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AFETY ADVISOR
Operations & Proficiency No. 5
Fuel Awareness
Almost Home
Yo u’re almost home. Through your headphones the
engine beats louder as you wait for the sound of silence,
and the knot in your stomach grows larger as time and
the airplane seem to slow down. Your last refueling
opportunity is well behind now. It will surely take
longer to turn around than to press on and you wonder
if backing off on the power will make a difference. But
the airplane’s going so slowly now you decide to leave
things as they are. One good thing about this ground
speed – it gives you plenty of time to pick out suitable
landing sites – at least in daylight. But night fell an hour
ago and your pilot’s sense – what little you possess at the
moment – tells you that surviving a forced landing now
will be more a matter of luck than skill. It’s cool in the
airplane but sweat stings your eyes as you search for the
familiar airport lights over your nose.
Fuel-related
Fuel-related
Fifteen minutes later you shut down in front of your
hangar. For once the fuel truck is waiting for you and you
wish the lineman had tarried long enough for you to get
some strength in your legs, but he’s probably as anxious to
get home as you were an hour ago. The lineman shakes
his head and you shudder when you see how much fuel
went into your airplane. As you lock the hangar you
mumble thanks for the preservation of fools along with a
promise to never do this again. It’s early but the last hour
has left you unbelievably tired, and it’s an effort to stay
awake and focused for the short drive home.
accidents
accidents
occur at the
occur at the
rate of more
rate of more
This is how many fuel exhaustion accidents develop.
Through a combination of circumstances and a few, as
NASA might put it, “non-optimal” decisions, otherwise
prudent pilots crash short; often in sight of their desti-
nation. Most pilots can recall a time or two when they
dipped into the reserves and most vow never to do it
again. But somebody does it.
than three
than three
Fuel related accidents occur at a rate of more than
three per week.
In 2003, 91 fuel exhaustion accidents
occurred, and although there was nothing to fuel a
post-crash fire, eight were fatal. In that same year,
another 41 accidents (five fatal) were attributed to fuel
starvation, and 16 (three fatal) were a result of fuel
contamination.
per week.
per week.
There is much that pilots should know about fuel and
fuel management. In the following pages we’ll discuss
these subjects in detail but first let’s look at the five
things you can do to reduce your chances of having a
fuel-related accident:
fuel that is drawn from the tanks. These
devices will indicate your consumption rate,
but there’s another part of the problem.
•Next you’ll have to know for certain how much
usable fuel is actually on board. Fuel comput-
ers will tell you how much you’re burning and
how much you have left but pilots must input
the fuel quantity, so the old computer adage
applies – garbage in equals garbage out. A
calibrated dipstick is a good way to measure
fuel but be sure it’s calibrated for your air-
plane. Some airplane models have several
options for fuel tank capacity, i.e. a dipstick
calibrated for a Cessna 182 with bladder tanks
will indicate more fuel than is actually present
in a 182 with metal tanks.
1. Know How Much Fuel You Have -
You can’t know
how far you can go unless you know how much fuel
you have, but knowing that isn’t always easy.
•
The first step in knowing how much fuel you
have is to
think of fuel not in gallons or
pounds but hours and minutes.
Why think in
time rather than distance? Because fuel burn is
a constant – the engine, barring a malfunction,
will always burn the same amount at any given
combination of altitude, power setting, and
mixture setting, but range will vary constantly
due to changing winds and ground speeds. In
order to know how much time you have, you
must also know the rate at which your fuel is
being consumed. That means an intimate
knowledge of your engine’s fuel consumption.
The POH figures will get you close to the
answer but only experience will tell you for
sure.
Note: The Air Safety Foundation recom-
mends that pilots of unfamiliar airplanes add
one or two gallons per hour to their comput-
ed fuel consumption until they see how much
that airplane actually burns.
Departing with full tanks is a good tactic but
that isn’t always possible. Most airplanes
exceed weight and balance limitations with full
fuel, all seats occupied, and maximum bag-
gage. Some airplanes can be difficult to fuel
completely. And what about the pilot before
you who says, “I only flew an hour off of full
tanks”? Were they really full? Did the pilot
lean or was he operating full rich? What was
the fuel consumption rate for the previous
flight? Trust but verify. It’s your safety and cer-
tificate on the line, not his.
Some airplanes are equipped with fuel flow
computing devices that actually measure the
2. Know Your Airplane’s Fuel System -
Pilots must
also be familiar with and proficient in operating
Fuel System Schematic
Safe Pilots. Safe Skies.
• Pg. 2
the fuel system on their airplanes. Fuel manage-
ment on a Cessna 150 training airplane is easy.
Two wing-mounted tanks simultaneously gravity
feed fuel to the engine. The fuel selector is either
on or off. Compare this with a low-wing single
boasting two main, two wing auxiliary, and two
after-market tip tanks with an engine-driven prima-
ry fuel pump, electric boost pump, and electric fuel
transfer pumps. It’s not surprising that some pilots
have made forced landings with fuel still available.
grade of fuel and there are no contaminants. Fuel
drains are, however, the second line of defense.
Pilots and aircraft operators should take steps to
prevent contaminants from entering the fuel sup-
ply in the first place. For example, most water
contamination enters airplane fuel tanks through
worn or defective fuel cap seals.
Most aircraft fuel suppliers take great care to
ensure an uncontaminated product is delivered to
their customers but occasionally contaminated
fuel is pumped into an airplane. There are also
cases where line personnel have serviced air-
planes with the wrong fuel. That’s why it’s impor-
tant to supervise the fueling and sample the fuel
after each delivery.
A student pilot was flying a Piper Arrow on a
solo cross-country flight. While flying over a
large metropolitan area the engine stopped
due to fuel starvation. The student successful-
ly navigated to a small airport and made a
forced landing. The airplane was substantially
damaged during the landing but the student
was uninjured. A post-landing examination dis-
covered one fuel tank empty and the other
about half full – enough fuel to fly for at least
90 minutes. The student recalled completing
the engine failure checklist as taught by her
instructor. The list, including switching fuel
tanks, was spoken as each item was touched
but nothing was moved. In the heat of the
moment the student reverted to early learning
and performed the checklist twice exactly as
she’d been taught. As she recited the list she
touched each control but
didn’t move them.
In the 1970s, airplane manufacturers started to
identify turbocharged models with racing
stripes and text. A large
Turbo
on the engine
cowl triggered a rash of misfuelings with turbine
fuel. Overt turbo marketing ended as quickly
as it began, but there are still some airplanes out
there with the original markings. Pilots of these
craft should supervise every fueling.
Today there is a movement to install turbine
engines on airplanes originally designed for
reciprocating engines. Misfueling one of these
aircraft with avgas would not be fatal to the
engine, but if the mistake were made the other
way around and a recip. engine airplane got a
load of jet fuel the result could be disastrous.
Pilots of Piper Malibus and Mirages should be
especially careful that their airplanes aren’t
mistaken for the turbine-engine Meridian.
3. Know What’s in Your Fuel Tanks -
Pilots must
ensure their airplane contains the proper grade of
uncontaminated fuel. We’ve all been trained to
drain the fuel tank sumps during preflight to make
sure the airplane’s been serviced with the proper
4. Update Your Fuel Status Regularly During Flight -
It’s good to do thorough preflight planning but,
once in the air, things can change. Winds are
rarely exactly as forecast and weather deviations
add miles and minutes to your trip. The Air Safety
Safe Pilots. Safe Skies.
• Pg. 3
Foundation recommends that pilots evaluate their
fuel status each hour. If you know how many
minutes of fuel you have and how long it will take
to reach your destination or fuel stop, it’s easy to
know if you’ll be needing your reserve. And
speaking of reserves:
Compression and octane continued to rise through
World War II when high compression military engines
required an octane rating of 140. Under certain cir-
cumstances even 140 octane avgas would preignite,
so at very high power settings some military engines
injected water into the cylinders to slow down com-
bustion. The 1950s saw the introduction of turbine
engines, and although the early turbines ran on
avgas, jet fuels were developed to optimize their per-
formance.
[Note: Jet fuel burns hotter and more
easily than any avgas and although turbines can
run on avgas, reciprocating engines will be dam-
aged or destroyed if operated on jet fuel.]
Military
and commercial aviation quickly adopted the higher
performance and more reliable turbines, and by the
mid-1960s reciprocating engines were used almost
exclusively in general aviation applications. During
the 1960s, 140 octane gasoline gradually disap-
peared but avgas development continued. Today
100 low lead, color dyed blue, is the most common
avgas; but 80, red, and 100 octane, green, avgas can
still be found.
5. Always Land with Adequate Reserve Fuel -
Avia-
tion regulations require different fuel reserves for
different operations. For instance: The regulations
require flights conducted under IFR to have
enough fuel to go from A to B, shoot the
approach, execute a missed approach, fly to the
alternate, and then be able to fly for another 45
minutes at normal cruise speed, not throttle back
to milk the maximum endurance from the
machine.
The Air Safety Foundation recom-
mends that pilots never land with less than one
hour of fuel in the tanks. That way all the regu-
latory reserve requirements are met and
exceeded by at least 15 minutes.
Now that we’ve introduced the big five let’s add
some detail.
Avgas Composition
Avgas is required to be an all hydrocarbon product.
This means that the components must be chemicals
that contain only carbon and hydrogen atoms. The
use of chemicals that contain oxygen atoms, alcohol
compounds, and ether compounds is not permitted.
Approved additives are alkyl-lead anti-knock additives,
color dyes for identification, and other additives that
improve storage stability and stop gum formation.
A Little History
The earliest airplanes used automobile, motorcycle, or
tractor engines, and low octane automotive gasoline
was sufficient to power them. But with the introduction
of high compression engines and the special require-
ments of flying machines, aviation gasoline – avgas –
was developed. Volatile, low octane fuel burned too
easily in high compression engines. This resulted in
combustion before the spark plug fired while the piston
was still compressing the air/fuel mixture. To prevent
this damaging preignition or detonation, lead was added
to avgas to slow down the combustion process. The
combustion quality of fuel is expressed as an octane
number. Paradoxically the higher the octane, the more
resistant to burning will be the fuel.
Lead is a pollutant and Environmental Protection
Agency requirements resulted in low lead gasoline for
cars and airplanes. As the EPA continues to reduce
the amount of lead in all types of gasoline, the for-
mulation of avgas will probably move away from lead
as an additive.
Avgas: Riding a Fine Line
Avgas must easily vaporize and mix with air prior to
combustion. If avgas remains in the (original) liquid
state, it will wash lubricant from the cylinder walls,
causing engine wear and diluting crankcase oil. In car-
bureted engines, fuel that does not vaporize quickly is
not distributed evenly in the cylinders. On the other
hand, if the fuel vaporizes too easily, it can cause vapor
lock, carburetor icing, and excessive fuel loss through
fuel tank vents. Avgas manufacturing and control speci-
fications ensure that the gas you put in your tank will
not be too liquid nor vaporize too easily.
Early engines were notoriously unreliable, so
pilots who survived their profession were quite
proficient at forced landings. When the engine
quit and the propeller (stick) stopped turning,
the result was usually a
dead stick landing.
Knowing that each minute could be their
engine’s last, the pioneers endeavored to
always have a suitable landing field within glid-
ing range – a tactic that today’s pilots would do
well to emulate.
Safe Pilots. Safe Skies.
• Pg. 4
Jet Fuel Is Different
•
Automobile gas has much looser manufacturing
specifications and quality control is less stringent,
so quality and performance vary widely.
•
Because of less careful handling, the risk of conta-
mination is greater for automobile gas.
•
Physical and chemical property differences can
lead to poor fuel distribution, poor anti-knock
properties, and excessive motor oil dilution.
Additionally, automobile gasoline is less stable and
is more likely to gum up.
•
Because automobile gasoline is more volatile than
avgas, it is more prone to loss through excess
vaporization, vapor lock, and carburetor icing.
Jet fuel is very different from avgas. Similar to
kerosene, jet fuel burns at much higher temperatures
than avgas engines can withstand. Most jet fuel dis-
pensing nozzles are wide and flat while avgas nozzles
are thinner and round. New airplane fuel tank open-
ings are too narrow to accept jet fuel nozzles and
many older airplanes have retrofitted restricting rings in
their fuel tanks to prevent misfueling. But don’t count
on technology to ensure proper fueling.
The Air Safe-
ty Foundation strongly recommends supervising
every fueling,
making sure that the type of fuel and
amounts are correct. If that’s not possible, be sure to
cross-check the fuel ticket for type and amount in
addition to sampling the fuel in your airplane.
However, many pilots use automobile gasoline in
their planes successfully. This is possible by having an
Inspection Authorized (IA) mechanic complete modi-
fications to the plane mandated by a Supplemental
Type Certificate (STC). After the STC has been com-
pleted for your airplane, you will be allowed to use
80- or 100-grade automobile gasoline, depending
upon the type of certification.
Note: Although plas-
tic gas containers are increasingly common, it is
impossible to properly ground them. Always use a
metal gas can and ground it to the airframe. This
will prevent the possibility of fuel ignition due to
static electricity.
Can I Use Automobile Gas in My
Airplane?
Aircraft Fuel Systems
General aviation airplanes carry fuel in one or more
main fuel tanks and some have auxiliary tanks as
well. Fuel tanks are predominately metal but some
airplanes have synthetic rubber bladders to contain
the fuel. In rare cases a number of tanks may be
interconnected and filled through one opening, but
usually each tank has a capped opening to fill the
tank, a fuel line to the engine, and, in fuel-injected
designs, a return line to convey excess fuel from the
engine back to the tank. Each tank also has one or
more vents to admit air to the tank and one or more
drains to sample fuel for correct type and grade,
water, and other contaminants. If the tanks were not
vented they would collapse as fuel is consumed.
Some tanks have external indicators or internal tabs
to help pilots gauge how much fuel is contained
within them. Each airplane will also have a means of
selecting which tank or combination of tanks is in use
and of shutting off all fuel to the engine. Some air-
planes such as the Cessna 150/152 feed from two
Although automobile gasoline can be used in some air-
planes, remember that airplane engines are designed
to run on avgas. For a number of reasons, your air-
plane might not be able to use automobile gas:
Safe Pilots. Safe Skies.
• Pg. 5
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