14th Jun 2012, 12:55
Recently I have seen some Captains using the wing tanks before the centre tank on the 737-800 to avoid non environmental icing on long 4 hour sectors. I don't see this procedure written anywhere and I'm just wondering what other 737NG drivers think? I have also been told that flying high speed with the wing anti ice on during the descent can warm up the wing enough to avoid nei. Again this does sound a bit strange to me!
14th Jun 2012, 13:27
Can't speak to the NG specifically but I would expect that there is an AFM and WBM limitation requiring the use of centre before wing fuel due wing bending considerations ?
14th Jun 2012, 13:30
Sounds like a real good way to kill yourself...
Speed during descent will add to the fuel temp, but I would imagine it to be a negligible amount.
Wing A/I only heats 3 slats and would probably be outboard of any fuel that late in the flight.
These are captains you say?
Ask them to draw you the Boeing 737 CG movement vs. fuel quantity graph before they start switching off main tanks.
14th Jun 2012, 15:06
Please tell me the name of the airline so I can never, ever fly with them.
14th Jun 2012, 15:24
Just to make it clear, they don't burn the wing tanks completely first, just about 1500 to 2,000kgs from each side to apparently stop the fuel coming into contact with the top of the tank. These Captains are experienced with thousands of hours on type but it all sounds very dodgy to me:(
A much-discussed topic here if you search. It WAS done, quite safely and successfully, with all the caveats JT and others mention, and frequently avoided waiting for ice to melt where there was no de-icing. I believe the introduction of the 'FFIcing' lines on the wings made it no longer necessary.
If anyone cares to study 737NG weight and balance/limitations they will understand how it was done (or read the threads). It was not that difficult to understand.
Forgot to mention - it was written into a CAA approved Ops Manual.
14th Jun 2012, 15:46
The easy answer is of course what it said in Vol.1 Limitations:
Main tanks 1 and 2 must be full if center tank contains more than 453 kgs.
14th Jun 2012, 16:11
Thanks to BOAC. Unfortunately our airline has to have a completely clean upper surface, so even if we only have ice inside the black lines we still have to de-ice. It's a real pain in the rear end :ugh:
Bet they are pleased they spent the money on the mod!!! Flying into the the Med or other coastal strips you can really suffer. The best solution is to refuse any tankering where it will be a problem.
14th Jun 2012, 18:43
This question stems from the Boeing Bulletin fuel usage policy without modified centre tank fuel pumps, and then people using 'out of the box' ' lateral thinking'. This allowed the centre tank to have 2300kgs in it and use wing tanks first for takeoff. There was no instruction when to switch on the wing tanks on. Airmanship says that the centre tank fuel needs to be added to the a/c ZFW if the wing tanks are not full, but that was also not included in the bulletin. There was then a further instruction that in the descent the centre tanks should be switched off if 1400kgs were present. Thus in both cases wing tank fuel was used before centre tank was empty. If centre tank fuel is added to ZFW, and the total is below ZFW limits, I see no structural problem. The 'limitation' of fuel usage is another thing, but in the event of picking up NEI, and having no de-icing facilities available, I thought part of our job was to use our technical nouse and be preventive. There is a conflict in 'limitations' and one has to choose the lesser of 2 evils.