Fuel Sending Units.

EdFred

EdFred

Taxi to Parking
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The float units suck in the Comanche. So I was looking at capacitance units. I didn't see any STCs for them. Can they be installed via 337 or field approval? Or am I stuck with crappy units that show 1/2 full when the bladder is dry?
 
EdFred said:
The float units suck in the Comanche. So I was looking at capacitance units. I didn't see any STCs for them. Can they be installed via 337 or field approval? Or am I stuck with crappy units that show 1/2 full when the bladder is dry?
Click to expand...

Here's a list of STC's, I don't see it listed there:

http://www.comancheflyer-eur.com/public/FAA STC PA24.pdf

A field approval is not out of the question. Have you mechanic get everything together and put in a request at the FSDO.

Also, have you talked to Airparts of Lockhaven? http://www.airpartsoflockhaven.com/

They rebuild the Piper style float units as well as the gauges. I've used them in the past and was happy with the work.
 
I would also recommend Airparts of Lockhaven. Fast turn-time and good work.

I send all of my PA46 senders to them. My 172 indicators were always lousy and now work great since they were repaired.

Kevin
 
Get a totalizer and fuggedaboud the Fuel Gauges. They're legal, and any more money put into them is wasted.
 
bbchien said:
Get a totalizer and fuggedaboud the Fuel Gauges. They're legal, and any more money put into them is wasted.
Click to expand...

FAR 23.1337 says:

-----------------
(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);
--------------------



So the OP's gauges that "show 1/2 full when the bladder is dry" are illegal and need fixing.


Dan
 
these are what I converted the F-24 to

http://www.aircraftspruce.com/catalog/inpages/westfuelqty3.php

very easy Field approval.

they self calibrate, and are always right on.

your cover letter to request approval should have phrases like

this system change is improve the accuracy and maintainability of the system, plus the additional safety.
 
Dan Thomas said:
FAR 23.1337 says:

-----------------
(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);
--------------------



So the OP's gauges that "show 1/2 full when the bladder is dry" are illegal and need fixing.


Dan
Click to expand...

Even if you bent the needle to read "0" always, it will be legal.
 
Dan Thomas said:
FAR 23.1337 says:

-----------------
(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);
--------------------



So the OP's gauges that "show 1/2 full when the bladder is dry" are illegal and need fixing.


Dan
Click to expand...

The OP's aircraft is a CAR3 airplane. CAR 3.672 applies, but to be fair it says pretty much the same thing. :thumbsup:
 
bbchien said:
Get a totalizer and fuggedaboud the Fuel Gauges. They're legal, and any more money put into them is wasted.
Click to expand...

I've got a JPI installed, and it's always within 1 gallon when I top off. But, the fuel gauges are still incorrect - at least one of em.
 
Tom-D said:
Even if you bent the needle to read "0" always, it will be legal.
Click to expand...

No, it would not. The FAR says "There must be a means to indicate to the flightcrew members the quantity of usable fuel in each tank during flight." A gauge that always reads zero does not provide a means to determine the quantity of fuel during flight.

This misconception (a gauge that just reads zero being legal) has gotten more than a few folks into trouble with the regulators.

Dan
 
Dan Thomas said:
No, it would not. The FAR says "There must be a means to indicate to the flightcrew members the quantity of usable fuel in each tank during flight." A gauge that always reads zero does not provide a means to determine the quantity of fuel during flight.

This misconception (a gauge that just reads zero being legal) has gotten more than a few folks into trouble with the regulators.

Dan
Click to expand...

The only time a fuel gauge is required to be accurate is when the tank is empty. So, any gauges that reads empty all the time is accurate when it is required to be.
 
Tom-D said:
The only time a fuel gauge is required to be accurate is when the tank is empty. So, any gauges that reads empty all the time is accurate when it is required to be.
Click to expand...
----------------------------
§ 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.
<snip>

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

A gauge that reads zero all the time is not indicating the quantity of fuel.

And more:
http://www.av8n.com/fly/fuel-gauges.htm


Dan
 
Dan Thomas said:
----------------------------
§ 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.
<snip>

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

A gauge that reads zero all the time is not indicating the quantity of fuel.

And more:
http://www.av8n.com/fly/fuel-gauges.htm


Dan
Click to expand...

OK so we got the gauge, now tell where it says "Calibrated"
 
Tom-D said:
OK so we got the gauge, now tell where it says "Calibrated"
Click to expand...


FAR 23.1337

(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);

Definition of "Calibrated:"
cal·i·brate (k
abreve.gif
l
prime.gif
schwa.gif
-br
amacr.gif
t
lprime.gif
)tr.v. cal·i·brat·ed, cal·i·brat·ing, cal·i·brates 1. To check, adjust, or determine by comparison with a standard (the graduations of a quantitative measuring instrument): calibrate a thermometer.
2. To determine the caliber of (a tube).
3. To make corrections in; adjust: calibrated the polling procedures to ensure objectivity.
 
Last edited:
EdFred said:
I've got a JPI installed, and it's always within 1 gallon when I top off. But, the fuel gauges are still incorrect - at least one of em.
Click to expand...

Ed,

What ended up being the problem back when it was indicating the higher flows? Glad you figured out a fix... And curious as to what it was in case it happens in the 182.
 
The gauges in the 310 read accurately. It's very nice to have.

Yet, my friend's Travel Air with a fuel totalizer seems to be more accurate still.
 
flyingcheesehead said:
Ed,

What ended up being the problem back when it was indicating the higher flows? Glad you figured out a fix... And curious as to what it was in case it happens in the 182.
Click to expand...

Transducer was kaput. It would read high, then low, then 0, then 99.99. Replaced it, and it's been pretty much spot on.
 
Dan Thomas said:
FAR 23.1337

(b) Fuel quantity indication. There must be a means to indicate to the flight crew members the quantity of usable fuel in each tank during flight. An indicator calibrated in appropriate units

OK we got gallons or pounds or empty 1/4-1/2-3/4 and full

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);
Click to expand...

Equal to the unusable fuel is empty, you are not getting any more from that tank in level flight.
 
bbchien said:
Get a totalizer and fuggedaboud the Fuel Gauges. They're legal, and any more money put into them is wasted.
Click to expand...

Thing is, garbage in, garbage out. If they aren't programmed properly...

Also, it won't really help if you develop a fuel leak, or, heaven forbid, you forget to check the fuel caps on a high wing airplane and siphon about 20 gallons of fuel out of the tank.

Ask me how I know.

On the other hand, don't.
 
Tom-D said:
Equal to the unusable fuel is empty, you are not getting any more from that tank in level flight.
Click to expand...

FAR 23.959 defines Unusable Fuel:

Sec. 23.959

Unusable fuel supply.

[(a) The unusable fuel supply for each tank must be established as not less than that quantity at which the first evidence of malfunctioning occurs under the most adverse fuel feed condition occurring under each intended operation and flight maneuver involving that tank.Fuel system component failures need not be considered.

It's not level flight. It is (as Canadian law also defines it) the attitude most critical for flight. In many airplanes the tank outlet is at the bottom of the tank but maybe halfway between the front and rear so that in a steep gliding attitude (like with flaps) the fuel sloshes forward and could unport when below unusable fuel. Sometimes it's the climb attitude that will do it. In any case, the TCDS for the airplane usually gives the unusable fuel. The 172M's unusable fuel is two gallons per side, and the fuel senders will still float a little in level attitude on that fuel, so the gauges are supposed to read Empty at that point. Any dipsticks should read Zero in that fuel. I know of at least two engine stoppages on final when the pilots ate into their unusable fuel.

Dan
 
Tom-D said:
these are what I converted the F-24 to

http://www.aircraftspruce.com/catalog/inpages/westfuelqty3.php

very easy Field approval.

they self calibrate, and are always right on.

your cover letter to request approval should have phrases like

this system change is improve the accuracy and maintainability of the system, plus the additional safety.
Click to expand...


Tom -

My A&P talked to the FSDO, and the guy at the FSDO asked if there was a copy of the paperwork that was done for any other field approvals. He said something about needing some engineering drawing to make sure it worked once already, so he could send it to Chicago. I dunno, that's just what I'm being told.
 
EdFred said:
Tom -

My A&P talked to the FSDO, and the guy at the FSDO asked if there was a copy of the paperwork that was done for any other field approvals. He said something about needing some engineering drawing to make sure it worked once already, so he could send it to Chicago. I dunno, that's just what I'm being told.
Click to expand...
His ASI is a Dork. he should know the FAA no longer excepts 337s from different aircraft as approved data.
 
Last edited:
Dan Thomas said:
FAR 23.959 defines Unusable Fuel:

Sec. 23.959

Unusable fuel supply.

[(a) The unusable fuel supply for each tank must be established as not less than that quantity at which the first evidence of malfunctioning occurs under the most adverse fuel feed condition occurring under each intended operation and flight maneuver involving that tank.Fuel system component failures need not be considered.

It's not level flight. It is (as Canadian law also defines it) the attitude most critical for flight. In many airplanes the tank outlet is at the bottom of the tank but maybe halfway between the front and rear so that in a steep gliding attitude (like with flaps) the fuel sloshes forward and could unport when below unusable fuel. Sometimes it's the climb attitude that will do it. In any case, the TCDS for the airplane usually gives the unusable fuel. The 172M's unusable fuel is two gallons per side, and the fuel senders will still float a little in level attitude on that fuel, so the gauges are supposed to read Empty at that point. Any dipsticks should read Zero in that fuel. I know of at least two engine stoppages on final when the pilots ate into their unusable fuel.

Dan
Click to expand...

You just don't get it, do you Dan?
 
Tom-D said:
His ASI is a Dork. he should know the FAA no longer excepts 337s from different aircraft as approved data.
Click to expand...

Well, he's the guy we gotta go through, so I gotta dance for the man. I even asked if it had to be for a Comanche, "Nope, just need to see something that the units are reliable in a certified A/C."
:dunno::dunno:
 
EdFred said:
Well, he's the guy we gotta go through, so I gotta dance for the man. I even asked if it had to be for a Comanche, "Nope, just need to see something that the units are reliable in a certified A/C."
:dunno::dunno:
Click to expand...

You would think the manufacturer of the unit would have copies of that stuff.
 
I dunno. I've never gotten a FA on anything before. It's all been STC'd stuff, so it's new for me.
 
EdFred said:
I dunno. I've never gotten a FA on anything before. It's all been STC'd stuff, so it's new for me.
Click to expand...

The 337 on my 24 won't be what they want to see, because it also uses auto fuel gauges.
 
Tom-D said:
The 337 on my 24 won't be what they want to see, because it also uses auto fuel gauges.
Click to expand...

I talked with them again. The guy just wants to see anything that's out there that's already been done with them. Whether the gauges used were the ones I'm going to or not. If another FSDO approved anything in regards to those sending units, that's going to help.
 
EdFred said:
I talked with them again. The guy just wants to see anything that's out there that's already been done with them. Whether the gauges used were the ones I'm going to or not. If another FSDO approved anything in regards to those sending units, that's going to help.
Click to expand...
If you succeed or even find some useful data I'd like to hear more about it. I've been wanting to convert my Baron's fuel level sensors to capacitive probes for a long time and that's going to be especially important if I ever get the Xerion Auracle I ordered (which happens to be compatible with capacitive sensors). In the meantime if I can help in any way let me know.
 
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