View Full Version : crossfeed valve check
Pleese, could anyone explain the reason of fuel crossfeed valve checking by pilots and marking this check in TLB.
Junkflyer
10th Nov 2009, 16:40
Not sure what airplane you are talking about, but crossfeeding is used for feeding from a different tank for an engine out or balancing wings if burn is uneven among other things. 747 classic has bigger tanks on the inboard section of the wing (and center if a big fuel load) so fuel is fed to outboard engines from here when necessary.
vwreggie
10th Nov 2009, 17:14
the fuel crossfeed check is done on 737 and I am assuming all twin engine jets as part of a set of procedures to allow a comapany to operate greater than 1 hour single engine flight ( approximately 400 nm 737) up to 2 hours 737-400 and 3 hours 737-800 from a suitable airport for landing. If you lose 1 engine you will need to access the fuel from the other tank and checking the crossfeed valve functions will be a pre requisite to allow the next sector to be operated extended range. The tech log entry records that the check has been made
lederhosen
10th Nov 2009, 17:22
The most obvious reason on the 737 is to check that in the case of an engine failure you can feed fuel from the dead side to the live engine. If you cannot it is a no go item. Marking this in the TLB is a means of making sure people carry out the check for example on extended overwater flights. In Europe there are not many sectors where this would be critical so my company does not require it. If you are in Russia maybe it is different.
Thanks, cf. It's obviously the crossfeed is checked to be sure the fuel from any tank can reach the operating engine in critical point, but at what stage does this check is usually done: preflight or inflight?
I don't remember the references but I think it may be concerned long-houl flights especially with prolonged operation in air-masses with very low temperatures which can affect the valves ability to operate.
In my ETOPS experience it was 'required' to be done towards the end of the ETOPS sector which satisfies the 'next sector' ETOPS requirement, but if the a/c has come off an non-ETOPS sector you would have no idea until the engine failed.....:confused:
Having found 2 x-feed valves actually seized in BA 737's in my time, I always checked it EVERY flight pre-flight anyway.
Checkboard
10th Nov 2009, 18:10
The crossfeed valve on the 737 is checked for ETOPS in the cold soaked condition - if the initial leg is non-ETOPS (i.e. an overland segment before heading into the ETOPS sector) then it can be done at the end of that leg, otherwise it is done before descent on the previous leg.
The 737 performs this check because it is fitted with a single crossfeed valve. The 767 (which is fitted with two valves) isn't required to perform a check (at least when I was flying ETOPS in Australia).
In the same sense, the 737 runs the APU throughout the ETOPS sector, to guarantee two sources of power after an engine failure - but the 767 doesn't need to, as it has a RAT (Ram Air Turbine).
FE Hoppy
10th Nov 2009, 18:20
Embraer 190 has a RAT but must run the APU for ETOPS. Also has the XFEED valve check and was required to have a second electrical system for operating the xfeed valve.
Checkboard
10th Nov 2009, 18:43
Does the 190 RAT provide electrical and hydraulic backup?
May be there are some references about in any ETOPS documents. I could not find.
FE Hoppy
10th Nov 2009, 19:08
RAT provides electrical backup. Hydraulic backup is by electric pump from the BUS that the RAT powers. Not sure if that makes it a yes or a no!!
The crossfeed valve on the 737 is checked for ETOPS in the cold soaked condition - not a lot of help if it has seized before departure, is it?
Oxidant
10th Nov 2009, 20:35
We are required to check it prior to the (ETOPS)flt (A320/321)
Checkboard
10th Nov 2009, 20:55
BOAC - I thought I was agreeing with you! Just explaining why it's normally checked on the previous sector - because that is when it's cold soaked and (presumably) the most likely to freeze up, if it is going to freeze up. :)
I think the answer for Yury is that we have not come up with any regulation requiring its check, but that it is a good idea to check it before an ETOPS sector, preferably on the ground where it can be fixed if required as well as in the last hour of cruise for the next ETOPS sector. Basic airmanship, I would suggest. Also a good idea to give it a quick check after a long leg pre-ETOPS (if you do that). I do not think it is practical to have it checked in the air on the trip before an ETOPS flight UNLESS it is written in the Ops Manual as a check EVERY flight, since I do not know of any crew that will reliably know the a/c is next departing on an ETOPS flight.
mustafagander
11th Nov 2009, 04:34
The B767 actually has an APU which is certified to start at high altitude and cold soaked. It is checked regularly when maint puts a notice in the tech log to start the APU nn minutes prior to descent.
The fact that the B767 also has a RAT has nothing to do with not running the APU continuously on an ETOPS sector.
As for checking the cross feed valve every sector, we always expected that it would be worn out the one time we needed to use it in anger. Later deliveries came with two cross feed valves, hence no in flight check required.
lederhosen
11th Nov 2009, 06:41
In reality we use the crossfeed almost every flight in order to comply with the centre tank fuel procedure on the NG.
leder - can you amplify that procedure please?
My research has been finished on the Australia CASA AIRWORTHINESS DIRECTIVE AD/B767/220.
Requirement: Unless previously accomplished, amend the aeroplane Flight Manual by including a statement to the following effect:This aeroplane should not be operated beyond the single engine cruise range of an
adequate aerodrome whilst on direct fuel feed, unless a satisfactory operational check of the fuel crossfeed valve has been carried out. This check should be performed during the last hour of the previous flight or prior to reaching the above critical phase of the extended range flight after adequate cold soak time at cruise altitude to include temperature effects on valve performance.
lederhosen
11th Nov 2009, 08:20
As outlined in our operations manual based on Boeing procedures (AD 2002-19-52 etc.) During climb or cruise set one centre tank fuel pump to off when centre tank fuel quantity reaches 950kg. Open crossfeed valve to minimise imbalance. Set remaining center tank pump to off and close crossfeed valve when MC and Fuel annunciator light iluminates. All dating back to the Thai explosion in BKK. Mod to avoid this being rolled out but procedure still in place.
vwreggie
11th Nov 2009, 08:58
the check for us is done as an SOP last 60 minutes of the flight. No tech log records as it is done normally as part of pre descent procedures.:ok:
TURIN
11th Nov 2009, 09:11
It used to be on the 737 RAMP1 (Daily) check many years ago. Never had one fail in 10 years. :ok:
leder - that is not the procedure I am used to for unmodified tanks. I cannot see how that eliminates the risk of ignition?
Turin - obviously not at LGW then?:)
Please, craig freier, may be you remember some references to any ETOPS manuals or so... In our TLB beside the "ETOPS flight performed" column there is the "Cross-feed valve check peformed" gap and my colleagues argue about it. I could find too little information, we don't have the company regulations concerned. I read one statement that in case of two valves installed the check was not required.
Yury - you need to state which aircraft you are asking about! Do we assume it is the B767?
lederhosen
11th Nov 2009, 14:15
BOAC that is straight out of our OM, which is Boeing procedure based. The idea is not to let a pump run dry. The master caution logic will only trigger if both are dry, thus the procedure of switching one off so you get a master caution warning. Minimum quantities are 2300kg for takeoff, 950 for climb and cruise and 1400 for descent.
But I am always keen to learn. How do you do it? Comparing notes like this is one of the main benefits of Pprune for me.
leder - we just used 2300/500 as per the AD (NB Not 930- where does that come from?) and 1400kg. BOTH Pumps off if below those figures, and allow scavenge to start to empty the tank in the cruise/descent phase. No crossfeed used (unless for balance). It seems to me that your procedure (as you wrote it) runs a main pump dry? We just turned off both while they were still 'fuel cooled'..........:) You also MAKE an imbalance.
From the AD, with my bolding
Both center tank fuel pump switches must be selected OFF when center tank fuel quantity reaches approximately 1,000 pounds (500 kilograms) during climb and cruise or 3,000 pounds (1,400 kilograms) during descent and landing.
lederhosen
11th Nov 2009, 16:34
Works a treat I promise you and the wording is straight from the OM, 950 not 930 was what I wrote, but that is by the by. Just goes to show there is many a way to skin a cat. I think the disadvantage of your procedure is that on the NG the scavenge pump only kicks in just below half tanks. We have been flying the NG from the beginning and I am confident we know what we are doing.
The problem as I see it is that your 'procedure' is contrary to the AD? I still read that you are running a pump dry? That is a no-no if the tanks are pre-mod. Unless you have a modified AD, where does 950 come from?
Sorry BOAC, I am looking for B767 procedures.
lederhosen
11th Nov 2009, 20:00
I'll PM you BOAC, taking Yury's cue we seem to be a bit off his topic.
mustafagander
11th Nov 2009, 22:17
Yury,
I think the AD you refer to in post #19 is superseded by the two xfeed valve installation.
Switching off one CWT pump almost guarantees an imbalance on the B767. As I recall it, the left pump feeds the left engine and the right pump the right engine. Each CWT pump only runs when its engine is above 50% N1.
porch monkey
12th Nov 2009, 07:25
Lederhosen is correct, as there are alternative methods of compliance with the requirement. We use the same method, but are now allowed to use centre tank fuel on one pump and crossfeed for descent until the Master Caution lights up. Didn't used to do that. Also, the same figures apply for us, ie, 2300/950 kg.
PM - Leder has taken this off thread by PM since it is 'off topic', but for you - of course if it is in the company manual it is 'correct' for a company pilot to do it. However, I have often heard pilots describe the (500kg) fuel remaining in the centre tank (following AD2002-19-52) as 'unuseable' - which it is not. The confusion I have is:
1) It seems to apply to post-mod a/c
2) If so, why not just run the tank normally? What does fiddling around with single-pump ops achieve? I can see no advantage and would be interested in the logic.
Do you have an AD ref for this procedure?
Perhaps a new thread is required or you can join the PM trail?
skerry
12th Nov 2009, 09:05
To come back to the 737;
BOAC, do you have a reference for the AD you are discussing? And what is the mod? And what effect does it have?
Presumably the point of fiddling with cross-feed and single centre tank pump operations is to ensure a Master Caution is generated when that pump runs dry; if both pumps are on then one may run dry for a considerable period, with no MC until the other does too.
But flying the Classic we only have restrictions on operating the centre tank fuel pumps on the ground.??
lederhosen
12th Nov 2009, 09:07
In our OM it is listed as AMOC to AD 2002-24-51. It also states 'During the last hour of cruise on ETOPS flights do a Fuel Crossfeed Valve Check.' So I am actually back on the original topic! I would be happy to discuss the 737 fuel system on another thread as it is self evidently not without its complications.
Thank you lederhosen, and do you state about the crossfeed check in TLB?
Best regards to everybody for discussion. I clarify at last the situation for myself. B767 FCTM states:
"...during the last hour of ETOPS cruise, the FAA currently requires that a fuel crossfeed valve check be performed on airplanes with a single crossfeed valve. This verifies that the crossfeed valve is operating so that on the subsequent flight, if an engine fails, fuel feed is available from both main tanks through the crossfeed valve."
Thanks...
New 737 centre tank thread!