There is even a placard on the dash saying you shouldn't do it, just like you shouldn't slip a Cessna with the flaps extended... But unless somebody can explain exactly what the issue is a lot of people, including me, will continue to ignore it. What is the concern the valve will fail? I would contend excising the valve a bit more often would be the best insurance that it won't fail... Or if you forget to switch it back you run the risk of un-porting the tank while maneuvering? That would apply to a lot more than Aerostars.

One of the biggest complaints I have with the just put it to "ON", or in the case of a Cessna, "BOTH", and leave it there is that if the engine sputters you are done. Guess I spent too many years flying airplanes with crappy fuel quantity indicators out to the limits of their range to trust may butt to a gauge. Especially when there was nothing below me for hundreds of miles but ice, water, or rocks.

Perhaps somebody like Jim C. can provide an explanation that contains more than just the because it says so...

Jeff

There is even a placard on the dash saying you shouldn't do it, just like you shouldn't slip a Cessna with the flaps extended... But unless somebody can explain exactly what the issue is a lot of people, including me, will continue to ignore it. What is the concern the valve will fail? I would contend excising the valve a bit more often would be the best insurance that it won't fail... Or if you forget to switch it back you run the risk of un-porting the tank while maneuvering? That would apply to a lot more than Aerostars.

One of the biggest complaints I have with the just put it to "ON", or in the case of a Cessna, "BOTH", and leave it there is that if the engine sputters you are done. Guess I spent too many years flying airplanes with crappy fuel quantity indicators out to the limits of their range to trust may butt to a gauge. Especially when there was nothing below me for hundreds of miles but ice, water, or rocks.

Perhaps somebody like Jim C. can provide an explanation that contains more than just the because it says so...

Jeff

Doesn't that seem a little weak? After all wouldn't the same would apple to any twin that carries the fuel in the wings that was flown in and un-coordinated manner? After all in DCF the A* is consuming the fuel in the same manner of pretty much every other twin out there does, the only difference is the fuel supplied to the engine is coming from the opposite side. Even a SE aircraft typically carry the warning that prolonged un-coordinated flight may result in power interruptions.

Jeff

FIFMyself

The only safe tank for all attitudes in the Aerostar is the fuselage tank. I think the prohibition of using double crosfeed is because there can be up to 22 gallons of unusable fuel in each wing in pitch down attitudes of 14 degrees. In uncoordinated flight while in crossfeed, power interruptions and surging can be realized with up to 42 gallons of fuel in each wing. If one engine surged or quit while in double crossfeed it could cause the other engine to quit as well, and it will take up to 10 seconds for the engine to restart once fuel is restored. I understand you might want to get all the wing fuel out of the tank before descent but I would only put one engine at a time in crossfeed.

Thanks Jim, that confirms pretty much what I recall as well. I didn't recall it being 44 gallons, but 14 degrees is a pretty steep descent profile as well. I suppose in theory all the gas is suppose to drain the the main once you raise the nose and slow down, I just never liked having a few gallons here, and a few gallons there, especially when I am close to the ground. A ten second power interruption when I am 4 miles up doesn't do much other than remind me I forgot to switch tanks, but in the pattern I may need new shorts...

Jeff

One of the best lines on BT yet!

Tim

I’ve pretty much always been in the “don’t do DXF” camp. I just don’t understand the reason it could be needed. If there is something wrong with your wing tank that causes fuel to be left behind, it will probably be left behind in XF also. If you doubt the gauges, calibrate them, fix them, and/or just watch the flight time. I’ve never heard of an Aerostar that crashed due to fuel starvation because they left their tanks ON instead of burning the wings empty in DXF first. Conversely there have been many accidents because pilots left their planes in DXF and forgot to switch. In fact, that’s exactly where the bad reputation for the “killer complex fuel system” in the Aerostar came from. There are enough risks in aviation. Why add more potential human error opportunities when doing so yields no advantage. My current twin doesn’t even have XF as an option so I can’t be tempted anyway!

Here is the problem, you can run out of gas on the descent with an hour worth of fuel still in the wings. Lets just say you are at the TOD and have 15 gal left in each tank, put the nose down and 20 minutes later the main will be empty and 30 gallons will still be in the wings. Unless of course my plane acts differently than it should, it is the only one I have ever flown so I have nothing to compare it to.

From the A* almighty himself:

....using double cross-feed is because there can be up to 22 gallons of unusable fuel in each wing in pitch down attitudes of 14 degrees.

So far the only solution I have found it to burn the wings out before TOD so the main is basically full for the descent and approach allowing all the fuel to be usable regardless of the aircraft attitude just in case things don't go as planned and all that gas becomes vitally important. Cross-feeding one tank at a time as Jim suggested will certainly work but will require a lot of tank switching to keep the plane in balance.

I am still not seeing why burning the fuel from the opposite wing is any different than burning it from the same wing as most every other airplane out there does. All will suffer tank porting issues if flown in an un-coordinated manner with partial tanks. What make the A* so different? Just asking.

And yes, if I forget to switch tanks when I should the engine quits...just like every other plane I have flown.

Jeff

I guess that is a theoretical possibility. 14 degrees is pretty darn steep and I’d guess that 20 minutes at that deck angle with power on would have you descending rather rapidly. Most real descents don’t happen that way. You step down with periods of level flight and the deck angle is usually not that steep. If you do go that steep, you’ll probably need to pull the power back and FF will drop way off. I don’t know if your plane is unusual or not. I only know that I operated two different Aerostars over 10 years, almost always flying in the flight levels, doing descents as instructed by ATC and I never used DXF. I never once saw the scenario you describe play out in that way. In fact, in 10 years flying the plane, I never saw the low fuel light illuminate except when tested. The fuel system is very well designed to be fool-proof as long as you just let it do its thing. Clearly you need to be “aware” and monitor for an anomaly, but I think they are exceedingly rare (Walter’s experience not withstanding).

I suppose it all depends on the length of your flight, if you always land with a couple hours of fuel it probably doesn’t matter much, but when making 8-900nm legs it takes on a greater importantance. A bit like approach speeds, when using a runway a mile or more long, fly whatever speed you want. But when operating out of something like our airpark with a 2200’ runway those pesky details can be the difference between success or failure.

I never had the courage to see if the wings will drain completely in a long descent, I always error on the side of caution and make sure all the gas is where I need it if it appears reserves will be tight upon arrival.

Blame my habits on flying where the the next landing strip might be in another time zone.

Jeff

14 degrees nose down, you are likely coming down fast. This is effectively are coming down at 1400 ft per NM traveled. Assuming an average of KTAS of 240; you are traveling at 4 miles per minute. You then have a descent rate of 1400 * 4 = 5200 FPM.
Not sure what altitude you are flying, but I doubt you can do a twenty minute descent at that rate. Let alone what ATC says.

Tim

You miss the point, it almost appears to be intentional, the point is the A* wing doesn’t allow for all the fuel to drain to the main unless in level flight. Apparently it is up to 44 gal. according to AAC depending on the deck angle. But be it 44 or even 10, it’s range that just might come in handy, an A* will go 70nm on 10 gallons of gas. That’s a long walk.

Now if you never are on a flight where you need all the wing fuel to be useable, no worries, but if you do need it you may want to consider burning the wing fuel before you put the nose down.

Jeff

Again. I never saw the need. My Aerostar took me and my family all over America, across Alaska and Canada, to the Caribbean, on flights pushing five hours at altitude. No DXF, no low fuel light. I used lots of “tricks” like lifting wings, filling the main tank headspace etc, but never needed DXF. It may be that our planes are (were) different in the way the fuel system operates. I know our operational environment was different because my ground roll alone was over 3000 feet on takeoff so I suppose we are approaching it from slightly different viewpoints, but the gauges were pretty darn accurate and you’ve got the low fuel light as backup. Just leave it ON and monitor its function. Trust but verify as they say.
In my experience, in my planes, DXF is a solution in search of a problem. Have you ever actually seen your aircraft land with say 5 gallons in the main and 15 in the wings? If so, I'd suggest you should have the fuel system looked at, and if not, I'd suggest you are introducing additional risk of human error for no gain. Certainly the number of pilots who've come to grief due to double cross-feed would agree that while we try to be vigilant, when doing DXF in an Aerostar, s--t happens.

Up to my arm pits looking at it now

Even found that some of those that have gone before had a sense of humor. For those familiar with the breed will recognize this as the access cover behind the right MLG.