Top Five Pre-Flight Mistakes

The pre-flight inspection is something we learn about during our first flight lesson. We poke, prod, uncowl, measure and eyeball various fluids and components while the airplane is still safely on the ramp, all to help decide if it's safe to fly. Yet, once we take off, we often find we missed something. Hopefully, what we missed is relatively insignificant and merely embarrassing, rather than a safety-of-flight issue. In any case, we should be striving for perfection and ensuring we've not forgotten anything. So, based on our long experience in missing things during a pre-flight inspection, here's our list of the top five pre-flight mistakes.

Your pre-flight inspection really begins as you walk up to the airplane. You should be visually inspecting it, where and how it's parked, how it's secured and its overall condition. Are all the big parts attached, and in the condition you expect? Are cowling plugs, cabin covers and pitot covers, if any, properly installed? If not, why—was there some major weather that dislodged them? If so, additional inspections may be necessary. Is the airplane clean and clear of snow, frost, bird droppings or other contaminants?

A dirty airplane is, well, dirty, and a little grease and grime under engines and on struts and wheels is to be expected. But major cleanliness issues like oil or fuel stains, or bird droppings should be cleaned up before any further flight preparation. Why? Because they promote corrosion, for one thing, and left untouched will also harm the paint or dull a polished finish. Another reason? Cleaning them up now will help determine if there's a chronic leak problem after your upcoming flight.

Look also for evidence of oil streaks trending aft of the engine compartment(s) or blue stains near fuel filler caps. All tires should be properly inflated. Don't just eyeball them; use a good-quality tire gauge and inflate them to the recommended pressure. Is the airplane sitting in a normal attitude? If not, a strut could need filling. Also pay attention to any liquid on the ground near the main wheels; it could be a rain puddle the sun hasn't evaporated but it also could be brake fluid.

What about the tiedowns? Are they stretched in one direction or another? That could be another sign of some major weather since the airplane was parked, or perhaps a thoughtless pilot did his run-up nearby, blowing the airplane out of its parking spot. In either case, further investigation is warranted, and the control surfaces given some extra attention.

A final task is to inspect the propeller(s). We want to do this without rotating it, preferably. We're looking for nicks and cuts in the leading edges, along with pitting corrosion. Is the spinner securely attached? Wiggle it left/right and fore/aft. Any movement in which the prop doesn't also move means something's amiss. Meanwhile, any fore/aft movement of the spinner and prop assembly could mean a crankshaft or mounting problem and should be investigated.

The Cowl Many airplanes are so tightly cowled a detailed engine-compartment inspection demands two people and special tools. Others are relatively easy to open and inspect. Regardless of which you're dealing with, you never should start the engine(s) unless you're positive everything is as it should be.

If you can open the cowling easily, do so, even if it requires a special tool. You're looking for leaks, cracks and foreign material, among other things. If your cowling doesn't come off without major effort, begin at the front and bring a flashlight. Use the light to help illuminate the engine cooling inlets and let you peer past the first pair of cylinders. You're looking for foreign material that could hint of an animal taking up residence. You're also making sure there's nothing else amiss.

Any obviously loose hoses or clamps can show up here, as well. Open the oil filler access door, and use the flashlight to illuminate other viewable items. Once you've checked the oil, be sure to secure the dipstick and/or oil-filler cap, plus the door itself.

At the rear of the engine, get down on your knees and peer back up past the exhaust pipe(s), perhaps through the cowl flaps. Use the flashlight. Wiggle the exhaust pipe(s) to check them for security. Loose pipes can leak, allowing exhaust gases into the cockpit.

Sampling the fuel in each tank is a time-honored exercise during the pre-flight inspection and after each refueling. Many pilots, however, have never seen a bad sample and might not be sure what they were looking at if they did. Also, raising a sampling cup filled with blue 100LL fuel up to a blue-sky background doesn't help much.

Presuming we're flying a gasoline-powered piston engine, the fuel we drain from the sumps should have what many think of as a sweet, aromatic odor to it. If it doesn't, you could be looking at Jet A fuel, or something else. Jet fuel—which works fine in turbine engines and diesel-powered airplanes—is either clear or straw-colored. It's a bit oily, and won't evaporate from your finger like 100LL will. It also won't get you very far if you're trying to burn it in a conventional, spark-powered piston engine.

In either fuel type, water is a no-no. When present in 100LL, it sinks to the bottom of the sampling cup after a few seconds and its dirty appearance screams "drain the tanks." Water in Jet A initially will present itself as a hazy fuel sample, literally caused by the droplets being in suspension. The water will separate out to the bottom of the sample after a few minutes without motion or agitation. Other contaminants—like dirt or deteriorated fuel tank sealant—likely will show up as small, dark particles floating in the fuel, which will eventually sink to the bottom.

If there's any doubt what you're looking at in the sampling cup, especially if the airplane has been siting outside, you're justified in drawing more and larger samples until what you see is clean fuel of the proper color and grade.

Disposing of the sampled fuel can be problematic. The also-time-honored practice of flinging a sampling cup's contents into the breeze to evaporate is officially an environmental hazard these days, resulting in small, red sample-disposal cans sprouting up near fuel pumps and tenant hangars. That said, pouring the remains of a good sample back into the tank is acceptable, especially if you use a sampling cup like a GATS jar, pictured above. The GATS jar and similar products screen out any small particles before the fuel goes back into the tank.

Any airplane parked outside is susceptible to wind or propwash damage. When a strong wind flows over it, it can get bounced around with its primary control surfaces repeatedly forced against their stops. Extreme encounters can snap control cables or damage their pulleys. And many basic maintenance tasks can result in reversed controls or binding. Thus, it pays to closely inspect an airplane's control surfaces to ensure they're securely attached, move freely and operate in the correct directions.

First off, enter the cockpit and remove any locks or seat belts constraining the controls. Your overall visual inspection when approaching the airplane should have highlighted any external gust locks; remove them, too.

Then, gently move each control surface through its full range of motion. Listen for any abnormal noises and ensure that its movement is smooth and consistent throughout the surface's full range. Watch the cockpit, too, to ensure the controls moves with the ailerons, for example.

While you're there, check each surface for security by gently wiggling it fore and aft. Ailerons on many airplanes use a piano hinge, with a length of wire through each half. Check that the wire is present and bent on the ends so it won't slide out. Other surfaces will be mounted with screws; check them for security.

Once your pre-flight inspection is complete, you'll probably load up any baggage, brief the passengers, dig out headsets, iPads and other gadgets from your flight bag and strap in. Wrong. Before all that, you need to walk around the airplane again and take a good look at it before flying. Ideally, step back several feet and try to look at all the tires, the tail and the wingtips in one view.

Why? You're looking for stuff you forgot: errant wheel chocks, tiedown ropes that can get caught in wheelpants, still-attached towbars, the chartbag that never got loaded, the pitot tube cover that's still installed, the FOD you left on the ramp. All these things and more have happened to us over the years. We've even left our airport car on the ramp, with the door open and our cellphone sitting on the driver's seat. (Hint: There are some wheel chocks you just can't taxi over, no matter how much power you pull.) Leaving some of these items unattended is merely embarrassingly bad airmanship; leaving your charts and approach plates on the hood of your car can mean a really rude surprise a few hours down the road.

The Compleat Pre-Flight? Short of doing an annual inspection (and we'd argue the first flight after an annual means we need to be even more thorough than normal), there's no such thing as a pre-flight inspection that checks everything. Instead, we're looking for the big, obvious stuff that may have happened since the airplane was parked or that was missed after its previous flight. But we can approach the pre-flight in a methodical manner, doing things in a logical, planned fashion that allows us to ensure it's as ready for flight as we can.

One other thing, before we forget: Doing all this in the presence of anxious passengers might not be the best decision. Their foot-tapping, watch-glancing and well-meaning questions are nothing but distractions. Politely but firmly ask them to wait somewhere else while you poke and prod the airplane they're about to ride in. You need to focus on the tasks at hand, the upcoming flight and ensuring the airplane is ready for it.

Jeb Burnside is Aviation Safety magazine's editor-in-chief. He's a 3000-hour instrument-rated ASEL/ASES/AMEL commercial pilot and aircraft owner.

This article originally appeared in the May 2013 issue of Aviation Safety magazine.

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