CFI Preflighting From Cotter Pins to Piano Hinges: Lesser-Discussed Things You Should Mention (and Look At) on Your Flights and Checkrides

If you don’t know what to look for, you definitely won’t know what to talk about. A good preflight goes well beyond kicking the tires, wiggling the ailerons, and swinging the rudder before you hop in the aircraft and taxi merrily along to the runway.  

So what are we looking for? In this article, I talk about a number of things you should plan to mention on your checkride preflight, but you should check these on every flight. Even if particular terms not specifically named on your checklist, they are definitely part of a larger item.  

I am linking to some of the parts on Aircraft Spruce – the parts retailer I used when I was an aircraft owner. Looking at the parts themselves may give you some insight into how parts or systems work, and may help you explain their function better.  Because your airplane may be different, check with your CFI to make sure you are explaining components accurately. 

I am not a mechanic. I am a CFI, a ground instructor, and a former aircraft owner. I owned a Cessna 172 R model from 2015 to 2018, and during three years and through three annuals, I still didn’t learn everything. No matter what stage of training you are, take every opportunity to learn about how the aircraft you fly works. 

A few points before we begin: 

This article is not about how to read a checklist. Of course, there are many preflight checklists available. You may use one made by your aircraft’s manufacturer, or you may use one made by Checkmate Aviation or even made by your CFI. 

While your preflight should match what the manufacturer recommends, no matter what you use, stick to a checklist. Whether you’re taking a private or a CFI checkride, your Designated Pilot Examiner (DPE) will not be impressed by your attempts to preflight from memory, no matter how accurate you are. Another way of emphasizing this: Do not go to your checkride without a preflight checklist. And I would say – do not go fly without a preflight checklist. 

This article is also NOT about how to do a preflight. Your CFI can show you a basic preflight and you can find many videos on the internet for how to preflight your trainer aircraft.  This article is about things you should mention on your preflight to show your DPE you know what you’re talking about, and that you know some of the little things to point out, that other people miss. After you read this article, you might make sharpie dots or column notes on your preflight checklist, to make sure you don’t forget to mention certain buzzwords. 

One last point. This article is about the Cessna 172. While some of the items on this article will be on your different trainer aircraft, obviously check your aircraft and verify with an instructor or mechanic before telling an examiner about them. And remember, every DPE is different. What one examiner might question you at length about, another examiner might not be particularly concerned. 

1. The Alternator Belt 

What to Say: “This spins the alternator and generates electricity.” 

What It Does: The purpose of the alternator belt is to spin the alternator creating electricity. If you hear about “belt-driven” alternators – well, this is what that’s all about. DPEs love to ask if the airplane will still fly if the alternator belt breaks. The answer to that question is yes, the aircraft will still fly, but all of the electrical stuff in the plane (your lights, instruments, radios, flaps, etc) will be powered by the battery. An electrical failure at night should be considered an emergency. 

Where to Find It: When you are standing at the nose of your aircraft, looking into the cowl inlets, you’ll see rubber belt on the left inlet. 

Basic Information:  This belt is 32 inches long and .42 inches wide, and is around $50 at Aircraft Spruce. 

2. The Wheel Cotter Pin 

What to Say: “This keeps the castle nut from backing off the wheel assembly.” 

What It Does: Cotter pins (called split pins outside of U.S.) are used on aircraft and engine controls, landing gear, and tailwheel assemblies. They are used because when properly secured, they will not loosen. Read the FAA’s FAAST Team Brochure about the importance of safety wire and cotter pins. 

Where to Find It: The wheel cotter pin is located inside the castle nut in the wheel assembly. The pin might not be visible if a hub covers it. See this video showing a cotter pin being removed. 

Basic Information:  Incorrectly installed cotter pins can cause or contribute to loss of braking control. Cotter pins are cheap – around the price of a nickel. The FAA has specifically said in an Advisory Circular that cotter pins should not be reused. So – if you’re changing a tire, you better have a new cotter pin. 

Fun Fact: Sun N Fun airshow’s 2017 Project Preflight event had a 172 with a missing cotter pin in the right wheel. Only 28% of the pilots participating noted the missing pin. Touching and mentioning the Cotter Pin is a way to show your examiner that you are detail oriented and understand the importance of verifying hardware and components are connected properly. 

3. The Cowling Fasteners 

What to Say: “These cowling fasteners keep our cowling from coming apart in flight. We want to check for any missing fasteners.” 

What It Does: Your airplane is is subject to a lot of vibration when you fly (remember the torque left-turning tendency). The cowling (metal pieces that cover your engine) is not attached directly to your engine but is positioned very close to it – it is “cantilevered” to the firewall.  The cowling is two parts because a one-piece cowling would require removal of the propeller and spinner anytime engine access was needed. Fasteners that hold the cowling together are similar to screws, but fasteners are used to hold things together vs screws are connected directly into an object or base. 

The cowling must be strong enough to handle the rush of the incoming air and the heated exiting air, and therefore, cowl fasteners must be strong enough to handle the pressure and the vibration. If the cowling was just screwed on, the vibration from the engine would put a lot of stress on the hole, and over a short period of time, the holes would get bigger, and the screws would likely fall out quickly.  If the holes become oversized, a standard fastener will no-longer fit.  Some cowls have latches to allow access, those must be checked too. See this video of a cowling coming loose during flight. 

AOPA accident analysis from about 20 years ago details a crash in Colorado where a pilot departed with several missing cowl fasteners. The engine cowl opened in flight and eventually separated entirely, striking the tail and causing loss of control, which led to a fatal crash. The accident investigation revealed hat three primary cowl fasteners on the left engine were not properly secured and six others were missing completely. 

Where to Find It: Find the cowl fasteners on the nose portion of your airplane, connecting the upper and lower half of the cowling. If fasteners are missing, tell your mechanic. 

Basic Information: Many pilots will fly an airplane with a missing cowling fastener. Is the aircraft still safe and airworthy to fly? Probably, but remember as PIC, you make that determination. Either way, your DPE will not be impressed (read this forum rabbit hole or Reddit missing screw deep dive) that you think it is okay. Make this a non-issue on your checkride by doing a preflight before your checkride and making sure none are missing. 

4. The Rivets

What to Say: “All these rivets hold our aircraft together. We want to look for any smoking or smoked rivets – where vibration causes a black ring around a rivet and a trailing black streak.” 

What It Does: The most basic level explanation of rivets is they hold the plane together. A rivet is a metal pin that holds together two plates of metal. On a typical trainer aircraft there are thousands of rivets. They are sold individually or by the pound. Specifically, they hold outer aluminum skin together and attach it to the structural skeleton. You can see pictures of rivets on a 777 on this forum

Where to Find It: You can find Rivets all over your aircraft. Walk around, and look at the little bumps. 

Basic Information: If your rivets are smoking, they aren’t trying to kick a Benson & Hedges habit. Smoking rivets are a sign of loose rivets. I don’t know why they don’t just call them loose rivets, but it may be because the rivets might not be that loose. A little moisture, a little oxidation can cause oxidation and smoking. Even if they’re not really loose, smoking rivets need to be replaced. You can read more about smoked rivets here on in this kit plane article, but keep in mind your trainer airplane is not a kit plane, and a licensed mechanic needs to handle any rivet replacement for structural fasteners (Remember Appendix A to Part 43 – Preventive Maintenance) 

5. The Fuel Vent  

What to Say: “We want to make sure the fuel vent is free and clear of dirt oor obstruction, and fuel isn’t pouring out of it.” 

What It Does: The fuel vent allows air to enter the tank as fuel is burned. Think of it as the second hole in a can of pineapple juice to allow the liquid to pour without “plugging.” If fuel comes out of the vent you may have a stuck or broken open vent valve. 

Insects called Mud Daubers have been known to build nests in fuel vents and pitot tubes. If you ever fly and notice your airplane is burning more fuel on one side, you may want to check the fuel vent. Or better yet, check it before you fly. 

Where to Find It: The fuel vent is located near the strut under the left wing. 

6. The Oleo Strut 

What to Say: “The oleo strut is a pneumatic air–oil hydraulic shock absorber. We want to make sure it’s properly inflated and not in need of servicing.”

What It Does: The oleo strut is a suspension component. It looks like a motorcycle suspension, but it doesn’t have  a spring component, just compressed nitrogen gas under pressure.  If the strut extension is too low causing the prop to be too close to the ground, it needs to be serviced. Check your aircraft for the exact range,  but nose struts should generally be around four inches. The  air is usually nitrogen gas and the oil is almost always red 5606 aviation hydraulic fluid.

Where to Find It: On a 172, the oleo strut is the metal pole part of the nose wheel assembly. 

7. The Piano Hinges 

What to Say: “We want to check for wear on the piano hinges on the ailerons and elevator by visually looking at them and moving the control surfaces in all directions. “

What It Does: Cessna used “piano hinges” on the ailerons and elevators. Engineers say that piano hinges are a favorite of the aerospace industry, due to their reliability and strength. A piano hinge connects a part that doesn’t move (like the wing), to a part that moves (like the aileron). A pin runs through the Inge assembly and holds the two parts together. The pin may form a loop at the end or be held in place by a nut or bolt. 

Where to Find It: On a 172, piano hinges can be found under the elevator and under the ailerons. 

8. Aileron Push-Pull Rods 

What to Say: “We want to check the push-pull rods to make sure they’re not bent. If the airplane was serviced recently, it could have been reinstalled incorrectly. If there was a crazy wind storm, even if there was a gust lock installed, but especially if there wasn’t, the wind could have given the pushrods a wild ride. “ 

What It Does: Aileron is French for “little wing”. The push pull rods, or aileron control rods, connect the aileron to a bell crank. 

Where to Find It: You can find aileron push-pull rods, sometimes called aileron control rods, on each wing. 

Do I need to add anything to this list? What must-mention items do you have on your flight? Any lessons learned (big or small) from preflights? Share in the comments below!  

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