Exterior Preflight

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There are many ways to complete the preflight. Choose your favorite method then follow the same procedures every time. A written checklist followed step-by-step will ensure checking everything in the proper order.

For preflighting multi-engine aircraft, I prefer to start at the door and continue around until reaching the door again, now ready to get in and go. The exterior preflight of a single-engine trainer, a Cessna 152, for example, might go as follows: Start at the engine access door, open it up, and take a good look inside. Look for any obvious discrepancies, such as a magneto lying in the bottom of the cowling. Look for security of nuts, bolts, wires, and harnesses. If a wire is disconnected, point it out to a mechanic. If the aircraft hasn’t been flown for a few days, check for any signs of bird nests or the presence of mice. Once I found a nest complete with mother bird and five little blue eggs…it happens. If a nest is not removed, it can ignite when the engine is heated up (usually in the air).

Check the oil level and add as necessary. Some circumstances may cause false indications and may need to be retested. For example, cold oil has a tendency to climb up the stick; wipe the dipstick and recheck for accuracy. Also, if the engine has run recently some of the oil will remain up in the engine for a time; wait to test until everything’s settled. Never lay the dipstick down; hold it in your hand until you replace it securely. This helps prevent getting it dirty, ruining clothes, or forgetting it entirely.

Next drain the engine fuel sump. Give it time to drain out any unwanted water or debris. Three to five seconds drain time should be enough for most situations. If possible, it is best to try to catch the drained fuel in a clear container. This way you can see any debris or water that might be contained in the fuel. Continue draining the sump until the fuel is clear. Remember, water is heavier than fuel, so it will quickly settle to the bottom.

If you don’t have a glass container to catch the fuel, draining it out onto a hard surface (not grass) and then looking for any bubbles of water also works, only not as well. Be sure the valve is completely off and not leaking.

Close the engine access door and move toward the front of the aircraft. Examine the cowling for any sign of loose rivets, etc., as you make your way to the prop area. Once in front of the aircraft, look inside the cowl on top of the cylinders for any signs of birds’ nests or other material that might have collected on them. Be sure all visible wires and harnesses are in place and secure.

Next grasp the propeller about half way out and gently push and pull it to make sure it is secure. There should be a small amount of movement in and out, but nothing monumental. Check the leading edges of the propeller for any signs of nicks or cracks. As a propeller rotates, it creates a tornadolike suction that can pull up rocks, dirt, or other foreign material. These particles can strike the leading edge of the prop and cause nicks. If you find a nick on the leading edge of the prop, have a mechanic file it down. Remember, the prop is a very delicately balanced airfoil; even a small nick is capable of posing a potential problem. If a prop has many nicks and blemishes it would be wise to remove the prop and send it to a prop repair shop for rebalancing or possible replacement.

Next, squat down directly in front of the aircraft and check the air filter that is located directly beneath the prop and landing light. It should be clean and secure. Check for security of the exhaust pipes with the toe of your shoe (this prevents burnt fingertips if the aircraft has run recently).

Check the nose gear for security and proper inflation, tread wear, and any signs of cords showing through. If the cord is evident, it’s time for a tire change. Also check the nose gear for stability and any sign of missing cotter pins, washers, and nuts. I tell my students that while it is important to check the things that are there, it is even more important to find anything that is not there during the entire preflight.

With the front of the aircraft secure, move on to the cowl on the opposite side from the engine access door. Check for any loose or missing rivets and be sure the static port, which is located just in front of the pilot-side door, is clean and free of any wax, dirt, or insects. For some reason, insects like to nest in the tiny static ports of aircraft.

Now, to check the fuel, grasp the handhold located on the fuselage and place your left foot on the step provided along the lower fuselage. Step up and place your right foot gently to the step provided in the middle of the wing strut. It is important that you keep the majority of your weight on the fuselage step because the strut is not formed to take much weight at a right angle. If your aircraft is not equipped with steps, it is best to use a ladder. Look in to see the fuel level. If you cannot see into the tank, you can try to feel the fuel level with your fingers, or use a clean stick to measure the fuel level. However inconvenient, it is important to verify fuel levels; don’t trust electric fuel gauges because, as mentioned previously, sometimes they lie.

Secure the fuel cap and begin the check of the leading edge of the wing. As you move along the wing, check for any dents, loose rivets, or tears if your aircraft is fabric covered. Also be sure the strut is secure and free from any bends, dents, etc. As you look over the wing and strut, lean down and take an overall look at the wing bottom. Be sure it is free from any problems that might hinder a safe flight.

Moving down the wing, you come to the pitot tube at about the point where the strut joins the spar. It must be free of any foreign matter if it is to supply adequate ram air pressure to the pitot instruments. A reminder: Do not blow into the pitot tube to free any debris. This usually results in ruining the airspeed indicator. The force of the human lung has such power that a short blast of air expelled from the mouth can have more pressure than the pitot tube experiences in flight. If the pitot tube has any foreign debris, try to pick it out with a small, pointed object such as a paperclip. If this fails, you might try blowing gently into the pitot tube while someone else watches the airspeed indicator to make sure you don’t blow it away. If you aren’t sure of what to do, take it to a mechanic and let him solve the problem.

Finish the preflight of the leading edge of the wing and arrive at the wingtip and examine the navigation light to be sure it is secure. While at the wingtip, check the general condition to be sure it has suffered no hangar rash. (Hangar rash is a common disease caused by the careless movement of aircraft in or around other aircraft that can result in wrinkled wingtips.)

Moving to the aft section of the wing, pivot the aileron up and down, checking for freedom of travel. At the same time, watch the aileron on the opposite wing to make sure it is moving in the reverse direction. Besides freedom of travel, you want to check the aileron hinges for security and smooth operation, and to be sure that all cotter pins are in place. When examining the aileron hinges and actuating rods, hold the aileron firmly in the up position so that any wind gust will not crush your fingers.

Since the flaps are already in the down position, examine them and their tracks, operating rods, and hinges very carefully. Most flaps will have a slight amount of play in the down position, but not much —maybe a half inch. If there is much more play than that, have them checked by a mechanic before attempting flight.

Now is a perfect time to drain the wing fuel sump. While on the subject of checking the fuel, always be certain the fuel you drain out is the correct octane for your particular aircraft. You can tell the octane rating of the fuel by the color. 80-Octane fuel is red. 100-Octane fuel is green. 100 low-lead fuel is blue, and jet fuel is clear.

If two different octane grades are mixed in your tank, they will turn clear like water or jet fuel. This chemical process is formulated at the fuel refinery as a safety measure to alert the pilot of the problem. Since a mixture of two different fuel octanes may or may not be healthy to feed the aircraft, some precautions should be taken if the drained fuel comes out clear.

First, check the possibility that you have a tank of water or jet fuel. Jet fuel has a very distinctive smell like kerosene. If this is the case, drain the tank and replace it with the proper octane. If you have a load of water, continue draining through the sump until you get the proper color fuel for your particular aircraft.

After eliminating the water or jet fuel possibilities, it is likely that the fuel in the tank is a mixture of two differing grades of fuel. Now the problem lies in researching and discovering just which two are in the tank. If the octane mixture in your tank is of a higher number than your aircraft requires, then it should be okay to fly. But if the octane is of a lower number than you require, you may want to drain and replace the entire tank with fuel of the desired octane. 

Directly below the fuel sump, check the landing gear, tire, and brake assembly. Watch for any sign of moisture on the ground beneath the inner portion of the wheel. If your brake line has developed a leak, this is one of the primary spots to find an accumulation of fluid. Also check the brake and tire for any signs of unusual wear.

As you move back along the side of the aircraft toward the tail section, check the side and underneath for any loose rivets, tears, dents, etc. Be sure the surface has not buckled from any undue stress or strain. 

Reaching the tail section, check the leading edge of the horizontal stabilizer as you did the leading edge of the wing. It should be free of any large dents (although you are apt to find quite a few rock chips and nicks) and fairly solid as you try to move it gently up and down.

The elevator should move very freely and should travel all the way to the stops that are found just beneath the rudder. Now is a good time to check the external rudder cables for proper tension and security. Watch for any loose or missing cotter pins, nuts, or bolts. Move the rudder from side to side and feel for smooth travel all the way to its stops. Look up and check your VOR antenna and anticollision light (strove or rotating beacon). If you can reach them, feel for the proper security.

Now complete the right side of the aircraft as per the methods utilized for the left side. With the completion of the walk-around preflight, you have the peace of mind that comes from knowing you have done everything in your power to determine that the aircraft is ready for flight.

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