"BTIZ" wrote in message
news:niBtb.3221$Ue4.826@fed1read01...
| I was once told.. that the Cessna type gauges only have to be accurate
when
| the tank is empty.. it should tell you so.. it does not need to be
accurate
| at a full or partially full tank..

You were told incorrectly, but you are in pretty good company. Even Rod
Machado made this error in one of his columns. He wrote back to me and told
me that he thought my interpretation of the regulations was probably more
correct. (But then, John King teaches the equal transit theory of lift, so
even "world famous" flight instructors like us get things wrong sometimes.
:-) Seriously, if you took all the faults and bits of misinformation taught
by just the top ten flight instructors in the country and put them into one
guy, you would probably have a really terrible flight instructor. But I
digress.)

The actual regulation states that the gauges must be calibrated so as to
read empty when usable fuel (as opposed to total fuel) is gone. Part 91
requires fuel gauges to indicate the quantity of fuel in each tank. I do not
believe that the momentary flickering caused by a bad sending unit in the
Cessna tanks seriously interferes with getting an accurate reading of the
amount of fuel in the tank. It is an annoyance at worst and you have to
watch it very closely to even see it.

Just how accurate a fuel gauge has to be to meet the requirements of Part 91
is not spelled out. I know of one guy (one of my instructors, actually -- I
was there) who was busted because his gauge read 2/3 full when it was
actually full. I know of at least one airplane that the gauge always reads
zero until you start the engine. I wonder how an inspector would feel about
that?