Fuel Tank FOD

Finding objects in the fuel tanks or fuel system isn't as uncommon as one might think. Many years ago a mechanic was found dead in a tank after the aircraft had made several trips. Finding objects left behind is inexcusable, but very possible.

A flashlight near a tank entrance does have the potential for a fire or explosion. Fuel-safe sealed lights should be used. Someone mentioned that a spark in a tank full of (or partially full of) avgas and avgas vapor won't cause an explosion. Don't bet on that. It very well could.

As for sparks from the fuel qualtity float, the answer is no; it doesn't spark and isn't an ignition source. Yes, it's sealed, and yes, the electricity isn't live in the tank. It's external, and no, it's not going to cause your fuel tank to explode. Neither capacitance probes nor floats will cause tank explosions.

I've found various objects in fuel and in tanks, from a dead mouse to leaves to a large blue shop rag, once.
 
DouglasBader said:
I've found various objects in fuel and in tanks, from a dead mouse to leaves to a large blue shop rag, once.
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At NAS Pt. Mugu (naval missile center) the A3D was being re-configured from a tanker to a missile test platform, and when the bomb bay fuel tank was removed the crew found a mattress and step ladder in it.
 
DouglasBader said:
As for sparks from the fuel qualtity float, the answer is no; it doesn't spark and isn't an ignition source. Yes, it's sealed, and yes, the electricity isn't live in the tank. It's external, and no, it's not going to cause your fuel tank to explode. Neither capacitance probes nor floats will cause tank explosions.
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The fuel senders that I have removed and put into fuel tanks consist of a wire wound around an insulator and a wiper attached to the float. One end of the wire is grounded to base of the sending unit, and the other end comes out of the center of the sending unit and goes to the gauge. There is a plastic cover over the stuff, but it is just a shield - not a sealed unit.

The impedance is high and inductance is low so you wouldn't typically get any sparks.

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This version (Cessna) looks a little more sealed than the typical auto style sending unit...

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There are capacitive sensors that are mounted on the outside of the tank.
 
The impedance is high and inductance is low so you wouldn't typically get any sparks.
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Precisely. There are no sparks from a fuel sending unit, and it's not a source of ignition.

There are capacitive sensors that are mounted on the outside of the tank.
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And on the inside, as virtually all advanced aircraft use an array of capacitance probes with a temperature-adjusted averaging unit to compute fuel volume and weight.
 
bigblockz8 said:
Has anyone ever dropped stuff into a fuel tank? I am still confused on how they did so!
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I dropped the cap into a fuel tank, once. Had 5-gallon cans and had too much for my plane, so decided to do a friend in the next hangar a "favor" and put the excess into his. Didn't understand how his cap work, loosened it too far, and *plop* right into the fuel.....

Ron Wanttaja
 
Loosing stuff in the fuel tank is trivial stuff, wait until you loose the tip of the bore scope about 4 feet into a jet engine.

or your ball cap.
 
jesse said:
At the right angle it'll go in. Never underestimate a human's ability to screw up. I was once walking up to a door holding my keys with the intent of unlocking it. The keys slipped out of my hand, hit the floor, and slid under the door into the locked room.
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gkainz said:
I have mental images of my keys dropping from my hands and disappearing down the crack between the floors when I step onto elevators. I hope it's not self-fulfilling prophecy.
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I dropped my keys upon exiting the elevator at work. They managed to slip through the threshhold opening and dropped 34 floors to the sub-basement. Never found most of them. Just my housekey.
 
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I reported it immediately and though the IA said it was OK to fly, my CFI said no and the plane was grounded until Monday (one student had to fly the Piper instead and it was all my fault). I tried for hours to get it out, and I was super bummed because I didn't get to solo that day. IA says it happens all the time:
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I keep some long needlenose and duckbill pliers in my box just for such occasions. Sometimes a bit of twine taped to a stick works well too; a loop on the end can be used to catch the object and trap it, then pull it out of the tank. Long flexible magnets work for ferrous objects.

I also keep an assortment of different medical forceps for such things. They work for retaining wire bundles while working through an instrument panel, fishing things out of fuel tanks, putting washers in really hard to reach places, and for various practical needs as the day wears on. It's really amazing how often they come in handy.
 
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