?

do we take from this that he was unaware of the warnings?

SilsoeSid 15th Feb 2014 11:01

I get the feeling that may be the case scuffers.
The CPDS and it's relevance in all of this will be a very interesting read.

RVDT 15th Feb 2014 11:09


Is it possible that, having had one engine fail, he was looking up and back to load shed, with his hand off the collective, when the second engine unexpectedly failed?
No reason to - SBC1 & SBC2 are closed when either EPU connected or at least ONE GENERATOR.

SHED EMER only operates when GEN DISCON 1 AND GEN DISCON 2 active.


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