172S and R fuel guages.

JordanD

Honorary Member
I've noticed this problem quite a bit on the fuel gauges of the fairly new 172s that I fly. One tank (usually the right side) will bounce between empty and full throughout the flight. Yesterday I don't think it ever showed a reading between empty or full, and it was almost constantly jumping around, causing the R LOW FUEL light on the annunciator to come on quite a bit. Is this problem unique to Cessnas? I never noticed it on the older M that I used to fly. I know the problem has been checked out a few times. Not that it's a big deal since I always check the fuel and plan my fuel extremely conservatively, but it's kind of a nuisance, and any passengers I have always seem a little conserned until I explain to them that the fuel gauges aren't really required to be all that accurate... which usually makes them more uncomfortable. :laff:
 
until I explain to them that the fuel gauges aren't really required to be all that accurate...

§ 91.205 Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.
(a) General. Except as provided in paragraphs (c)(3) and (e) of this section, no person may operate a powered civil aircraft with a standard category U.S. airworthiness certificate in any operation described in paragraphs (b) through (f) of this section unless that aircraft contains the instruments and equipment specified in those paragraphs (or FAA-approved equivalents) for that type of operation, and those instruments and items of equipment are in operable condition.

(b) Visual-flight rules (day). For VFR flight during the day, the following instruments and equipment are required:

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



Be careful out there

91.205 http://ecfr.gpoaccess.gov/cgi/t/tex...v8&view=text&node=14:2.0.1.3.10.3.7.3&idno=14
 
I've never seen that happen on the R/SP either. Maybe you can have it checked out. The 172M/N on the other hand...
 
probably a bad fuel sender/level sensor whatever they call it.

just remember the guage is only legally required to show the correct amount when empty, not saying you shouldn't get that looked at though
 
It's a common problem with the R/S models. Many times it has been the wiring that runs through the wings. During the first few years of Independence production, I think they put a POS connector for when the wing was mated to the fuselage. They must have changed it along the way because I haven't seen the problem in the newer NavI/II models from, maybe, 2003-5.
 
It's a common problem with the R/S models. Many times it has been the wiring that runs through the wings. During the first few years of Independence production, I think they put a POS connector for when the wing was mated to the fuselage. They must have changed it along the way because I haven't seen the problem in the newer NavI/II models from, maybe, 2003-5.

:yeahthat:

I had it happen on a 2000 S model once. Right after takeoff, the gauge for the right tank dropped to empty. By the time I worked my way back around the pattern it went back to full and worked OK the rest of the flight.
 
Never seen that problem, but on the newer R's (2006 or so) the gauges develop this problem where they will show more fuel than is in the tank, slowly creep upward (over 10 seconds or so), and eventually red X on the G1000. The red X will go away if you shake the airplane or bang on the bottom of the wing. As a rule I don't trust Cessna fuel gauges farther than I can throw them.
 
just remember the guage is only legally required to show the correct amount when empty

I believe this to be a myth. Part 23 requires providing a measure of usable fuel in each tank, and this is not being done if the gauge is inaccurate except on zero. As I think you can see, accurate on zero is a useless instrument.
 
I believe this to be a myth. Part 23 requires providing a measure of usable fuel in each tank, and this is not being done if the gauge is inaccurate except on zero. As I think you can see, accurate on zero is a useless instrument.
but i have only flown 1 airplane that has an accurate fuel guage, and i have probably flown over 120 different airplanes(not types), and very rarely do i ever see a proper indication on the guages. all of the arrows we have when at tabs should be 25 gallons, or 27.5 total yet, the guages always show over 30 maybe even 35. same with the seminoles, we have calibrated rulers on the tank caps and even though you check them and should have the same in each tank because you have the exact same measurement, one guage always reads higher than the other.
 
but i have only flown 1 airplane that has an accurate fuel guage

I know. I think this requirement is widely ignored, or at least interpreted very liberally. How accurate do the gauges need to be in order to be legal? Within a gallon? Within 1/4 tank? 1/2 tank?

Of course, now that you've confessed in a public forum to flying unairworthy aircraft for most of your flying career, the FAA will probably be knocking on your door soon.
 
I have found the R/SP models fuel gauges to be pretty accurate in the airplanes I fly.
 
§ 91.205 Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.
(a) General. Except as provided in paragraphs (c)(3) and (e) of this section, no person may operate a powered civil aircraft with a standard category U.S. airworthiness certificate in any operation described in paragraphs (b) through (f) of this section unless that aircraft contains the instruments and equipment specified in those paragraphs (or FAA-approved equivalents) for that type of operation, and those instruments and items of equipment are in operable condition.

(b) Visual-flight rules (day). For VFR flight during the day, the following instruments and equipment are required:

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



Be careful out there

91.205 http://ecfr.gpoaccess.gov/cgi/t/tex...v8&view=text&node=14:2.0.1.3.10.3.7.3&idno=14
I know about that requirement. The thing is, the problem never occurs during the preflight. A lot of the time it will show the same reading as the other tank and still jump around.
 
I know. I think this requirement is widely ignored, or at least interpreted very liberally. How accurate do the gauges need to be in order to be legal? Within a gallon? Within 1/4 tank? 1/2 tank?

Of course, now that you've confessed in a public forum to flying unairworthy aircraft for most of your flying career, the FAA will probably be knocking on your door soon.

Real constructive.
:whatever:

14 CFR 23.1337 is worth a look.
 
Real constructive.
:whatever:

14 CFR 23.1337 is worth a look.

It good you brought this up so I could find this:

4) There must be a means to indicate the amount of usable fuel in each tank when the airplane is on the ground (such as by a stick gauge);
Where is this located on a 172? I know of all the Warriors, Sundowners, Sports I've flown have a tab. But the 182's, 172's and 152's I've flown don't have them.
 
I believe this to be a myth. Part 23 requires providing a measure of usable fuel in each tank, and this is not being done if the gauge is inaccurate except on zero. As I think you can see, accurate on zero is a useless instrument.
Part 23 (and the reg is posted below) only requires that the instrument be calibrated at zero (empty). That means that while it's supposed to tell you how much fuel is in the tank, just because the gauge says 10 gallons doesn't mean you have 10 gallons. The gauge isn't required to be calibrated each gallon...only at zero.

So, no...it's not a myth.

Part 25 planes.........same regulation.

14 CFR 23.1337 is worth a look.
I'm pretty sure it's 25.1337 if anyone wants to see how similar the part 25 airplanes gauges are to the part 23 planes.

-mini
 
Part 23 (and the reg is posted below) only requires that the instrument be calibrated at zero (empty).

No, let me help. Note the part in red:
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.
The regulation goes on to say:
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);

Note that it says "In addition"? This means it's an additional requirement, not the sole one.
 
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