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

yellowbird135 10th Dec 2013 13:55


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".

Sasless,
The design of the fuel system is based on the criteria as outlined in CS-29.953 Fuel System Independance.
Although the 135 is a CS-27 (Small Rotorcraft) certified helicopter; it is also certfied for CAT A Ops. For this, it also has to comply with some paragraphs from CS-29 (Large Rotorcraft) requirements.

dowot 10th Dec 2013 14:08

Sorry to upset you, that is certainly not my intention.
I have a very high regard for the work pilots and the police have to do.
I am also very aware of the associated deaths that occurred.
This is a very distressing event which will only be solved by the appropriate authorities, when all the facts are known, something I suspect nobody on this forum has at this moment and as such posts are all speculation just as mine was.
As I explained, my thoughts were simply a fictional extension of some of the facts and bare no relationship to what must have happened.
The terrible thing is that my surmise tends to fit with some of what is known, and concurs in some ways with what some earlier posters have intimated.
Once again I apologise for upsetting you or anyone else.

Lonewolf_50 10th Dec 2013 14:38


The terrible thing is that my surmise tends to fit with some of what is known
Maybe in Hollywood ...

Once again I apologise for upsetting you or anyone else.
That's all that needed to be said, and thanks for saying it.

One35 10th Dec 2013 15:03

The section headed 'Warning Unit' in the AAIB report on the (unrelated) G-IWRC crash back in 2007 makes interesting reading:

The Warning Unit is mounted near the top of the
instrument panel and generates the visual and audio
warnings for a number of systems. A memory within the
unit stores, in chronological order, the last 31 warnings
generated when the helicopter is in the flight condition.
Whilst there is no timebase to determine when each
warning was generated, there is a flag within each
message code which toggles at the end of each flight.
Consequently it is possible to determine the warnings
which were generated during the last flight.


Edited to add: DAPT, you beat me to it by seconds!

SilsoeSid 10th Dec 2013 15:19

A couple of things;
 

The "GONG" every 3 seconds might get your attention hopefully.
Unless of course, it is cancelled!

200kg/h may be the figure to work around, but today we're burning 180.

The LOW FUEL warning action is to land within 10 minutes, however if you just get the one, does that mean that until the second one comes on, you still have at least 10 minutes before you need to land?

RVDT 10th Dec 2013 15:28

As follows -

– LOW FUEL 1
– LOW FUEL 2
– AP 1 or AP/A.TRIM (Autopilot) if fitted
– AP 2 (Autopilot) if fitted
– ROTOR RPM
– BAT TEMP
– BAT DISCH
– XMSN OIL P
– STBY HOR if fitted
– CARGO SMOKE if fitted

Of note - LOW FUEL 1 & 2 generates a "GONG" which can be suppressed.

There are four kinds of audio signals. They have different priority and some of them can be suppressed
by the switch AUDIO RES . But they will sound again with every new error message.

The following exist in order of priority:

Continuous Tone: it has a frequency of approx. 2400 Hz and cannot be suppressed.
The continuous tone is only activated by the signal ROTOR RPM > 112 %.

Pulsed Tone: it has a frequency of approx. 600 Hz and is generated with a 5 Hz rhythm.
It can be suppressed. The pulsed tone is activated when ROTOR RPM < 95%.

Fire Warning Bell: it can be suppressed and is only activated by a fire warning.

Gong: it is generated every three seconds and can be suppressed.
The gong is initiated when a warning display illuminates; and at ROTOR RPM if the value 106 % is exceeded

Powered off both ESSENTIAL BUS 1 & 2.

Details of the data storage capability is not in the AMM.

RVDT 10th Dec 2013 15:35

Sid,

Apparently LOW FUEL is at 24 kg remaining in EACH Supply tank.

So based on your burn figure each one will come on when ~ 16 minutes remains. So if you stretch it to 10 minutes you will have 6 minutes remaining until the first one (No. 2) stops.

No.1 will be a bit later depending on a few variables as mentioned.

nodrama 10th Dec 2013 15:37

The EC135 is merely a follow on from the Bo 105 ??

Wasn't the bo105 originally designed as an anti-tank helicopter ?

The only similarity I can see between their fuel systems is that they have overflow pipes and transfer pumps to fill the supply tank (in an EC135 that is tanks, plural)..... Just like many other helicopter fuel systems, so what's so unusual about that?
Surely a supply tank is there to ensure a dedicated engine 'supply' of fuel, regardless of what else is happening in the the fuel storage system and with the attitude of the helicopter?

Munnyspinner 10th Dec 2013 15:40

Police helicopter crashes onto Glasgow pub
 
Approach to Clyde heliport is over water. Crash site has a large park ( Glasgow green) a short distance east, a park to the south, Richmond park? And a big car park to the north. I'm also fixed wing but wonder if the rotors can be stopped by pulling up/ flare in autorotation? Can high angle of attack produce enough toque to stop the rotor?
Looking west from the crash site there are few landing opportunities except the Clyde. Rail Bridges with rail overhead electricity, a high motorway bridge and residential/ offices on both sides. If ,under normal descent on approach along the Clyde, perhaps to the west if the Clutha, there was an emergency then it is a reason for turning back to the east. If it znt hen became apparent that an autorotation ( with forward speed ) to either park wasn't an option the the next available site might reasonably be the big car park to the north of the eventual crash site and/or if short, the intersection- at which point all forward speed was used to try and extract height when the blades stopped. Doesn't explain why engines lost power but FADEC problem might explain.

RVDT 10th Dec 2013 15:43


With the engines off, the rad alt loses it's power
Along with all other consumers on the SHED bus which includes the AFT Fuel pump!

SHED BUS activates on 2 x GEN failure.

Arkroyal 10th Dec 2013 15:59

Munnyspinner,

The flare ad the end of an auto tends to increase rotor RPM, as does any positive 'G' manoeuvre.

This energy is beneficial and allows more collective pitch to be used to cushion the following touch down.

Lonewolf_50 10th Dec 2013 16:26

Generators and stalled blades
 
Two questions of technical clarification:

With the engines off, the rad alt loses it's power
Are the EC-135's generators run by the engines or by the transmission? Don't know the type, which is why I ask.

SHED BUS activates on 2 x GEN failure.
Thanks.

henra made a point about stalled main rotor blades a few pages back. With the thought that EC-135 is a low inertia rotor head ... I will walk through this and see if the logic holds, or if it doesn't. Please critique.

For reason "X" drive to the rotor head stops abruptly and rotor RPM begins to decay. Poster henra pointed out that there is a "point of no return" where the blades are likely to stall. Once stalled, the amount of time/alt/control manipulation to unstall is, for the sake of discussion, more altitude and time than was available to the crew on this occasion.

Following along this train of thougth: with the rotors slowed and then stalled, but still rotating at "Y" percent, does the finestron (still rotating as far as one can tell from info available) still produce thrust of a nominal amount?
If yes, one could perhaps explain the tumbling/rotating that the witness reported as residual thrust about the vertical axis overcomes roughly "no" torque from a stalled rotor head (finestron being there for anti-torque). Even though the Nr decay continues for whatever reason, monentum sustains that rotation/tumble since there is insufficient force to counteract it (lack of Nr generated thrust and torque) and also less finestron residual thrust to try getting the thrust heading the other direction as Nr further decays, thus slowing the finestron to an eventual stop.

Feel free to shoot holes in that idea.

As to why the thrust goes away: I think the AAIB would have reported if they found bird remains in the engine/engines by now. Pretty sure that likelihood has been covered and can be safely put to bed.

Robin400 10th Dec 2013 16:37

non return valves
 
If either of the non return valves on the transfer pumps is jammed in the closed position,
are there any flight deck warnings? Pitch change will have interesting results.
Having studied the diagram of the fuel system left me with an uncomfortable feeling.
I have fixed wing experience only. 16000 hours on many types, some with good fuel systems and a few which gave me concern. The one thing that always stops any engine is lack of fuel.

SilsoeSid 10th Dec 2013 16:39

Sorry RVDT, I had to amend my post as the Rad Alt remains on.
(memo to self: don't pretend to understand the electrical diagrams in the engineers office!)

Double Generator Disconnect will see the loss of;

Comm/Nav 1, Strobe/Nav lts, TCAD, ANR,
Steerable LL, Role Kit, Pitot 1, ADF/DME,
Gooseneck lights, Aft Tx Pump, Air Blowers, ATT Trim,


(My thought was that with the engines chopped and the rad alt gone there would be little reference of height in the descent other than out the window. As it happens, the rad alt would still indicate, although any aural warning would depend on the bug setting and the setting of the preset height warning system. Of course over a built up area the rad alt would be an area weapon!)

Flying Bull 10th Dec 2013 16:51

Hi,
Reading the prelimary report, I could think about a few possibilities, that could lead to a non significant NR.
I.E. an overspeed on one engine. You than need to pull the collective underneath your armpit, to keep NR on the clock.
Killing that engine, i.e. with fuel cut (firebutton) will result in a massive decay of NR, if you don't drop the collective rapidly, cause the remaining engine just can"t spool up that quick from 0TQ to 120% or so, which would be needed, to save the NR with a high pitch setting.
Seen it at the simulator - and was busy, even with the Copilot killing the engine on a countdown...
That in mind, I'm back to the operators decission, to excecute night ops single pilot....
Yes, there heros outside, who can handle all and even can transmit a MayDayCall - but thats the old breed of pilots, which were choosen by the military, cause their character has a part - overconfidence...
Which is good, if you want to send the guys in dangerous - lethal - situations, but isn't, what you want for normal commercial operations.
Big operators payed for surveys, cause that's cheaper than an accident and if you're clever, you look, what they have found to human capabilities under stress.
For the heros- continue as before
For the others, who want to survive and enjoy their pensions - aviate, navigate, communicate...
What can help you in case of - and doesn't distract to much from aviating - Switch the ELT on - it doesn't always go of after a crash - so if there is only little or no time for a MayDayCall, this may save your butt - if you know, where the switch is - and you don't have to search for it....
With amount of the fuel found in the helicopter engine starvation doesn´t seem to be the cause.

xlsky 10th Dec 2013 17:12


Wasn't the bo105 originally designed as an anti-tank helicopter ?
it was designed as a light twin engine multi purpose helicopter for tasks like air ambulance and police, which means flying over heavily populated areas. Due to its maneuverability it was suitable for anti tank missions, quiet important for the main land Europe defense lines during the cold war.

The Bo105 and ec135 design is all about performance, reliability and practicality e.g the rear load compartment to fit stretchers in a light helicopter.

what happened in Glasgow should have never been possible just from one technical failure and there might be a lot more than just one technical failure behind the scene. Not sure if some areas in Glasgow are safe to fly at lower levels these days. Quiet often the Strathclyde Police did so, especially on Friday nights, to show presence and power. I really hope they don't need a armored machine in the future and I am just too concerned and over-sensitive.

SASless 10th Dec 2013 17:17

Ultimately the question to be answered is "Why no Rotor RPM?".

One would logically conclude that simple fuel Exhaustion/Starvation itself would not lead to any situation that would, in and of itself, lead to no Rotor RPM. Logically, the two engines would cease running in a sequence several minutes apart.....if the usable fuel was totally consumed.

In a Fuel Starvation situation....it does not logically follow that both engines would be affected unless it was fuel contamination and again....it would seem both engines would not shut down simultaneously.

Even if both Engines failed simultaneously without any warning.....that alone does not explain the loss of NR.

Thus far, physical evidence shows a MGB that appears to rotate normally and at least one engine driveshaft that when rotated by hand drives the MGB. The MGB has overriding clutches....thus even a seized engine cannot stop the MGB.

Flying Bull presents a good suggestion for a situation that could lead to a loss of Nr. A prior Accident Report discussed at least one Accident with a 135 that resulted from such an event.

Nothing said the by the AAIB has suggested Fuel Exhaustion/Starvation might have played a role in this accident. They also have not indicated any evidence the Engine Governor Controls may have played a role. They give no hint at what they think caused the loss of Main Rotor RPM.

In Sim Training....how thoroughly are Governor Malfunctions practiced by Police Unit Pilots?

RVDT 10th Dec 2013 17:58

Sid,

You may need to re-visit the engineers office or maybe your police fit is different.

As I mentioned before -

Go to your machine - BAT ON - Avionic Master 1 & 2 on and AC if it makes you feel better - Voila instant GEN I & II fail.

See for yourself what does and does not function.

Possibly easier than dredging through a manual and it will be instantly type and model specific as results can vary.

RVDT 10th Dec 2013 18:10


I.E. an overspeed on one engine. You than need to pull the collective underneath your armpit, to keep NR on the clock.
Killing that engine, i.e. with fuel cut (firebutton) will result in a massive decay of NR, if you don't drop the collective rapidly, cause the remaining engine just can"t spool up that quick from 0TQ to 120% or so, which would be needed, to save the NR with a high pitch setting.
Lots of things have to go wrong for this to happen.

1. You need an overspeed for a start

2. Overspeed protection has to fail.

You will be doing the wrong action by removing your hand from the collective and then moving it to a fire button which raises the issue of pushing the wrong one. Why not just roll back the throttle on the over-speeding engine?

Methinks you should review your SIM procedures!

RVDT 10th Dec 2013 18:13


With amount of the fuel found in the helicopter engine starvation doesn´t seem to be the cause.
As long as it was in the right place for continued flight.


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