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

skyrangerpro 10th Dec 2013 10:21

clearance
 
AAIB: "At 2218 hrs, the pilot requested clearance
from ATC to re-enter the Glasgow Control Zone and
return to GCH; this was approved. No further radio
transmissions from the pilot were received."

Minor point. I would expect the pilot to repeat back the clearance so that would have been the last transmission rather than the initial request for clearance. So either it never happened or it was inferred in the narrative. Slightly ambiguous though.

RVDT 10th Dec 2013 10:40

Cabby,


Black boxes (FDR's) should be made mandatory on all emergency a/c which per ate over towns. Lets hope it doesn't take a year to do it.

Following a train crash in the US they are now calling for cameras to be fitted facing the driver and another facing the tracks, why not fit a camera facing the pilot like the police and Hems shows on TV.

One camera phone pointing at the pilot/crew, the other mounted on the centre post looking at the panel. Simple to use and a way of sending the information to another contact point.
See next -

This was fitted to the P3 I saw last year and can be fitted to "legacy" aircraft. Retrofitting an FDR is not economic and FDR data is a little rudimentary anyway.


I know by flicking the Shed bus switch the navigation lights and other elec power would be restored but having tried to reach that Shed Bus switch which is behind and above the pilots left shoulder its highly unlikely.
(worst place for a switch i've known - hard to reach)
Yet is not so bad as you would be used to it with every preflight operation of the BTC switches you test prior to take off to check for fuse failure in EMB?


Airbus (makers of the EC135) already have the capability of using satellite uplinks to send real time data from their panes in flight.
(Highlighted when the Airbus A330 went down in South Atlantic) Airbus tracking systems had picked up the decent problems on board in real time. It was sent in micro burst data streams I believe.
Satellite equipment to provide this kind of bandwidth would probably not fit on an EC135.

ACARS has been around for donkeys but probably wouldn't have the low level coverage.

And also -


In the wake of the crash of Air France Flight 447, there has been discussion about making ACARS an "online-black-box."[4] If such a system were in place, it would avoid the loss of data due to: (1) black-box destruction, and (2) inability to locate the black-box following loss of the aircraft. However, due to high bandwidth requirements, the cost would be excessive and there have in fact been very few incidents where the black boxes were not recoverable.

Thomas coupling 10th Dec 2013 10:44

One good thing that has come out of this thread for me are the contributions made by people I'd never come across before, like HENRA, CABBY and several others which, in my opinion, add to the discussion - thank you.
Obviously the old guard contributors continue to stay calm and educational to others from outside the aviation world.

IF.....one is to believe that eye witnessess heard popping/misfiring, then I would suggest there was an element of stall/surge going on. I've had both on two separate occasions whilst doing police ops. One was an air bleed breaking off the engine casing causing a surge with associated misfiring noises. The other was a compressor blade going for a walk at max chat and stalling the air flow temporarily before going into sulk mode all the way down to a forced landing on a cricket pitch where the game was in full swing!
On both occasions and for several very long seconds, I was confused by what the engine instruments were telling me. Ng/Nf were erratic, Nr was doing its best to stay governed but it was wandering! T4 was mad!
The point is, it took me about 20-30 seconds to isolate the causes each time (one was at night). Interestingly, I instinctively lowered the lever to arrest any decaying Nr that might have developed.
NOW - IF I had switched the wrong engine off duirng those early seconds, at night, whilst in the descent....the duff engine would have continued to protest, the Nr fluctuations would have increased because of only one (weak) engine remaining and my only choice them would have been to put the duff engine out of its misery. Doing that - then (in decent with lower than normal Nr) could easily have prejudiced the outcome for the worst.
Over the city, at night, getting very close to the roof tops, no engines - just PULL and hope???

[I still keep seeing posts from newbies assuming the crash was some kind of 'second bite' at landing. Believe me, we should all now be singing from the same hymn sheet - this cab hit hard...very very hard. Think 30G+.

Bertie Thruster 10th Dec 2013 10:58

Are the LHS pedals 'live' on police 135s?

zorab64 10th Dec 2013 11:06

Too fast-moving for busy people to catch up on all the posts but, having done so, I find only one poster has had almost identical thoughts to me, but the other way round. Thanks Puntosaurus, although I have felt particularly uncomfortable when posting this theory, as I imagine you may have been?

Firstly, a quick update on fuel quantities, as there appears to be a little confusion. Airframes post s/n 250 have slightly larger tanks so, given that SPAO is s/n 546, built in 2007, she will have had supply tanks that read 47 & 43 kgs respectively (the only relevant figures for the moment). This very conveniently comes out at the 90kgs normally used as night Police MLA.

Taking off with 400kgs equates to 310kgs useable to MLA, at 200kgs per hour, that's 1:33ish, plus a few mins if they'd spent a little time in "loitering" flight, rather than a typical max cont transit, with max cont hovers in between.

At a certain stage, they may have found themselves in a high nose-up hover, possibly around 80-100kgs in main tank after 60-80 mins flight, whereupon the fwd transfer pump runs dry, amber warning on CAD, & is switched off, i.a.w. SOP/FLM. No problems, since aft transfer pump keeps supply tanks topped up.
The transit to forward flight takes the remaining fuel down to the forward pump, but something distracts the team from switching the forward pump back on & the aft transfer pump caption soon illuminates, and is also turned off - meanwhile the supply tanks are now feeding the engines and 70ish kgs is indicating in main tank. Now two amber TXFR PUMP captions on the CAD. Plenty of fuel at a glance (if a "glance" at the main tank is all that's absorbed) but it's not in the right tanks. It's recoverable, but needs an appreciation of what's been done after 1:30 in the air, and a good read of the CAD will be required when, & if, No2 winds down as the RH supply tank runs dry. Tired crew, still on a job, lots of captions, and a PC3 aircraft over a built up area well below 1500' and reducing options, reduced further a few mins later while scurrying back to base? Still 75kgs in the "tanks", but which ones? As p3bellows #984 mentioned first, I'd be most interested in the position of the Transfer Pump switches, more than the engine switches. It's a question / theory only, but would very much like to be proved wrong.

And to clear up a few other comments; Whitehead 06 # 1029 - Yes, longer transits and less time doing the job, re #1044 - I'd suggest there's no "normal" when fuel runs out, it "normally" doesn't happen. SCFool #1024 - unless absolutely necessary, pilots will not touch engine controls at any time when airborne operationally. DXWombat # 1020 - As Police radios are digital and coded/secure, and whilst I'm not a radio ham expert, I don't believe they can be listened into at all. Stevo67 #1010 - no, engine switches are on the dash, a long way away from the rotor brake on the overhead console.

zorab64 10th Dec 2013 11:10

Bertie - no. Dual controls are removed completely, unlike the 902. Floor covers shield Cyclic & Collective holes, a box covers the stubs of the pedal mount. Not easy for anyone to interfere with them.

Arkroyal 10th Dec 2013 11:25

Klingon,

Sorry, I mean no disrespect to you and your perfectly valid input. I do, however disagree.

I really cannot think of any sensible cause. Whatever happened led to a high speed drop on to the roof with rotors stopped. It did not land, shut down and then fall through the roof.

I do so hope that there is enough evidence recoverable to enable the AAIB, for whom I have the greatest respect and admiration, to discover the cause.

puntosaurus 10th Dec 2013 11:30

I'm not uncomfortable at all about posting the theory, because if it's true, it should point to an unbelievable human factors black hole in the design of this fuel system. Who would design a system where your job is to switch a fuel pump off when the fuel runs low, and in doing so, you create a variable unusable fuel amount whose impact depends on the flight regime and your subsequent manipulation of the fuel pumps.

Reminds me of the electrics in the 109, where for certain electrical emergencies you have to switch the battery OFF.

However I'm only struck by the coincidence of the fuel remaining amount. I still can't explain why someone would be able to overlook the cacophony of warnings including the gongs that RVDT pointed out.

Evelyn Higginbottom 10th Dec 2013 11:40

Sadly, this accident seems to have prompted some highly inappropriate responses from various quarters.

902Jon 10th Dec 2013 11:43

Cabby
 

If the rig operators want 2 pilot operations and thats why they get them, I don't see why operations over the towns and cities at night which have members of the public under the operating area shouldn't have a 2 pilot crew incase of pilot incapacitation. London HEMS use a 2 pilot crew.
The oil & gas industry started bringing in 2-crew ops in around 1986 (for those aircraft that didn't require it anyway). The CAA mandated 2-crew sometime later as a safety system for offshore passengers.



Police pilots fly 6monthly flying tests, the CAA should make it mandatory for all autorotations to be carried out down to the ground with engines at idle instead of using Sims or TRE's asking for the pilot being tested to flare and pulling away with power at low level. (no touch down).
Now I have no idea of your qualifications/experience wrt flying helicopters. However, that statement makes me wonder. The idea of doing double engine failure autos to the ground, at night is at best ridiculous. There would be a seriously damaged/totalled airframe every week. Helicopters would be completely uninsurable, and therefore couldn't fly at all. Autorotations are only conducted in simulators down to the ground because the risk of damage to an actual airframe is immense. An autorotation in a twin-engined helicopter is an extremely unusual occurrence.

I believe there is a degree of confusion with a number of thread contributors here as to what is meant by an AP. An AP in this context is basically a Stability Augmentation System, which just helps the pilot fly the aircraft. You can trim the aircraft, to a degree, but it is only when using the higher level functions with the coupler, (HDG, Alt, IAS etc) that there is any input from the machine itself. Even when a coupler is engaged, the autopilot only has a certain level of authority, and the system can be easily overruled by using the controls directly.

I am not going to pass any comment directly on this tragic incident as I do not feel qualified to do so (I'm not 135 rated & have never flown Police Ops).
However, RIP to all those who lost their lives, and a swift recovery to those that were injured.

Thomas coupling 10th Dec 2013 12:07

Zorab says:

Taking off with 400kgs equates to 310kgs useable to MLA, at 200kgs per hour, that's 1:33ish, plus a few mins if they'd spent a little time in "loitering" flight, rather than a typical max cont transit, with max cont hovers in between.
.

The cab in question takes off at 2045 local. Last radar returns: 2222 local. Time airborne: 1:37hr.
But when gas turbine engines starve of fuel they simply stop, they don't make fuss by popping/misfiring do they?

My imagination doesn't stretch to him being in a hover when one engine flames out, followed very quickly by the other doing the same. He finds himself in a zero spd EOL, cushions early and runs out of Nr at height...............

sarboy w****r 10th Dec 2013 12:22

Zorab, such a situation would indeed result in the drive to the rotors stopping and seems very possible.

Whatever it was, something happened that stopped the engine providing drive to the rotors, that much is evident. There is then the question of why there was no/little Nr at the ground.

Even assuming that a pilot recognises what has happened and is able to understand what needs to be done, it doesn't take very long at all before Nr will decay to the point at which there isn't anything that can be done if the collective is not lowered extremely quickly. Failure to respond sufficiently quickly has been seen more than once in an accident report.

There's also the possibility that the blades were rigged incorrectly i.e. too much residual pitch on the blades even with collective fully down and thus won't allow for autorotation - unlikely as an autorev check should capture this, but it wouldn't be the first aircraft where there is an issue with the blade rigging.

Finally, there's the possibility that something interfered with the collective such that it wasn't able to be lowered fully when the need arose. Cockpit was dark, who's to say that something hadn't slipped under the collective and wasn't noticed?

Fundamentally, what concerns me is that the SOP / RFM seems to allow for a latent failure mode to go unchallenged. To my mind, a 20 min / 30 min fuel allowance should allow 20 mins / 30 mins until the engine(s) stop. That's why it's a reserve fuel allowance; if you can't use it, it's not in reserve. I don't think it is a reserve fuel if you need to remember to switch something on or off to make use of it, because you are designing into the system a latent cause of potential cognitive error. I accept that if there is a failure of a subsystem then there may be fuel that becomes unusable: for instance, an A109 has some cheeky gotchas with booster pump failures if you fail to close the cross feed. However, you are not saying that. What you are saying is that there is a SOP that allows a pilot to get to a situation where under normal circumstances the minimum usable fuel is below the minimum fuel reserve?

If a procedure offers up the possibility of making a mistake, sooner or later, someone will make that mistake. That's life. That's why parts for aircraft should never be designed so they can be put onto the aircraft the wrong way round. The same should apply to SOPs. Does anyone else agree, or am I in a minority of one in this regard?

Puntosaurus, you appear to have arrived at the same conclusion whilst I was typing.

paull 10th Dec 2013 12:41

Am I in a minority of one in this regard?
 
Since you ask, NO! If this scenario is a real possibility (I'm not qualified to say) then I am absolutely shocked! In fact, since seeing it posted I have been busy designing an alternative fuel system.

Even the design with the mouse inside a spirit level running over a rocker switch seems better than the current set-up. Black humour, sorry this is very upsetting, I think everyone has gone a little quiet since this was proposed. Please tell me it does not work like that!

cattletruck 10th Dec 2013 12:45

I would image any seasoned patrol pilot on this type would be accustomed to regularly switching the XFR pumps towards the latter part of the flight regime and that it would be second nature. It doesn't make sense to me. Even if he lost the first engine to fuel starvation wouldn't it be wise to at least select both XFR pumps?

With both XFR pumps off and both engine feeder tanks running low is the machine now subject to maneuvering restrictions particularly with regards to roll angle and yaw rate?

Just curious if any driver can describe the XFR pump selector on this machine.
Is it a single multi position switch - (OFF*)/FWD/AFT/BOTH
Or are they two separate switches - OFF/ON - for each XFR pump
Not that it matters too much, however logic seems to suggest the multi position switch to be more ergonomic and convenient.

chopjock 10th Dec 2013 12:54

Ok so if the first engine was already out, the low fuel light already on and two minutes to base, what else could he do over a built up area at night?
What would you do? try to land in a populated area at night on one engine or cross your fingers and expedite to base(which is in sight) less than two minutes away?

SASless 10th Dec 2013 12:56

If I recall properly, the original design for BO-105 fuel system stemmed from a desire to meet Certification Requirements to allow for a Fuel Dump capability to lighten the aircraft following a single engine failure. That required the use of the Supply Tanks to isolate a certain amount of fuel from being jettisoned. The EC-135 is merely a follow-on to the 105 series aircraft.

That is why the Fuel system is the laid out the way it is.

Sometimes that results in "Unintended Consequences".

paull 10th Dec 2013 13:01

Cattletruck:

Is it a single multi position switch - (OFF*)/FWD/AFT/BOTH
Or are they two separate switches - OFF/ON - for each XFR pump


As you say, a three way FWD/BOTH/AFT with a separate OFF elsewhere might increase your chances in normal operation of not inadvertently selecting them both off.

A mini-version of the fuel tank, in front of your eyes, filled with mercury and suitably wired, might save you the trouble of selecting/deselecting. :rolleyes:

zorab64 10th Dec 2013 13:04

TC, Cattletruck & others - I quite agree that this should not happen, and there would have been gongs and RED CWP captions between both transfer pumps being turned off (with AMBER captions) and before the first engine flamed out, which would have pointed out the error of leaving both pumps off, in plenty of time to get one or other back on again, and re-fill the supply tanks. One transfer pump will supply enough for both engines, and a bit.

I don't think there's anything wrong with the fuel system at all and (Cattletruck) you are correct in that Police pilots will be used to turning a front pump off in the hover, and turning it on again as soon as they transition to forward flight - if they've forgotten, as soon as the aft pump runs dry, there's a caption "reminder" & the position of the switches will be swapped (front on, rear off) - it's pretty-much automatic.

Paull - the switches are both on/off, one for each pump and next to each other on the overhead panel. Experienced 135 pilots will know where they are by feel.

As I said, I hope it's a wild theory and can be sensibly discounted. In the meanwhile, if they actually had the fuel they accounted for on take-off, they were likely very close to, or below, MLA - which would easily have got them back to base. So still a mystery.

m.Berger 10th Dec 2013 13:10

If the position of the switches is swapped, is it then possible to have operated the wrong one the wrong way ?

cattletruck 10th Dec 2013 13:21

Thanks zorab, the suggestion that the machine was at or near MLA and 2 minutes from its destination is a good sign of experience on type.


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