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

Guys, yes you are missing the point. It's not about flying LOP, hauling you family or flying around in circles. Rather it's that according to AAC and the related documents for the aircraft that up to 25% of the fuel capacity in a nose down attitude will become unusable. Is it linear, so a 5 degree nose down attitude will make 15-gal unusable? I have no idea, I have never found an reference to such. Additionally the main tank needs to be as low as 12 gallons before all the fuel will drain to the main in level flight. So unless the low fuel light is on at TOD, some additional wing fuel will become unusable as soon as you push the nose over. Not my opinion, that is straight from the manufacture.

So the only question I was asking was what difference does it make which wing the engine is burning fuel from? Yes, we all know uncoordinated flight can un-port a fuel tank, nothing new there, same with forgetting to switch to the appropriate tank in a timely manner. After all, we all have been flying around in airplane that carry the fuel in the wings and consume it directly. And many have limitations of what tank you can use when, again nothing new there. So exactly why does having the left engine burn fuel from the right side, and visa-versa, create any greater hazard than if the left engine burned fuel from the left tank? Having skinny wings with only a couple degrees of dihedral, isn't the exclusive domain of the A*, so I have a hard time believing it is simply a constraint of the wing design.

Let's consider the argument of un-porting the tanks, yep we all know that when low on fuel if you fly uncoordinated long enough, like a long slip, the fuel will flow away from the outlet and the respective engine will quit... Do that with the A* and the only difference I could see if using DCF is the other engine would quit. In order to get both to die from fuel starvation, providing the tanks actually contained fuel, would seem to require slipping/skidding in both directions at the same time. Seems a bit far fetched as a rational explanation. Now if the idea is the plane would be yawing around so much it would cause flow interruption to both engines, wouldn't that also be a problem for any twin that didn't have a common center tank? As many time as I have burned tanks dry in "conventional" twins I have yet to encounter this issue, including the A* in DCF, I would think if this really was a concern I would have experienced it by now. Doing stuff like polar flights you burn every tank dry.

Jeff

At the end of a long flight with minimal fuel left for descent, vectors, holding, go around and God knows what , I like to have all (or almost all) of my fuel in the main tank and not be concerned what is or want is not in the wings.

Walter

The Aerostar fuel system got a bad name back in 1976 when there were about 26 accidents in one year due to double engine failures caused by fuel starvation with fuel remaining in the wings. It wasn’t solely due to double crossfeed operations and in fact I think most accident aircraft were operating with fuel selectors in the “on position” and had fuel in the wings but none in the fuselage.

I was a tech rep at the factory during this time. I got numerous calls from owners saying we needed to fix the low fuel warning light because it was coming on when they had X number of gallons remaining. I heard amounts of as high as 90 gal. remaining. The owners didn’t understand that the low fuel warning light would illuminat when a float switch in the fuselage tank stopped floating and made a complete circuit. At the time the low fuel light would come on when you had 16 gal. remaining in the fuselage tank. There was also only one gauge for fuel with a spring loaded to the center toggle switch that, in the center position read “total fuel” and when selected left read, "quantity in the left wing” and right it read, “quantity in the right wing.”

The fuel gauging system needed improvement because the only way you could know how much fuel was in your only safe tank was to add the wing fuel readings together and subtract from the total. If you had, 90 gal. total and 45 in each wing, your fuselage tank was empty. It was determined that the reason the fuselage tank was being depleted prematurely was because the fuel caps were loose and the low pressure created by the air rushing over the wing put a negative head pressure on the wing tank compared to the head pressure on the fuselage tank. When full of fuel the wing tank vent doesn't let air into the tank which allowed the airflow to create this low pressure.

When the fuselage tank went dry each engine was then being fed by the wing on that side. Most accidents happened on final approach when due to pitch attitude, or uncoordinated flight, the wing tank pickup would unport, which caused that engine to quit and the associated yaw caused the other wing to unport, resulting in a double engine failure.

The solution was to replace the wing tank caps with ones that could be adjusted to seal properly and to install a fuel quantity indication system that had a gauge for each tank. The low fuel light float switch was also lowered to 12 gal. in the fuselage tank, at which point the wings should theoretically be empty. I am speculating now that test pilots and the FAA then asked the question, “What else could cause a double engine failure?” Well, double crossfeed isolates the fuselage tank from the system, which would have the same effect so they prohibited that way of operating. It is allowed in an emergency but with warnings about being in level flight only and in coordinated flight only.

Jim....thanks for your excellent explanation of our A* fueling controversy

Walter

Jim,

Were pilots also thinking of the fuel system in a "conventional" sense and only fueling the wings, therefore the limitation "Do not add fuel to the wings unless the fuselage tank is full" or did that limitation exist earlier? Before they knew it, the fuselage was empty, and the only fuel available was in wings. Start down at the end of a flight with minimal fuel and they became a glider?

Jason

Thanks Jim,

I hoped if I stirred the pot enough you would chime in and set the record straight!

Jeff

Jeff, I’m sure you are a very careful pilot and (like other pilots who have flown Aerostars a long time...Walter K, Jack D, etc) it is quite likely that you can safely use DXF as a tool and that you will not forget to switch to the main tank before descending or get so used to using DXF in cruise that you accidentally place the fuel valves in that configuration for takeoff by mistake. But the fact is, it happens.
You suggested that only people who fly short distances would elect to just leave the system in the ON position all the time, but if you fly long distance, pilots will always want to use DXF...that’s why I posted the point about how I used my plane for very long flights and never needed DXF. I’m not missing the point, I fully understand the system and what you are saying. It just seems you are suggesting that DXF should be used as a routine operational practice and that it is safer than just leaving the system in the ON position. It is not.
—You suggest that Jim C “set the record straight” with his historical narrative but recall that a only one post earlier he wrote: “ 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.”
—The aircraft flight manual indicates that DXF is for “emergency only.”
—Flying Magazine when writing a review and history of the Aerostar wrote: “Other accidents have been caused by pilots operating on double-crossfeed...although illegal, this method (to avoid draining the main tank) seems to work until the pilot forgets the valves are on double-crossfeed.”
—NTSB: SEA97FA094...pilot forgets he’s on DXF and dies
—NTSB: ERA12FA146...pilot becomes accustomed to flying on DXF and positions valves in that condition prior to takeoff, and dies.
There have been others, but I don’t want to spend my whole evening researching the NTSB database.
If you have a normally operating Aerostar fuel system, you don’t ever need to use DXF as it will not exhaust the main and leave fuel in the wings. The type of operational condition with a continuous descent from altitude for 20 minutes at 14 plus degrees never happens. As you level off in the steps or change heading, the remaining fuel in the wings drains into the sump and gets used. If that is not how your system works, you will notice and then you can get it fixed. I’ve never seen it happen. Please do not suggest to new/prospective owners reading this forum that DXF is a “normal” and “safer” way of operating the plane. That is contrary to the manual, the Vice President of AAC’s recommendation, and that of the instructors who provide recurrent training in the aircraft.
I’m not missing your point, I just don’t agree with you.

As a former Aerostar owner/pilot, I cannot give enough "likes" to evidence my support for what Thomas posted.

I would only add that is seems superfluous to start making an issue out of flights to the "outer regions" of the aircraft's range and capability. Perhaps if you are having to do all these gyrations to get the last few gallons from the wing tanks, you should consider stopping for some more fuel.

The Aerostar is an incredibly capable airplane and completely safe to operate until pilots start to rewrite the POH and standard/sensible operating procedures.

Jg

The must fundamental issue with what Jeff proposes is "human factors". People are just not reliable.
This is one of the reasons I think Cirrus is so successful; the extensive focus on the human factors to reduce tasks and simplify items. Sure, remembering landing is not hard, until it is. Why do so many people say single engine is safer than two? Because in an emergency with your air on fire the single gives you no choices, no decisions, therefore you perform better. While twins offer choices, require though and a decision tree which often leads to wishful thinking or bad choices.
Never underestimate a persons ability to screw something up at a critical time.

Tim

Summarizes the whole "human factors" problem. Helmet fire/fuzzy thinking/brain farts can affect any of us. Fatigue/distraction add to the problem.

As a current Aerostar Owner/Pilot, I am surprised that John and Thomas if not missing the point at least failed to understand it.

When I first purchased the aircraft it came as a bit of a surprise to discover a considerable amount of fuel became unassailable in the wings at a nose low attitude, according to AAC as much as 44 gallons at 14 degrees. Now, it would be nice if there was a little more information between the 44 gallons at 14 degrees and 0 at level flight when the main tank is below 12-15 gallons. Perhaps there is and somebody will provide it; for example how much fuel is inaccessible in a more "normal" descent from the FL's at say 1000 fpm? 5 gal, 10? That information would be useful at least to know, in my opinion.

Obviously some you don't really care and would rather resort to jabs such as "if you are having to do all these gyrations to get the last few gallons from the wing tanks, you should consider stopping for some more fuel" rather than entertain the notion that some of us, at least me, like a bit more back ground into the design quirks of the machines we operate. Guess it is just the inquisitive engineer in me. Besides I never considered the fuel management technique of consuming all the usable fuel in a tank in a flight attitude that promotes complete draining as a "gyration". My Glasair has a similar quirk, the last 20 minutes or so of fuel in the aft wing tank is only accessible at an IAS of 130kts or less. Again, it relates to deck angle. Perhaps the should be a section in the POH tabed "Gyrations" to file information like that... Sorry, just having a bit of fun there.

Now back to the actual question I asked: What makes burning the fuel from the opposite wing directly to the engines with DCF any different that burning it directly from the adjoining wing as is the normal practice in the vast majority of other light twins? If it is the propensity to induce a second engine failure in the event of inadvertently running one side dry, it would actually appear the lateral displacement of the remaining fuel caused by the initial yaw from the failing engine would actually promote the reestablishing/maintaining fuel flow from whatever fuel was remaining for the still operating engine; when the fuel was being drawn from the opposite tank. Or perhaps it is nothing more than a blind belief in the sticker on the dash saying you shouldn't. In any case I would think the corrective action would again be the same as any other aircraft; select a tank still containing some gas.

I don't know how many of you actually maintained your aircraft and have had the opportunity to deal with the fuel system beyond the selector switches and gas caps, but both of the 601P's I have worked on have exhibited the same fuel flow peculiarity that has probably led to at least part of my skepticism to simply "trust the system". When sitting in the hangar the last 5-10 gallons of fuel wouldn't simply "gravity" into the main. When defining the aircraft to facilitate repair and maintenance to the wing tank(s) it has always been necessary to remove the fuel as outlined in the MM with the boost pump, rather than simply pumping out the main. I haven't quite figured out exactly why; resistance in the flapper valve? No dynamic pressure on the vents? The same curious nature that leads me to ask "why" when it comes to the DCF matter is also curious about the "gravity" thing as well.

Jeff

It’s not just yaw that’s involved, there’s also lift. In DCF you lose an engine and you lose lift in the adjoining wing. The other wing with the good engine is producing more lift than the wing with the dead engine. Hence, the wing with the good engine rises while the wing with the dead engine drops causing unporting of the remaining engine. While this may be an oversimplification and may be a small part of the overall dynamics that occur during DCF engine failure, it may be just enough to kill the second engine given the shallow nature of the tank and very low fuel.

Jeff,


Understanding the design has never been an issue for me.
I have some some time, not a lot, crawling around the guts of the A*.

When i started flying the Aerostar, I read a lot about people using DCF. I even made use of it when i was going on 1000nm or even a few times 1200nm trips; I then made it a habit to use DCF in cruise.

Around this time I started paying attention to the overhaul in training by COPA for the Cirrus SR line. Not only the success they were having with the program, but the emphasis on the human factors was having a significant change in accident results.

I then had a few interesting flights where I had a false alarm dealing with oil pressure and did a preemptive shutdown of the engine; followed by a flight a couple weeks later where one alternator failure took out the other alternator and shutdown most of the electronics in the plane. In both cases, I was minutes from TOD to get home, in the flight levels cruising in DCF as SOP. In both cases it was a reasonably short flight. In both cases I landed in DCF; thankfully I had full tanks for the short flights.

Now, I pay a lot more attention to the human factors in how I plan. After those incidents, I switched to always leaving the the fuel in the "on" position, unless I needed to solve a fuel balance problem. When solving for a balance problem, I left my hand on fuel selector as a reminder I needed to switch it back to on.

Tim

Tim,

Why were you using DCF as SOP? Leaky caps? Until I got rid of the leak prone Shaw-Aero caps, I got a lot of practice with DCF just keeping the fuel in balance. But since then the only time I use it is on long flights when making sure all the gas is available is a priority, and then I burn out the wings first so if I do have a brain fart the engine quits in the FL's, not on approach. This is especially important when there is nothing between the departure and destination but cold water or inhospitable terrain.

One of the nice things about the A* is the accuracy of the gauges, unless I'm asleep at the switch, I can burn the wings down to a gallon, or less, before switching simply by doing a tail wag and watching for a needle twitch. Compare the to the fuel system in the twin Co. where you have to carefully monitor the totalizator as each tank empties (6 of them) due to the gauge providing not much more than a hint to the actual quantity remaining. Until I installed a Shadin it was pretty common to have an hour, or more, of fuel remaining in the wings but scattered between enough tanks to make it rather un-nerving. Flew a few approaches with one hand on the fuel selectors...

Really no different than the procedure I used for flying SE Cessna's; when gas is not an issue, put it on both and forget about it, but when you were flying to the limits of your range, a little more management may be in order.

Jeff