B737 cross-feeding after engine close down
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B737 cross-feeding after engine close down
When I did my B737-200 rating under a Boeing instructor 24 years ago, part of the engine failure and shut down drill was cross-feed valve open. The wing tank fuel pumps were left on. In fact with engine failure above V1, the PNF got the APU on line and cross-feed valve open within a few seconds of engine failure. This saved fuel imbalance problems at a time when hands were full coping with one-engine inoperative and sorting out where to go navigation-wise.
I understand that this policy is no longer valid and that Boeing (?) require that following (say) engine failure at V1 you have to wait for the imbalance to occur. Then, after it reaches the maximum im-balanced permitted, you open cross-feed and switch off the fuel pumps of low contents side until fuel balanced, then back to normal feed until the imbalance again rears its ugly head. Repeat ad nauseum until safely on the ground.
I understand that the "old" procedure lost favour due possible differing fuel pump output could white-ant attempts to keep fuel balanced. Is that a correct assumption?
Before my old company arranged simulator re-current training, we practiced simulated engine failures in the real aircraft by throttling to idle at V1 or just after, then flogged around the circuit or instrument approaches. With the old system of cross-feed valve immediately opened a few seconds after simulated engine failure, we never experienced fuel imbalance on one engine inop. Maybe all the pumps gave same output?
Now what I see in the simulator, is after engine failure at V1, the crew stuffing around with fuel pumps and cross-feed and often forgetting to monitor the cross-feeding with two pumps off. In fact, often the fuel imbalance becomes reversed because the crew are too busy coping with the one engine inoperative game plan.
It seems to me that in attending to a supposed problem of possible fuel pump unequal pressure output, there is a far greater danger of inadvertent significant fuel imbalance than there was with the "old" method of simply opening the cross-feed valve immediately after engine close down and leaving all wing tank fuel pumps on.
Anyone struck this situation during one-engine inop flying in the simulator? ie forgetting to continually switch fuel pumps on and off as part of cross-feeding policy?
I understand that this policy is no longer valid and that Boeing (?) require that following (say) engine failure at V1 you have to wait for the imbalance to occur. Then, after it reaches the maximum im-balanced permitted, you open cross-feed and switch off the fuel pumps of low contents side until fuel balanced, then back to normal feed until the imbalance again rears its ugly head. Repeat ad nauseum until safely on the ground.
I understand that the "old" procedure lost favour due possible differing fuel pump output could white-ant attempts to keep fuel balanced. Is that a correct assumption?
Before my old company arranged simulator re-current training, we practiced simulated engine failures in the real aircraft by throttling to idle at V1 or just after, then flogged around the circuit or instrument approaches. With the old system of cross-feed valve immediately opened a few seconds after simulated engine failure, we never experienced fuel imbalance on one engine inop. Maybe all the pumps gave same output?
Now what I see in the simulator, is after engine failure at V1, the crew stuffing around with fuel pumps and cross-feed and often forgetting to monitor the cross-feeding with two pumps off. In fact, often the fuel imbalance becomes reversed because the crew are too busy coping with the one engine inoperative game plan.
It seems to me that in attending to a supposed problem of possible fuel pump unequal pressure output, there is a far greater danger of inadvertent significant fuel imbalance than there was with the "old" method of simply opening the cross-feed valve immediately after engine close down and leaving all wing tank fuel pumps on.
Anyone struck this situation during one-engine inop flying in the simulator? ie forgetting to continually switch fuel pumps on and off as part of cross-feeding policy?
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In my company the procedure is roughly as follows:
If you get an engine failure at V1, after the memory-items you do the clean-up. Then the emergency checklist, in which you find the item fuel balancing. Uptil now, nothing`s done with the fuel system.
Then you switch the crossfeed open, fuel pumps low side off, and here`s the nice part: We set the timer!. We calculate how many minutes we`ll need to be crossfeeding at 40 kilo`s per minute, and we set the timer. This timer is a add-on on the whole fleet. Brilliant add-on.
When the timing is over, and the fuel balanced, we switch on all fuel pumps and leave the crossfeed open, until final approach, when the crossfeed needs to be closed because of certification demands.
Golden rule: Whenever we do anything with the fuel panel we set the timer.
If you get an engine failure at V1, after the memory-items you do the clean-up. Then the emergency checklist, in which you find the item fuel balancing. Uptil now, nothing`s done with the fuel system.
Then you switch the crossfeed open, fuel pumps low side off, and here`s the nice part: We set the timer!. We calculate how many minutes we`ll need to be crossfeeding at 40 kilo`s per minute, and we set the timer. This timer is a add-on on the whole fleet. Brilliant add-on.
When the timing is over, and the fuel balanced, we switch on all fuel pumps and leave the crossfeed open, until final approach, when the crossfeed needs to be closed because of certification demands.
Golden rule: Whenever we do anything with the fuel panel we set the timer.
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For the fear of getting an imbalance of fuel if you just open the crossfeed after an engine failure, Boeing wants us to balance fuel when necessary. That way we are guaranteed to get the maximum imbalance possible if we forget to constantly monitor the fuel system. Makes sense if you're, eh, if, that is, maybe...
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Out of interest, in BA there is no requirement to close the cross-feed for landing, so I assume that the 'certification' you refer to is a FAA-only thing? Once opened in the drill it stays open, with balance monitored by the timer referred to above.
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Fuel balacing is considered part of cockpit management, during normal or non-normal operations. An important consideration during takeoff and landing with crossfeed valve open, is that leaving it open would increase exposure time to an event, like compressor stall with severe damage or an uncontained engine failure which causes debris to penetrate the crossfeed fuel line.
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Our company policy (UK 737 classic operator) is to have the crossfeed closed during asymmetric flight and allow an imbalance to occur up to but not exceeding 453kgs. You then crossfeed to imbalance up to 453kgs the other way and so on. The aim of the game is not to exceed 453kgs and to try and judge it so that you land with a zero imbalance. Not easy while managing the whole engine out problem.
When I did my 737 conversion, after flying many aircraft with more complicated fuel systems and crossfeed methods, I questioned this technique and asked why not just leave all pumps on and have the crossfeed open to allow the engine to draw fuel equally from both tanks. The answer I was given was that the check valves in the tanks may have slightly different pressures so an unintentional and hence unnoticed imbalance could occur. Personally I think I would rather to take my chances with the pump pressures being close enough to maintain an acceptable imbalance, rather than me not cocking up the crossfeed in the heat of the moment.
There is also the whole issue of the crossfeed valve itself, I remember a particularly keen trainer failing this valve on me during an IRR (when the IRR had to be done without a/p or f/d) because I did not check that the VALVE OPEN light changed from bright blue to dim blue each time it was moved. The all pumps & crossfeed open method would also solve that problem.
If anybody has a Boeing reference for this method and a good reason why we have to do it this way I would like to hear it.
S & L
When I did my 737 conversion, after flying many aircraft with more complicated fuel systems and crossfeed methods, I questioned this technique and asked why not just leave all pumps on and have the crossfeed open to allow the engine to draw fuel equally from both tanks. The answer I was given was that the check valves in the tanks may have slightly different pressures so an unintentional and hence unnoticed imbalance could occur. Personally I think I would rather to take my chances with the pump pressures being close enough to maintain an acceptable imbalance, rather than me not cocking up the crossfeed in the heat of the moment.
There is also the whole issue of the crossfeed valve itself, I remember a particularly keen trainer failing this valve on me during an IRR (when the IRR had to be done without a/p or f/d) because I did not check that the VALVE OPEN light changed from bright blue to dim blue each time it was moved. The all pumps & crossfeed open method would also solve that problem.
If anybody has a Boeing reference for this method and a good reason why we have to do it this way I would like to hear it.
S & L
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Centaurus I am with you. On the DC9 and the 737 and also the B767 the crossfeed was opened and left open. It is true that unequal pump pressures may result in some imbalance in which case pumps on the low side are turned off and then turned back on when in balance.In fact I have seen this imbalance occur during actual engine out training in the B737/767 having conducted this type of training over many years.
Why Boeing have changed this I can not comprehend. It makes no sense to hasten to an unfavourable imbalance when by opening the crossfeed the rate of imbalance, if it occurs, will be reduced and in fact may be in the favourable direction.
Indeed there is a good possibility that the maximum imbalance will be exceeded if delayed on take off on the 767 with full wing tanks when the maximum imbalance is 680kg but the warning is set to 1100 kg.
Of course it is always important to monitor fuel contents but opening the crossfeed early reduces workload significantly.
Typo's again!!
[This message has been edited by pterodactyl (edited 23 April 2001).]
Why Boeing have changed this I can not comprehend. It makes no sense to hasten to an unfavourable imbalance when by opening the crossfeed the rate of imbalance, if it occurs, will be reduced and in fact may be in the favourable direction.
Indeed there is a good possibility that the maximum imbalance will be exceeded if delayed on take off on the 767 with full wing tanks when the maximum imbalance is 680kg but the warning is set to 1100 kg.
Of course it is always important to monitor fuel contents but opening the crossfeed early reduces workload significantly.
Typo's again!!
[This message has been edited by pterodactyl (edited 23 April 2001).]
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CaptainSandL,
I'm not sure you can find it on the web. I've got my copy some years ago with my airline and it has 131 questions from B737 operators. There, you can find these two questions and the Boeing point of view about the use of cross-feed valve during single engine operations and during takeoffs and landings to avoid fuel imbalance when the center tank has 453 kgs or less.
Regards, Captain.
I'm not sure you can find it on the web. I've got my copy some years ago with my airline and it has 131 questions from B737 operators. There, you can find these two questions and the Boeing point of view about the use of cross-feed valve during single engine operations and during takeoffs and landings to avoid fuel imbalance when the center tank has 453 kgs or less.
Regards, Captain.
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Had a Sim session not that long back that had dual failure scenario of 'N-1' and then 'Inadvertant fuel into CWT'. The N-1 approach ECL actions required cross feed off which we did, however, that just set up the next phase of Inadvertant fuel into CWT which you had to go through again after the Go Around (IMC at Minima ... of Course !). On de-brief the instructor recomended leaving the CWT pumps ON and the X-Feed open despite the N-1 approach ECL. The reasoning being requirements of dual failures which the ECL does not address, may have higher priorities than the ECL actions for an individual problem. So in this case X-feed open on the approach was not seen as a problem, or it was the lesser evil. Quite interesting eh!
