C21;Very good point.
A while ago I asked our engineer (you know who you are!) to confirm that when the warning came on, it indicated that the pump was either 'running dry' or u/s, as opposed to warning the pilot that it had turned itself off. It wasn't the latter.

It seemed to make sense that as the drill is to turn the pump off when the caption comes on, why wouldn't/doesn't it do it automatically.

As I'm aware, the F PUMP warnings will come on in only 3 circumstances;
If its running dry, it gets turned off.
If it's unserviceable, its not working.
If the cb has gone, should you be resetting it in 'normal flight'?

If its a case of the first instant, when the pump becomes wet again it would switch itself back on and alleviate any of the problems associated with either not switching it back on, or switching the prime pumps on by mistook.

Skyranger,

There were Amber captions for Tx Pumps - because they were switched off - and Prime pumps - because they were switched on. The Amber Fuel caption, (there is only one), is operated as a mathematical sum of total fuel remaining and comes on circa 70 - 75 kgs total fuel. (How much did the AAIB find?).

There was no attempt at a restart - in order to carry out a restart in flight, the engine main switch has to be moved to "Off", which entails opening both guards.
Even if the guards were both opened and the switch moved to "Off" and then to "flight", the engine will not restart until N1 has reduced to below 17%.
(Where did the AAIB find the ENG Main Switches)?

question.

ignoring all the possibilities of any issues with fuel gauges (and I thought the known issue was with the main tank gauge or is it all three? and was it not about them over-reading when subjected to water contamination?), if they started with full tanks (which we are lead to believe?), then surely an experienced EC135 pilot would have a good idea what the typical range (in hours/minutes) are for this 'copter?

if we ignore the fact he crashed, and assume he had the Xfer pumps on, and landed safely, just how much fuel would have been left? main tank would be empty by then and I'm guessing the supply tanks would be significantly down from full?

if we are saying that nighttime min fuel is 90Kg's, then he was going to be well under that no matter what, anybody want to put a number to this?

The fuel was found in the MAIN tank by AAIB!!! The caption FUEL is related to the supplytank! It normally comes on whenever the amount of fuel is arround of 36kg for Supply1 or 32kg for Supply2!

skadi

AnFI, that's a naive statement. If you can come up with an autopilot that works without hydraulics you might make your fortune.

Perhaps you are unaware of the requirement for an autopilot in helicopters used for PT by night?

-------------------------------

Wrt to the pilot's actions. As an experienced police pilot on type; it's likely that Dave would have flown the EC135 at a low fuel state on a number of times in the past; because this isn't an unusual situation, due to the reactive nature of the job. I would presume that he would therefore have been aware of the correct procedures / drills for doing so and the limitations & quirks of the aircraft systems.

Many thanks to those who have posted fuel tank and fuel switch diagrams. I have questions about operating detail:

Several pilots on this thread have said they leave the XFR pumps running, and if I were I a pilot I think I'd do the same, though someone ought to tell the guys in the design labs that they need to design/test/certify for this mode of operation. At least one pilot has mentioned the need to juggle with the pump switches, or simply leave them switched off, when in orbit about a task.

So what is the standard procedure, please? Do the switches have to be manipulated all the time, or is there any gravity feed when the main tank is full? If "all the time" I guess that would be a few minutes out of every twenty minutes?

What I'm getting at here is that the gauges, annunciators and switches would have been operating properly throughout the flight with several successful fuel transfers taking place. Would the final fuel transfer at low main tank level have been any different?

The pilot has not responded and tried to land after 2 red low fuel warnings. Why? He may be unaware that the transfer fuel pumps are off. and is seeing the main tank still displaying adequate fuel levels. Did the display of the supply tanks fuel level somehow reset to zero because of a (sensor) failure that then made the pilot focus on the main tank display which gave him total comfort, and he thus deliberately ignored the supply tank display. The pilot then ignored the subsequent red low fuel warnings as being also erroneous as they were linked to the supply tanks display showing zero fuel. The pilot was rational and acted rationally at least in his own mind. Is there any way that the supply tank fuel display can reset to zero during a flight?

Henry,

The operation of the XFER pumps are mandatory as laid down in the manufacturers flight manual, the procedures in this manual may NOT be altered by local operators. The fact that some pilots apply common sense to this requirement is outside of the regulations. I can't be clearer than that. The drill is, Amber Caution and master caution illuminate, Cancel master caution, check CAD, Check fuel in main tank, Check Switch to on, Check CCB in. If all are okay, switch pump off. Pilots will know if the aircraft attitude has caused the caution to illuminate, and this is where they (some) apply common sense deviate from the regulation.

As to the times at which the amber aft or fwd pump cautions appear, it has been explained at length earlier in this thread, and will depend on the amount of fuel in the main tank at the start of the flight and the aircraft CofG and attitude. We're certainly not talking about the whole flight here, perhaps typically on the G-SPAO last flight the last 30 minutes (if it had landed at base with the MLA remaining in the supply tanks).

Scuffers,
They did not start with full fuel, they started with 400 Kgs. Full fuel on the 135 - dependent on serial number - is around 540 Kgs.

Folks,

If you're diving in to this thread in the last few pages, please don't be put off if your question doesn't get answered or the terse reply directs you to a post sometime back, but it really is worth doing some looking back at the last 6 or 7 pages before asking repeated questions. Imagine what the long term posters see when your really obvious questions pop up alongside the fact you've newly joined and have 1 or 2 posts?

That said this is the internet and all are equal.......now, any questions on the 135 fuel system?;)

Henry, your last line of your post is very good. For the main tank to end up with the 76Kg it would suggest heavily that the transfer pumps had been operated at some time during the flight, this tends to tie in with (Sids?) the hypothesis that having juggled the switches in flight, the fatal mistake COULD have been to select the prime pumps to on by mistake in the dark instead of the transfer pumps, of course IF the CAD was working the cautions would have shown the error if the pilot looked to verify his action. Still doesn't in any way explain the failure to act on all of the subsequent warnings and fuel level indications before flame out.

Ah, OK, thanks for that, missed it somewhere...

That still leaves the question of if you start with 400Kg's, as a pilot, you must have a good idea how long this will last for?

does the CAD display not give a consumption rate and fuel time?

Art - many thanks, understand from you that XFER pumps are not operated until main tank fuel is very low, ie that there is gravity feed for most of the flight. This has not been clear to me from previous explanations. The diagrams do not show details such as pump mechanisms nor air vents.

I can confirm that I followed all of the first third of this thread (until the repetitions became boring) and all of this thread since the AAIB Special Bulletin. My interest stems from experience of avionic design, including mechanical items and black boxes, for example autopilot and FADECs.


Edit - okay reading and digesting Art's 10:25 edit

Has anyone turned on the wrong pumps before?
 

How often do people flip the wrong switches, only to be 'pulled up' by the CAD? Anyone done it? If it happens a lot then CAD fault alone might give us two slices of cheese lined-up.
Would the CAD failure take out any of the other subsequent warnings?

edit: Looking at the panel in post 2192, I guess, if you did not intend to flip those switches, you would be at most one switch out, and get one of each.
To actually flip the wrong pair would suggest being confused as to the position on the panel of the pair you want.

Henry,

Nearly there, the pumps are ON for flight, just that at some time into the flight the level will reduce and the pumps will detect that they are no longer pumping fuel, THAT is the point at which the pilot 'interferes' with the switches according to the RFM.

Paull,

Wrong pump switch selection happens as they're all the same size, shape, and colour and are 4 tiny switches all in a row in a not very visible location (particularly at night wearing helmet, goggles and perhaps specs, that's why visual verification of the CAD is important, if the CAD fails, then a VEMD display will take over SOME of the functions of the CAD in a reduced and simpler format, though page switching will be required. As some have said, an automatic function really is the answer.

Henry,
After engine start, prime pumps go off, transfer pumps go on.

Paull,
400 Kgs - planning figure about 1:40 by day and 1:30 at night as I need to land above Minimum Landing Allowance.
Actual figure will depend on flight profile - spend a lot of time in the hover = less time. Spend a long time in 50 knot orbit = more time.
As a police pilot you are continually assessing how long you've got left on task.

Art, thanks, understood :ok:

To the pilots:

During your scans, to what extent do you take in the detail of the fuel indication, by which I mean do you distinguish fuel levels in each cell separately (i.e. take in and process three readings) or do you, to some extent, assess the fuel quantity remaining across the fuel tank group as a whole?

What I'm trying to understand is whether the ergonomics of the Fuel Indication display, reproduced a number of times in this thread, gives sufficient prominence to the supply tank levels.

Of course they give sufficient prominence, there is nothing wrong with the format of the display

JayT, am I right in thinking that after switching the transfer pump off the caution dissapears after a few seconds, ie...there would be no residual indication that the pump was OFF?

I'm be-fuddled this morning!

Here's the manual for CAD failure which could explain why no fuel cautions!

3.3.3

– CAD screen blank or abnormal data appearance
– CAU DEGR appears on VEMD
– “CAD FAILED” and “PRESS OFF” appears on the FLI (message zone)
– FLI 1 DEGR and FLI 2 DEGR appear on lower left/right side of the FLI page on the
upper VEMD
– If HIGH NR mode is selected, rotorspeed increases to high rotorspeed
– No fuel indication available
– Degraded Master Caution indication (only one lamp)

NOTE

CAUTION

SYSTEM I MISC SYSTEM II

ENG CHIP XMSN CHIP ENG CHIP
FADEC FAIL FADEC FAIL
FLI FAIL FLI FAIL
FLI DEGR FLI DEGR
ENG MANUAL ENG MANUAL
TWIST GRIP TWIST GRIP
FADEC MINR FADEC MINR
ENG FAIL ENG FAIL
HYD PRESS HYD PRESS
ENG EXCEED ENG EXCEED

D

AVAILABLE. PROPER FADEC FUNCTION CAN BE CHECKED BY THE

Catch,
The fuel display is constantly monitored as, together with a "time remaining" crib on my kneeboard, I need to be able keep the crew informed of how much time we have remaining on task.
The 135 fuel display is clear and easy to read by itself but it is part of a system. The system has warnings built in to it which have been described many times on this and the 135 thread. The fuel display is essentially an airborne planning tool. However, should the warnings appear, expected or not, the clock becomes the primary planning tool.
To quote an old and bald QHI from my military days, "Airspeed is life, altitude is life insurance and you cannot buy either of them without fuel".

Art,
if the TX pump captions were on then they remain on once the pumps are turned off.