Beware Running Fuel Tank Dry!

[Nick]

On Wednesday, May 21, 2014, at about 7:00 a.m., I was at 7,000 ft. enroute to Houston Hobby from Waco. Had filed IFR. Weather was varying between overcast and VFR conditions. About 20 knots NNW of Bryan I was cleared by Houston Approach Control to proceed direct Hobby. About 2 - 3 minutes later the engine dies. The right aux tank was dry. I have been flying in Comanches since 1967 when I was a teenager. My Dad ran tanks dry dozens of times - even at night. No problem. Since I bought my Comanche B 10 years ago, I have done it at least a dozen or more times. Never a hiccup. My wife as has always complained of the risk. I have assured her it is not a risk becuase the engine is turning and the pump will pcik up fuel and restart. No problem.

Okay. I Switch to left main where I have at least 24 - 25 gallons. Hit boost pump. Nothing. Quiet. Prop is windmilling. Open throttle. Nothing. Full Rich. Nothing. Go to Right main with same amount of fuel. Nothing. Have now lost about 800 - 900 feet and still dropping. Doublbe check posititioning of fuel selector on both main tanks. Still nothing. Knew this is not right. Informed Houston Approach I have engine problem - have lost power. He Advised of distance to College Station Easterwood Field - about 15 -16 knots. No. I'll go to Coulter Field which is a couple of miles northeast of Bryan. A good airport with a nice long runway. Tune in KCFD on GPS and it shows a bit over 10 knots. I set up best glide speed. Then have to descend through overcast layer, but they are calling the ceiling at 1900 feet. Okay. Watching altitude and distance. Back and forth. Try boost pump again. Nothing. I break out of clouds at 1,800 feet AGL. Coulter Field is ahead and to my left and 1-2 miles. Think I can make it. Notify local traffic of emergency and to "give way". Good thing. A Bonanza is taxiing out for departure. Head straight for end of runway. Looks like will make it. At 250 - 300 yards from runway put gear down. Going to be close - very close. Hoping I clear the runway end lights. Clear them by three or four feet but she's really shaking - stalling. It's a good hard carrier landing, but I'm down. Rolling out the prop stops. Made it!!!:D

Once on ramp, a genral inspection of engine revelas everything normal. The auxilalry pump can be heard running. Engine will NOT start sitting there on ramp. The line is disconnected and auxillary pump engaged. Air and fuel spit of line for several seconds and then a steady stream of fuel. Pressure test shows 20 lbs. Conclusion drawn by 2 different mechanics (one who knows Comanches and my airplane) is that the diaphragm in pump is weak and with air in the line it could not pick up the fuel from the main tank.

I am not a mechanic, and I don't have the adavanced degree of techinical skill and understanding of all of this that many of you in the ICS have. However, my mehcanic, who has worked on everything over the last 40 years from Cubs to DC10s and 737s (and Comanches) says he is not a proponent of running fuel tanks dry in piston aircraft engines. Of course my wife is a very strong antagonist to this practice, especially now. You can draw your own conclusions as to what happened and engaging in this practice. But, lesson learned. I will carefuly monitor fuel levels and time on each tank to avoid this again in the future.

[N3322G]

Nick, Great job on handling the situation!!!!!

44 years and counting on running aux and tip tanks dry whenever we use them on longer trips. We watch the fuel pressure like a hawk and change when it becomes variable to 4 GPH. Engines don't even burp under those conditions for us. Before we had nifty fuel computers and upon fuel selector problems, we have had silence but not for long - on the other hand, we have two engines - only once have they both hit dry tank at the same time but that is a longer story. Ran a tank dry by mistake on a 400 at max power and it came back too.

Let me say AGAIN, Way to go on handling this emergency!

[Dave Fitzgerald]

Interesting story with safe ending.  Like Pat, I have run the tips and aux dry on special occasions.  I also watch very close and change them as the fuel pressure starts to fluctuate. Some may ask, Why do you want to run your tanks dry At the end of a long journey when you're trying to reach the maximum safe range of your plane, you need to know exactly where the remainder of all your fuel is. Only on a couple occasions have my engines sputtered for about 2 - 3 seconds and I don' think that's long enough to cause any damage. Nick pointed out,    The diaphragm in the pump was weak and with air in the line it could not pick up the fuel from the main tank. I would have thought that the electric pump should have compensated for any weakness in the diaphragm pump—apparently not.
I believe Nick was flying a single and I'm not sure what the difference is, if any between the single and the twin fuel delivery system.  In any case it's good information and should be carefully considered before running your tanks dry. 

Thanks for the story Nick

[Andres Darvasi]

Great job Nick, congratulations!