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

Jet Ranger 10th Dec 2013 08:03


So what feeds the SUPPLY Tanks then? XFER pumps no? :ugh:
@RVDT

Yes, off course...BUT...you have separate indications of fuel quantity in cockpit (left supply/ main tank / right supply), and during normal flight, quantity in supply tanks is always the same - 44 and 40 kg...in case of malfunction of X.FER PUMPS you will have caution light...at least, WARNING LIGHT "LOW FUEL 1" (or LOW FUEL 2 ... "respective supply tank fuel quantity below treshold value") will bring you on ground in 10 minues!

DOUBLE BOGEY 10th Dec 2013 08:06

Jet ranger, what if you had these indications over the built up area more than 10 minutes from base??

Prawn2king4 10th Dec 2013 08:08

DB:

Exactly!

klingonbc 10th Dec 2013 08:22

Fenestron
 
ShyTorque's point about control method reminds me of a phenomena Gazelle operators experienced and it was debated at great length. Not sure if the theory was ever proved true or false but here goes. There were a number of incidents/accidents? in military service were the Gazelle Fenestron was thought to have "stalled." IIRC - if the aircraft was yawed at such a rate that the airflow to the fenestron/fan overwhelmed the normal flow = no flow and no effective control of yaw. I think the incidents were mostly in hover with strongish wind and the yaw could not be stopped by opposite pedal input. Pilot diagnoses tail rotor/yaw control failure, but there was no mechanical failure of the fenestron or drive train. I think the incidents may have been put down to pilot mishandling but there were some emergency drills developed subsequently.
So - EC135 has a fenestron. Have there ever been incidents similar to those of the Gazelle? Was that Gazelle phenomena ever resolved? Is it possible the EC135 was in a high hover with a wind in the critical direction and loss of yaw control occurred? Diagnosis by pilot = mechanical yaw control failure and actions taken to shutdown engines and execute EOL from a far from ideal situation. Low NR after first impact, pause, roof collapse by which time rotors actually stopped = no obvious evidence of failure of mechanics and no evidence of NR at point when aircraft broke through roof.
Sorry it is all speculative thinking but fenestron stall does not seem to have been discussed on the thread.
Klingonbc

Jet Ranger 10th Dec 2013 08:29

@DB

Jet ranger, what if you had these indications over the built up area more than 10 minutes from base??

Than you are in problems, but RFM says you MUST land in 10 minutes (when warning light LOW FUEL 1 or 2, is ON).

One more thing...in moment when first indication of BOTH !? (fwd and aft) transfer pumps failure comes, you have 84 kilos of fuel in supply tanks, which is 25 min of flight with 125-130 kts...so, pretty unrealistic scenario !

Arkroyal 10th Dec 2013 08:37

Police helicopter crashes onto Glasgow pub
 
Klingon

So he's on his way back to base with a low fuel state and elects to loiter in a high hover, then gets into a hitherto unknown 'fenestron stall' situation.

Hmmm

RVDT 10th Dec 2013 08:45


then gets into a hitherto unknown 'fenestron stall' situation
After millions of flight hours and operation in rescue ops at high altitude where it has never been apparent.

Low on the list I would think.

Mick Strigg 10th Dec 2013 08:45

Several Points
 
1. The "misfiring engine" is often reported by supposedly reputable eye-witnesses, but can usually be put down to "blade slap" or something similar. Beware eye-witness statements that give a conclusion; a little knowledge is a dangerous thing.

2. There has been several accidents wher Nr has reduced to zero before impact. It is a natural reaction to prevent impact by raising the collective as much as possible. If done even slightly too early, Nr reduces to zero and the aircraft assume brick-like aerodynamics.

3. If the AAIB say that the drivetrain and engines were capable, then they are saying it was all serviceable before impact.

4. There seem to be quite a few similarities to the HMS Portland Lynx Accident in 2006 (I think). Zero Nr, Vertical descent etc. I'm sure the AAIB are comparing.

RVDT 10th Dec 2013 09:04


Than you are in problems, but RFM says you MUST land in 10 minutes (when warning light LOW FUEL 1 or 2, is ON)
Which is 4 minutes from an engine failure.

mad_jock 10th Dec 2013 09:08

Air Accidents Investigation: S9/2013 - Eurocopter EC135 T2+, G-SPAO

Non-PC Plod 10th Dec 2013 09:13

If we cut to the quick:

If there was nothing wrong with the gearbox, then the only conceivable way I can imagine to end up with the rotors stopped in flight is:

Engines were stopped (Either flamed out or switched off)

AND Collective was too high (Either pulled up inadvertently or deliberately, or there was something (foreign object?) preventing lowering.)

AND MAYBE rotor brake could have been applied

There is little further speculation to be done. We can only wait to find out which of the above options happened.

HeliComparator 10th Dec 2013 09:18

Rotor brake would have made no significant difference in flight.

Question: would it be likely or possible that arms (ie guns) were being carried on board?

puntosaurus 10th Dec 2013 09:19

This from post #83 of the 2004 Post about the EC135 fuel system.


The fuel from the Main tank is fed by 2 transfer pumps Forward and Aft in the Main tank to the Supply tanks. This fuel is fed through flex lines which pass through the "overflow channels" to exit into the lower part of the Supply tanks. The "overflow channels" are approximately 50 mm in diameter and the transfer hoses maybe 15 mm. The fuel from the Supply tanks when the quantity is above 92 kg runs through the "overflow channels" back into the Main Tank until it is empty. Each transfer pump is capable of 6.6 litres per minute or about 315 kg/hour or more than 150% of cruise fuel flow. When the fuel level in the Main tank is below the level of where these pumps can pick up they should be selected OFF.

This is detected by the caution indication "F PUMP AFT" or "F PUMP FWD" and is completely normal per the FLM.

Failure of the FWD pump can result in an unusable quantity of as much as 59 kg if above 80 KIAS and is 3.6 kg if below which is effectively the same as normal unusable fuel in this cell.

Failure of the AFT pump can result in as much as 71 kg in the hover reducing to 7.5 kg above 80 KIAS increasing the unusable by 4 kgs.

With a little arithmetic the maximum increase in unusable at the failure of BOTH pumps could be as much as 215 kg in the level attitude. This would be the maximum that you couldn't get to by being a little bit cunning. This of course depends on when both pumps become inactive.

If the fuel is no longer being transferred to the Supply tanks by either gravity or pumps there is 92 kgs remaining of which 86.7 is usable. Due to the shape of the tanks Engine 2 will stop after approximately 23 minutes and then engine 1 after 27 minutes. The "LOW FUEL 1" and "LOW FUEL 2" Warning indications come on at the minimum of 24kg per cell. Hence the procedure "Land within 8 minutes."
So SOP is to switch off the Xfer pumps when advised by the caution that they have run dry. Let's assume that the pilot switched off the aft transfer pump in the cruise above 80Kt when it ran dry. That would be when the supply tanks were full and around 70 something Kg left in the main tank. Let's further assume that the a/c returned to the hover. After 15 minutes in the hover with that main tank fuel now unusable LOW FUEL 1 light comes on, followed by LOW FUEL 2 four minutes later. If those captions were missed then a further 8 minutes later Engine 1 quits, followed by engine 2 after a further four minutes.

Here's another quote from post #98 of the above thread:


The EC 135 sounds as if it has a similar fuel system to the BO105. In the case of the BO, the supply tanks are in front of the main, and they are of equal size so that if the transfer pumps fail both engines will quit within seconds of each other.

When checking out in the BO, we were told of a tall pilot who left his transfer pumps off and subsequently had a dual engine failure because the glareshield of that particular ship blocked his view of the "FUEL LOW" caption. We were told that you might have approx. 20 minutes to flameout in such a case. (I might add here that I remember thinking the requisite "Oh, that'll never happen to ME!") As a hedge against such a brain fart, I got into the habit of always without fail leaving the transfer pump switches on and NEVER shutting them off.

One day, I was shut down, showing another pilot the avionics suite in my ship. To save battery power I had turned the transfer pumps off. You guessed it, I forgot to turn them on at startup next time. I had been airborne for fifteen or twenty minutes, cruising along, fat dumb and happy when I began idly looking around the cabin for no specific reason. When my eyes spied the transfer pump switches, I about had a heart attack. YIKES! The "FUEL LOW" light was not on, and my supply tank quantity gage still showed full. What the...?

RVDT 10th Dec 2013 09:19

JR,

Your 84 kg number is for older aircraft prior to SN 250 unless modified.

On this aircraft it would be ~ 48 + 44 = 92.

Unless of course you notice how a 135 flies in the cruise left wing low and in truth it is ~ 83 kg as the fuel falls
forward over the fence on the LH front corner of each supply tank back into the main tank.
In the cruise you will have something like 45 + 38 indicated.

95 litres was removed from the system.

Less ~ 9.45 unusable = say 85 litres usable at best as there must be some unusable in the supply tanks. 69 kg.

Unusable fuel with FWD Transfer failure above 80 knots = 59 kg.

10 kg (12 litres) the difference and where?

Given the possible attitude with NIGHTSUN, FLIR, FLOATS (assuming they were fitted) that unusable figure could be higher.

Yes 25 minutes available if you just use the bare figures and a total but I would say in the cruise at 22 minutes you would be into the first engine failure and the second at 26 minutes due to the bias in the tanks.

Non-PC Plod 10th Dec 2013 09:23

Heicomparator,

Unless things have changed massively in the last few years since I flew police missions, then there is no likelihood guns were on board.

RVDT 10th Dec 2013 09:25


After 15 minutes in the hover with that main tank fuel now unusable LOW FUEL 1 light comes on, followed by LOW FUEL 2 four minutes later. If those captions were missed then a further 8 minutes later Engine 1 quits, followed by engine 2 after a further four minutes.
The "GONG" every 3 seconds might get your attention hopefully.

P.S. I wrote your first quoted post in 2004.

klingonbc 10th Dec 2013 09:28

Fenestron
 
RVDT - Thank you, questions answered. You clearly have lots of EC135 experience, glad to know this phenomena has never been seen on this aircraft.


Arkroyal - I see your point but just trying to add to the corporate thought process. Even at very low fuel states I have paused and loitered to observe something that caught the eye, especially when close to base, and even at night without the benefit of NVG/NVD. It is in the nature of this form of flying and I know police crews do the same.


I now remember why I do not post very often - do try not to be dismissive of ideas and alternative views, they all add to the knowledge base and just sometimes might hit the nail right on.

rotorspeed 10th Dec 2013 09:32

Non-PC - agree all (post 1057).

HC - rotor brake would make a difference if applied after engines were shut down and RRPM dropped, but then maybe only a bit - if the collective was just left high with no power would the rotors totally stop or windmill slowly? I would guess the latter, though I wonder when the AAIB say they were not turning on impact they mean exactly that - or could it mean just not turning fast enough to be damaged on the leading edges?

Do we know whether the engines were both actually switched off or not? I don't think so yet. Be interesting to know.

Jet Ranger 10th Dec 2013 09:41

@RVDT ... Our 135P2+ in much higher S/N than 250 (late 600īs), and during flight we have 44kg / 40 kg indication (84 kg). When you approach to very low fuel state in the MAIN tank, letīs say less than 10 kg, indication is something like (40-44 / 10 / 36-38 kg ), soon followed with F PUMP FWD caution on CAD...

...if 95 lit (76 kg) was removed from the system, he was probably on supply tanks in approach for landing, which is normal situation.



Unusable fuel with FWD Transfer failure above 80 knots = 59 kg.

...important to emphasize (to escape confusion for somebody)...unusable fuel in the MAIN tank is 59 kg...not in the supply tanks (where is additional 84 or 92 kg)...

RVDT 10th Dec 2013 09:56

JR,

And when the quantity is above the fence the supply tanks will read ~ 47-48/- 43/44?

Below the fence there is a difference which indicates that some of the fuel falls forward.

The ones I have flown are in the late 100's and late 900's i.e. either side of 250.


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