Time, running out of fuel and fuel gauges

A couple of points with regard to running out of fuel:

1. I think many pilots forget about the time factor (i.e. keeping track
of it) once they are a few months out of student training.
2. I think teaching that the fuel gauges are useless (which is very
common) is teaching a dangerous myth.

With point (1), if you keep good track of time it's almost impossible to
get lost, certainly during daylight VFR. My instructor certainly harped
onto me about the importance of keeping note of time (not just time off,
but time passing X on your route). Many pilots I've flown with don't (or
worse still rely on VOR/DME or GPS).

With point (2), so far I've only flown one aircraft with truly useless
fuel gauges. Few people ever bother looking at them because:
1. they do a visual fuel inspection before the flight
2. they know the fuel burn and endurance of the aircraft
3. they have been taught that the fuel gauges are useless

But 3. is most often wrong. Even though I've never been in a light plane
with particularly precise fuel gauges, all but one light plane I've
flown has had fuel gauges which were good enough for performing a cross
check.

I'll now tell you a story about how I avoided running out of fuel.

About 3 years ago, I got checked out in a C182, the 1960 model (which
was the only year model to have a swept tail but no rear window, if I
remember correctly). It also doesn't have fuel tanks as big as the later
C182. However, I knew all of this as well as pertinent information (such
as fuel burn) from reading the manual before getting checked out. Our
flying club required a short open-book written exam for any plane you
were getting checked out in to get everyone to at least look and try and
remember all the pertinent information, including computing a weight and
balance and fuel burn calculations.

So a couple of weeks after first getting checked out, I have the plane
booked for a long trip from Houston to Utah. Knowing I wouldn't be able
to get fuel the next morning since I was setting out at 6am, I went out
to Houston Gulf the night before and checked the fuel so I could get it
topped off if necesary. I got on the little ladder and looked in the
tanks, and it looked full, so I went home. I filed my IFR flight plan
that evening, so I could just get ready, and go out to the airport and
fly.

I did another visual check of the fuel as part of my preflight - yep,
still full.

So off I went, climbing to altitude, and got the engine leaned out
nicely. The weather had turned out to be much better than forecast, but
I still went IFR - after all, there was a high overcast and it was still
dark. My first leg was long enough that I'd have only an hour worth of
fuel on landing.

Passing over Waco, I cross-checked my time en route with the fuel
gauges. They showed a little LESS than expected; they had been
indicating F on departure. About 45 minutes on, they were showing
sufficiently less than I expected that I decided to land before
reaching my intended fuel stop. I told ATC I wanted to change
destinations, got the field in sight, canceled IFR and landed.

The FBO had just opened. They topped the plane off. When I did the
visual check, I noticed what I thought was full wasn't really full - now
it was truly full, I realised the fuel being an inch below the filler
neck was actually the best part of an hour's worth of fuel! Looking at
my fuel receipt, I calculated I'd have landed at my original intended
destination with only 15 minutes of fuel left. Any vectoring or holding
could have quite easily blown that. Had I ignored the fuel gauges as
being useless, that's what would have happened. After topping off, I
noticed the fuel gauges indicated slightly over the F mark instead of
being right on it - rather like my car really.

So my lesson is - keep track of time AND cross check time and your
expected fuel burn with the fuel gauges. If the gauges show less than
expected, land and check it out. They might well be right.

Of course we'll never know - but perhaps the fuel gauges on that Archer
that ended up in Lake Michigan were telling the pilot all along that he
was running out of fuel. Perhaps he hadn't leaned the mixture right,
perhaps he hadn't kept track of time and had a higher headwind than
expected and perhaps his flight plan said he'd make it with adequate
reserve. And perhaps the fuel gauges were telling him all along, but
he'd been admonished never to trust them, so never even thought to
include them in his normal cross-check.

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

I have owned and flown a Cessna 182B for almost 27 years, and have
found that the
fuel gauges are pretty accurate in level flight (checked with a
dipstick after landing).
Like you say, the tanks will take quite a bit more when they look full.
Also, it is not
uncommon for the gauges to be hard against the pin (full) for an hour
after takeoff.

Be that as it may, I always start the stopwatch when I take off - and I
believe whichever
indication is the most pessimistic about fuel remaining (calculated
endurance or
gauges).

David Johnson

Fuel gages can also be made inaccurate by fuel tank deformation. The
Aeronca Sedan on floats I was flying 40 years ago had fuel cells, which
I didn't really understand the consequences of at the time. It also
had sight glass gages directly into the two wing tanks. After all,
what could be more accurate and reliable I thought.........

My cross country aerial adventure with my then new girl friend started
out by a magneto failure (stone dead) discovered at altitude on the
outbound trip. That got fixed by a local tractor magneto repair shop
(Yeah, he'd seen that mag used on old Allis Chalmers - but they were
considered quite troublesome). It needed a new coil for $3.00.

But the old bird also had leaky fuel caps and possibly a plugged fuel
vent system. At any rate on the return leg the fuel levels still
indicated nice and high while cruising along. The fuel cells were
collapsing, while those wonderful gages showed lots of fuel on board.
I'd swear that thing went from 1/2 tanks indicated to a complete engine
stoppage in 5 minutes. We deadstick landed in a swamp and drifted to
shore, up to a very surprised farmer's house to ask for fuel.

It was quite an adventure. I understand it is now an AD on Aeronca
15ACs.

As for peeking into the tanks and seeing what's the we have
made calibrated dipsticks for every airplane we operate, with the zero
on the stick being the unusable-fuel level in the tanks as specified by
the POH, and full being FULL, which usually coincides with the tank
capacity given by the POH. These aircraft are used for training
commercial pilots who will be flying in Third-World
jungle/desert/mountain/sea operations, for outfits that demand an exact
fuel figure before every takeoff. Fuel mistakes in such environments
are usually fatal.
The calibrated stick isn't hard to make, but it surely is a pain
to get every drop out of the system, put the unusable fuel amount in
each tank, then add three or five gallons at a time to determine the
level for that amount. The airplane has to be fairly level, too,
without being rocked around by wind or moved while determining dipstick
calibrations.
The stick is handy for confirming accurate fuel flows after
landing from cross-countries and seeing what the real burn is at
various mixture settings. Cessna, for example, calculates their cruise
charts based on a pretty lean mixture, where few low-time pilots
operate.

Dan

wrote:

The stick is handy for confirming accurate fuel flows after
landing from cross-countries and seeing what the real burn is at
various mixture settings.

I used a dip tube extensively when I flew in a C172. This allowed me to
provide very specific refueling instructions for the lineman when weight
and balance required less than full tanks.

In the Bonanza I now fly, the wing tanks slope from the cap to the back of
the wing. Below about 26 gallons, I cannot see the fuel nor dip a stick to
determine fuel quantity. Thus, to be absolutely sure of fuel when it is
out of sight like this, I am forced to fill at a minimum to the bottom of
the tabs, or 30 gallons useable. I miss the certainty and flexibility
that the C172 tanks provided.


--
Peter


















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The only regulations for fuel gauges are that they read correctly at
empty. They are not reliable for determining the amount of fuel in the
tanks, but as they approach empty, they should be believed.
--
Gene Seibel
Hangar 131 - http://pad39a.com/gene/plane.html
Because I fly, I envy no one.

"Gene Seibel" wrote

The only regulations for fuel gauges are that they read correctly at
empty. They are not reliable for determining the amount of fuel in the
tanks, but as they approach empty, they should be believed.

Bull****! I am repeating an e-mail that I sent to a young man
who posted the same information on his web site.

Russ......

I stumbled on your web site while searching for some C-172 Fuel Cap
information.
I found the following statement which while completely false, seems to be
circulating quite widely.

"The FAA only requires the gauges to read accurately when the tanks are
empty. Yeah, you're right, that's really stupid, but it's the law."

I have quoted the applicable portion of the Federal Aviation Regulation
"law".

Section 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 §23.959(a);

Paragraph (b) of course is the controlling portion and requires the
indicator to indicate the quantity of fuel at all times. Since no
tolerance is specified other than the indicator must be marked and
calibrated, it must be assumed that it must be calibrated accurately.

The intention of paragraph (1) is to require that the "zero" reading be
applied to "useable fuel" and not "total fuel". The C-172 that I fly
(1959 model) can be filled with a total of 42 gal. of fuel of which only
37 are useable. It obviously would not be acceptable to have the engine
quit from fuel starvation with 5 gal. showing the gages.

Paragraph (1) has nothing to do with gage "accuracy" but rather the
calibration of the system to indicate zero with zero useable fuel
remaining.

It might be wise to remove the erroneous "hangar talk" from your web
site.


Bob Moore
ATP CFII

Dan
Having operated for much of my 22,000 hours in remote areas and/or
hostile terrain where help was where you could find it, I made it a
point to take the time and trouble of making a calibrated stick for
each of my aircraft. I have run out of fuel a couple times in about 50
years of flying for various reasons. Fuel gages to me, are simply
indicators to assist in aircraft operations. They may or not be
accurate. In any case, when they indicate below 1/4 I get nervous and
watch my fuel burn vs time even more closely and in particular when I
am over hostile terrain.
I've experienced mechanical failures when either the gages went offline
as in an electrical failure, or I was losing fuel from a poor
connection or venting from a faulty drain. The end result was not
pleasant but no injuries to anything either. If you are not flying a
glider, you sure better know specific fuel burn for your operations and
aircraft lest you turn into a glider pilot of a lousy glider with a big
chunk of iron hanging on the nose!!
One hour of fuel remaining in the tanks at my destination usually gives
me that warm fuzzy feeling. Sometimes I never had that option or
capability. As a segue to that, GOOD navigation is a requisite skill so
you don't find yourself wondering where in hell you are or where you
are going?!
Cheers
Ol S&B

Thanks for the correction.
--
Gene Seibel
Gene & Sue's Aeroplanes - http://pad39a.com/gene/planes.html
Because we fly, we envy no one.

The cherokee series has a fairly prounounced wing dihedral. If the
airplane is parked on a non-level surface, it's possible for the lower
tank to appear full when in fact it can be a good half hour short of
full.