Cessna 172 with Wild Fuel Gauge Needle

[jls]

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?

[Bob Noel]

In article >, " jls"
> wrote:

> 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?

loose connection somewhere?

--
Bob Noel

[Rick Glasser]

On Mon, 16 Feb 2004 15:59:47 -0500, jls wrote:

> 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?

There was a service bulletin for the fuel sensor in the late model Cessnas
(don't know the number). Last winter, almost all of the 172s at our club
would exhibit the same problem. This winter (after a few 100-hour and
annual inspections) none that I have been flying are acting bad. It
used to be quite a nuisance.

--
Rick/JYO
PP-ASEL-IA
remove 'nospam' to reply

[C J Campbell]

" jls" > wrote in message
...
> 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.

[Larryskydives]

I would never trust a fuel guage. I was taught to alway visually check and
know the aircrafts fuel usage.

[C J Campbell]

"Larryskydives" > wrote in message
...
> I would never trust a fuel guage. I was taught to alway visually check
and
> know the aircrafts fuel usage.

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.

The reason you are to check the fuel in each tank is to see if your fuel
gauge is accurate. If it is not accurate, your airplane is not airworthy. I
think it is very strange for people to say that they do not trust a fuel
gauge, but they trust other, equally unreliable instruments such as the
ammeter, oil pressure and temperature, fuel flow, etc.

Your fuel gauge must be accurate, no matter how good you are at estimating
fuel flow and using your watch. Your fuel tank could leak, for example, or
your fuel cap could come loose during flight. The only way that you would
know that you are losing fuel would be from your fuel gauge, especially if
you fly a high wing airplane or you are flying at night. The fuel line from
one of your tanks could become blocked, creating an imbalance and
effectively cutting your fuel supply in half. One of the most common fuel
mismanagement accidents occurs when pilots switch to an empty tank. Your
fuel gauge is a critical item of fuel management, possibly the most
important one.

[Dan Thomas]

"C J Campbell" > wrote in message >...
> " jls" > wrote in message
> ...
> > 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.

Dan

[Newps]

If your fuel cap comes off in flight in your high wing Cessna you will
never be able to tell you are losing fuel by looking at your fuel gauge.
The problem is so bad that 182's have to have a placard stating that.
The problem is that the air flowing over the wing creates a suction
from the tank that makes the gauge read full.

C J Campbell wrote:

> "Larryskydives" > wrote in message
> ...
>
>>I would never trust a fuel guage. I was taught to alway visually check
>
> and
>
>>know the aircrafts fuel usage.
>
>
> 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.
>
> The reason you are to check the fuel in each tank is to see if your fuel
> gauge is accurate. If it is not accurate, your airplane is not airworthy. I
> think it is very strange for people to say that they do not trust a fuel
> gauge, but they trust other, equally unreliable instruments such as the
> ammeter, oil pressure and temperature, fuel flow, etc.
>
> Your fuel gauge must be accurate, no matter how good you are at estimating
> fuel flow and using your watch. Your fuel tank could leak, for example, or
> your fuel cap could come loose during flight. The only way that you would
> know that you are losing fuel would be from your fuel gauge, especially if
> you fly a high wing airplane or you are flying at night. The fuel line from
> one of your tanks could become blocked, creating an imbalance and
> effectively cutting your fuel supply in half. One of the most common fuel
> mismanagement accidents occurs when pilots switch to an empty tank. Your
> fuel gauge is a critical item of fuel management, possibly the most
> important one.
>
>

[mikem]

Google Groups result:

Your shorter link is: http://makeashorterlink.com/?D23212077

jls wrote:
> 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?


MikeM
Skylane '1mm
Pacer '00z

[[email protected]]

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.


--
Jim Pennino

Remove -spam-sux to reply.

[Jon Woellhaf]

"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?

[[email protected]]

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.

[Newps]

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?
>
>

[Ron Natalie]

"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.

[Dennis O'Connor]

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.

[C J Campbell]

> 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.

[C J Campbell]

"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.

[C J Campbell]

"Dan Thomas" > wrote in message
om...
> "C J Campbell" > wrote in message
>...
> > " jls" > wrote in message
> > ...
> > > 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.

[Dan Thomas]

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

[Travis Marlatte]

"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

[C J Campbell]

"Travis Marlatte" > wrote in message
ink.net...
>
> 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?
>

Every aircraft has a type certificate which details what the condition of
the aircraft must be in order to conform to type. These are kept on file and
are available through such services as Summit Aviation. The certificates are
updated as new models are introduced. There are some real surprising things
in there, such as airframe life limits (if any), etc. There are many
variants of the Cessna 172, for example, and not all of them share the same
type certificate. IIRC, the 172RG and 172 XP share their type certificate
with the 175, not the 172. That implies to me that the 172RG is the same
type aircraft as the 175 fixed gear airplane, but is a different model,
while the 150 and 152 are two different types entirely. I doubt if it is
really all that important for anything except the occasional maintenance
question, since none of these airplanes require a type rating, but I thought
it was interesting anyway.

So, anyway, you look to the type certificate to see what version of section
23 applies to a particular aircraft.

[G.R. Patterson III]

C J Campbell wrote:
>
> 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.

Really? Mine have five hash marks labeled "E", "1/4", "1/2", and "F". The mark
for 3/4 full is not labeled at all. The plane does have a placard beside the
tank selector valve indicating the total fuel capacity. Perhaps that's a fairly
new requirement? My aircraft was certified in the late '80s or early '90s.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.

[Newps]

>
> C J Campbell wrote:
>
>>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.

Perhaps on the new models. But on older models this is just flat out
wrong. My gauge has an F and an E and four lines, that's it.

[C J Campbell]

"Newps" > wrote in message
news:chSYb.73130$uV3.528318@attbi_s51...
>
>
>
> >
> > C J Campbell wrote:
> >
> >>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.
>
> Perhaps on the new models. But on older models this is just flat out
> wrong. My gauge has an F and an E and four lines, that's it.

Gee, I've seen some pretty old airplanes and they all had the fuel quantity
calibrated on their gauges.

Of course I could be wrong. It is not like that would be a new experience
for me. :-)

[Larryskydives]

That what makes this world such a great place - you trust your gauge and I will
trust a visual check for full tanks, and known fuel burn.

And we can agree to disagree.

[Newps]

C J Campbell wrote:
> "Newps" > wrote in message
> news:chSYb.73130$uV3.528318@attbi_s51...
>
>>
>>
>>>C J Campbell wrote:
>>>
>>>
>>>>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.
>>
>>Perhaps on the new models. But on older models this is just flat out
>>wrong. My gauge has an F and an E and four lines, that's it.
>
>
> Gee, I've seen some pretty old airplanes and they all had the fuel quantity
> calibrated on their gauges.

The only place the majority of Cessnas even list the quantity where it
is visible is on the fuel selector.

[Mark Mallory]

Ron Natalie wrote:
>
> no requirement for accuracy at all. All the misinterpreted rule says is the
EMPTY
> mark means zero USABLE fuel.

Actually, the rule says that zero USABLE fuel will give an EMPTY indication, not
the other way around as you stated.

An empty indication does NOT necessarily mean zero usable fuel.