Bond ground all UK EC135s

[airsound]

Statement received this morning from Bond Air Services.
During normal operations yesterday, one of our EC135 fleet has experienced an indication defect that requires further technical investigation. Therefore as a precautionary measure we have temporarily suspended service operations whilst we undertake detailed diagnosis. We commenced investigations overnight, are continuing this morning and are in close liaison with Eurocopter regarding this investigation.

We apologise for the disruption to service and expect to provide a further update around 10.30 GMT.Further statement at 1140
Further to our update earlier this morning we can confirm that we continue to investigate the technical fault that resulted in us temporarily suspending service operations yesterday. We are now conducting functional tests across each of our EC135 aircraft in order to gather more specific information.
Eurocopter tell me that the wording is important. This is not a grounding, they say.

airsound

[SASless]

With the latest news....a question about "Fuel Gauge Calibration Checks" arises.

Are they a part of routine maintenance procedures and done at specific intervals or just when a problem is reported by the Pilot?

Are the Fuel Cells ever opened and the interiors inspected during major Inspections?

[toptobottom]

I think you'll find that Bond grounded its 135s some time ago, following concerns with mis-reading fuel gauges, as I tried to indicate here (http://www.pprune.org/8193522-post773.html)

[Digital flight deck]

Have any other EC135 operations suspended services?

[aeromys]

I think you'll find that Bond grounded its 135s some time ago, following concerns with mis-reading fuel gauges, as I tried to indicate here (http://www.pprune.org/8193522-post773.html)

No, they continued flying up until an incident yesterday evening.

[flap15]

BBC have just announced that Bond have found a fault and grounded all their EC135 helicopters.

[fatmanmedia]

BBC News - Glasgow crash helicopters grounded by Bond Air Services (http://www.bbc.co.uk/news/uk-scotland-glasgow-west-25353001)

[toptobottom]

AeromysNo, they continued flying up until an incident yesterday evening.

Are you sure they were all flying until yesterday evening?!

[aeromys]

Aeromys

Are you sure they were all flying until yesterday evening?!

Are you saying Bond have not operated any 135s' since the Glasgow crash ? On what date are you saying Bond grounded their 135 fleet ?

[CJ Romeo]

Definitely they were still flying a Police EC135 in Glasgow last night.

From whats on here, they werent pulled till late last night.

[fenland787]

According to the Beeb anyway:

BBC News - Glasgow crash helicopters grounded by Bond Air Services (http://www.bbc.co.uk/news/uk-scotland-glasgow-west-25353001)

[Digital flight deck]

Sky news seems to think that Bond operate all police and air ambulance EC135s. As I understand it NPAS have not grounded their EC135s serviced by ECUK. Unless anyone knows to the contrary?

[silverelise]

BBC News are reporting that NPAS have issued an instruction to operate with increased minimum fuel level.

[Digital flight deck]

Differing levels of risk averseness.

[SilsoeSid]

Did you say all UK 135's?

[Fortyodd2]

Just in case anybody is interested in facts;
NPAS instruction as at 23:04, 11 Dec is to operate with an increased MLA of 100Kgs in the Main Tank until further notice.

[SilsoeSid]

So why haven't Bond said the same?

[Richard J.]

Did you say all UK 135's?

All of Bond's EC135s, according to the BBC report. (No press release on Bond's website yet.)

"Bond Air Services suspended flights on all 22 of its EC 135s after a fault was found on the North West Air Ambulance. ... Eurocopter said the decision taken by Bond did not apply to the rest of the Eurocopter fleet in the UK - a total of 57 aircraft."

[fenland787]

I could have worded it better perhaps but yes, according to the Beeb, Bond have grounded all their EC135s
Bond Air Services suspended flights on all 22 of its EC 135s

[Pittsextra]

Is this related to the Glasgow accident, in so far that there might have been increased sensitivities/checks after this event, or just a co-incident in terms of timing? Or we don't know yet...?

[fromredtogreen]

According to BBC news bond have said the grounding is not related to the Glasgow crash.

If true, that may prove an important claim.

[vulcanised]

Just been announced the EC135 is to resume service.

[Kluseau]

BBC News are reporting that "Emergency helicopters run by Bond Air Services back in air after being grounded"

BBC News - Emergency helicopters run by Bond Air Services back in air after being grounded (http://www.bbc.co.uk/news/uk-scotland-glasgow-west-25357442)

[SilsoeSid]

Just the fine print;

Bond Air Services said that aircraft confirmed as having "no fault" would return to service.

So, at what point do you think NPAS should lift their restriction?

[fenland787]

From Bond:
A statement read: "Following an issue with the fuel indication system on one of our aircraft yesterday we temporarily suspended service operations whilst we undertook further technical investigations of our fleet of EC135s."
It added: "We will continue to work with the manufacturer Eurocopter on any aircraft which are found with this fault, with the aim of resuming normal service as soon as it is safe to do so."
From which, as they had previously said there was no linkage between the Glasgow incident and this suspension of all their EC135s I presume the former is not considered fuel quantity related?

[toptobottom]

aeromys

Quote:
Originally Posted by toptobottom http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/rotorheads/528850-police-helicopter-crashes-onto-glasgow-pub-64.html#post8202516)
Aeromys

Are you sure they were all flying until yesterday evening?!
Are you saying Bond have not operated any 135s' since the Glasgow crash ? On what date are you saying Bond grounded their 135 fleet ?

I'm saying that at least one of Bond's EC135s was grounded before or about 4th December because of concerns over misreading fuel gauges. This was the focus of the AAIB from an early stage in the investigation - hence my first post. (http://www.pprune.org/8193456-post769.html)

SS - I didn't call you a nob; I said your arrogance made you sound like a nob. You dismissed my contribution on the basis I was misinformed, however, I can assure you I am very well informed, hence my comment about not posting speculatively.

[SilsoeSid]

Just to make it clear;
Bond Air Services said that aircraft confirmed as having "no fault" would return to service.

[nodrama]

Ian Whitehouse NPAS COO - "If such a notice is put in place (by the CAA etc) then we would immediately and carefully consider it"

...... Nollocks, you would DO it.

Why haven't NPAS taken the same precaution with their EC135 fleet?? Because they haven't got their own in- house maintenance or engineering management team.

[Blind Pugh]

nodrama, I can only agree. You are legally obliged to comply...or stop flying.
If you've been around UK aviation long enough then you would know that... Surely NPAS crews want their airframes checked in the same way the Bond ones have been as a reassurance measure if nothing else. They say "safety is our number one priority", well, demonstrate the same.
If the ambulances are being checked as ok, let's check the police cars too....

[Fortyodd2]

nodrama,
"Because they haven't got their own........engineering management team."

Are you sure??

[Thomas coupling]

Blind Pugh - are you aware they may have had their a/c checked by one of the biggest maintenance organisations in Europe?

[Sir George Cayley]

Radio 4 this evening reported that the fault related to fuel gauges.

SGC

[Blind Pugh]

TC, Fantastic, then why not say so in your press release? Have they by the way?

[aeromys]

I think you'll find that Bond grounded its 135s some time ago, following concerns with mis-reading fuel gauges, as I tried to indicate here (http://www.pprune.org/8193522-post773.html)

You are now saying they grounded at least one, a bit different to your earlier implication they grounded all their135s'. Checking a fuel indication defect on one of their135s' is not grounding the fleet.

[mathers_wales_uk]

It seems that the latest is that 2 of 3 Wales Air Ambulance are back in service leaving one plus the South & East Wales Police Air Support Unit still grounded until inspections have been completed.

[toptobottom]

aeromys
You are now saying they grounded at least one, a bit different to your earlier implication they grounded all their135s'. Checking a fuel indication defect on one of their135s' is not grounding the fleet.

Not quite sure where you're going with this. What I'm saying is that Bond quickly grounded at least one of its wet lease 135s quickly after the Glasgow incident because of a known problem with said 135's fuel gauge; that's the significant bit. I also said that I believed a big factor in the demise of G-SPAO was fuel starvation.

[Rigga]

TTB - That sounds like a normal "Snag" to me.

[Fortyodd2]

Cabby,
"Eurocopter can't be contacted"

At anything after 1701 on a Friday evening that's "Ops normal". Hardly earth shattering news!

[2F1B]

So, Bond have grounded all their 135's until they have all been individually checked and cleared to fly again by Bond Maintanence. I understand that and appreciate that, due to recent events.

NPAS have imposed an additional limitation of 100kg min in the main fuel tank UFN. When is this limit going to be lifted again as each aircraft is very unlikely to be individually checked and cleared by ECUK Maintanence as they have already publicly stated that it was not them that have issued the checks.

Seems a bit of a knee jerk reaction by someone in NPAS who should know better without thinking yet again just because one aircraft had a fault. This limit imposed is affecting real time operational capabilities, and hindering the service that should be being provided. NPAS, if you are actually that concerned then ground the aircraft and pay to have them individually checked, otherwise stop making half hearted attempts to make it look like you know what you are doing is best.

If ECUK refuse to carry out the checks as (like most of us) they do not see a fleet wide problem, what is Plan B? Will You just lift the limitation again next week once Bond have had all their checks completed and returned all the other 21 aircraft back flying again. Would that be a duty of care to your own NPAS pilots by doing nothing except making the job more difficult in the mean time!

Is this going to happen for every fault over the next few months until the findings of Glasgow are published?

:ugh:

:\

[chopjock]

just because one aircraft had a fault

more than just one EC135 with faulty fuel gauges. Air ambo in Dorset has one too.

[2F1B]

Ok, it may be confirmed now that more than one have been found with the same fault, so why are we still flying with only an additional limit? Ground them, check them, fix them, fly them.

That should take up most of the weekend and it is the Christmas season after all.

The point I was trying to make was why only impose a limit of 100kg? Why not get them all checked, and if ECUK refuse to check them all without costs, then ground them until ECUK acknowledge there may be a problem fleet wide. If NPAS feel there is any doubt, which they obviously do to impose additional limits, then as a duty of care they should not be allowing their staff to fly them in the first place. :ugh:

[Fortyodd2]

2F1B,
NPAS Aircraft underwent a "Fuel System Confidence Check" today. Our current steed passed and we have been back to normal since I came on shift this evening. Have heard all the other aircraft in the region operating normally as well.

PS2A95BRAS :ok:

[2F1B]

Who conducted the checks? ECUK?

There goes the festive weekend ahead :{

Has all NPAS aircraft been checked? Any faults found?

[RVDT]

SIN No. 2673-S-28

SUBJECT: FUEL SYSTEM

Information concerning LOW FUEL warning

Applicability EC135 T1, T2, T2+, P1, P2, P2+, 635 T1, 635 T2+, 635 P2+ MBB BK117 C-2

Eurocopter has been informed by Bond of an issue involving the fuel indication system on one of its
EC135 EMS aircraft during normal operation. Following this incident, tests performed on EC135 have
revealed supply-tank fuel gauging errors on some aircraft.
The first analysis shows that the indication of the fuel quantity in the supply tanks could be
overestimated. All crews should be aware that in the worst case a red warning LOW FUEL 1/2 could
appear without any amber FUEL caution before.
The red LOW FUEL 1/2 warnings are generated by an independent switching logic with separate
sensors in each supply tank. The red LOW FUEL 1/2 warning lights continue to operate correctly
even if the fuel gauging is inaccurate.
Therefore we want to remind you that:
• After illumination of LOW FUEL warnings the procedure iaw. the Flight Manual must be strictly
complied with, notwithstanding of the fuel quantity indication.
In addition we want draw attention to the proper airmanship iaw. Air Ops NCC.OP.131 “Fuel and oil
supply — helicopters” and NCC.OP.205 “In-flight fuel management” to ensure situational awareness
concerning fuel usage and flight time left.
Furthermore, we want to remind you of Information Notice 2535-I-28 “Notes about possible water
contamination of the fuel system”.

SIN No. 2535-I-28

SUBJECT: FUEL SYSTEM

Water contamination of the Fuel System

Applicability EC135 T1, T2, T2+, P1, P2, P2+, 635 T1, 635 T2+, 635 P2+ MBB BK117 C-2


EUROCOPTER has been informed about several fuel quantity indication failures. Following the
replacement of the affected fuel probe, the indication returned to normal and the functional check of the
fuel quantity indication system has been performed successfully.
When the subject probes have been returned to EUROCOPTER for repair, the probes showed no
external damage or contamination within the two concentric metal tubes and most of the probes have
been tested, with the result, “no fault found” (NFF). To investigate the reason for these NFF’s
EUROCOPTER performed several tests to simulate the failures. As a result from these tests, the most
probable root cause is contamination of the fuel probe with water.
These tests have shown - when water is entering the space between the two concentric metal tubes of
the probe - it will decrease the output signal (frequency) of the probe. In case of a high concentration of
water, the frequency can decrease to such a level that the CAD recognizes the probe as failed –
showing either an F QTY DEGR or F QTY FAIL caution on the CAD. Also there is a potential risk that the
CAD shows a higher fuel quantity level compared to the actual fuel level within the fuel tank system.
In addition, customers have reported, when removing the defective sensor from the helicopter, that after
removing the water by the use of shop air and warming up the sensor for a certain period of time, the
sensor has been working again without any fault.
It should be noted that even for operators that regularly drain the fuel tanks, a couple drops of water
concentrated between the metal tubes of the sensor may be enough to affect the signal.
There are several possibilities for the fuel system to be contaminated with water:
· Condensation within the fuel tank system. This is mainly caused when the fuel tanks are not
completely filled and the helicopter is parked outside and/or is exposed to great changes in
temperature
· Heavy rain during refueling of the helicopter – water is entering through the filler neck
· Contaminated fuel from the source – for example fuel truck, tank, supply system or barrels
· For EC135 when performing an engine compressor wash, the water from the combustion
chamber is drained into the drain bottle. On some helicopters there is a chance that water from
the drain bottle is sucked into the engine fuel system via the Fuel Control Unit. Operating the
prime pumps prior to the next engine start will allow the water to enter the helicopter fuel system
through the fuel return line and the fuel expansion box. From the fuel tank expansion box the
water will then flow back into the RH Supply Tank.
Therefore, as explained in the AMM Task 71-65-00, 7-1, it is recommended to follow the procedure and
to disconnect the combustion chamber drain tube before prior to starting the compressor wash process.
Due to the reason mentioned above, EUROCOPTER wants to point out the importance of keeping the
fuel system free of water and other contamination. When draining the fuel system, in reference to the
documents listed below, it must be performed before the helicopter is moved, in order to allow the
maximum amount of water to be drained from the tank.

EC135
AMM, Chapter 12-30-00, 3-5
MSM, Chapter 05-25-00, 6-1
FLM, Section 4 – Preflight Check
FLM, Section 8.3 – Drainage Procedure

BK117C-2
AMM Chapter 12-30-00, 3-16
MSM, Chapter 05-25-00, 6-1
FLM, Section 4 – Preflight Check
FLM, Section 8.3 – Drainage Procedure

In addition EUROCOPTER wants to point out that water – if not drained from the fuel system – can
cause different malfunctions within the fuel and engine system.
If there is doubt that the fuel system is free of water, EUROCOPTER recommends to take a fuel sample
from the helicopter tank system and to test it for the presence of water by using commercially available
Test Strips, for example the SHELL Water Detectors or another commercially available product.

[SilsoeSid]

If NPAS feel there is any doubt, which they obviously do to impose additional limits, then as a duty of care they should not be allowing their staff to fly them in the first place.

Of course you're forgetting that if the pilot and or crew weren't happy, they didn't have to fly!

[airsound]

Update statement from Bond Air Services this afternoon Monday 16 Dec:
Following our discovery during routine operations of an issue with an indicator system on one of our aircraft on the 11 December, Bond Air Services temporarily suspended service operations to allow precautionary testing. This involved detailed examinations and tests to evaluate the function and accuracy of the fuel indicator and alert system on our fleet of EC135s. Following these tests, we were able to release a number of aircraft back to full operational service immediately. Over the last few days, we have worked with the manufacturer Eurocopter to fix those aircraft which were discovered to have a fuel indication anomaly. Our EC135 aircraft are now fully operational and are available for missions with our air ambulance and police customers.

As an extra safety precaution, all our operational EC135 aircraft will now carry a minimum of 90kg of fuel at all times. We will be working with all our customers to discuss the impact of this additional precaution, and ensure we continue to meet their service needs.

Our decision to temporarily suspend service operations underlines Bond Air Services' commitment to maintaining the highest standards of safety in all our operations.airsound

[ShyTorque]

So am I correct in reading that the fuel contents gauge and the amber contents warning light are working off the same signal input, but the red low contents warning light is independent from them?

So, if unknown water contamination has taken place, a red light alone might have been incorrectly seen as a spurious warning where the gauged fuel contents appear sufficient and the "early warning" amber light has not yet illuminated?

Yes, having read it again, I think it does mean this. Normally crew are trained to look for confirmation of a fault or caption by looking at a gauge, or vice versa. It appears that this is potentially a very hazardous thing, especially if only a few drops of water can seriously affect gauge accuracy.

[Thomas coupling]

Shy: you are one step ahead of me..................:suspect:

[Fortyodd2]

Shy,
It was always drummed in to me when training on the 135 and on subsequent checks that, if the Red Low Fuel Lights came on, regardless of what the gauges read, assume the Red caption is telling the truth and land.
Interesting that Bond have decided to up the MLA to 90Kgs - so, now you have a situation where you never get to use the fuel in the supply tanks and never get to see the levels reducing so you never know whether the gauge is reading correctly or simply "stuck".
Beginning to sound to me as though the 500/1000 service ought to include a fuel system drain and re-fill to check the gauge accuracy.

[ShyTorque]

Beginning to sound to me as though the 500/1000 service ought to include a fuel system drain and re-fill to check the gauge accuracy.

I'd agree; I don't know how often this is done for the 135 but even so, the problem is that the aircraft could get water contamination very shortly afterwards. It sounds like the routine water drain checks are vital on this type.

[airsound]

Bond Air Services issued a further statement yesterday evening, 16 December
We note that Eurocopter has today issued a Safety Information Notice to operators of the EC135 across the world confirming that some of their aircraft have a fault in the fuel indication and alert system which means that warning system may not work properly. This was a fault discovered by Bond during normal service operations on Wednesday 11th, which we immediately reported to Eurocopter and the appropriate authorities. We understand other operators have since conducted similar tests and found similar problems with their aircraft. As soon as we discovered this issue, in line with our commitment to the highest standards of safety, we took the prudent decision to temporarily suspend service operations whilst we conducted checks on our fleet of EC135s. The results of these tests were subsequently validated by Eurocopter, and appropriate repairs made before returning the aircraft to service. We also took the decision to increase safety barriers by mandating that all our EC135s should maintain a minimum of 90kg of fuel onboard at all times.airsound

[Fortyodd2]

Shy,
Water drain/sample checks are part of the Check A. Also, to answer your earlier question, yes, the Amber Fuel Caption is a function of a certain quantity of fuel or less being reached dependent of type of fuel tank but it's around the 70kg mark - the information coming from the contents sensors. The Red Low Fuel Warnings come from a different set of sensors which "detect" in a different way.

[EPAC]

An EC135 operator practices a stringent policy of checking both the bulk fuel supply and the aircraft fuel tanks for water every morning before the commencement of operations. They use the standard ‘Shell’ detecting capsules, which will detect water in aviation fuel at 30 ppm (the recommended ICAO standard).

They are fully aware of Eurocopter SIN 2535-I-28, and have been for some time.

Yet potentially serious fuel indication problems still occur with their aircraft.

At present, there is no requirement by the manufacturers Master Servicing Manual (MSM) to inspect or function check the fuel quantity indication system at 500 or 1000 hrs. The fuel sensing probes are an ‘on condition’ component (that means they are not subject to time-life or overhaul).

So, if the probes correct operation is so susceptible to water, why is there no requirement to check them at regular intervals? There is always water in aviation fuel, it may be only a couple of ppm, but it’s there. I would even go as far as to ask if the probes are fit for purpose?

The EC135 Technical Briefings from Heli-Expo 2011 (pg24) and 2012 (pg29) are of some interest.

When Eurocopter talked about a ‘worse case’ in their last SIN relating to fuel indication, they were talking about this……

Both transfer pumps off, 170 kg in main tank, 47kg in No 1 supply tank, 30 kg in No 2 supply tank. FUEL amber caution illuminated and both No 1 and No 2 FUEL LOW red warnings illuminated (I can't get the photo to paste).

If the No 1 supply quantity indication was correct, the No 1 FUEL LOW light wouldn't be on. There was actually 13 to 21 kg less fuel in the No 1 supply tank than the display was indicating. A 27 - 44% error.

[RVDT]

If the No 1 supply quantity indication was correct

Which it obviously could not be unless No.1 engine was burning less than No.2? Or No.2 SUPPLY TANK had a hole in it?

FUEL LOW 1 and 2 ON is the key.

FUEL LOW is FUEL LOW is FUEL LOW!
Entirely separate circuit. As pointed out in the IN.

Regardless of what the gauge indicates. Its an indication that should be backed up by fuel management policy, pilot proficiency and understanding of the systems.

Policy on FUEL LOW - RFM - Land within 8 minutes?

The scenario you quote "Doesn't look right or make sense so therefore something is wrong"
The trick is knowing what is wrong.

It is no different to a couple of other makes and models I could quote.

[EPAC]

Yes, it may be the key.
If a pilot knows his fuel uplift, the aircraft's average burn time and has an understanding of the aircraft's fuel system then, yes, he can second guess the indication system and know that a fuel warning MEANS that something is not right and the warning should be taken notice of...

but I'm not talking about good aviator practice, I'm talking about a system component that seems to be sensitive to a water content in fuel that is below what can be detected by commercially available testing methods.

Why should a pilot have to be suspicious of a system's integrity and have to 'second guess' it because it doesn't do what it says on the tin. It should meet the criteria of its design approval under common circumstances. If it doesn't, then it should be improved to meet those criteria and at least have a maintenance/ monitoring programme put in place in the meantime.

[cockney steve]

Unfortunately, designers get sucked-in to incorporate the "latest technology" *
No doubt they've successfully used this measurement system for many years in industrial processing and Laboratory work.
An Aircraft is operated under somewhat more "rugged" conditions. If impurities can contaminate the fluid under measurement, to the extent the reading is wildly inaccurate, it is, IMHO, the wrong technology for that job.

float/resistance-wire and sight-glass (tube) systems are crude but robust and effective.
The pilot, however well-trained, is not normally an electronics engineer or laboratory technician. How the hell is he expected to know, memorise and understand the foibles and complexities of a "simple" fuel-gauging system which is too delicate for unmonitored field conditions.

Bloody stupid, needing to monitor the monitor :rolleyes:

[RotaryWingB2]

It's not the water in the fuel (in parts per million) causing the probe to misread, it's the water pooling around the probe either causing corrosion, or as it's the lowest point in the tank, and water has a different capacitive value than fuel, causing misreading. This will happen on any capacitance type system.

If you carry out your fuel drains/checks and the same is said for your supplier then you shouldn't have this problem, which is the gist of the IN from ECD.

No doubt every pilot will claim to religiously carry out their fuel checks 100%, I call 'bull****'. :E

[DOUBLE BOGEY]

Cockney Steve -


float/resistance-wire and sight-glass (tube) systems are crude but robust and effective.



Would not the "float" float on the water content thus causing the tanks to overread the amount of "fuel" available anyway regards of where the water is in relation to the fuel.

[Robin400]

I believe that there was around 95 litres of fuel in the main tank. Even with possible faults on the supply tank warnings, why did the supply tanks not remain full from fuel transfered from the main tank. I still think there was a problem with fuel transfer.

[jayteeto]

Robin, where did that fact come from? If it is correct, we now know the accident cause!

[Robin400]

According to the press and this was the quantity removed from the helicopter on site.
Had this been in the supply tanks the engines should have carried on running.

[DOUBLE BOGEY]

My understanding is that with main tank transfer pump failure (either or both) or indeed with them switched off, you may end up with a little over 70 kgs stuck in the main tank, depending on AC attitude and which pump(s) are failed/off.

[RVDT]

True -

Failure of AFT Transfer pump in hover attitude can result in up to 71 kg unusable.

FWD Transfer pump above 80 knots up to 59 kg unusable.

How it all works here (http://www.pprune.org/rotorheads/189945-ec135-5.html#post1209255) give or take.

[Robin400]

The NRV valves on the transfer pumps are the weak link in the system. Either stuck open or closed will cause problems with pitch change. At low fuel levels one pump will be above the level of the fuel. My guess is after engine flame out return to level pitch restored fuel to the supply tanks. The popping noise may have been the engines doing there best to relight.

[jayteeto]

Robin, your post said the fuel was in the main tank? How do you know that? The release didn't say that???

[Robin400]

A fractured fuel pipe or loose conection in the tank could have the same effect. Please feel free to shoot me down in flames if you wish. Fuel starvation is the most likely reason for two engines to stop at the same time.

[Robin400]

If it had been in the supply tanks the engines would have remained running.

[RVDT]

Robin400,

As Donald Rumsfeld said "Known unknowns"

I could give you a million reasons as to why - do any carry much probability?

NO.

This is not a competition to see who ultimately has the answer. There is no prize.

[Robin400]

Correct. Saftey and prevention of accidents is the prize. I am just trying to stimulate the brains of many for the cause if this terrible accident.

[jayteeto]

Robin, I happen to agree your theory is a good one. You don't know which tank that fuel was in, do you? A simple yes or no will do.

[Robin400]

No. I do not know for a fact the tank or tanks where the fuel was located.

[Lonewolf_50]

DB:
Would not the "float" float on the water content thus causing the tanks to overread the amount of "fuel" available anyway regards of where the water is in relation to the fuel.
Isn't fuel lighter than water? :8:} It would seem that the floats will float to the top of the total volume of fluid, with the uppermost layer being the fuel. (Pour a little water in a jar, pour some gas on that, let is set for a bit, and see which floats to the top. PS: Elfin Safety says "No Smoking" whilst doing this! :E And do it in the garage, as the ball and chain will have a fit if she smells gasoline in the kitchen! :} )
That said, any water in the tank is displacing a volume of usable fuel that the level of the float would be indicating by its position, so yeah, set up for a wrong indication of how much gas you have usable ...

Back to the case at hand:

From the points being made in the bulletins, it does not appear to be a problem of a signficant volume of water fooling the fuel indicator or low fuel warning system, but a fairly small bit in the wrong place leading to erroneous signals.

jayteeto:
This post intrigues me (http://www.pprune.org/rotorheads/529773-bond-ground-all-uk-ec135s-4.html#post8211811). Won't ask how you arrived at that conclusion.
EPAC:
Why should a pilot have to be suspicious of a system's integrity and have to 'second guess' it because it doesn't do what it says on the tin. It should meet the criteria of its design approval under common circumstances. If it doesn't, then it should be improved to meet those criteria and at least have a maintenance/ monitoring programme put in place in the meantime.
The discussion on A330 Thales vs Goodrich pitot tubes strikes a parallel concern. In that case, though, Airbus was in the process of a fleetwide refit ...

[AnFI]

Worth watching, the genius of Donald Rumsfeld was really identifying the unknown unknowns:

? Donald Rumsfeld Known Knowns, Known Unknowns, and Unknown Unknowns - YouTube

Something a helicopter pilot should always bear in mind...

[SASless]

.....and there are those known things we don't know too!

[DOUBLE BOGEY]

....and surely the worst are........unknowns that were hitherto known....lessons forgotten!

[cockney steve]

re= float- measurement of liquid.
The whole point is, the total volume is measured. It is a given that a certain amount of tank-contents is UNAVAILABLE TO THE PICKUP -This allows for dirt, water and other contaminants to settle clear of the drawoff point.....a well-designed tank would have a low-point sump well away from the pickup and incorporating a transparent sedimenter and drain point. there is absolutely no point in drawing a sample from a higher level,which is why some designs need multiple drain-points.
Having said that, PROVIDED regular sample- drains are carried out, the water coalescing ,is pretty-much irelevant.....IT IS IN THE UNUSABLE "SUMP" AREA
The CONTENTS gauge will show how much usable fuel you have......if a portion of that is water, then you, the Pilot, are guilty of gross incompetence and negligence.....retire immediately!
A Capacitative system, calibrated to a laboratory-standard,pure liquid, is not fit for the purpose of measuring a liquid of "stated" quality. Clearly, there's a tolerance on commercial fuel hudrocarbons...I guess the on-board computers and sensors are not smart -enough to pick up a deviance caused by contaminated fuel....which brings us back to my original proposition....

An electronic system of fuel tank contents measurement is not fit for commercial aircraft operations....it's measurement is arbitrary and dependant on the quality of the fuel.
A sump-drain will not necessarily show water, but that does not mean there is not a high water content dispersed in the fuel itself (see the Heathrow BA crash threads for that one! ) Ultimately, it can precipitate, but you need a very large amount before you have trouble under normal operating and check regimes.

Helicopters have a poorer unpowered flying ability than fixed-wing...therefore it would seem a priority to design any such craft around an "Inherently safe" regime. Eliminate as many traps, "gotchas" and flaws at the design stage...together with good ergonomics, a safer aircraft should ensue.

[jimjim1]

@cockney steve
An electronic system of fuel tank contents measurement is not fit

Seems a bit harsh. Capacitance based sensors seem problematic. There are alternative solid state methods.

e.g. Ultrasonic, optical pulse/time based, optical refractive, thermal using differential heat conductance of air vs fuel.

[AnFI]

re= float- measurement of liquid.
Helicopters have a poorer unpowered flying ability than fixed-wing...therefore it would seem a priority to design any such craft around an "Inherently safe" regime. Eliminate as many traps, "gotchas" and flaws at the design stage...together with good ergonomics, a safer aircraft should ensue.

Helicopters with lower disk loadings perform very well unpowered - it is one of the upsides of the single engine soloution.

Regrettably complexity has unforseeable implications. Simplicity is hard to acheive - but worth it.

[DOUBLE BOGEY]

Helicopters have a poorer unpowered flying ability than fixed-wing


Cockney Steve,

A helicopter, nicely established in autorotation, has the ability to manouvre in any direction and we can even keep the autopilot in for stability and speed datum. It can land at 60 Knots or Zero knots (especially in hands of our ex "Nam" brethren).

An airliner is committed to a touchdown at well over 100 knots.

I would suggest the helicopter fares a lot better in unpowered flight, especially at the end.

[EPAC]

Information concerning LOW FUEL warning

"This incident is currently under in-depth investigation by Eurocopter"

[skadi]

ASB 28A-018 FUEL SYSTEM

This actual ASB requires a fuel system check on all EC 135 within four weeks or 30 flighthours.

skadi

[cockney steve]

I would suggest the helicopter fares a lot better in unpowered flight, especially at the end.

I'd agree with tha last bit...the transition to,and execution of, unpowered flight seems to be the problem....the actual landing, less-so.
( I have tried to master a Nitro-powered model, flights tend to cost ~£50 a go in crash-damage:O Not as expensive as flying full-size, but vastly more twitchy and the complication of orientation , flying from an external viewpoint.
I was heartened to hear from a Pilot who flies both full-size and models, that the latter are infinitely harder! ) Plenty of youtube footage of model pilots cutting and then autoing to their feet !

@ Jim Jim 1... yes, harsh, but you are advocating an unneccessary layer of complexity. It is fallacious to assume the contents being measured, are of a tightly -controlled consistency and constituency...not so! laboratory-standard measuring-systems have no place in an industrial environment, especially when, as demonstrated, the measurement is error-prone and based on a theoretical standard of purity which is not borne out in practise.

[EPAC]

http://www.eurocopter.com/site/docs_wsw/RUB_1330/ASB_EC135-EC635-28-018-Rev0-EN.pdf

http://www.eurocopter.com/site/docs_wsw/RUB_1330/ASB_EC135-EC635-28-019-REV0-EN.pdf

[Bill4a]

I'm having a very hard time trying to imagine how the amount of water that would need to be in a fuel tank in order to give a significant 'float' based system error would get there!
Unless the drain checks haven't been carried out for a very long time, surely the amount of water present in the tanks would be minuscule?

[SASless]

It can land at 60 Knots or Zero knots (especially in hands of our ex "Nam" brethren).



Well not always......



http://farm5.staticflickr.com/4038/5144193297_4537b5c0a0_z.jpg

http://www.youtube.com/watch?v=8jlCD4x2swI

[ShyTorque]

SASless, moving as casually as he could, on the way to hand his notice in before the Boss found out.... :p

[SASless]

Actually, some locals shooting at him after downing his aircraft. I would be legging it too in a style we knew as "Low Running!".

[Mechta]

Can anyone say what type of gauging system operates the red warning light?

[Fortyodd2]

Mechta,
It's a Thermal Sensor - basically, it senses whether it is in liquid - or not.

[Mechta]

Thanks Fortyodd2. :ok:

The fact that the Eurocopter technical bulletins state that the capacitance fuel probes need cleaning and that some inspected probes worked correctly after cleaning, suggests that the probes could be getting a build up of bacteria. This can cause water droplets to be retained between the probe's concentric tubes. This in turn would give an incorrect capacitance reading, an incorrect remaining fuel reading and a false sense of security for the pilot.

Fuels (http://www.echamicrobiology.co.uk/pages/fuels/1,22/default.aspx)

Larger aircraft use multiple probes to determine the location of the fuel surface across the whole tank. An incorrect reading from one probe would show up as a fault. The Boeing 777's ultrasonic system also uses an inverted probe to look for the water/fuel interface.

In response to Bill4a's query about water in the fuel tank, this generally takes four forms that I am aware of:


Water pooled on the bottom of the tank below the fuel (what one is generally looking for when taking a fuel sample).
Water molecules sitting between the fuel molecules throughout the fuel.
Condensation on the tank components in the ullage (area above the fuel).
Water droplets free floating in the fuel due to fuel sloshing.
Water trapped by bacteria or by tank hardware.

If the problem is water droplets sitting between the probe tubes on a clean probe, then the very act of getting at the probe to inspect it may cause the droplets to be washed off or dislodged before the evidence can be seen.

[Bill4a]

Thanks Mechta, but I was referring to a previous post where it was posited that water in the tank was sufficient to cause a float system error. I still can't see it!