Bad fuel gauges?

Despite my years of fighting ignorance, many pilots still seem to
believe that the fuel gauge only has to be accurate when it reads 0. In
fact, I have seen both Rod Machado and the Kings assert this. We have
an uphill fight, my brother.
--
Waddling Eagle
World Famous Flight Instructor- Hide quoted text -

- Show quoted text -

Rod Machado. I have his audio CD book and it may well be that this is
where I heard the idea of being accurate only when full or empty. I
can't remember at the moment but I'll find out.

An earlier post explained the guage can be off by as much as four
gallons. Is that far enough off to not meet regulations?

Well, the important thing to note is they are not accurate. The only
sure-fire method of tracking your fuel, it seems to me, in a GA
aircraft, is to measure starting values, measure your actual
consumption after shutdown, compare to the TDF to climb & cruise
performance charts. Especially if you plan your flight down to the
reserve! (Does anyone really plan to stretch fuel use clear to the
limit of the regs?)

The fuel gauge that goes to zero in flight WILL get my attention....
Other than that, my watch/timer is my fuel gauge...
Being it is my airplane I know how much I takeoff with and what the
burn rate is... From experience I know that engine surging and tank
switching is normally within five minutes of what my watch calls
for...
Tips are always burned off first then switched with 30 minutes fuel
remaining... This puts me back on the mains and the timer is reset to
put me back on the ground with 30 minutes, or more, left in the
mains... All told an hour of fuel is always left on board and my
personal check list does not allow eating into that reserve for
anything other than a life or death situation... This iron clad rule
is the result of learning the hard way no flameout but the tanks took
exactly the usable amount listed in the POH and has served me well in
the 4 decades since...

wrote:
different formulations all have varied dielectric constants, meaning
that the gauge could indicate 22 gallons one day and 18 the next; do you
want to bet your life that there's four extra gallons in the tank?

TheSmokingGnu

Ye Olde E6B and zeroing in on real fuel consumption at cruise gleaned
from actual flight should save the day (older planes not up to chart
performance, usually).

Well, even there you have significant challenges; you have to account
for the fuel in takeoff/climb (according to power/leaning), as well as
in descent, and you have to somehow figure out how much you've used in
taxi and runup. There are still large areas where the best you can do is
guesstimate at actual fuel usage.

Even then, unless you have a penchant for wingwalking, it's exceedingly
difficult to measure actual fuel usage in cruise without the fuel
gauges, which we have already established as really "best guess"
instruments anyway.

TheSmokingGnu

On Feb 23, 2:11*pm, wrote:
Despite my years of fighting ignorance, many pilots still seem to
believe that the fuel gauge only has to be accurate when it reads 0. In
fact, I have seen both Rod Machado and the Kings assert this. We have
an uphill fight, my brother.
--
Waddling Eagle
World Famous Flight Instructor

Rod Machado. I have his audio CD book and it may well be that this is
where I heard the idea of being accurate only when full or empty. I
can't remember at the moment but I'll find out.

Maybe the only-accurate-on-empty myth started as one of Rod's jokes
and got out of hand.

wrote in
:

On Feb 23, 2:11*pm, wrote:
Despite my years of fighting ignorance, many pilots still seem to
believe that the fuel gauge only has to be accurate when it reads
0. In fact, I have seen both Rod Machado and the Kings assert this.
We have an uphill fight, my brother.
--
Waddling Eagle
World Famous Flight Instructor

Rod Machado. I have his audio CD book and it may well be that this is
where I heard the idea of being accurate only when full or empty. I
can't remember at the moment but I'll find out.

Maybe the only-accurate-on-empty myth started as one of Rod's jokes
and got out of hand.


I heard it years ago. It doesn't make much difference. They're not reliable
anyway. You wouldn't want to fly around without them, but you woulnd't want
to stake your life on them..


Bertie

On Feb 22, 11:24*pm, WingFlaps wrote:
A recurring theme seems to be that one should should not rely in fuel
gauges. I can understand that from a safety point of view (I always
dip the tank before start), but I get the feeling that they are
considered just plain inaccurate.

The admonition not to rely on fuel gauges is half-right. The half
that's right is important; the half that's wrong is dangerous.

The half that's right is that you need another way to know how much
fuel there is, because the gauges have limited accuracy, and because a
previously working gauge can always fail suddenly. For the GA planes
I'm familiar with, a visual preflight inspection of the tanks is
required by the POH. From there, you calculate your fuel consumption.
If the gauges say you've got more fuel than you expect, trust your
calculations instead (double-checking if necessary). Aviation safety
is about redundancy.

The half that's wrong is that the admonition ignores a vital
possibility: the gauges may show way LESS fuel than you expect. (Say
you're supposed to have 3/4 of a tank left, but the gauge shows 1/8.)
In that case (if the gauges are working well enough to meet the
airworthiness requirements) you know you've got a problem--perhaps a
fuel leak, which your consumption calculations can't warn you about
without the gauges. A leak may be a very infrequent event, but
aviation safety is about being prepared for unlikely problems, rather
than unnecessarily relying on the gamble that it will never happen to
you.

The Part 91 airworthiness regs (which pilots are required to know
before being allowed to solo) mandate a gauge that indicates the fuel
level in each tank. No specific accuracy is mandated, either in Part
91 or in the aircraft-certification regs in Part 23. So it becomes a
matter of common sense: a working fuel gauge has to be accurate enough
to serve its intended purpose, which (in familiar light GA planes
anyway) is to provide a rough cross-check of the consumption
calculations, to warn of a leak or other problem.

On Feb 23, 5:23*pm, Bertie the Bunyip wrote:
wrote :





On Feb 23, 2:11*pm, wrote:
Despite my years of fighting ignorance, many pilots still seem to
believe that the fuel gauge only has to be accurate when it reads
0. In fact, I have seen both Rod Machado and the Kings assert this.
We have an uphill fight, my brother.
--
Waddling Eagle
World Famous Flight Instructor

Rod Machado. I have his audio CD book and it may well be that this is
where I heard the idea of being accurate only when full or empty. I
can't remember at the moment but I'll find out.

Maybe the only-accurate-on-empty myth started as one of Rod's jokes
and got out of hand.

I heard it years ago. It doesn't make much difference. They're not reliable
anyway. You wouldn't want to fly around without them, but you woulnd't want
to stake your life on them..

Yup, absolutely. They're part of a redundant system--nothing more,
nothing less.

Look at the Pilot's Handbook of Aeronautical Knowledge, too.

FUEL GAUGES

The fuel quantity gauges indicate the amount of fuel measured by a sensing
unit in each fuel tank and is displayed in gallons or pounds. Aircraft
certification rules only require accuracy in fuel gauges when they read
"empty." Any reading other than "empty" should be verified. Do not depend
solely on the accuracy of the fuel quantity gauges. Always visually check
the fuel level in each tank during the preflight inspection, and then
compare it with the corresponding fuel quantity indication.

Bob Gardner

wrote in message
...
There's an urban legend that the fuel gauge is only required to be
correct for an empty tank. The legend apparently arises from a
bizarre
misreading of 23.1337b1. What 23.1337b1 actually says is just
clarifying that the 'empty' reading must correspond to zero USABLE
fuel, as opposed to zero TOTAL fuel. There is nothing whatsoever to
suggest that non-empty readings needn't be correct--that would be
absurd. (If it were true, a gauge that ALWAYS says 'empty' would be
legal! You could just write 'empty' on a piece of paper and call that
your fuel gauge!)

The requirement for indications of a tank's fuel level (not just on
empty) is stated in 91.205b9, 23.1305a1, and 23.1337b.

Thank you!

What you say makes perfect sense. I'll go look at the regs too.

The best fuel gauge is a watch. If the book says that your plane burns 7.4
gallons an hour, subtract 8 gallons from your usable fuel figure and use
that number in all further calculations. Establish a conservative
wheels-on-the-ground time...."Let's see, it's noon now, I have fuel for four
hours on board, I will have the wheels on the ground somewhere (maybe not my
destination), at 3:30."

Bob Gardner

"WingFlaps" wrote in message
...
Hi all,
A recurring theme seems to be that one should should not rely in fuel
gauges. I can understand that from a safety point of view (I always
dip the tank before start), but I get the feeling that they are
considered just plain inaccurate. Why is that, every car I've driven
has a fuel gauge that seems accurate. Am I missing something?

A connected point is that I was taught that if you start to worry
about low fuel you switch to the lowest tank (2 tanks) and note the
time. When the engine splutters you know what time/range you have left
to find a good landing spot (after switching tanks). But if a gauge
can't be trusted is that the best thing to do?

Cheers

On Feb 23, 7:10*pm, "Bob Gardner" wrote:
The best fuel gauge is a watch. If the book says that your plane burns 7.4
gallons an hour, subtract 8 gallons from your usable fuel figure and use
that number in all further calculations. Establish a conservative
wheels-on-the-ground time...."Let's see, it's noon now, I have fuel for four
hours on board, I will have the wheels on the ground somewhere (maybe not my
destination), at 3:30."

Bob Gardner

"WingFlaps" wrote in message

...



Hi all,
A recurring theme seems to be that one should should not rely in fuel
gauges. I can understand that from a safety point of view (I always
dip the tank before start), but I get the feeling that they are
considered just plain inaccurate. Why is that, every car I've driven
has a fuel gauge that seems accurate. Am I missing something?

A connected point is that I was taught that if you start to worry
about low fuel you switch to the lowest tank (2 tanks) and note the
time. When the engine splutters you know what time/range you have left
to find a good landing spot (after switching tanks). But if a gauge
can't be trusted is that the best thing to do?

Cheers- Hide quoted text -

- Show quoted text -

That's how I'm being taught.

Wil