Simple question for discussion – under what circumstances would you select cross feed.
When there is a fuel imbalance – for whatever reason – that approaches or exceeds the maximum allowed one.
Depends on the fuel system, but on light GA airplanes this generally means that you are feeding from the opposite tank on a twin in order to balance the fuel during one-engine operations. Twins’ engines normally feed from the wing tank on their respective sides.
1) Engine failure on one side to keep the fuel balanced if flying single engine for a bit.
2) To test the cross-feed system actually works.
3) To even out the refueller’s sloppy work.
4) On some fuel systems, being parked on sloping ground can cause fuel to flow from the higher to the lower side (unless the pilot remembers to close the “crossfeed shutoff valve” when leaving the aircraft).
Do it on the Aerostar sometimes to just balance the wings, but briefly. Don’t want to do it too long as it bypasses the center tank, so if you forget (easy to do), the wing runs dry and the engine quits although there’s a full center tank… Also, the fuel valves are electrical, so if you get a complete electrical failure, then it’s stuck in cross feed mode..
Also, the fuel valves are electrical, so if you get a complete electrical failure, then it’s stuck in cross feed mode..
It’s the same on the Citations. A total electrical failure is bad enough, but knowing that you only got 20 minutes to get it on the ground otherwise you might lose (aileron) control authority makes things a lot worse. If there is amajor imbalance after refueling, I try to get rid of it during taxi and not in the air.
I am interested in circumstances of engine failure or rough running. Its possible it could be fuel contamination which could potentially transfer to the good engine.
In DA42 when cross-fed, the temperature of fuel in non-used tank goes down because of no warmed fuel inflow from the engine to tank, so I guess that prolonged cross-feed is not recommendable if really not needed.
In accordance with the AFM – too many variables dependent upon type. For example the Chieftain says only to be used in the event of an engine failure wheres the DA42 has a 5USG imbalance requirement.
I can’t think of a realistic scenario where one side is contaminated and the other not.
