Fuel Leak NG

[jonny dangerous]

Just going over the Non Normal Checklist for the NG, in the Fuel section. Suppose you're flying along and fuel quantity is dropping abnormally fast from a left or right main tank.

Our checklist has an "Engine Fuel Leak" checklist and a Fuel "Low" checklist. Is it possible on the NG to have a leak from the tank that is unlike the Air Transat Azores incident, i.e. it is not from the engine pylon area? What I am getting at, is that the "Engine" Fuel Leak checklist has a six or so criteria, any one of which may confirm an "Engine" Fuel Leak...this will then lead to a shutting down of that engine, if I'm not misreading the checklist.

Although our company is not ETOPS, I'll use that scenario as an example, as there are operators out there who are ETOPS with the NG. If you decide that it is a "Leak", the most applicable checklist that I see, is the "Engine" Fuel Leak checklist. Would I follow that checklist, shut down that engine, creating the need to descend, and divert to a suitable alternate? Or is there a way to diagnose this leak first, to see if there is a need to shut the engine down? (Diversion still to follow). Does Boeing allow for the possibility of a leak from elsewhere?

I can't remember what the 320/330 does in that situation, post Air Transat.

The Fuel Low checklist mentions crossfeeding etc, and no shutdown. But seems to be for a different situation. What say you aviators?


Cheers

[jonny dangerous]

Okay, rephrased.

I've had more time to think about my scenario. To follow the question, I submit my thoughts as I see it, and with no FOM directly in front of me, I trust I will be corrected as warranted.

I'm flying along, burning fuel from the center tank. No engine feeding is thus taking place from the left or right main fuel tank(s).

I notice the fuel quantity dropping in the right main tank.Subsequent comparison shows CTR tank quantity to be dropping at the same rate as the fuel flows (2) combined from each engine.

Do I end up at the "Engine" Fuel Leak checklist. And then shutdown the right engine? Is that what I do? Or have I incorrectly interpreted the checklist? Do any other NG operators have an Fuel "Tank" Leak checklist or equivalent in your FOM's?

Would I be prudent to assume the following: Since I am not feeding from the wing tanks, yet the fuel quantity is dropping abnormally fast in ONE of those tanks, could I assume that the engine has nothing to do with the leak, and therefore I will not shut it down right away?

Might I diagnose the scenario and decide to actually cross feed the other engine from that dropping tank. Would I want to burn as much fuel as I could from it, while the fuel is still onboard (and not scattered through the atmosphere)?

What about an imbalance of one wing tank full and the other empty in an emergency situation (after I have hastened the reduction in fuel quantity in one side)? Can I expect aileron trim (manual flight) to help me maintain straight flight, even if it means higher speeds required?

All of these questions being asked to avoid wishing for 45 minutes ago (as no doubt the Air Transat fellows might have wished). If I could start my diversion with two engines going and then use whatever fuel was onboard to get me there, could I do that?

My company's checklist leaves me a little confused. I don't want to bother the appropriate guys with this scenario until I have exhausted my own resources trying to understand what the answer is.

Cheers

P.S. ECAM, I miss you. But I am learning to think for my self. It's just so, well, hard.

[barit1]

Okay, rephrased.
I've had more time to think about my scenario. To follow the question, I submit my thoughts as I see it, and with no FOM directly in front of me, I trust I will be corrected as warranted.
I'm flying along, burning fuel from the center tank. No engine feeding is thus taking place from the left or right main fuel tank(s).
I notice the fuel quantity dropping in the right main tank.Subsequent comparison shows CTR tank quantity to be dropping at the same rate as the fuel flows (2) combined from each engine.
Do I end up at the "Engine" Fuel Leak checklist. And then shutdown the right engine? Is that what I do? Or have I incorrectly interpreted the checklist? Do any other NG operators have an Fuel "Tank" Leak checklist or equivalent in your FOM's?
Would I be prudent to assume the following: Since I am not feeding from the wing tanks, yet the fuel quantity is dropping abnormally fast in ONE of those tanks, could I assume that the engine has nothing to do with the leak, and therefore I will not shut it down right away?
Might I diagnose the scenario and decide to actually cross feed the other engine from that dropping tank. Would I want to burn as much fuel as I could from it, while the fuel is still onboard (and not scattered through the atmosphere)?

Gee, that seems prudent - There's no reason to think shutting one down will be of any benefit, is there? The leak is clearly NOT associated with an engine.



What about an imbalance of one wing tank full and the other empty in an emergency situation (after I have hastened the reduction in fuel quantity in one side)? Can I expect aileron trim (manual flight) to help me maintain straight flight, even if it means higher speeds required?

Yes, aileron trim (and maybe a bit of induced rudder trim too) should work, and I doubt you'll need more than normal cruise speed. But after the leaky tank is drained and you switch back to the opposite side, you'll be heading toward a balanced condition again.

Is there any reason to believe you won't have sufficient aileron available in an emergency unbalanced approach condition? I'm not 737 rated, so you'll have to tell me. Boeing certainly has the data.

One concern I might have is the FW CG condition from a full center tank.

[mbga9pgf]

Inexperienced at etops, but do pond crossings on a regular basis.

Thought process would go like this

1) Diagnose actual snag. If the gauge is going down, is it a leak or gauge error? I would suggest noting the trim gauge whilst sending either a trolly dolly or poss First officer down the back to see if you were trailing. IF it was a leak, move on....

2) Pan call and turn towards nearest Diversion. Decend A/R 500' for oceanic par example

3) if fuel leak could cause fire, (IE SPRAYING near nacelle) SHUT IT DOWN!!!! you should have plenty of gas to get back with one full wing and centre tank. Might be wrong tho. Do some perf sums at worse case (PNR?) and see what figures you get.

2) Cancel Ctr tank feeding, and feed engines tank to engines. Would not advocate feeding both engines from a leaky tank... Instead operate at Max continuous, whilst also transferring fuel into Main tank and possibly centre tank from leaky one. as to Structural fuel limits, Its a tough call... Id try to remain in as long as in doing so, I was not sacrificing Fuel to get to diversion (assume tank empty for rough fuel calc)

3) Think ahead. Is it worth landing with fuel leaking all over the shop? Is foam laying available? Fire carts a must I reckon. I would personally shut the engine down before it flamed out, then just top up the other tank A/R. I wouldnt worry about fuel emmissions in the environment, Ive heard about 50t thrown out with no comeback from greenpeace! Personally, you practice assy all the time, and would much prefer to land with one shut down than land with both working and 2 KGs per second flowing out the wing.

As I say, not the most experienced, but thats what id do at a push. Why not ring your sim guys and run a scenario? Or speak to your head honcho pilot? The only stupid questions in this game are those that arent asked then come back to bite you in the ass.

[jonny dangerous]

Gee, that seems prudent - There's no reason to think shutting one down will be of any benefit, is there? The leak is clearly NOT associated with an engine.


My thoughts precisely Barit1. Just that I don't see that specifically spelled out in my FOM. In a previous Airbus life, everything was pretty much identical QRH to QRH, SOP to SOP, and outfit to outfit. With Boeing, I am left somehow feeling that as my sim guy just said 2 wks ago,"Boeing assumes that you have a good working knowledge of the systems." Perhaps I had been lulled by Airbus's follow the ECAM (until such time as to do so would be less than prudent...) methodology. Now I am unsure if Boeing expects to me disagnose the above without the use of the NNC, or if it perhaps is something that was accidentally missed at the company level, or I am misreading the NNC. (Input needed from NG drivers)


Is there any reason to believe you won't have sufficient aileron available in an emergency unbalanced approach condition?

No Barit1, there isn't really. Just a limitation of 1000 lbs per side for random imbalance during normal ops. This being an emergency, that must go away, and certainly (Smokey?) it would have been flown during flight certification trials with a max imbalance.


2) Cancel Ctr tank feeding, and feed engines tank to engines. Would not advocate feeding both engines from a leaky tank... Instead operate at Max continuous, whilst also transferring fuel into Main tank and possibly centre tank from leaky one. as to Structural fuel limits, Its a tough call... Id try to remain in as long as in doing so, I was not sacrificing Fuel to get to diversion (assume tank empty for rough fuel calc)



Seems sensible advice to me, mbga9pgf.
One concern I might have is the FW CG condition from a full center tank.


I too had that concern. Then I thought of the swept wing design and the placement of the wing tanks is probably close to being near to inflight Center of Mass ranges. I rarely see it move appreciably during longer cruise segments.

I will definitely bring this to the attention of a TRI I know. Maybe he'll be able to shed some light. Any others with thoughts?
Thanks.

[barit1]

Some good brain-flogging going on here. Keep us posted, Jonny D!

[BOAC]

A leaking tank was an exercise presented to me once in RAF days and the procedure there was indeed exactly that - 'use it before you lose it'. There was no 'drill', just human logic.

That, (as a 737 pilot) is where I see the great divide. I have recently heard from an ex AB pilot (so this is very much 3rd-hand) of an AB 'event' where up popped the ECAM saying (in blue) 'Shut down engine using xxx button' (I'm not familiar with a/c!). The crew did just that. I am told the message actually meant 'when/if you shut down the engine, use the xx button' as apparently that would be the only way. The Boeing philosophy is to rely, as JD says, on 'knowledge'.

I'm sure somewhere I have seen a statement that a 737 will be controllable with one wing-tank full and one empty. I assume a low-speed handling check would be prudent in arriving at a Vref! C of G wise, as barit says, you are eventually going the right way on lateral balance, and I doubt you could get to a serious longitudinal C of G problem. My personal inclination would be to feed both off one tank if I was fuel critical - ie tight ETOPS, at least to use as much leaking fuel as possible (down to a prudent amount) and if possible it would be worth stopping every now and then to see if the fuel level has dropped below the 'hole'.

JD's scenario is one where there is no manufacturer's 'drill'. The only one is 'Engine fuel leak'. That will get you home UNLESS you do not have enough and there is nowhere else to land. There have to be some situations in flying where you make up your own solution.:)

[Shaka Zulu]

Indeed BOAC the 73 flies perfectly well with one maint tank full and one empty. But I would fly a little faster than Vref, just in case!
Trying to use the fuel in the leaking tank as much as possible, if the QTY drops below the hole then hopefully Suction Feed from the other tank will be enough so we don't get a flameout

[BOAC]

Pedant's hat on here, SZ:) Vref is going to be what YOU set! Hence the 'low speed handling check'.

[jonny dangerous]

Hi BOAC. Your comment about the AB does highlight the occasional hiccup that pops up during the ECAM approach to fault diagnosis, although I don't specifically remember that example. Most of the time it was simply action the instructions, wait for that line to 'turn white', and move on to the next instruction.

There were times, as a result of previously having run a scenario through the simulator, one might remember to go into the QRH for a little background either before or during the implementation of ECAM's suggestions.One of those scenarios might have been the fuel leak scenario, which was altered post Azores fuel incident.

I pose the fuel scenario now, though I was given a fuel leak in the simulator some time ago. Unfortunately, the exercise was set up differently: Short trip, no fuel in CTR tank, fuel leaking from right main tank. We, as a crew, followed the checklist (correctly we thought), and shutdown the right engine.

The leak continued. Then the TRI, who was new to the NG (ex 3,4,500), pulled the Fire Handle, to "see if that would stop the leak". It didn't. Then we tried to complete the exercise (short of time), having now forgotten the TRI had pulled the handle and not put it back down. Oops...

Well we farted around looking at runways, and weather, and briefing the purser, and then got set up to land, and then, (some of you may see it coming), NO FLAPS. Simultaneously looking up at the HYD panel above, and notice we have a B ELEC HYD PUMP OVHT, as well as a loss of SYS B pressure.

As were short on time in the sim due to tardy previous crew, we didn't get time past deciding we would execute a missed approach and try to figure out where things were. We eventully did, and then reflew the scenario the following day, with improvements.

As our company is halfway through ETOPS approval process, this fuel leak scenario is intriguing. I do think however, that the scenario of having fuel in the CTR and feeding the engines from there, offers more training possibilities for malfunction diagnosis and checklist usage purposes. Like arriving at your last "Equal Time Point", burning off the last half hour or so of useable fuel in the CTR tank then and noticing a leak. Now you're fuel critical...


Anyway gentlemen, that's the background. Thanks for your comments.

[jonny dangerous]

Further to the original scenario.

Were I in a situation with the CTR tanks empty (I am feeding right engine from right main tank), and still losing from the right main tank, I would then be unable to immediately diagnose a leaking tank, or an engine leak. Therefore I would follow the checklist's advice and shutdown the right engine. If the leak stopped, I would remain single-engined and crossfeed fuel as required to balance and use all remaining fuel.

If the leak continued, and the fuel remaining were enough to warrant salvaging it, I would give consideration to restarting the engine (it musn't be the cause of the leak, if with the engine secured, leak continues, correct?) and continuing diversion with two engines. I might, as above, open X-FEED and feed both engines from the leaking tank.

Again, attempting a restart under the above conditions is not considered in the NNC. But I would have to give it consideration as an option...

For those with no access to the NNC, the checklist commences by X-FEED closed, CTR TANK PUMPS off. This is done to identify 'which engine' is the source of the leak. Again, we are assuming an engine leak, and not a tank leak.

[Shaka Zulu]

Mea Culpa BOAC

[mbga9pgf]

Further to the original scenario.
Were I in a situation with the CTR tanks empty (I am feeding right engine from right main tank), and still losing from the right main tank, I would then be unable to immediately diagnose a leaking tank, or an engine leak. Therefore I would follow the checklist's advice and shutdown the right engine. If the leak stopped, I would remain single-engined and crossfeed fuel as required to balance and use all remaining fuel.
If the leak continued, and the fuel remaining were enough to warrant salvaging it, I would give consideration to restarting the engine (it musn't be the cause of the leak, if the with engine secured, leak continues, correct?) and continuing diversion with two engines. I might, as above, open X-FEED and feed both engines from the leaking tank.


Why not just fill the Ctr Tank with the Right tank Fuel (or at least to the gunnels) then feed both engines off the Right main tank, or, possibly feed From the Ctr once its full, and keep topped up from the Right Main? Suppose million ways of Skinning a cat!

[barit1]

Thought process would go like this
...
3) if fuel leak could cause fire, (IE SPRAYING near nacelle) SHUT IT DOWN!!!! you should have plenty of gas to get back with one full wing and centre tank. Might be wrong tho. Do some perf sums at worse case (PNR?) and see what figures you get.
...

Not really sure where the selector valves and associated plumbing are located, but I doubt that a non-selected tank could leak into a zone where an operating engine could ignite it. Even if the leak were in the wing lower surface directly over an engine, the worst that would happen is the fuel would be blown away by the cold fan exhaust.

[B737MRG]

If the leak continued, and the fuel remaining were enough to warrant salvaging it, I would give consideration to restarting the engine (it musn't be the cause of the leak, if the with engine secured, leak continues, correct?) and continuing diversion with two engines. I might, as above, open X-FEED and feed both engines from the leaking tank.


I agree with the restart option, but when opening the crossfeed (and selecting pumps from the Left Tank to OFF I suppose) there is no guarantee that fuel from the Left Tank will not escape via the same leak...?

[jonny dangerous]

737MRG, from what I see, there's no way to get fuel from left side to right side (check valves) or vice versa (so no danger there). There is no way to transfer fuel in flight in the NG, (other than the scavenge pump, from CTR to Left Wing tank) you can only "crossfeed" one engine from the opposite side wing tank. And that also applies to mba's statement about filling the CTR tank from the right side (not possible, other than scavenge pump CTR to Left Wing tank at 177lbs/hr).

In some aircraft (310/330/340 e.g.), there is a "trim" tank in the tail section that has the ability to transfer fuel forward to the CTR tank, but no lateral shifts (in modern era jet transports).

Any Airbus drivers care to supply the info as to whether there is a straight forward "Fuel Leak" checklist that describes both a tank leak and an engine leak?

Or perhaps the risk is so little, that manufacturers don't see the need for a true tank leak c/l?



Note: This Boeing website (http://www.boeing.com/commercial/aeromagazine/aero_09/fuel_story.html#table02) document spells out that casues of a fuel imbalance may include structural leaks, or a tank to tank transfer. I stand corrected on this second point.

[B737MRG]

This is the flow chart that will be printed in the 2006 update of the b737mrg :

link removed due PPRuNe advertising policy - apologies.

The logic is similar to what you have explained on this forum. All remarks welcome !

Pat

Oh yes, the flow chart refers to the NNC [Inadvertent Transfer of Fuel into Center Tank] which does not exist anymore on the NG (don't know why...)

[jonny dangerous]

Well sir, kick over a rock sometimes and look what you find...


Thanks very much MRG, will spend some time reading it. (PPrune to the rescue!!)

JD

[jonny dangerous]

By the way, what is the MRG? Maintenance Repair Guide? Could I assume that the NNC would receive some sort of update with respect to this, or will it be status quo as far as that goes?

Cheers.

PostScript: Okay, the Management Reference Guide. The first time that I heard of it. Will look at the website (and mention it at the workplace website as well).

JohnnyD (So no change to NNC then?)

[B737MRG]

- reply removed -
pat

[jonny dangerous]

Sorry to hear that Pat. If you had time for one last post...how do the pilots that have your book incorporate it into their company's ops. Consider the fuel imbalance flowchart you posted the link to, I mean how do I respectfully pull that out during a sim exercise and use it? Obviously the manufacturer's recommmendations are what they are, but from the feedback you're getting from pilots that bought the book, do they find the "enhancements" to the NNC useful and accepted by the training cadre at their companies?

Here I am creeping my own thread, but good information is sometimes hard to find...

JD

[B737MRG]

- I perform the recall items (if any)
- I use the QRH NNC and JAR OM B from the operator
- I do the management as I was trained to do

Time remaining I use other b737 guides to check for additional info

[jonny dangerous]

That would seem to cover all the angles. Cheers.

[Streamline]

It looks like Boeing has decided only to publish a checklist for "engine fuel leak".

They did not call it in a general way: "fuel leak" followed by a decision tree.

In my opinion Boeing has decided to focus only on the most probable cause related to a single failure only that would cause a leak.

Having said that it remains the responsability of the Captain to analye the situation differently if multiple failures are present. Use sound judgement, as such the MRG from my old collegue pat does fit in.

[jonny dangerous]

Good points Streamline. My quandary started initially doing the post-mortem on a sim session. That got me looking in detail at the Engine Fuel Leak checklist. Of course famialiarity with all NNC checklists would better enable us all to handle an airborne malfunction, but with this NNC it would seem especially prudent to do so.

In my opinion, this particular NNC leads a little to be desired. It might lead to a little confusion when faced with a leak. I think a proviso should be included at the start of the checklist to

"assume that any fuel leak is an engine fuel leak, and carry out the procedures described below. Further troubleshooting may lead to the diagnosis of a fuel tank leak, but the procedures described below, should, as a minimum, enable the aircraft to safely divert to a suitable aerodrome."

Or something like that.

Once diversion underway, then use the sound judgement and experience as appropriate.

Still really curious as how the Airbus ECAM/QRH handles the scenario.


POST SCRIPT: just found this Airbus presentation on fuel leaks:
http://www.pilotosdeiberia.com/areatec/airbus_sfo/13fuel_leak.htm


From that link, an excerpt:

3.2.4. Hole in wing or center tank

The ideal course of action would be to firstly use the fuel from the leaking tank to feed all engines. Thus increasing the amount of available fuel. However, it is highly unlikely that the crew will be able to confirm the cause of the leak. Also, the procedure would be relatively complex. As this type of failure is rare, the procedure to be followed is to select all the pumps off. Once the leaking tank is depleted, the associated engine will flame out.

[Streamline]

So in summary for the B 737 NG:

Fuel leak suspected.

Boeing states most probably comming from engine.

Shut down engine to confirm this is true.

If so thats the end.

If not leak is somewhere else.

Try to get as much fuel as possible out of leaking tank (Airbus)

Enentually restart the engine.

A bit strange at first glance but probability is on your side if you start by shut down.

[john_tullamarine]

Pat,

I hope that you discuss the advertising side with those further up the totem pole as it would be sad for your work not to be readily available to those on PPRuNe who might like to purchase the information.

Unfortunately, PPRuNe costs a truckload of money to run and Danny et al provide a great service to the aviating community generally at no cost to those who use it.

The "downside" is that those who can benefit commercially from it really need to make some contribution to what is a very directed marketing avenue for aviation things.

Personally, I hope that you continue to play in the sandpit as your accumulated knowledge represents a very useful resource for the readership.


On the "why doesn't Boeing put this or that in their books" question

(a) I can't speak for Boeing but consider

(b) they have to make it

(i) reasonably simple

(ii) sufficiently general to avoid having to tailor the documentation set for every individual aircraft and operator, and

(c) they have to have a consideration to the possibilities for Regulator certificate action and/or litigation

[B737MRG]

Hi John,

no worry, I understand.


Jonny,

I have updated the flow chart (added a drawing) - Comments welcome

URL deleted .. Pat, please send the reference to Jonny by PM

Pat

[jonny dangerous]

A couple of follow up questions about the Engine Fuel Leak NNC for the NG. We are still pursuing our ETOPs certification, and the topic of the fuel leak over the water came up at last week's meeting with the poohbahs. Given that the NNC gives the following (one or more) as evidence of a fuel leak:


- Visual observation of fuel spray from strut/engine
- Excessive fuel flow
- Total fuel quantity decreasing at an abnormal rate
- Fuel IMBAL indication
- USING RSV FUEL message
- INSUFFICIENT FUEL message
- CHECK FMC FUEL QUANTITY message


Question: When does the CHECK FMC FUEL QUANTITY message pop up. i.e. what criteria activate it. Is it a didfference between PROG page fuel qty and the digital fuel quantity of XXX kilos?

Question: For non ETOPs operations, we use the RSV field of the PERF INIT page to put in ALT + 30 MIN RSV fuel. So, this might be 3000 kilos or so. For ETOPS operations, we plann to land with FOD of 5000 kilos or so. Ergo, if you're getting the USING RSV FUEL message, you are well into the fuel leak. Are there any operators who put in a high amount on the RSV field of the PERF INIT to get this message sooner?

[BOAC]

I must stress this is not an SOP, but you could put the calculated 'critical' ETP fuel (that is PLOG calculated plus your 'extras for granny':) ) in as 'Reserves' - until you get there.