Fuel Gauge Calibrations

[Roger]

Complete e-mail string:

RRRII@aol.com
03/05/2010 08:55 PM
To 9-AWA-AIRRGL/AWA/FAA@FAA
cc
Subject RGL Questions and Comments

I have a simple question (I hope)

While attempting to calibrate new fuel level gauges in both wings of my Cessna Skymaster, I need to know if it is permissible that after I drain both tanks to start at zero, can I then fill one wing at 1 gallon intervals (needed for the calibration) until full with new fuel, then transfer that fuel to the other wing in one gallon increments (the decrease in volume is also part of the calibration requirement) and while doing so use the filling at the one gallon intervals of the opposite wing as the beginning of that calibration, and so on and so on. It is good to run the cycle several times up and down in each wing to make sure the calibrations are correct. Therein the ability to transfer the fuel back and forth between the wings through an external pump running form tank to tank for this process would conceivable occur several times.

There is some argument among IA & AP's that say that once a plane is "de-fueled" you can not reuse that fuel. But it isn't being "defuled" it is being transferred directly into the opposng wing by pump and hose without ever going into another container. Nor is it being "reused to operate the aircraft, as it could be dumped after if needed (but I don't even know if that is necessary)

Please advise if you know the answer to this question.

Thanks you for your help
Roger N76BT
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From: Josh Peebles/AMC/FAA
AIR-140, Delegation & Airworthiness Programs
To: David McGhee/AMC/FAA@FAA
Date: 03/08/2010 07:50 AM
Subject: RGL Questions and Comments



Dave,

We don't know where to forward this email, if you could please take a look at it.

Josh Peebles
Information Program Manager
Aircraft Certification Service, AIR-140
Federal Aviation Administration
+1 (405) 954-1345
----- Forwarded by Josh Peebles/AMC/FAA on 03/08/2010 07:48 AM -----
-------------------------------------------------------------------------------

Roger:

Some thoughts on the process, not official FAA guidance.

.If the maintenance manual has a procedure, use it.
.Unless you are going to new technology gauges I doubt you will get any more accuracy and precision after several fills and empties than the first fill and empty; unless you are actually adjusting the system.
.One gallon seems too little an increment. Unless the MM says otherwise I would use something else, at least on the defuel.
.Back to the MM procedure, if you have one. Make sure fuel can't migrate left to right and vice versa through the feed lines or vent system.
.Make sure you start at the right "empty." Some gauges are set to zero at undrainable, most to unusable fuel. Check your flight and maintenance manual and the type certificate data sheet (on RGL).
.I would be very careful with an external pump, especially if it is electric. Any plastic can generate enough static to cause disaster. Also, you are going to find that putting a hose into the tank to get to the sump is challenging. If you are really planning more than one fill/empty consider removing the lowest sump drains and installing valves. You can then use a "calibrated" plastic fuel container (five gallon suggested) to carry the fuel.
.Make sure the proper voltage is on the electrical system when reading the gauges. My 172 reads very different between battery only and alternator online.


As far as defueled fuel. It is considered best practice and good policy not to reuse fuel that has been removed from an aircraft. It is also considered best practice and good policy not to use fuel from portable containers. The biggest reasons being the risk of water or other contamination and mixing of fuel grades. (AC 20-43 Aircraft Fuel Control, AC 20-125 Water in Aviation Fuels). That said it is done every day. Most facilities that do "recycle" fuel pay careful attention to possible contamination and put it back into the fuel truck so that it runs through the filters.

To be honest my 172 had "snarf" in both fuel tanks when I bought it. One tank was full of chunks of silicone from attempted repairs/gasket reuse. Never use silly-cone around fuel, it doesn't stick, it shrinks when dry (migrate through screens) and swells when wet (blocks lines). Both tanks had mysterious pink/red hard balls of to-this-day-not-identified material. The tanks had to be removed to clean the mess out. Last annual we chased gas smell several weekends before undoing a "minor alteration" to allow replacement of a gasket in the filler neck. I strongly suggest replacing every gasket and seal you encounter.

So, if you use proper static control (grounding) and keep all hoses, containers etc. clean and dry I see no reason not to use the same fuel for both tanks (is there a maximum fuel imbalance during fueling?) and use the fuel for flight at the end of the process. Make sure you watch what drains from the tank for contamination and don't put nasty stuff back in. Also, run the engines on the ground, from all tank feed combinations, to make sure all air is out of the fuel delivery system. AC 20-43 has suggestions for filtering fuel. I used a fuel filter funnel that has a fine screen and sump (available from Aircraft Spruce and West Marine, to name a few.)

Feel free to let us know if you have other questions.

Good luck, be careful.

David McGhee
Aerospace Engineer
Aircraft Certification Service
405.954-8721

[stackj]

My avionics man has a favorite saying. "Common sense does not constitute approved data."

It still seems that common sense would apply here. If you are using clean equipment/containers, what is the issue? Your fuel was stored at a refinery, transported by a truck or pipeline to a distribution facility, transported by truck to your airport, stored in some type of a tank, probably reloaded into a truck and finally pumped into your airplane.

Seems that moving fuel from one container to another does not harm it.

Just make sure you are properly protecting the fuel by using clean equipment. I woud say that doing this is no more likely to contaminate the fuel than the vendor(s) getting the fuel to your airport.

[hharney]

Legally the gauge only has to read "E" when empty. So that should not be too difficult to find that correct setting for each sensor. Then if you calibrate the gauge to read "F" when the sensor is all the way up (full) that again should not be all that difficult. Couldn't this be performed with no fuel on the bench? With both of these scenarios accomplished it should be close for what's in middle.

Maybe I am thinking to simple here.....................

[Skymaster337B]

Now that AVGAS is $6/gallon, it is too expensive to throw away. The reality is the fuel you purchased meets the highest quality from the point of sale. It doesn't "go bad" just because it is in your fuel tank and pore it out. You may have noticed the fuel tester cups with small strainers so that you can simply just put that fuel back into the tank...and not on the ground (thanks EPA). Well, you can do the same thing while draining...just make sure you have a mesh screen that will filter any dirt.

On the other hand. Even though AVGAS is $6/gallon, it's still the cheapest thing in/on your airplane.

[Roger]

Actually this fuel callibration issue has nothing to do with me. It was merely my attempt to resolve an issue that had been discussed under a different heading in a prior thread. Apparently there are some new digital fuel guages out there and there seems to have been some problem with the perceived rules on de-fueling the tanks to callibrate said gauges.

This new thread is meant to be a "quick search" heading so that in the future should anybody again encounter a mechanic who has questions on what is "permissible" for off loading and reusing fuel for this purpose, it can be easily resolved.