Fuel gauges in FAR?

[OnlyAnEgg]

For years, I have heard various versions of the limited reliability of fuel gauges in GA aircraft; and often the discussion mentions something to the effect that they are only required to work when they show "empty". Can anyone direct me to a valid section of 14CFR (any Part) which describes this requirement? Or is it another urban legend, like guy who flew inverted beneath the Verrazanno Bridge, in a glider, at night, naked?

Thanks in advance,

Jim

 

[Let'sgoflying!]

For years, I have heard various versions of the limited reliability of fuel gauges in GA aircraft; and often the discussion mentions something to the effect that they are only required to work when they show "empty". Can anyone direct me to a valid section of 14CFR (any Part) which describes this requirement? Or is it another urban legend, like guy who flew inverted beneath the Verrazanno Bridge, in a glider, at night, naked?

its in the a/c certification parts (23)

(1) Each fuel quantity indicator must be calibrated to read “zero” during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply determined under §23.959(a);

 

[gismo]

its in the a/c certification parts (23)

(1) Each fuel quantity indicator must be calibrated to read “zero” during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply determined under §23.959(a);

Which is something that folks have been misinterpreting for years to mean that "the only time the gauges are accurate is when the tanks are empty". The intent of this certification regulation was to clear up the meaning of empty as shown on a fuel gauge which is supposed to indicate when all the useable fuel is gone vs the tanks are totally empty (no unusable fuel), or that only reserve fuel is left. IOW this rule specifies a single point of calibration not accuracy. If you take that silly staement about "accurate only when empty" to the extreme, you could simply have a gauge that always read empty since it would indeed be accurate when the tanks were dry.

 

[Let'sgoflying!]

no disagreement here, just pointing out the ref for Jim. However some tanks don't need any gauges let alone working ones!

 

[Joe B]

no disagreement here, just pointing out the ref for Jim. However some tanks don't need any gauges let alone working ones!

Huh? 91.205(b)(9) says there needs to be a "fuel gauge indicating the quantity of fuel in each tank." I don't see a lot of wiggle room in that wording.

Addressing the original question in the thread: the NTSB ruled in Administrator v. Hammerstrand (1992) that an unreliable fuel gauge rendered the aircraft unairworthy. In that case the fuel gauge gave erratic non-zero readings.

Regards,
Joe

 

[cwyckham]

The FAR quoted above is 23.1337. The most recent version of this rule is

(b) Fuel quantity indicator. There must be a means to indicate to the flightcrew members the quantity of usable fuel in each tank during flight. An indicator calibrated in appropriate units and clearly marked to indicate those units must be used. In addition--
(1) Each fuel quantity indicator must be calibrated to read "zero" during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply determined under [Sec. 23.959(a);]

Note that the quote a few posts back missed the first bit. It doesn't explicitly state the degree of accuracy, but it does say that it must indicate to the flight crew the quantity of fuel, so it has to have some degree of accuracy other than at zero.

CAR3 from 1956 says essentially the same thing, so the rules haven't suddenly changed on this point.

Also, the catch-all equipment rule is 23.1301 which states

Each item of installed equipment must--
(a) Be of a kind and design appropriate to its intended function;
(b) Be labeled as to its identification, function, or operating limitations, or any applicable combination of these factors;
(c) Be installed according to limitations specified for that equipment; and
(d) Function properly when installed

That says to me that it has to do what it says it does, which is to measure fuel quantity with some level of accuracy.

Chris

 

[cwyckham]

Huh? 91.205(b)(9) says there needs to be a "fuel gauge indicating the quantity of fuel in each tank." I don't see a lot of wiggle room in that wording.

That's interesting. It seems that part 91 and part 23 disagree with eachother. The part 91 rule is an oversimplification of the part 23 rule which states in 23.1337:

(5) Tanks with interconnected outlets and airspaces may be considered as one tank and need not have separate indicators; and
(6) No fuel quantity indicator is required for an auxiliary tank that is used only to transfer fuel to other tanks if the relative size of the tank, the rate of fuel transfer, and operating instructions are adequate to--
(i) Guard against overflow; and
(ii) Give the flight crewmembers prompt warning if transfer is not proceeding as planned.

For example, the Cessna 421B has optional wing locker tanks with no gauge. You can't run off the wing locker tanks, they just transfer to the mains. Usually you simply burn enough out of the main on that side so that you know you have room for all the wing locker fuel, then flick on the fuel transfer pump and wait for the little light to go on to indicate that the pump has transferred everything it can. The main tank fuel quantity indicator then gives a crosscheck that you got all the fuel you think you should have.

Chris

 

[Graueradler]

If you take that silly staement about "accurate only when empty" to the extreme, you could simply have a gauge that always read empty since it would indeed be accurate when the tanks were dry.

Sort of like a broken clock showing exactly the correct time twice a day. You just don't know when. On the other hand, a functioning clock is essentially never correct.

 

[Greg Bockelman]

Huh? 91.205(b)(9) says there needs to be a "fuel gauge indicating the quantity of fuel in each tank." I don't see a lot of wiggle room in that wording.

Joe

I have an airplane that has three tanks and only one fuel guage. It is legal on mine.

 

[Stache]

I have an airplane that has three tanks and only one fuel guage. It is legal on mine.

Having one fuel gauge maybe legal, it all depends on the certification of the aircraft. If your aircraft was certificated as a part 23 aircraft it requires seperate gauges. If your aircaft is a CAR-3 or manufactured to specifications it may not required more than one gauge.

The best way to find out is to down load the type certificate data sheet and see what the certification was. Remember part 91 is a operations rule and CAR-3, part 23, 25, 27,29,and 33 are certications rules.

If you need assistance if finding out send me a private message and I will look it up for you.

Stache

 

[cwyckham]

Having one fuel gauge maybe legal, it all depends on the certification of the aircraft. If your aircraft was certificated as a part 23 aircraft it requires seperate gauges. If your aircaft is a CAR-3 or manufactured to specifications it may not required more than one gauge.

It looks to me like the CAR3 requirement's pretty much identical to FAR 23. My post above quoted the FAR 23 rule that says you only need one if the tanks are interconnected. CAR 3 (May 15, 1956) says in 3.672

Means shall be provided to indicate to the flight personnel the quantity of fuel in each tank during flight. Tanks, the outlets and air spaces of which are interconnected, may be considered as one tank and need not be provided with separate indicators...

CAR 3 also has the same requirements for auxiliary tanks that FAR 23 has (see my previous post).

Chris

 

[Greg Bockelman]

Having one fuel gauge maybe legal, it all depends on the certification of the aircraft. If your aircraft was certificated as a part 23 aircraft it requires seperate gauges. If your aircaft is a CAR-3 or manufactured to specifications it may not required more than one gauge.

The best way to find out is to down load the type certificate data sheet and see what the certification was. Remember part 91 is a operations rule and CAR-3, part 23, 25, 27,29,and 33 are certications rules.

If you need assistance if finding out send me a private message and I will look it up for you.

Stache

It's a 1941 Taylorcraft BC12-65. It's legal.

 

[wesleyj]

I have a Seiko, it is accurate almost to the ounce in every airplane that I fly, better and more relliable than any gauge.

 

[cwyckham]

I have a Seiko, it is accurate almost to the ounce in every airplane that I fly, better and more relliable than any gauge.

Assuming your fuel flow figures are correct, it's pretty accurate. I rent a lot of different aircraft, so I always wonder how good the fuel flow figures are going to be. I end up being pretty conservative.

The Seiko also doesn't take into account fuel being siphone overboard due to a loose fuel cap or any other malfunction.

Chris

 

[Stache]

It's a 1941 Taylorcraft BC12-65. It's legal.

Yep you are right as follows:

I looked up the Type Certificate Data Sheet (TCDS) A-696 for the BC12-65 and found the certification basis for your aircraft as Part 04 of the Civil Air Regulations effective as amended to May 1, 1938. Type Certificate No. 696 issued.

Under fuel it states (See item 115 for auxiliary tank), Auxiliary 6 gal. fuselege fuel tank installation. Under CAR Part 04A section 4a.561 it says:

§ 4a.609 Gauge. A satisfactory gauge shall be so installed on all airplanes as to readily indicate to a pilot or flight mechanic the quantity of fuel in each tank while in flight. When two or more tanks are closely interconnected and vented, and it is impossible to feed from each one separately, only one fuel-level gauge need be installed. If a glass gauge is used, it shall be suitably protected against breakage.

I would say you are legal based on the certification of the aircraft to have one gauge.

Just happen to have all the CAR’s in PDF and word files for easy reference.

Stache