Preflight Inspection

(Reference:  Flight Training Magazine - Features, 1994 by Robert N. Rossier)

  1. Cockpit

  2. External

  3. Empennage

  4. Tail Assembly

  5. Wings

  6. Landing Gear

  7. Cowling and Nose

  8. The Prop and Spinner

  9. Final Inspection

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From Flight Training Magazine - Features 1994 by Robert N. Rossier


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 throttle.

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 proper operation.



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 replace.

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 serious.

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 aircraft.

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 control surface.

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 failure.

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 mechanism.

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 during flight.



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 damage.

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 the slipstream.

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 breather tube.

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 removed.

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.



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