Fuel transfer prohibition during takeoff/landing? Reference?

ZapBrannigan

ZapBrannigan

If it ain’t a Boeing, I’m not going. No choice.
I seem to remember reading or hearing somewhere about a Part 25 certification requirement ... or perhaps a Part 121 regulation that prohibits the transfer of fuel during takeoff or landing (tank to tank, etc)

Has anyone else heard of this and, if so, could you provide a reference? Thanks!
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

ZapBrannigan said:
I seem to remember reading or hearing somewhere about a Part 25 certification requirement ... or perhaps a Part 121 regulation that prohibits the transfer of fuel during takeoff or landing (tank to tank, etc)

Has anyone else heard of this and, if so, could you provide a reference? Thanks!
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Not a clue man Zap, I do know that we have that restriction on the Dash 8 while they give no reason I assume it is because instead of using an AUX pump to back up the engine driven and scavenger fuel pumps you are using to to tansfer.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

Tank to engine to comply with 25.903 (b) (1) (2).
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

That's certainly in the right direction. I'm trying to find a source that explains why moving fuel between tanks would be prohibited during takeoff and landing. Takeoff seems like a no-brainer. Landing, not as much since, presumably, you've flown to your destination using that fuel the whole time, so the likelihood of contamination at that point is nil.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

i don't think fuel contamination is the concern, i think it's to help ensure a disruption in the fuel flow wouldn't affect more than one engine during critical phases of flight.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

ok, that makes sense. Thanks.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

In the ERJ we were told in systems it's because while crossfeeding, we only have 1 fuel pump (out of 6 total) feeding both engines. Not reliable enough during TO/GA power to feed both, so no x-feeding in case of GA.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

Baronman said:
In the ERJ we were told in systems it's because while crossfeeding, we only have 1 fuel pump (out of 6 total) feeding both engines. Not reliable enough during TO/GA power to feed both, so no x-feeding in case of GA.
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Wow, that's kinda puny.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

The disruption in FF is what I've been told when speaking with technical reps. For example, you don't want a transfer to interrupt/decrease an ejector's ability to maintain good motive flow into the collector/hopper tanks. Also, capacitance probes might not be accurate at takeoff/landing flaps, leading to improper balancing.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

ok, so is this an individual aircraft limitation or does the aforementioned paragraph from Part 25 apply?
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

ZapBrannigan said:
ok, so is this an individual aircraft limitation or does the aforementioned paragraph from Part 25 apply?
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I think it applies to the individual aircraft. On the G-IV, we continuously operate 4 boost pumps, providing about 4,500PPH of motive flow into each hopper tank (well over engine demand)... no takeoff limitation like there was in CL-65. I could certainly be wrong.
 
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Autothrust Blue said:
No, I meant that one boost pump, and only one pump, is connected to the entire system during crossfeeding. No bueno.
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**not an ERJ expert**

I'm not sure if it's only one pump - he might be referring only to BOOST pumps. The engine-driven fuel pumps (usually a low AND a high pressure pump attached to the accessory case) are running as long as N2 is spinning. Not an ERJ expert, but boost pumps don't do much in the jets I've flown aside from engine start and supplementary pressure at higher altitudes. In the CRJ, it didn't matter how many boost pumps were operational: if you lost the EDP, you weren't going to power the engine.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

C150J said:
**not an ERJ expert**

I'm not sure if it's only one pump - he might be referring only to BOOST pumps. The engine-driven fuel pumps (usually a low AND a high pressure pump attached to the accessory case) are running as long as N2 is spinning. Not an ERJ expert, but boost pumps don't do much in the jets I've flown aside from engine start and supplementary pressure at higher altitudes. In the CRJ, it didn't matter how many boost pumps were operational: if you lost the EDP, you weren't going to power the engine.
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Not an ERJ expert neither, and I really did mean "only one boost pump" there, too. It's still no bueno.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

Autothrust Blue said:
Not an ERJ expert neither, and I really did mean "only one boost pump" there, too. It's still no bueno.
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I'd completely agree if cross-flowing was commonplace with no manual reversion (stopping the boosted crossflow during an abnormal condition). We'll wait for Baronman, but I'm assuming there's an option for gravity crossflow and plenty of engine suction to make the design a non-issue. Could be wrong though!
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

C150J said:
I'd completely agree if cross-flowing was commonplace with no manual reversion (stopping the boosted crossflow during an abnormal condition). We'll wait for Baronman, but I'm assuming there's an option for gravity crossflow and plenty of engine suction to make the design a non-issue. Could be wrong though!
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It's entirely possible that it's permissible to fly the airplane with one wing tank dry and one wing tank full (the 757-200/300 are like this, you'll need something like 30% of the available roll control to maintain wings level on landing but it's perfectly doable). Again, one boost pump, and only one boost pump, while crossfeeding, sounds like unbelievable amounts of weaksauce to me. At a sufficiently high altitude, it also sounds like flameout city.

Someone who's gone to ERJ school, enlighten me.
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

Autothrust Blue said:
It's entirely possible that it's permissible to fly the airplane with one wing tank dry and one wing tank full (the 757-200/300 are like this, you'll need something like 30% of the available roll control to maintain wings level on landing but it's perfectly doable).
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On my aircraft this is a big no, no. Max imbalance is only 400#, with an emergency limit of 800#.
Fuel transfer from center to wings has to begin by one value, and no crossfeed and center to wing below another value. It all came about because the test pilots got an nasty fuel imbalance during certification.

Zap, it is probably an AFM limitation to comply with certification criteria.
 
Autothrust Blue said:
It's entirely possible that it's permissible to fly the airplane with one wing tank dry and one wing tank full (the 757-200/300 are like this, you'll need something like 30% of the available roll control to maintain wings level on landing but it's perfectly doable). Again, one boost pump, and only one boost pump, while crossfeeding, sounds like unbelievable amounts of weaksauce to me. At a sufficiently high altitude, it also sounds like flameout city.

Someone who's gone to ERJ school, enlighten me.
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When you say permissible, do you mean "physically possible" like for a test pilot, or do you mean day-to-day operations?

Because I'm pretty sure every transport category jet out there has a maximum fuel imbalance limitation. I'll let the resident 757/767 drivers actually get into this particular one though.

An interesting thing I was told during an oral once.

How is the maximum fuel imbalance derived?

For jets with spoilers, apparently it is generally at the point where the side with up-aileron first sees upward spoiler deflection as a result of the imbalance (this only applies to aircraft with spoilers that do that I guess).

The guy doing the oral went on to talk a bit about the different types and used the A-320 series as an example of a type that can have a larger imbalance, let's say 2000 lbs., than others its size because it is 'smart' in that the spoilers will not come up until later on vs. a DC-9 or 737 when they would have been deflected at an imbalance of say, just 500 lbs.

I don't know much about part 25 so don't hold me to that!
 
Re: Fuel transfer prohibition during takeoff/landing? Refere

C150J said:
We'll wait for Baronman, but I'm assuming there's an option for gravity crossflow and plenty of engine suction to make the design a non-issue. Could be wrong though!
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Ok...So even during crossfeed when there is only one electric fuel pump running (in the wing), "Engine driven fuel pumps will provide suction feed if the electric pumps operation is not available." The engine suction pumps are always running.

As I mentioned there are 3 electric pumps per wing, if one pump goes inop (system pressure below 6.5psi) , the plane automatically cycles to the other pumps.
 
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