View Full Version : 777 fuel leak

6th Sep 2007, 16:10
Can anyone please explain the symptoms / indications of a tank leak as opposed to an engine fuel leak in the 777 or similar fuel systems?

How would I know which one it was?

Many thanks:rolleyes:

6th Sep 2007, 16:42
Have a look?

6th Sep 2007, 16:52
a drip from the wing?????:E

6th Sep 2007, 18:59
The O-rings at the fuel boost pump just outboard of the gear tend to leak. As long as the wing is cold soaked, no problem, but ....
Other possibilities are loose tank entry plates.

[email protected]

7th Sep 2007, 01:20
Ha- yeah

Apologies, I meant from the cockpit in flight. In terms of CALC /TOT, total fuel descrep etc?

Thanks thou

7th Sep 2007, 02:56
Correct me if I am wrong; I did come across a bulletin a long time ago that the Boeing B777 QRH non-normals on fuel leak assumes an engine fuel leak if the leak rate exceeds 1000lbs per 30 minutes. As such one can possibly shut down a good engine when there is a leak from the tank ( assume no visual sighting of leak ) or from the fuel manifold prior to the spar valve.
Queries to Boeing receive an ambiguous and non definitive reply that the ECL and QRH procedures are sufficient to address all fuel leak scenarios. This has led to many to assume that leaks from fuel manifold before the spar valves or fuel tank leaks as improbable without visual detection. Sadly there are too many " ASS U ME " s here:ugh::{

7th Sep 2007, 06:10
This is exactly my point. The checklist calls for an engine shutdown but this certainly won't help if it's a tank leak......

7th Sep 2007, 07:12
That checklist is only meant for engine fuel leak,read the condition properly.Somehow I think a more appropriate title should be used.

7th Sep 2007, 07:14
That's why the title of the checklist is ENGINE FUEL LEAK CHECKLIST, there's nothing much you can do about a leaking fuel tank.

If it's an engine leak and you can stop it by shutting the engine down and closing the spar valve at least you haven't lost much useable fuel.

However if it's a tank leak about all you could do is feed all engines from the leaking tank until it's almost empty and then switch to the good tank.


7th Sep 2007, 08:51
jack - there is NO way you will know from the cockpit. You will have to get out of your seat and go and have a look.

7th Sep 2007, 09:14
Thanks guys - appreciate the input

I do understand the need for a visual inspection. The checklist is designed for an engine leak alone and no, nothing for a tank leak. If the checklist is therefore followed to the T you may not have the desired result.

The 200 assumes a centre tank issue if I'm not mistaken but the 300 is a little different.

I am merely seeking advice from the more experienced of you that have considered this situation

7th Sep 2007, 10:31
I know a former colleague who had an actual engine fuel leak. As far as I can remember he stated that he was unable to ascertain whether it was a tank fuel leak or engine fuel leak. From the ECL and QRH non-normal checklist, he knew that the latter portion of it addressed an engine fuel leak but conditional on visual observation or the leak rate of more than 1000lbs per 30 minutes. As the leak rate was far less than 1000lbs per 30 minutes and there was no visible sighting ( night flight ), he was unable to definitely nail it as an engine fuel leak. Due to the frequent fluctuations in fuel totaliser quantities very common on the B777, even with inflight real time data transmissions of aircraft engine and fuel parameters to maintenance control, the maintenance and engineering personnel were convinced that it was a false alarm due to totaliser fluctuations and he was instructed to continue to destination by both the dispatch and maintenance controllers. As the difference in left and right wing tank burn off ( as per the checklist ) was only about an average of 200lbs-500lbs per 30 minutes and no visible sign of any fuel leak from engines and tanks, he was reluctant to conclude that it was an engine fuel leak, but he was fully convinced that there was a fuel leak somewhere. He countermanded company despatch and maintenance instructions and diverted to a suitable alternate but kept the engine on the suspected side at reduced thrust, with plans to fully shut it down once he get confirmation from airport safety inspection vehicles after landing. Due to ETOPS considerations and possible lightning activities he chose not to shut down or proceed to the nearest alternate. After landing, airport safety vehicle found a small fuel leak from one of the engines and he promptly shut it down right after touchdown. For all his efforts he was grounded and a " kind of punished " for countermanding company instructions. The company claimed in its findings that Boeing recommended following the QRH and ECL closely with the ambiguous remark that the checklist addresses and assumes engine fuel leak, not other fuel leaks. His contention that fuel leak was far less than the criterion of 1000lbs per 30 minutes was not addressed and so were the possibility of tank or manifold leaks were similarly dismissed. Similarly his contention that the checklist did not have a an indent to definitively define it as an engine checklist were rejected. So as we can see, Boeing checklists do have grey areas and pitfalls.

7th Sep 2007, 12:51
Thanks very much cruiser - Good info

Brian Abraham
8th Sep 2007, 03:46
For all his efforts he was grounded and a " kind of punished " for countermanding company instructions.

Worrying. Management face saving? Not their asses or licence on the line. Fuel leaking any where is a problem, and who's to say that a seemingly minor leak is not about to turn into a gusher. Absolute correct decision made by the crew in my humble opinion.

8th Sep 2007, 15:15

My QRH checklist is only titled as Fuel Leak,is yours different?

8th Sep 2007, 15:40
G'day Flightleader,

I was just going on my experience with other Boeing aircraft I have flown where the checklist specifically mentions 'engine fuel leak'. I haven't flown the 777 so I don't have specific knowledge of that aircraft.

Does the B777 'fuel leak' check list cover both engine and tank leaks? If so I'd be interested to know what action is recommended for a tank leak.


8th Sep 2007, 17:53
This subject has always intrigued me because of the before-mentioned grey areas. My comments refer ONLY to B767 and any corrections are welcome.

My thinking is, 3 possible areas to be identified for the leak:
1. Downstream of the Engine Valve, in which case possible indications are higher fuel flow and greater Fuel Used (FMS) on the affected side. Engine Fuel Leak, which the Engine Fuel Leak Checklist should resolve by shutting down the engine.

2. Between Engine Valve and Spar Valve, in which case the only indication is affected Tank quantity reducing at a greater rate. Fuel Flow and Fuel Used (FMS) indications would be normal. Carrying out the Engine Fuel Leak Checklist should resolve by shutting down the engine (closes both the SparValve and Engine Valve).

3. Prior to the Spar Valve (and somewhere in the tank area); after shutting down the engine as per the Engine Fuel Leak Checklist, the indicated fuel quantity continues to reduce. Boeing does not address this situation and provides no guidance. Perhaps, the catch-all 'Commander's judgement' could be applied here, with the POSSIBILITY of re-starting the engine and consuming the remaining fuel (remembering that shutting the engine down did not resolve the initial problem).

An interesting incident was the 777-200ER departing LHR about 3 or 4 yrs ago streaming fuel out of the center tank via the Left Wheel Well. This was observed by the tower, other aircraft and left a 2 nm plume. It was caused by a 2.5 inch opening in the aft wall of the Center Tank at approx the 30,000 kg level. The opening was a Purge Vent and the cover plate had not been re-installed! Lucky there was no Rejected Take Off as the resulting brake temps would have ignited the fuel.

Input please.........

8th Sep 2007, 23:29
Perhaps, the catch-all 'Commander's judgement' - yes, the best solution would be to restart the engine and cross-feed the other from the leaking tank if fuel is critical - BUT be careful not to lose both!

9th Sep 2007, 06:28
Out of interest what would be the max fuel imbalance allowed and still maintain controlability, when running both engines from the same tank?

9th Sep 2007, 08:00
Thanks BOAC /gimmesumvalium

Good info - In fact the 777 is very similar in terms of the fuel/ engine relationship.

I find in interesting that Boeing only issues information for engine leak only and that the checklist only allows for this option. I guess as you say, if you follow the checklist and subsequently the fuel continues to indicate a loss - you would determine it may be a tank problem and crossfeed to the good engine. (even restart)....FMC fuel remaining would be useless and some quick calculations would be necessary

Practically speaking - a visual inspection may show up nothing. In the incident mentioned the pilots only knew of the leak after they were alerted from another aircraft at the hold point (due centre tank)


9th Sep 2007, 08:55
Good info you guys placed here.

I have been flying all sorts of 777 for the past ten years and to be honest, never gave too much thought on fuel leaks.

What Boeing tries to do is to give us some sort of guidance for possible failures and as they state in their manuals, they cannot write a checklist for everything. The crew judgment, after consulting engineering and other sources, is still the best option for unexpected and not-checklist-covered events. The crew must avail of the technical information provided by the experts on ground; however, it is up to the commander to decide the best course of action. IMHO, the guy who landed against company recommendation, did the right thing. The folks on the ground are not under pressure, they have the books in front of them, the coffee is ready, and everything seems to be all right. :E

9th Sep 2007, 12:58
Jack - the point of getting out of your seat would be to hopefully ELIMINATE the engine leak (not PROVE the tank leak) as if it is significant you will have a good chance of seeing it (even at night, when there is nearly always some background light - I speak from a few years of flying visual identifications on unlit targets. Only once out of many was I unable to see something). Of course, if you are in a Tristar or...............:)

'Max fuel imbalance' would be determined by controllability rather than manufacturers' limits if fuel quantity becomes a life-threatening issue.

9th Sep 2007, 21:07
787cruiser, if you are referring to the incident a few years ago on a pacific rim carrier I think it was not punishment per se ( for the PIC ) but delays in the findings caused by power play between the line operations and maintenance divisions against the safety division. This led to the extended grounding of the PIC casting aspersions that the company had found fault in his decision. The line operations division which ran the dispatch department and maintenance division were trying to cover their asses; the safety division did not know how to deal with issue when the PIC was clearly right but the other divisions called for his head. The issue was left hanging with the PIC finally cleared to fly without any resolution except for the Boeing letter reminding crew to stick to QRH/ECL procedures and that the fuel leak checklist assumes leak from strut to engine.

10th Sep 2007, 06:10
Out of interest what would be the max fuel imbalance allowed and still maintain controlability, when running both engines from the same tank?

From the 777 Flight Crew Training Manual:

"The primary purpose of fuel balance limitations on Boeing aircraft is for structural life of the airframe and not for controllability limitations."

"Lateral control is not significantly affected when operating with fuel beyond normal balance limits."

"The primary purpose for fuel balance alerts are to inform the crew that imbalances beyond the current state may result in increased trim drag and higher fuel consumption."

10th Sep 2007, 13:12
I had the chance to see fuel dump on the B777 myself(enroute diversion trying to save 1 pax's life),that's visible!! But engine fuel leak would be alot harder to spot.Smaller in volume and possibly somewhere below the big engine.

Sink Rate
10th Sep 2007, 20:38
The 777 checklist is only entitled FUEL LEAK.

We are considering very different cases with regard to an Engine Fuel leak and a fuel leak elsewhere (tank, line, pump etc).

The checklist actually assumes an ENGINE fuel leak, but sadly doesn't state that in either the Electronic checklist (ECL) or in the paper QRH.

Sadly in the case of a fuel leak not in the engine, blindly following the checklist may lead to problems.

It advises to shut the engine on the affected side down in the assumption that that will stop the leak.

It then advises that normal fuel balancing can be actioned. Not a great idea if shutting the engine down didn't solve the problem. You will now be in the position of pumping useable fuel from the good tank across to the other side and overboard. oops!

So there you are, mid atlantic, engine shut down, leaking fuel out of both tanks!! Doh!!

Consider the Airbus that managed to glide into the Azores. They were lucky...

PS TOP TIP - When the Fuel Imbalance message is displayed after an engine failure don;t just assume its due to an engine being shut down. Do make a positove immediate check as to whether you have developed a leak (a la Concorde). A quick look of Calculated vs Totaliser on progress page 2 gives a quick confidence check.

happy flying.


10th Sep 2007, 23:41
Hi Sink Rate,

Thank you for your well considered post. The fore-mentioned former colleague of mine indeed made these considerations during the incident. He deduced that there was indeed a fuel leak ( in spite of the fact that some B777 totaliser do behave wildly at times with fuel differences between calculated and sensed going as high as 6000lbs to 7000lbs ). However the leak rate was far below that ballpark figure of 1000lbs per 30 minutes, and there were no unusual fuel flow/fuel used indications. Even the maintenance control with real time engine data monitoring was fooled by the fluctuating totaliser readings, low leak rate and normal engine/fuel parameters. He realised that shutting down an engine during ETOPS operations would bring about more operational and safety issues especially that most of the available suitable airports and diversionary routes on that particular night had thunderstorm activities which could prove fatal in case of lightning strike should he still be leaking fuel in spite of engine shutdown. Like someone indicated, the engine could be restarted but during the time needed to positively ascertained that it was not an engine leak, the aircraft would have to be drifted down to cloud laden lower levels which he wanted to avoid. In his case it indeed turned out to be a small engine fuel leak; and the despatch and maintenance guys were all out to cover their embarassment. The safety guys were initially not happy that he did not follow Boeing procedures to shut down the engine...the safety dept was dominated by B744 guys who knew next to nothing about the intricacies of real life ETOPS operations.

As I had indicated earlier, the Boeing fuel leak checklist has pitfalls exactly as you alluded to...normal fuel balancing after the engine shutdown. I there is indeed a tank fuel leak and the engine shutdown without the crew being any wiser, it can be disastrous.

I was initially not aware of this fact, but that particular captain pointed out to me that he was well aware of the fact that the fuel leak checklist did cover other fuel leaks as well a engine fuel leak with the provision that visual confirmation being vital. The portion of the checklist dealing with engine fuel leak is generally misinterpreted by most crew memebers. He maintained that if there are procedural steps following a statement in the checklist, those procedural steps WILL HAVE AN INDENT immediately below that statement. This was something he tried enlightening the safety dept, but the B744 aces over there just laughed it off as a despaerate line pilot clutching at straws to prove his point! I learnt something old but highly forgotten.

11th Sep 2007, 01:31
Correct me if I'm wrong

Does the checklist not allude to the fact that correct normal fuel management procedures are used post shutdown....i.e remaining fuel can be used for the operating engine..?

Hence (assuming an engine leak)...the way I read the CL

You would use from the "live engine" tank til FUEL IMBAL displays then balance from the high tank (assuming no tank leak)

If it was a tank leak I don't believe the CL infers you balance from the good side to the leaking tank


11th Sep 2007, 02:08
Jack, you are right...what Sink Rate alluded to was " blindly " following the checklist and thereafter " blindly " ( highly unlikely, but does happen ) crossfeeding in " normal fuel management ". It is certainly hoped that this will not happen but in a stressful situation coupled with rapid loss rate and unreliable totaliser/fqi one cannot discount such possibility.

Mind you, I have seen 3000+ flight hours F/Os with ATP who are made cruise captains fouled up fuel management in this fashion in the simulator LOFT with fuel leak/engine leak problems!

11th Sep 2007, 02:55
Thought so....just wondering if I was missing something....Thx

Sink Rate
11th Sep 2007, 03:20
The checklist in itself doesn't differentiate between what type of leak you are dealing with (which IMHO it should).

It thus STATES in no uncertain terms that once the engine is shut down normal fuel management (ie balancing) can be accomplished.

In the cold light of day we have had the chance to think about it and common sense prevails that in the event of a tank leak then cross feeding would probably be unwise.

Having seen a tank fuel leak about 50 times now (in the simulator at least) I could tell you 50 different ways that line crews might handle it, some better, some worse.

What is apparant though is a reluctance to stray away from a checkilst even when it goes against common sense.

Its all about the big picture....:ok:

13th Sep 2007, 00:55
787cruiser, Sink Rate, Jack, etc. I believe Boeing has changed the fuel leak checklist several times after the incident mentioned by 787cruiser. The present checklist DOES NOT mention ENGINE FUEL LEAK after the condition of imbalance of 1000lbs per 30 minutes or more after initiating the checklist procedure. Billabongbill, I believe that was the incident of mentioned. Kudos to the PIC who had the guts to defy the know - alls from dispatch and maintenance who had all the time to scrutinise the real time data at leisure in the comfort of their snug offices on the ground, and still erred in their assessment! I had flown many times with the skipper of that flight and found him to be a consummate B777 operator. Sadly, he came from the backwaters of SEAsia and the powers that be deemed fit to let him sweat while they quibble over who to blame!

13th Sep 2007, 02:53
Right woody, had an observation flight with that skipper many years ago in & out of ORD and SFO. Pretty proficient and knowledgeable chap.
I understand that the dispatch and maintenance insisted that he return to home base when he exercised his command authority to make a precautionary diversion, and he countermanded that too. The company blokes must have been mighty pissed to be refused thrice!! Small wonder they decided to make him sweat before clearing him.

14th Sep 2007, 04:01
Woody & Billabong,
Sorry to hear about your PROFESSIONAL colleague's trauma. He is the sort of guy we need and would welcome in our outfit.

14th Sep 2007, 04:27
160 kts & BuzzBox,
Our 767 Sim training indicates no controllability problems (1 wing tank empty/1 wing tank full) (confirming Boeing's view).
In fact, with the engine shut down as per the checklist, all the control inputs are generally neutral (due to the heavy wing compensating for the yaw! tank on the good side FULL).
Perhaps JSA, MFC, LER, JOC, or JME could shed light on this subject on behalf of Boeing ( or perhaps anonymously!!!)

Brian Abraham
14th Sep 2007, 04:46
With respect to the command authority vice despatch, management etc can't help but think of a quote from either Len Morgan or Ernie Gann

Career flying is an uptight, stressful occupation. Laymen have little conception of the pressures under which a professional works. His work is regulated to the point of absurdity by non flying management and federal officials who pretend to understand flying better than he does. He carries a thick book of rules so confusing even its authors can’t explain them. In effect, a committee of deskbound experts ride with him on every trip, instructing, admonishing, warning, watching – until there’s a problem.Then all fingers are pointed at him.

30th May 2010, 11:37
I know this is an old thread but Boeing still haven't changed the checklist.

In my humble opinion the only way to determine if it is an engine leak or a tank leak is to pull the fire handle after shutting down the engine. This closes the pylon valve. If the leak continues then it is a tank leak. If it stops it is an engine leak.

It is my understanding that certification requirements define an engine leak as being between the pylon valve and the engine.

Clearly if it is a tank leak the engine may as well be restarted. Boeings checklist is very poor in this regard. It will save the day inall cases but can result in unnecessary single engine operations.

Some will argue you dont need to pull the fire handle and that once the engine is shut down continued leakage is a tank leak. This is not correct as there is still stuff between the fuel cuttoff valve and the pylon valve that could be leaking.

30th May 2010, 23:17
You are right. It is worth remembering that pulling the fire handle does involve any irrevocable action.

1st Jun 2010, 17:26
The book say:

• Opens the spar fuel valve
• arms the engine fuel valve (the EEC opens the valve when required)
• arms the selected ignitors(s) (the EEC turns the ignitors on when
• opens the spar fuel valve
• opens the engine fuel valve
• turns ignitors on.
• closes the fuel valves
• removes ignitor power
• unlocks the engine fire switch."

B777 fuel control switch actually control the spar valve as well as the engine fuel valve. Thus, not required to pull the fire handle.Of course, fire handle will also do the job of the fuel control switch.

If the centre tank has fuel and either wing tank loses fuel profusely, it is likely to be a tank leak as engine fuel leak would deplete centre tank fuel instead of wing tank fuel.

Have a look at the fuel schematic, notice how near are the spar valves to the engines? Personally, spray observed downstream of the engine pylon can be treated as engine fuel leak as closing the spar valve (by fuel control switch or fire handle) would stop the leak. But tank or pipe line leak upstream of the spar valve have no way to plug it. Also, very hard to pin point the actual leak location.Thus, a land ASAP may be a best option if unable to make destination. Don't forget fuel gauge error can appear to be fuel leak too. Leak downstream of fuel metering unit can cause a reduction of thrust even with thrust level at full forward.Fuel flow would be normal. Shutting it down would stop the leak.

Had a actual wing tank crack some time back in a B737 on a 2hrs flight over water. Captured the leak rate for 30mins then projected the total lost.Proceeded to destination with 700kgs lesser than planned. Saw the ground crew jumping like frog-on-a-hot-wok while docking in as the right wing was dripping.