With all the computation in the world… with all the looking in tanks… with all the fuel flow meters and the dipsticks, gages and formulas… you may have LESS fuel to use than you expect.

If you have never taken your tanks to zero, you may be in for a rude awakening at the worst time.Worth repeating:

If you have never taken your tanks to zero, you may be in for a rude awakening at the worst time.

My first clue was when my engine sputtered. I was on the right tank and my calculation was that I had six gallons remaining in that tank. I did – and – I didn’t!

Switching on the fuel booster and changing tanks took me the fifteen miles back to my home airport without incident. I verified that I had six gallons as I had calculated when I pulled up to the pumps… as it took nine gallons to get to the fifteen-gallon mark.

My long time A+P Jim Casey did all the checks for blockage and pressure, flow and scum and debris. None were found. We had suspected ice as winter conditions pointed to it. That would make it a transient event.

So, after all the good detective work, I moved fuel manually and brought the right tank down to seven gallons. Then I went back up to altitude and ran a controlled test over the airport.

Sputter, then, STOP eleven minutes after switching to the right tank. Booster on. No help. Back to the ground to look for an answer.

Today (12.15.04) I have the answer. The pick-up tube from the right tank was five (5), yes five, that’s FIVE inches from the lowest point in the tank.

We called Beech to verify the correct placement for the pick-up line. The original factory drawings showed that the pick-up should be at the bottom of the tank (there is a disk shaped spacer at the end of the strainer to give it an elevation about an inch from the bottom). Seems like a no-brainer, doesn’t it?

A careful search through my logs showed no repairs to the fuel quantity sending unit, which would have been the logical reason to open the tank in the past. The appearance of the parts indicated that they never had been replaced. Everything looked new. FACTORY NEW!

My Sundowner was built in 1978. Is it possible that no owner ever took that tank below six gallons? I’m going to try to find out. I’m going to search the logs again as there is no reason to replace an important part like a fuel quantity gage and not record it. – Note: It is not necessary to relocate the pick-up to change the sender. Also my pick-up line was not loose. The snug bolt kept it suspended in its elevated position.

This may be a FACTORY installation that was wrong and fixed twenty six years later in Massachusetts (Casey Aviation, 1B9, Mansfield Municipal Airport). Good job Jim Casey.

Is there a widespread problem? Unlikely… but, what are YOU counting on for your IFR/VFR reserves? Is there any fuel that you can’t get to because you never tried? Running a tank to zero under the right circumstances may save your bacon!

If you think you have a similar problem with your fuel pick-up, getting to it is not easy but not impossible.

Mike Rellihan generously gave me explicit instructions that helped get the job done correctly and without damage or unexpected results. I am paraphrasing Mike and the helpful words I got from Bob Steward.

Stop worrying! You can get into the fuel tank without a chain saw. And it is not through the filler hole. It is through the porthole where the fuel quantity sending unit sits. It’s about two inches from your outside hip as you sit in the front seats.

Remove the seat. Remove the floorboard. Remove the interior panel under the door. Magic. You see a rectangular panel with about thirty screws. It is about seven inches on each side. Mike warns that this panel is structural, forming a box structure below the door opening. It has to be put back the same way when you are done. So, he says try not to damage the screws. Use a new screwdriver, along with some friction paste like Scru-Grip, or auto-store fine valve grinding compound.. If you do strip a screw head, use a new one for reassembly. Note that these are AN525 washer-head structural screws. Do not substitute the weaker stainless-steel screws on this access cover.

Under that panel is what looks like a small porthole attached to the middle surface of a bigger porthole. There will be electrical wires and safety wires to be dealt with. Remove the large porthole leaving the smaller one intact.

Slip this assembly out and you are looking at the inside of the tank. In your hand is the fuel quantity sender. At this time Mike suggests that you consider sending the unit out for overhaul, unless the logs show recent re-work.

The hole that you have work through is about four or five inches in diameter. It’s big enough for a mirror, wrench or your fist. So, adjust your fuel pick-up, inspect the inside of your sump drain or just look around in a place you’ve never been before. One small thing worth doing, while the tank is open, is checking the alignment of the B-nut, on the fuel line fitting that lies next to the drain valve. If you can, make sure that there is a nut flat facing the drain valve, rather than a nut point. It could help with your selection of a replacement drain somewhere down the road.

Reassembly is straight forward. You should be prepared with a new gasket and some approved sealant. Bolts will have to be torqued properly and safety wired. Be sure the ground wire is properly secured as it was before. If you don’t see a ground wire, check BAC for the SB’s related to bonding. This is especially true if your left fuel gauge “jumps” when the Pitot heat or landing light is turned on. Some of the planes came with no wing-to-fuselage and no sender-to-fuselage ground wire. The treated wing mounts, and the gasketed/sealed sender mount, don’t always provide a good enough ground. Search BAC for “bonding wire” for more details.

Put enough fuel back in the tank to cover the porthole and check for leaks. Let it set overnight to be sure. Put the rectangular panel back on carefully and reinstall the interior.

When your A+P says that you have to get into the inside of your tank, don’t despair. Keep the chainsaw in the garage. There’s a little place near your hip that will be a lot less troublesome than you imagined… provided you do it right.

Tom Corcoran

Braintree, Massachusetts

1978 C23 s/n M2040

Thank you for adding to the resources available for your Fellow BAC Members.