Most preflight inspection checklists start in the
cockpit, and that's probably the best place to start. There's little
use in conducting the rest of the preflight if the paperwork isn't
in order or if the aircraft is unsafe to fly for some obvious
reason. I like to visually check the fuel and oil quantities before
I start. If I need either, I can order it immediately and finish the
preflight while I'm waiting for it to be delivered.
When you open the door, note if it seems stiff or
is difficult to open. A poorly fitting door could mean cracked or
sprung hinges or, worse, structural damage, such as a
"sprung" fuselage due to hard landings. Be aware of
unusual odors such as avgas or kerosene. A fuel odor might be caused
by a leaking fuel selector valve or engine primer. The odor of
kerosene means you have a leaking compass. Either condition is cause
for maintenance prior to flight.
After determining that the aircraft paperwork is
in order (see "Arrows Aviate," March 1993), turn on the
master switch to check fuel gauge indications. If you'll be flying
under instrument flight rules (IFR), listen for the electrically
powered gyro instruments to spool up. If the panel is equipped with
a cooling fan, ensure that it's running, too. An inoperative fan can
lead to in-flight radio failures.
If the aircraft has retractable landing gear, make
sure the handle is down and the "down and locked lights"
are on. You may want to cycle to flaps to make sure they operate
properly or extend them for the exterior preflight. When everything
is checked, turn the master off.
Remove the control locks and run the controls
through their range of motion to check their freedom of movement.
Check the trim controls to ensure they are operable, then set the
trim to the takeoff position. Make sure the fuel selector moves
freely and that it clicks into the proper detents. The instruments
should read appropriately and there should be no condensation or
apparent signs of damage.
Don't overlook the seat rails. Most single-engine
Cessnas have mandatory 100-hour rail inspections that look for
cracks and elongation of the holes for the seat lock mechanism. This
is critical. More than one pilot has had the unnerving, if not
fatal, experience of having the seat slide back on rotation due to a
failed seat rail. When this happens, the nose pitches up and the
power goes to idle because the pilot is holding onto the yoke and
Before leaving the cockpit, ensure that the
magnetos are off and the mixture control is at idle-cutoff so the
engine is less apt to accidentally start during preflight. Also look
through the windshield to see if it's clean. If not, clean it after
the preflight. Finally, make sure the fire extinguisher is available
and properly charged.
If the aircraft is to be flown at night, or
there's enough fuel on board to fly the aircraft into darkness (an
emergency, such as stuck landing gear, could force such an
eventuality), turn on the lights and quickly check all of them -
navigation lights, beacon or strobes, and landing/taxi lights - for
As you inspect the empennage, keep a sharp lookout
for some small details that are easily overlooked. Look for fuel
stains that may emanate from the top, bottom, and root of the wing
and run aft or downward along the side of the aircraft. This can be
a sign of leakage, either in the tank or from the fuel strainer.
If equipped, make sure the passenger and/or
baggage door is securely closed. Anything in the baggage compartment
or back of the aircraft should be secured with a cargo net. I've
seen the results of blending unsecured baggage with unexpected
turbulence, and those rear windows can be outrageously expensive to
Check the skin for wrinkles or bulging that could
be a sign of overstressing the airframe. Missing or
"working" rivets are another sign of a problem. A
"working" rivet, one that is no longer tight, can be
identified by a dark powdery substance around its head. One or two
may not necessarily be a big problem, but if you find several,
particularly in a row, it could be the sign of something more
Look at the airplane's belly. Damage from running
off a runway or taxiway might not be visible from the side. While
you're there, make sure all the antennas are intact and look for
excessive oil or soot. Excessive oil can be a sign of a leak,
spillage, or oil blown out the crankcase breather vent. Soot may be
a sign of improper mixture adjustment.
Somewhere you should find the ELT (emergency
locator transmitter) antenna. Make sure it's there and firmly
attached. Unlike other antennas, the ELT antenna is easy to overlook
and might not be missed until you need it.
Make sure any exterior gust locks are removed from
the tail and check the control cables and connectors to ensure
everything is secure and not worn or frayed. Check the elevator and
horizontal stabilizer/stabilator surfaces for damage. Dented or
bowed surfaces are often not just skin deep; they may be an
indication of structural problems. Tail sections on Cessnas are
particularly susceptible to structural damage caused by those who
push down on them to raise the nose while repositioning the
Don't forget to check the bottom of the horizontal
surfaces; serious damage may be more likely to occur there. This
area is prone to damage from rocks kicked up by the tires or from a
tail strike during a botched landing. Also inspect the outer edges
of the elevator or stabilator, and the tail tiedown, as they can
also be damaged from a tail-low landing.
When inspecting a Cessna 152 damaged in a tail-low
crosswind landing, the only evidence of damage on the top of the
horizontal stabilizer was a slight inward bowing of the skin - a
condition that perhaps a dozen pilots attributed to mere cosmetic
damage. The aircraft flew for three weeks in this condition and
nobody suspected a problem. Then a particularly observant student
questioned the indentation and checked underneath the stabilizer,
where he found major scrape marks on the bottom of the stabilizer
tip. The bowing of the skin was due to a bent spar. The aircraft was
unairworthy and the stabilizer had to be replaced.
On aircraft equipped with stabilators rather than
horizontal stabilizers and elevators, grasp the stabilator on the
outboard edge and check for any play in the hinge assembly. Excess
play can lead to flutter and subsequent catastrophic failure of the
Don't forget the trim tab. In one case, a cracked
trim tab on a Cherokee required full nose down trim to keep the
aircraft in level flight. Make sure it is securely attached and free
of any cracks.
Remove any external gust locks attached to the
wing and look for signs of damage, such as wrinkled skin, dents, or
missing or crooked rows of rivets that can be a sign of structural
damage. If the aircraft, such as the Grumman Tiger, has bonded
rather than riveted wing skins, look for any signs of delamination
on the trailing edge. Also pay attention to the wing tips. Scraped
wing tips can be a sign of a ground strike and possible structural
damage. If in doubt, have a maintenance technician check it.
The ailerons should be secure and have freedom of
movement. Look for cracks in the hinges and for loose or missing
hinge pins. The actuator and rod end, which connects the rod to the
aileron, should have a little bit of play and should rotate freely.
Some aircraft have balance weights attached to the
ailerons. On Cessnas they are rectangular weights fitted to the
front of the aileron. They are designed to aerodynamically balance
the ailerons and prevent flutter. Flutter can lead to catastrophic
Flaps should receive the same attention as the
other control surfaces. Check the actuator rod and rod ends for
freedom of movement and the hinges for security. Some flap systems,
such as those on Cessnas, use a roller and guide system. Make sure
the roller is within the guides and that there's nothing to jam the
General aviation aircraft are equipped with a
variety of different stall warning systems. Cessna singles have a
vent on the left wing that activates the horn under conditions of
reduced pressure. If you're tall enough, you can place a
handkerchief over the vent and suck gently to check its operation.
Other aircraft have a stall warning vane switch on
the wing. It is electrically powered, and must be checked with the
master switch on. You should hear the horn when you lift the vane
up. These vanes sometimes stick in the "on" position,
particularly after the aircraft has been washed. If the stall horn
sounds when you turn on the master switch, jiggle the vane; it may
return to normal operation.
The pitot/pitot-static assembly is typically found
on the wing. Make sure the pitot tube and static port are clear of
obstructions such as insects, ice, or mud. If you do find a
blockage, do not blow into the pitot or static holes; this can
damage the system. Call a maintenance technician.
Sampling the fuel for contaminants is an important
yet controversial practice. Concerns have been raised regarding the
effects of avgas on human health. If you're concerned, wear gloves
while taking a fuel sample. You may not want to smell the fuel
sample to ensure that it is, indeed, avgas, not jet fuel. Regardless
of your concerns, always sample the fuel and check for contaminants,
such as water or ice crystals, and verify its octane color coding.
Although it may look strange, it's a good idea to
rock the wings before taking the fuel samples. If condensation has
formed on the inside of the tank walls - or is trapped in the folds
of fuel bladders - it's best to shake it loose on the ground rather
than having turbulence do it in flight. If you find something amiss
in your sample, continue draining fuel until you consistently get
good fuel samples.
The wing also has a fuel tank vent. And some
aircraft have vented fuel tank caps. In either case, make sure the
vents are clear of obstructions. A blocked fuel vent means that air
can't get into the tank to replace the fuel burned during flight.
This results in a vacuum that may overpower gravity or the fuel pump
and stop the flow of fuel to the engine. You can guess what happens
next. When you remove the fuel caps to check fuel quantity, check
the rubber gasket that seals the tank and, if it's a vented cap, the
rubber flapper for the vent. If the tank doesn't seal properly, you
can get excessive amounts of water in the fuel, or you can lose fuel
either through a poor seal or as a result of the cap coming off
Landing gear is only used during taxi, takeoff,
and landing. But because the largest percentage of accidents occur
during these operations, the landing gear deserves some attention.
Unless the aircraft has wheel fairings that preclude a thorough
inspection, check the wheel for cracks and other damage, and make
sure it is securely attached.
Look for leaking brake fluid and abraded hoses or
brake lines. Check the brake pads to make sure they're serviceable.
At minimum, they should be a little thicker than a quarter. The
rivet head that holds the pad to its backing plate is about as thick
as a quarter. If the pad wears thinner than this, the rivet head
will start wearing on the brake disk, causing scoring and other
When checking the tires for inflation and
excessive wear, roll the aircraft back to inspect the entire surface
of the tire. A smooth tire is getting old, and if the cords show,
consider it unsafe for flight. Flat spots can be caused by excessive
braking or landing with the brakes on. It's relatively easy to wear
a flat spot to the cord while the rest of the tire looks fine.
Murphy's law says that when you abort a takeoff, the tires will lock
up with the flat spot on the bottom, the tire will blow, and you'll
run off the runway.
Don't disregard the tires' sidewalls. On a
retractable gear aircraft, unusual sidewall wear or slicing can be a
subtle sign of more complex problems, such as a bent gear leg. While
a bent gear leg represents a structural problem itself, a tire
rubbing on the edge of the gear well may also lead to a jammed
landing gear or blown tire.
If your airplane has retractable gear, check for
leaking or abraded hydraulic lines as well as brake lines, and check
for any obstructions in the gear well which could cause a tire to
jam. It's a good idea to check the security of the gear doors and
linkage to ensure everything is secure and operating properly.
A few years ago I watched a pilot land a Cessna
310 with a fouled nose gear. The aircraft had just come from an
inspection and the nose gear door had been improperly reattached.
When the pilot retracted the landing gear, the nose gear was jammed
by the door and subsequent attempts to lower it were futile. Good
training enabled the pilot to make a textbook emergency landing, and
he and his passenger were unharmed.
Check inside the cowling for debris. Birds are
notorious for building nests here, and like surgeons, mechanics will
sometimes leave something behind when they finish work. Bird nests
and rags can catch fire once the engine reaches operating
temperatures, and tools can rattle around and break things.
Some aircraft, such as older Piper singles, have
hinged cowls that will enable you to give the engine and accessories
a thorough inspection. Look for loose or abraded belts, abraded or
separated hoses, fuel or oil leaks, and any other obvious problem.
If possible, check the brake and hydraulic fluids to make sure
they're at the proper levels. With a good flashlight, you can also
check the cylinders for cracks.
Don't over-tighten the dipstick when checking the
oil quantity. It should be snug, finger-tight. This
"tightness" increases when the engine heats up, and if the
dipstick starts out over-tight, it causes excessive wear to the
O-ring seal - and it may be nearly impossible for the next pilot to
remove the dipstick to check the oil level.
Check the cowl's exterior for any loose or missing
fasteners. Losing the cowl in flight can cause serious damage,
especially if it hits something, such as the tail, as it blows by in
Some aircraft have static ports on one or both
sides of the nose. Make sure they aren't blocked by ice or debris.
As before, don't blow into them under any circumstances because this
can damage the system.
It's important to check the crankcase breather
tube located somewhere on the bottom of the engine cowl, especially
during winter. This tube relieves the excess pressure that builds up
in the crankcase as combustion gases escape past the piston rings.
If the tube is blocked, as it can be during winter by frozen
condensation from exhaust gases or slush thrown up from the nose
wheel, the pressure will find another way out. One likely exit is
the main seal on the crankshaft. If this blows, so does your oil.
Then you get to practice emergency landings. To check for blockage,
stick a pen or other similarly shaped object into the end of the
The nose gear gets the same inspection as the main
gear, with some extra attention given to the shimmy dampener. When a
Piper Dakota landed with a failed shimmy dampener, the resulting
vibration, transmitted via the control rods, was so violent it
destroyed the rudder. Make sure that all fasteners are secure and
there's no sign of damage.
On some aircraft, the air filter is visible on the
nose. There are two basic types of filters - pleated cardboard and
foam rubber. The cardboard pleats should look straight and uniform.
If some of them are starting to spread or break down, this is a sign
of deterioration that could result in a failure that might cause the
carburetor to ingest the cardboard. You'll probably want to have it
checked by a mechanic. Oil-impregnated foam filters are not prone to
this problem. Regardless of filter type, check for other loose items
near air intakes that might be ingested.
Make sure all the fasteners on the spinner are
secure. You really don't want the spinner to come off during flight.
Besides the fact that it might hit something important, an important
function of the spinner is to improve engine cooling through
improved air flow. Remove the spinner and the aircraft will likely
fly slower due to the drag, and air may blast around the cowling
rather than through it, causing the engine to overheat.
Your problems will be much worse if the spinner
only comes off part way. This can cause an out-of-balance situation
resulting in severe, damaging vibration. Even a single loose screw
can cause a problem, such as hitting and damaging a propeller blade
on its way out. During winter, check inside the spinner (if you can)
for snow or ice as this, too, can cause a prop imbalance. Naturally,
snow or ice should be removed before flight.
Inspect the propeller's front and back, as well as
leading and trailing edges for nicks and other damage. Nicks can
cause stress points that might result in propeller failure. This is
serious trouble. Even if you lose a small piece of the prop, the
prop becomes severely imbalanced. The resulting vibration can be so
severe that it's been known to shake the engine off the airframe.
This causes an extreme aft CG condition that usually results in a
flat spin to the ground. Get the picture?
If inspecting a constant speed propeller, look at
the cowling and windshield for any signs of oil spray. This can be a
sign of damage to the prop seals, or worse. Twist each blade and
note any play in the hub. For some props, it's OK to have a small
amount of play. For others, none is acceptable. Also grasp the tip
of each blade and try moving it fore and aft. Again, you're checking
for play, and there shouldn't be any.
The last step in a preflight inspection is a final
overview of the aircraft. At a distance of some 20 feet behind the
aircraft, squat down and look it over. Check the fuel caps and make
sure they are properly aligned. Make sure the wings are still clear
of snow and frost. Make sure all tie-downs and chocks have been
Finally, check to see whether the aircraft is
sitting squarely, or if something looks bent, like from a hard
landing. If anything looks wrong in this big-picture perspective,
have a maintenance technician check it out, as he or she should fix
almost anything else you find during your preflight before you fly.
Our quick preflight inspection is complete, and it
only took 3 hours! Seriously, not everything in this article will
pertain to the aircraft you fly, but once you know what to look for
on the plane you fly, the preflight will go quite quickly. One hopes
that you found a thing or two here that will make your inspections
just a little more thorough. Remember, problems are best left on the
ground. If something goes wrong up there, you can't just pull over
and fix it.