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Gas cap missing and far from home--now what?

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Theoretically, you are 250 miles from home when you discover on preflight that the guy who fueled your plane the evening before did not replace the gas cap and it is now MIA, 16 hours later.  Despite a through search, the cap is on vacation. What do you do now? Spruce can get you another cap in a few days....

21 gallons on board for a 2.5 hour trip. One could try duct tape.  Maybe double over the duct tape for the part that covers the hole so that fuel doesn't see the adhesive, and then tape it down real good.  That should seal it up tight.

That solution would probably work for about 1/2 hour when you might discover that the fuel in the wing with the gas cap is now less than 5 gallons. Then less than 2 gallons.... And the level of the fuel in the sight tube of the tank with the duct tape seal is even higher than you can see.  

Eventually, there will be a stream of fuel from the wing on the side with the duct tape seal. 

Probably time to land and regroup.

The lesson from this theoretical situation is that there is a huge low pressure on the top of the wing and no matter how well you apply duct tape, the low pressure will eventually communicate with the tank.  This low pressure will suck fuel from the other tank until it is full, and eventually the fuel will be sucked overboard, once it overflows the tank.

Once you realize the physics involved, you put the remaining gas cap on the tank that is now full (to overflowing) and dig out of the kit in the baggage compartment the fuel line clamp (for a light weight example see attached) and clamp off the fuel line from the empty tank as it exits the A pillar, right above your feet.  You apply a duct tape cap to the empty tank and proceed home with one full tank (16.5 gallons usable for the 2 hour flight remaining) and one unusable tank. You will be glad you did those fuel flow tests at the last condition inspection and know that the fuel flow from one tank is more than enough to supply the engine at full throttle.

When you arrive home, you will likely note that the two gallons of fuel in the isolated tank with the duct tape cap has not even sloshed up to the duct tape seal. 

The advice you now give to others is that a fuel line clamp is worth throwing in the plane, somewhere, in case the fuel guy has ADD and you are far from home. You will have to kiss off the fuel in the tank with a duct tape seal but you can run on one tank.

This proves that life, and the area above the wings, suck.

Theoretically speaking, of course.

Fuel line clamp.JPG

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My old Cessna had the caps tethered to ring with a short chain, I'd have to loop the ~6" of chain back into the tank to reinstall the cap.  Kind of a pain but solves the problem.

Good thing you noticed it, LS not having the stand pipe could have been over looked.  

A couple months ago buying fuel there was a cap left on top of the pump by the previous pilot, long gone.  This happens more often than pilots likely share / admit.

Just Friday night I was topping off and upon returning home I had a sinking feeling Saturday morning I had stood a cap up on top of wing (SW with stand pipe), and my visual check that caps was installed didn't catch it was installed back - thankfully they were.  That's one aspect of the SW's I like, easy visual indicator, but I will be laying them on their side for fueling in future.

I've tried to develop the habit of reinstalling the caps after fueling before doing anything else, once done fueling and pulling nozzle from tank - Stop and put cap back.  Leave the pump running, hold the nozzle, don't get down off ladder / stand, do it one handed, immediately place cap on.  Then, after buttoning up the fueling station and returning to plane ask and confirm are the caps back on as a second check.  This has worked well for me, having a process / routine is part of that safety in aviation thing.

Now, in the theoretical situation, all is out the window if the fuel boy screws up.  You caught it, managed the situation, and shared good content, good job.

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Well done sir! Excellent deductions. Congratulations.

Years ago, I came across a similar theoretical situation where it was my own stupidity that left the cap setting on top of the pump in the other LA. I discovered my error at a stop in Texas and went the duct tape route too… but I duct taped in a straw as a ram air vent.

However, by my next stop the duct tape had dissolved. So I replaced it with what my logbook describes as a bottle cap. I don’t remember the details of this, but I think it was still held in place by duct tape, with the cap acting somewhat like your doubled over tape, protecting the adhesive. The next log entry says it wasn’t drawing fuel from that side and that I stopped again and “vented the bottle cap”.

The next leg I remember perfectly, and probably always will.  It was night. I was crossing a poorly lit stretch of southern New Mexico, heading for Lordsburg. Watching the sight tubes, the situation was becoming way more exciting than I felt like I really needed. In an unusual moment of clarity, I turned 90 degrees and landed at the nearest airport, Las Cruces.

On landing, the wing with the normal cap was completely empty while the tank with the vented “bottle cap” was completely full; just as you had observed.

But I hadn’t figured out your “pinch the line” idea. Instead, I waited 3 hours for the fuel to level out between the tanks, by which time any remnants of sanity had evaporated, and took off again into the night.

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