"Gene Seibel" wrote

The only regulations for fuel gauges are that they read correctly at
empty. They are not reliable for determining the amount of fuel in the
tanks, but as they approach empty, they should be believed.

Bull****! I am repeating an e-mail that I sent to a young man
who posted the same information on his web site.

Russ......

I stumbled on your web site while searching for some C-172 Fuel Cap
information.
I found the following statement which while completely false, seems to be
circulating quite widely.

"The FAA only requires the gauges to read accurately when the tanks are
empty. Yeah, you're right, that's really stupid, but it's the law."

I have quoted the applicable portion of the Federal Aviation Regulation
"law".

Section 23.1337: Powerplant instruments installation.
(b) Fuel quantity indication. 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 §23.959(a);

Paragraph (b) of course is the controlling portion and requires the
indicator to indicate the quantity of fuel at all times. Since no
tolerance is specified other than the indicator must be marked and
calibrated, it must be assumed that it must be calibrated accurately.

The intention of paragraph (1) is to require that the "zero" reading be
applied to "useable fuel" and not "total fuel". The C-172 that I fly
(1959 model) can be filled with a total of 42 gal. of fuel of which only
37 are useable. It obviously would not be acceptable to have the engine
quit from fuel starvation with 5 gal. showing the gages.

Paragraph (1) has nothing to do with gage "accuracy" but rather the
calibration of the system to indicate zero with zero useable fuel
remaining.

It might be wise to remove the erroneous "hangar talk" from your web
site.


Bob Moore
ATP CFII