Erratic fuel gauges

[Ernie Martin]

And on the subject of fuel exiting the airplane through a hole in the wing, you should know enough about your fuel system to decide what to do if that happens. Specifically, once all the fuel is gone from that wing, it's often preferable to shut off the engine fed by that wing and operate on a single engine, rather than leave that engine on and cross-feed it from the other wing. Why? Because in the cross-feed mode, roughly half of the fuel coming from the other wing ends up in the leaky tank and will go out the wing.

In fact, if fuel conservation is critical (say, over a wide expanse of water), then one should consider doing the opposite cross-feed -- so both both engines are fed from the leaky tank -- as soon as you confirm that fuel is going out the wing. Not only are you now feeding both engines from fuel that will soon be gone, but you are actually moving fuel from the leaky tank to the good one (obviously, this accumulation in the good tank only happens if there is space in that tank, because you've already used some). And in that mode where both engines are fed from the leaky tank, it may be wise to use up as much of the fuel from the leaky tank as possible before it's gone, by climbing to a higher altitude at maximum climb rate. In a utopian scenario, fuel from that tank runs out when you've reached maximum altitude and regained cruising speed. At the slightest sound of fuel starvation -- and it will be very noticeable because both engines will starve -- promptly switch the cross-fed engine to its regular (non-leaking) tank (if you do it quickly, you should not even need to use the boost pump to regain full power) and shut off the other engine.

Disclaimer: These are my procedures based on my understanding of the fuel system, and are not intended as recommendations. My only recommendation is that you learn how your fuel system works and use that knowledge if you encounter a fuel starvation problem.

Ernie

[edasmus]

Point well taken! This does bring up and interesting question. Let's assume we have had an engine stop running in cruise and there has been no apparent loss of fuel from the wings. Years ago during my multi training one of the trouble shooting steps to attempt to regain the engine would be to attempt to x-feed fuel to the engine not producing power (try to get fuel from another tank). I have a 1973 C337G (no turbo, no pressure) and this configuration is not addressed anywhere in my manual. The manual does not suggest it as a trouble shooting step or pohibit it. I do however have in my posession an old "Air Facts" magazine from 1973 where a review was written by Leighton Collins (father of Richard Colllins, Flying magazine editor for 1000 years) of the brand new 1973 P337 (yes, pressurized model). In this extensive column, Leighton writes that under no circumstance should both engines be run from the same wing at the same time as this can result in double engine failure. He does not however explain why. I was always curious if this was true and if it applied to my non-pressure model. I have asked my mechanic about this and he cannot see why this would be the case. I have tried running on the ground with both engines running from the same wing with no problems but I have not had the desire to attempt it in flight. Can any of you 1973 P-model guys confirm this and explain why. I am not familiar with the P-model fuel system. Is it different then the non-pressure model of the same year?

I do have a theory but I do not know if it is true. Is it possible that with both engines running from the same wing that fuel could be drawn from the boom tank faster than it can be replaced? It looks as if that small boom tank only holds about a gallon or two of gas though I have never actually messured this? Any feedback!

Thanks Ed

[Ernie Martin]

I have never heard that you should not feed both engines from the same tank, and I thought I knew a bit about the subject -- see the Fuel Supply Management Page in my "backup" site at www.SkymasterUS.com

It's not recommended that you take-off or land in that configuration, for obvious reasons, but why would the option of cross-feeding an engine be included if it should not be used?

Because most of my flying is over water, I routinely excercise the cross-feed function and operate at cruise with both engines feeding from the same tank, and it's never been a problem. In fact, I was once coming back from a lengthy Search and Rescue mission on my '69 with four separate tanks and, for reasons I can't recall, I was running both engines out of the same tank when that tank ran out of fuel. Behind me were two passengers who had begged me and my co-pilot to search for their family members lost at sea. You should have seen their faces when both engines quit. I knew where my fuel was and got both engines restarted in seconds.

And on your first subject, an engine stopping, I would certainly consider as one of my options re-starting the engine with fuel from the other tank. I would excercise caution by making sure I understand the problem before I try the opposite-tank restart. For instance, if the engine died from lack of fuel because of a leak in the tank, then (as explained in my earlier message) I would continue with a single engine.

Ernie

[edasmus]

Thanks Ernie. I am not at all familiar with all the different fuel systems on all the different skymasters. This article from 1973 that I referenced made this statement about the 73 p-model and it would be interesting to know why. Do you and I have the same model? I have the 73 G model, no-pressure, no-turbo. Which do you have?

[Ernie Martin]

Exactly the same -- 73 G model, no-pressure, no-turbo.

Ernie