Cessna 172 with Wild Fuel Gauge Needle

"Newps" wrote, "... The problem is that the air flowing over the wing
creates a suction from the tank that makes the gauge read full."

Is this true for Cessnas with wet wings, too?

wrote:
C J Campbell wrote:


You were taught a very popular myth. No doubt you were also taught the myth
(spread by Rod Machado and others) that your fuel gauge is only required to
be accurate when it reads zero fuel. The FAR require you to have a fuel
gauge that shows the quantity of fuel in each tank, whether you trust it or
not.

Which FAR covers this?

I can find the one that requires a fuel indicator, but nothing about
accuracy.


Answering my own question...

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 Sec. 23.959(a);


So, (b) would imply that the 172 I rent that shows the right tank at
about 3/4 full when the tank is actually full is not airworthy since
it is not indicating the quantity of usable fuel in the tank.


--
Jim Pennino

Remove -spam-sux to reply.

I'm not 100% sure if it has anything to do with the tank. Mine has
bladders and I have the placard.

Jon Woellhaf wrote:

"Newps" wrote, "... The problem is that the air flowing over the wing
creates a suction from the tank that makes the gauge read full."

Is this true for Cessnas with wet wings, too?

"C J Campbell" wrote in message
You were taught a very popular myth. No doubt you were also taught the myth
(spread by Rod Machado and others) that your fuel gauge is only required to
be accurate when it reads zero fuel.

The myth is that they have to only be accurate at zero. The truth is that there's
no requirement for accuracy at all. All the misinterpreted rule says is the EMPTY
mark means zero USABLE fuel.

By your method of reading the regs, then every airplane in the world has to
be grounded because the compass cannot be adjusted to read correctly at each
and every heading...
Whereas, in the real world a compass deviation card is perfectly legal, and
is in fact, required..

So too is a fuel indicator correction card legal as long as the gauge
directly reads correctly at one point - zero useable...
In fact, I have a fuel gauge correction card on the panel... My gauge(s)
reads empty at zero useable - and it ain't kidding, you've got about 90
seconds to switch, or else...
Now, a gauge that reads full all the time in flight due to some tank vacuum
problem, doesn't meet the regs...
denny
wrote in message
...
wrote:
C J Campbell wrote:


You were taught a very popular myth. No doubt you were also taught the
myth
(spread by Rod Machado and others) that your fuel gauge is only
required to
be accurate when it reads zero fuel. The FAR require you to have a
fuel
gauge that shows the quantity of fuel in each tank, whether you trust
it or
not.

Which FAR covers this?

I can find the one that requires a fuel indicator, but nothing about
accuracy.


Answering my own question...

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 Sec. 23.959(a);


So, (b) would imply that the 172 I rent that shows the right tank at
about 3/4 full when the tank is actually full is not airworthy since
it is not indicating the quantity of usable fuel in the tank.


--
Jim Pennino

Remove -spam-sux to reply.

wrote in message
...
wrote:
C J Campbell wrote:


You were taught a very popular myth. No doubt you were also taught the
myth
(spread by Rod Machado and others) that your fuel gauge is only
required to
be accurate when it reads zero fuel. The FAR require you to have a
fuel
gauge that shows the quantity of fuel in each tank, whether you trust
it or
not.

Which FAR covers this?

I can find the one that requires a fuel indicator, but nothing about
accuracy.


Answering my own question...

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 Sec. 23.959(a);


So, (b) would imply that the 172 I rent that shows the right tank at
about 3/4 full when the tank is actually full is not airworthy since
it is not indicating the quantity of usable fuel in the tank.

That is correct. However, there is no regulation specifying exactly how
accurate the gauge is supposed to be. The one case I know of was a FSDO
inspector doing a ramp check who noticed the gauge read 2/3 full when the
tank was actually full. He said that was unacceptable and wrote it up. He
also failed my instructor on his assistant chief flight instructor check for
coming to the check ride with an aircraft that was not airworthy.

23.133 only defines zero fuel on a fuel gauge. After all, the manufacturer
could say that "empty" means zero total fuel if there were no regulation
defining what zero fuel means. The gauge has to indicate the quantity of
fuel in gallons or pounds, none of this business of unlabelled marks at each
quarter level like you see on cars. It does not give a blanket allowance for
the gauge to be inaccurate at any other level. 91.205 says:

(9) Fuel gauge indicating the quantity of fuel in each tank.

"Ron Natalie" wrote in message
. ..

"C J Campbell" wrote in message
You were taught a very popular myth. No doubt you were also taught the
myth
(spread by Rod Machado and others) that your fuel gauge is only required
to
be accurate when it reads zero fuel.

The myth is that they have to only be accurate at zero. The truth is
that there's
no requirement for accuracy at all. All the misinterpreted rule says is
the EMPTY
mark means zero USABLE fuel.


That is pretty much what I said, except that 91.205 says that you have to
have fuel gauges indicating the quantity of fuel in each tank. However,
91.205 does not say how accurate a gauge has to be to meet this requirement.
I do know from painful personal experience that some FAA inspectors will
write up a plane if they think the gauge is too inaccurate.

"Dan Thomas" wrote in message
om...
"C J Campbell" wrote in message
...
" jls" wrote in message
news
Anybody know the reason for this? The needle on the pilot's side is
stable, but the needle on the co-pilot side swings wildly, especially
when
the tank is full. A float moves the needle around the dial. Why
doesn't
it stay still and be good like its brother?

It probably is a bad sending unit, especially if it is a late model 172.
You
can replace the sending units, but they just go bad again.

The earlier ones do it, too. They have a wirewound potentiometer
that wears out and starts getting intermittent.


You would think they would have fixed the problem by now, but the new ones
are even worse than the old ones.

Newps wrote in message news:QJsYb.206924$U%5.1138302@attbi_s03...
I'm not 100% sure if it has anything to do with the tank. Mine has
bladders and I have the placard.

Jon Woellhaf wrote:

"Newps" wrote, "... The problem is that the air flowing over the wing
creates a suction from the tank that makes the gauge read full."

Is this true for Cessnas with wet wings, too


It applies to Cessnas with bladders. The loss of a cap (or the
ignoring of the AD that demands an annual check of the cap O-rings)
will cause suction to pull the fuel out, collapsing the bladder toward
the filler neck and forcing the gauge sender float upwards. I can't
see that it applies to wet wings or aluminum tanks.

Dan

"C J Campbell" wrote in message
...

wrote in message
...
wrote:
C J Campbell wrote:


You were taught a very popular myth. No doubt you were also taught
the
myth
(spread by Rod Machado and others) that your fuel gauge is only
required to
be accurate when it reads zero fuel. The FAR require you to have a
fuel
gauge that shows the quantity of fuel in each tank, whether you
trust
it or
not.

Which FAR covers this?

I can find the one that requires a fuel indicator, but nothing about
accuracy.


Answering my own question...

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 Sec. 23.959(a);


So, (b) would imply that the 172 I rent that shows the right tank at
about 3/4 full when the tank is actually full is not airworthy since
it is not indicating the quantity of usable fuel in the tank.

That is correct. However, there is no regulation specifying exactly how
accurate the gauge is supposed to be. The one case I know of was a FSDO
inspector doing a ramp check who noticed the gauge read 2/3 full when the
tank was actually full. He said that was unacceptable and wrote it up. He
also failed my instructor on his assistant chief flight instructor check
for
coming to the check ride with an aircraft that was not airworthy.

23.133 only defines zero fuel on a fuel gauge. After all, the manufacturer
could say that "empty" means zero total fuel if there were no regulation
defining what zero fuel means. The gauge has to indicate the quantity of
fuel in gallons or pounds, none of this business of unlabelled marks at
each
quarter level like you see on cars. It does not give a blanket allowance
for
the gauge to be inaccurate at any other level. 91.205 says:

(9) Fuel gauge indicating the quantity of fuel in each tank.




Speaking of section 23, how do you know which version of section 23 was in
place when a plane was certified? In other words, there are rules there now
which don't apply to older planes, right? Maybe the fuel gauge wording has
been there all along but how do you know? Section 23 only applies when
applying for certification, not for any plane flying, right?

-------------------------------
Travis