Measure of Skill

Perfecting Preflights

February 5, 1997 By Peter A. Bedell

How to make the most of your walkaround

It is hoped that every pilot has at least some sort of preflight routine. Some inspections may be more thorough than others, but that may be true because some pilots simply don't know why they're looking at specific items or performing specific tasks. Sure, you take a fuel sample before the first flight of the day, but do you know why? In the second part of our Measure of Skill series we'll take a look at preflights and, we hope, answer some questions and clear up a few mysteries.

Sensible senses?

One of the biggest traps when preflighting is complacency. Are you looking for discrepancies or just going through the motions? Jiggle this, shake that, listen to those, smell this — nearly all of the senses come into play during the preflight. After seeing the same airplane in great shape hundreds of times, it's easy to glaze over a new squawk. Take in the big picture at first and then focus in on more detailed areas. Are there any birds' nests? Are there any major leaks in the engine compartment? Check the oil. If it needs a quart or two, look in the logs to see whether other people have been adding oil to the engine. If oil consumption has taken a decisive upturn, the engine might be trying to tell you something. Check individual hoses and wires for breakage or chafing. Look over the cylinder heads and crankcase for cracks. Visually check bolts for snugness. For the owner of an airplane whose engine compartment is not readily accessible, it's a good idea to remove the cowling once every 10 hours or so just to take a peek. And, perhaps the best learning experience is to peek over the shoulder or involve yourself in the airplane's routine maintenance, such as oil changes and annual inspections. There you will learn how and where to look for problems and can ask the mechanic questions regarding wear signs of certain parts, such as exhaust components or magnetos.

As with the engine compartment, look for the obvious on the airframe at first. When you walk up to the airplane, note whether it's sitting correctly. If not, the struts or tires may need service. Did a leadfooted lineperson back the Jet-A truck into it and bend the wing tip? After an overall look at the airplane, perform the preflight walkaround prescribed in the pilot's operating handbook. Again, take in the big picture and narrow down the search from there. Look, feel, and listen is the name of the game when preflighting.

No fuelin'

Fuel-related accidents range from simply not having enough fuel to actual mechanical failures of system components. In between are many opportunities for something to go wrong: contamination, misfueling, collapsing bladders, and even leaving the fuel caps off. Although the answers to some of these situations are pretty obvious, other responses may be a little more difficult to comprehend.

Why must we take fuel samples? One reason is to check for water. Once the engine inhales a slug of water, it can be momentarily rough or, if the contamination is bad enough, can quit altogether. The water can also freeze in the lines, blocking the flow of fuel. Airplane fuel tanks can easily be contaminated with water. Poor cap seals can let rain water in, and even a change of temperature can cause condensation inside the tank. Checking the fuel is very important on the first flight of the day and after re-fueling. Some pilots like to do it before every flight, in case some water worked its way loose from the bowels of the tank during the previous flight.

Some fuel-related aircraft accidents stem from a more serious problem. A few years ago in Texas, an inattentive line attendant and an equally oblivious pilot allowed a Cessna to be filled with jet fuel. Just after takeoff the engine quit, and all on board were killed in the ensuing forced landing. Witnesses stated that before the flight the pilot had quickly taken a fuel sample, looked at it, and thrown it out. It's likely that the pilot was looking for water but neglected to see what kind of fuel the water was in. When taking fuel samples look at the fuel — is it the right color? Jet fuel is clear, 100LL is blue, and 80 octane is pink. Mixtures of 100 and 80 will be clear, so be careful. Does it smell right? Jet fuel is essentially kerosene and has the same odor. Rub it between your fingers; if there's jet fuel mixed in, it will leave an oily film.

Thumbing the controls

When you move the control surfaces during your walkaround, do they move smoothly, freely, and correctly? If the airplane just came out of maintenance or a paint job, it's entirely possible that the mechanics rigged the controls backwards. Don't laugh — it's happened, and often with fatal results. Listen for unusual noises that could be caused by a binding cable or a nut that has fallen off inside the control surface. Be sure to deflect the controls so that any water that has collected inside can drain out.

Before takeoff, it is important to check the controls again. Here you want to see that the yoke or stick in the cockpit can manipulate the controls in full deflections without any impediment. Are your passenger's legs in the way of the stick or yoke? Is your yoke-mounted GPS hitting the throttle quadrant or the panel? Remember, too, that the checklist says free and correct. Many pilots simply row the controls through the motions without looking to see what they're doing. A simple trick to check ailerons is to grasp the yoke or stick so that your thumb points upward. When you rotate the wheel, your thumb will point to the aileron that is deflected up. It may seem unnecessarily repetitive to double- and triple-check these items, but remember that there have been countless accidents — many of them fatal — because of flight control problems. Believe it or not, many of them occurred because the pilot simply neglected to remove the control lock, usually the first item on a preflight checklist.

Type-specific gotchas

Many airplanes have items that need special attention. For Cessna singles, pilots should always ascertain that the fuel caps are snug and seated properly. Since you can't see them from the cockpit, you wouldn't know if one blew off after takeoff until a significant amount of fuel siphoned out. Besides, it is a very good idea to get up on the wing and visually check the fuel level, since gauges can be wildly inaccurate. Become a member of a type-specific organization such as the Cherokee Pilots Association or Cessna Pilots Association to learn the quirks of the airplane that you normally fly.

Beyond the checklist

Before starting the engine, shout "Clear!" well before you turn the key — to give people outside a chance to comprehend what you said, let alone get out of the way. Look all around the airplane for people or anything else that might be imperiled by your propeller or its blast. You should also turn on the aircraft's beacon light to warn others that your ship is powered up and ready to start. This sort of consideration for others will truly impress your instructor, examiner, and peers.

On the way to the runway, verify that the turn coordinator and directional gyro move, in relation to turns on the ground. In a 90-degree left turn, for example, the airplane in the turn coordinator should bank hard to the left, while the ball will skid almost all the way to the right. After the turn, your heading indicator should indicate a completed turn of 90 degrees to the left. Keep in mind that at low idle speeds the engine may not be providing adequate differential for the instruments to be 100 percent correct.

When running through the checklist, you should say, touch, and feel for every item. If the fuel selector should be on Both, check it visually and feel for the detent. After completing the checklist, it's helpful to look at every instrument to check its operation and remind you of related items. For example, looking at the VOR indicator will remind you to set the OBS and check that the proper VOR frequency is tuned and identified.

Bad mag? Don't taxi back yet

If a check indicates a bad magneto during your runup, it doesn't mean that you have to immediately taxi back to the ramp The problem may be simply oil or lead that has temporarily fouled a spark plug. To clear a bad mag, try this technique:

Leave the throttle at the runup rpm.
Return the magneto switch to the Both position.
Gradually lean the mixture to peak EGT to burn out the oil or carbon deposits. (If the airplane does not have an EGT gauge, lean the mixture until the engine runs rough, then enrichen it just enough so that it runs smoothly again.)
Return the mixture to the normal takeoff position and recheck the magnetos.
If the engine is still rough, return to the ramp.

Note: It's very important to position the magneto switch in the Both position when trying to clear a plug; if not, there will be no heat generated in that cylinder to burn off the oil or lead deposits.

Final items

Try to make a mental list of gotchas that need to be done in case you are hurried to the runway at a busy airport. Are the doors and windows closed and locked, with nothing hanging out of them? Are the fuel selector, trim, and flaps in the correct position? Are the necessary lights and transponder on? Of course, there will be variations to this quick-and-dirty checklist, depending on the aircraft you fly, but this should cover most airplanes.