I love preflighting

Written By Ben Lehman
Preflighting a Cessna 172N

Preflighting an airplane is not fun, for most. But I love it! I can spend an hour peering in every hole, checking this, looking at that…trying to satisfy my wonder.

What is a preflight? Before each flight the Pilot in Command is to determine if the plane is in an airworthy condition for safe flight. Using a checklist (aka habitual flow) a pilot will carefully inspect systems, controls and mechanical items on the inside and outside of the plane to determine if everything is functioning as required. It’s a common sense safety step.

We all have our strengths, I think wonder might be mine? Can wonder be a strength? Maybe it’s curiosity, but something drives me to go beyond what you find on a preflight checklist. I can’t help but want to know and understand, for example, how those aileron cables work, where do they disappear to?

This wonder has led me to a lot of answers and more than a few real safety concerns. For example, here’s some items I’ve found during my preflights:

Broken cowling vibration mount found only by shinning a flashlight into the interior base of cowling.

This loose vacuum line was only found by placing a hand on the line and wiggling it.

A bee decided the stall horn opening was a great place to homestead. Sadly for the bee we found his project before construction was completed.

Large oil leak from near top of cylinder. it was enough oil that the A&P (aircraft mechanic) recommended remediation before flight.

Other items I’ve discovered during preflights include: loose horizontal stabilizer, unscrewed oil dipstick, broken cowling mount, loose cowling and common items such as burnt out strobe light, dead battery, low tire pressure, birds and mouse nests.

All this is said not to scare you but to help you intentionally consider how and what you’re looking for during a preflight. Like the old saying, “if your hands aren’t dirty you haven’t preflighted.”

I encourage you to develop your own in-depth and airplane specific preflight checklist, building on what your Pilot Operating Handbook outlays. Here’s one I developed for my students specific to a Cessna 172: Ben’s Check-It-All Preflight

Here’s a visual walkthrough of important parts of my typical preflight:

Always start by inspecting the cabin first. Is it summer? Check for murder hornets, trust me you do not want to discover you have a very large bee stowaway during takeoff (ask me how I know). And have you ever taken the time to peer under the dash and see how all those cables and wires intersect? I bet once you see you’ll be curious to check in regularly and make sure everything is in order. Also, preflights are a great time to engage your little one’s curious mind!

Did you know that if you only get your knees greasy you can peer through the front wheel strut opening or exhaust opening and inspect the throttle cable (cable on right), mixture cable (cable on back of carb), oil / gas leaks, carb heat ducting, fuel lines.

Again, if you put some effort in you can see both the positive crankcase and battery vent tubes. Are they are? Are they plugged or dripping excessively? What exactly are their functions? Hmmmmm

You can’t preflight without a great flashlight. Here’s a perfect example, with a small bright light you can look in the vent openings and inspect for your arch nemesis, wasps!

Guess what? These piano hinges wear out. They can begin to crack from the wingtip side in. Also, note that the hinge rod is securely fastened and not working its way out.

That thing there, it’s called a jam nut. It should be tight against the pushrod end. If it’s loose that pushrod could become loose. I point this out because I asked an A&P, I was never taught what to check here, only that it should be checked…ask your CFI not only what to check but to explain the why.

When those flaps are extended you can see a lot! Take your time and familiarize yourself with it all. Check those cables over, they do in fact fray and there are tolerances for how many individual pieces can fray before requiring replacement. Why wait for your A&P to find it…you’re the one that’s about to go fly it. If you’re a real geek you can even bring your Milwaukee / Ryobi / Dewalt inspection camera with you and peep inside these openings until your heart is happy and full of cable-y goodness.

It’s like they say, you don’t know until you know. I didn’t know that a brake fluid leak could be easily overlooked. It’s probably not going to be a large puddle of pink fluid on the ground, more likely it could be a darkish staining sweeping back from the brake caliper or lines. Yes, clean brake fluid is typically pink but if it’s been overheated it can turn to a gray and often will collect dirt and oil when on a wheel skirt. Now I take an extra close look at wheels skirts, you must think like the fluid…be the fluid. lol

Ever since the one time I went to fly a rental C152 and found the rear horizontal stabilizer loose I always check for rigidity and glance underneath because this is where a previous pilot’s off runway adventure might show up as mud, dents, etc.

Here’s a great example of why a small flashlight is invaluable, look at all you can see in the rear empennage! This is where I once found a mouse house. Not a big deal? Guess what, unmitigated mouse droppings are corrosive.

Get yourself a great flashlight! I recommend Nebo.

One preflight with a kiddo and you’ll realize they have to touch everything. At first I was scolding not to touch, then I realized I had no idea what the tensions of the cables felt like. What was I missing by only visually inspecting? Now I touch everything I inspect, this helps build muscle memory and you learn much more about the rigidity and tensions of things and how they normally feel. Just maybe this will help you spot a problem early!

Know your planes belly! It can be a world of information about fuel and oil leaks. When you fly the same plane regularly you’ll be accustomed to what is normal so you’ll be able to spot what isn’t when it occurs. Be wary of a cleaned plane, all the evidence might have been wiped away!

Again, using a flashlight you can illuminate compartments you wouldn’t normally be able to see well.

The firewall and rear of the engine is one of my favorite places to peek at. You can examine everything from engine mounts, to oil lines, to electrical. Take your time and get accustomed to what you’re seeing and learn what normal is so you can spot when something isn’t.

I watch A&P’s (airplane mechanics) closely. Once, I saw one run his hand across the back of the prop. When was the last time you checked the back for dings? Surprisingly when I did this I felt many abrasions, now I familiarize myself with it so I have a benchmark for every flight going forward.

Ever started a plane where the entire engine cowl almost came loose? I have. And that’s why I always check to make sure the cowl is securely fastened. It’s just a guess, but I bet you don’t want it coming loose mid-flight.

Using your flashlight you can inspect the cowl cooling baffling, push rod tubes, cylinder fins, alternator, starter, belt, and so on. I recently learned how important that cooling baffling is, I encourage you to google it. A small leak can create high cylinder head temps because the pressure cooling will be compromised.

That’s it! What did I miss or get wrong? Let me know in the comments below.

Ben Lehman
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