Call it the 50-foot rule. Almost every airplane looks great from 50 feet away. But get close and any problems start to reveal themselves. A thorough and complete preflight inspection is the only way to ensure that an airplane is ready for safe flight. Here are some common problem areas, what to look for, and how to know the difference between something that's merely imperfect and a truly unairworthy condition.
Cockpit
Smart pilots will ensure the ignition and avionics switches are off and then turn the master switch on to check fuel quantity on the gauges. Remember that one of aviation's greatest wastes is air in the fuel tank.
While that master switch is on, listen to the sounds in the cockpit. You should hear the normal noises of gyros spinning up and the avionics cooling fan. Listen for anything unusual.
Turn on all the exterior lighting and check for burned-out bulbs. Check the anti-collision (strobes), beacon, navigation, and landing and taxi lights. If night flight is anticipated, also check the cockpit illumination, including items such as dome lights, instrument "eyebrow" lights, instrument back lighting, map lights, and control yoke lights.
Ensure that the required documents are onboard (AROW: airworthiness certificate, registration, operating limitations or POH, and weight and balance data). Make sure you have your documents as well. This means pilot certificate, medical certificate, picture ID, and any navigational charts you need. Verify the master and the ignition switches are off before beginning the walk-around.
Flight controls
All of the flight-control surfaces--the ailerons, elevator or stabilator, rudder, and flaps, should be free of mud, snow, and ice. All airfoils must be completely clean of any frost or ice contamination. The ailerons, elevator, and rudder should move freely, and without excessive free play--there should be no binding, and no strange noises. The balance weights on the control surfaces should be installed and secure. If you can, look into the cockpit and observe that the control wheel moves in the correct direction as you move the ailerons up and down.
Structure
Start with the structure or empennage of the airplane. Look for anything mechanically unsound: loose or missing rivets or fasteners, cracks, dents, or scratches. Loose rivets are sometimes called smoking rivets, because a trail of black soot streaks back from the rivet. You may see small holes at the ends of cracks in plastic trim pieces. Most likely these cracks have been stop drilled, which slows the crack until a repair or rework can be performed. Wrinkled skin is serious and can be a sign of damage or overstress, perhaps from a hard landing or unauthorized "aerobatics." Inspect the various antennas for security, cracks, and general condition. Take stock of any pitot covers, cowl plugs, "remove before flight" streamers, gust locks, tiedowns, and chocks, as all of them will have to be removed before flight.
Landing gear
As you can imagine, the landing gear on a typical training airplane takes a lot of abuse. Thus, tires, brakes, and oleo struts can often be deal breakers when it comes to your go/no-go decision. Visually check the tires for proper inflation, and note the general condition of the tread. Look for any flat or bald spots, deep cuts or nicks, and bulges or blisters. On the main wheels, look over the brake lines for leaking fluid.
Check the inflation of the oleo struts to make sure they are not "bottomed out." On tricycle gear airplanes, check the nosewheel strut to make sure the shimmy damper is secure. A loose shimmy damper can cause nosewheel vibration during takeoff and landing. If you find anything that looks suspicious, ask the A&P mechanic to investigate it.
Flight instruments
The airspeed, altimeter, and vertical speed indicator depend on the pitot static system for proper operation. Ensure that the pitot tube and static ports are clear and free of obstructions. If flight in cold weather is anticipated, the pitot tube heater can be checked on the ground at this time. If your airplane is equipped with a stall warning horn or sensor, that should be checked for proper operation as well. The last person to wash the airplane may have even left tape over the static port, as shown here.
Visually confirm the quantity of fuel in the tanks before every flight (not just the first flight of the day). Use a calibrated fuel dipstick to measure fuel quantity, and don't rely on the gauges, which may only be accurate when reading empty. Locate the fuel drains for your airplane and, using a fuel sampler cup or fuel tester, obtain small amounts of fuel to check for sediment or contaminants. A small amount of water is very common, and will sink to the bottom of the fuel tester because it is heavier than aviation gasoline. (Fuel and water behave like oil and vinegar, in that they don't mix.) If practical, keep the fuel tanks topped off to reduce condensation and water contamination. Sometimes decomposing bladder tanks, gaskets, or sealant can contaminate the fuel system with sediment. This can look like small particles of dirt floating around in the fuel sample. If in doubt, get it checked out by an A&P mechanic.
Check the fuel caps and their "O" rings for general condition and security. Colored stains on the paint near a fuel cap or fuel drain are a telltale sign of fuel leakage. Ensure that the fuel vents are clear.
Fuel Doors and windows
Nobody likes a dirty windshield, so if need be, clean it before flight. Use only approved cleaners and polishing cloths on aircraft acrylics to prevent scratching and crazing. Make sure windows and cabin and baggage doors are closed and latched.
Nose
Check the security of the cowling. Then take a peek inside. Birds, insects, and small animals love to build nests in cowls, especially if the airplane has been sitting for a while. Check the oil level and then secure the dipstick. It's a good idea to top off the oil as per the POH for extended cross country flights.
The propeller is one of the hardest working airfoils on the airplane, and is subjected to a lot of stress during flight. Check it carefully to make sure that it is free of deep nicks, scratches, and gouges. Generally, a nick less than one-thirty-second of an inch wide or deep can be deferred until the next maintenance cycle. But anything larger, or if there is a preponderance of nicks, should be "dressed out" or filed smooth immediately by a qualified A&P mechanic. The spinner also should be checked for security. First, make sure all the fasteners are in place around the spinner. Then, grasp the tip of the spinner firmly and gently try to move it in a circular pattern. The spinner and its backing plate are lightweight and easily damaged; never move the aircraft or lift the nose by pushing the spinner. If your airplane has an alternator belt, make sure it has firm tension. The belt should be in good condition without a shiny or glossy appearance that could indicate slippage. Take a look at the engine air intake filter: it should be unobstructed.
At the bottom of the cowl, locate the exhaust pipe. Make sure it is secure. The exhaust pipe should have a normal color, and the belly of the airplane shouldn't have excessive black soot or exhaust trails.
Ready to go?
A good preflight concedes that no airplane, and no person, is perfect. Something may have been overlooked. Thus, it does no harm to make a quick final check before you climb in. Look for unsecured doors, dangling seat belts, and missed chocks, tie downs, or streamers. If you feel uncomfortable with anything you find on your preflight inspection, have it checked out by an experienced A&P--you'll know that the airplane is safe to fly, and expand your growing knowledge of preflight procedures.
Christopher L. Parker is a CFI and an aviation author, speaker, and FAA remedial training specialist. He flies internationally as a contract captain on a Bombardier Challenger business jet and lives in Los Angeles.
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