Part 9 of 9: Cessna Annual 172P - Reflections

As I write this piece, it has been about four months since I sat in on the annual inspection of the Cessna 172P that I call Red. An inherently stable aircraft, she is also known as a trainer, used by student pilots learning how to fly. I have taken a few scenic flights in Red.

Something changed when I saw Red’s last annual inspection. I saw her up-close and personal, taken apart. I suppose you could say that I saw her naked. But it was more than that. I still remember the love and care that Brent and his apprentice John took with her annual. It is hard to explain what I experienced as I watched them work on “Red.”

Yes, I was assured of Red’s safety.

Yes, I know that Brent and John love what they do, and live out the aviation mechanic creed. I'd like to thank Brent for opening up his shop to me. It was great. I learned a lot from both Brent and John.

I hope that what I have written here along with the pictures give you some idea of what is involved in the annual inspection of the Cessna 172P and similar trainers. I am so glad the Brent opened up his shop, State Line Aviation, to me.

Red is an airplane, loved by many. But if it is possible to bond with an airplane, than I bonded with Red over the course of those three days.

Part 8 of 9: Cessna Annual 172P - finishing up the annual

Final installment in this series on May 18, my reflections

Part 6 of 9: Cessna Annual 172P - magneto services

Blogger had an outage on May 12 and I have (temporarily) lost the posts that I made on Wed. May 11 including "part 6 of 9: Cessna Annual 172P - magneto services." I am reposting this now, out of order. Thanks for your patience.

I will write about the magneto service here, and will continue discussing magnetos when I write about the engine and propeller service in part 7 of 9. The  three photos below show the magneto service.

I watched Brent do the magneto service over the course of about 30 to 60 minutes (I think). I enjoyed watching him work. Unfortunately, I spent most of the time listening, and did not take a lot of notes. Sometimes it is better to just watch and listen. so, I regret that I don’t have more to say about this service. Perhaps I’ll have an opportunity to watch him do another magneto inspection in the future.

However, while Brent was talking, I did make some notes about what the magneto does. Single-engine planes such as the Cessna 172P have two magnetos. Simply, they are self contained ignition systems. One of the items on the pre-takeoff check is checking that both magnetos are operating on their own. If one of the magnetos doesn't work, you are grounded. While you only need one magneto for flight, you always want to go up with two working magnetos. You do not want to take off with only one working magneto and risk having that one working magneto fail in flight. It may not be a good outcome.

Part 7 of 9: Cessna Annual 172P - magnetos (cont), propeller, and engine services

I was taking some notes as Brent showed me around the engine of this 172P. The Lycoming engine of this 172P is a horizontally opposed engine. One magneto is wired to the bottom left side and the top right side of the engine. The other magneto is wired to the top left and the bottom right side of the engine. In the photo below, you see a close up of this wiring on one side of the Lycoming engine.

For those of you who are interested, a magneto works by means of a rotating magnet. A charge is created a that eventually travels through the distributer cap to a wiring harness to the spark plug on the engine.

The bottom spark plugs are disconnected during the inspection so the propeller can be safely turned. While you can start a Cessna 172P by turning a key inside the cockpit, you can also start the plane by turning the propeller by hand (known as hand propping). So, disconnecting the bottom spark plugs is a safety measure. There is no risk that the 172P will start accidentally. See the two pictures below.

The engine service includes but is not limited to servicing the alternator belt, inspecting the engine controls, and inspecting the engine.

After the propeller is inspected it is polished. In the photo below you see John polishing the propeller.

Next up on Monday, May 16: Finishing up the annual.

Part 5 of 9: Cessna Annual 172P - Inspection

There are many inspection portals in aircraft, including the Cessna 172P, where the Airframe and Powerplant Mechanic with Inspection Authorization can inspect what is “underneath”. Mostly various wires and cables. In this series of photos, you will several such portals, finishing up with a couple of shots of Brent performing this phase of the annual inspection.

Next up: magneto service

Part 4 of 9: Cessna Annual 172P - Battery Service

Unlike the battery in my car, I learned that the battery in the Cessna 172P is not a sealed unit. That is the battery in the Cessna 172 can be opened up to add distilled water. In the photo below, the battery is being charged. Distilled water has already been added to the battery, if necessary, prior to being charged.

Part 3 of 8: Cessna Annual 172P - Emergency Locator Transmitter Service

I watched the service of the Emergency Locator Transmitter (ELT). I learned that the batteries are replaced after 1 hour of cumulative use or after 50% of their service life is expired. The ELT is designed to activate and transmit a signal after being subject to forces generated in a crash. I understand that the ELT is in different locations in different airplanes.

Next up: battery service

Part 2 of 8: Cessna Annual 172P - landing gear, wheels, and brake service

My first afternoon at State Line I watched Brent’s apprentice, John, work on the landing gear and brakes. John works under the direction of Brent. Brent is a Airframe and Powerplant Mechanic with Inspection Authorization and is the one who “signs off” on the annual inspection. John cleans the landing gear with mineral spirits in the first two photos. The wheel bearing is cleaned with mineral spirits in a parts cleaning machine in the third photo.

In the first photo below you see the new brake pad (L) and the old brake pad (R). The brake calipers are shown in the next three photos.

Landing gear wheel back in place.

Next up: emergency locator transmitter service

Part 1 of 8: Introduction to Annual Service of Cessna 172P

Late last December I spent two half-days and one full day at State Line Aviation on the field of Alexandria Airport (N85) watching one of N85's Cessna 172P trainers, (I refer to her as “Red”), get her annual maintenance. I had a great time and I learned a lot. As I watched the inspection and had the opportunity to ask Brent or his apprentice questions, I took notes on what I saw and heard. Over the next few articles, I am going to take you on a photo tour of my time watching the annual along with some commentary about what I learned. This is not meant to be a chronicle of an annual maintenance from beginning to end. Rather, I suppose you can say that I am touching on certain highlights of this annual. This is the first of eight articles that I will post over the next 2 to 3 weeks.

I want to start with the aviation mechanic's creed that is posted on the wall of the State Line Aviation. Please take a moment to read it. When I was talking to the owner, Brent, we got talking about what makes aviation mechanic's tick. He took me out and showed me the creed. I stood there, spending a few minutes reading the creed and letting the words soak in. As I watched Brent and his apprentice, John, work on Red over the course of the next couple of days, I saw the creed in action.

See the image below for a copy of the 100 hour/annual inspection checklist. In the case of the 172P, this is her annual inspection.

This is Red with her engine cover taken off, this a side view of the engine compartment. Having done a couple of pre-flight inspections that included checking the oil and checking one of the belts, it was something special to get my first glimpse at what is under the hood (or cowling). What is under the hood and the propeller (out of the picture) provides the thrust. Thrust along with the lift provided by the wings are two of the four forces of flight that act on an aircraft in flight. The other two forces of flight are drag and weight. Drag works in opposition to thrust and weight (gravity) works in opposition to lift.

Remembering the days when my car had a carburetor, I wanted a photo of Red’s carburetor.

One of the things on the done in the annual is changing the oil filter, note the date on the filter. That is the date the new filter was installed. The number 3998.4 is, according to Brent, the tach time (akin to an odometer in an automobile) found on the bottom of the tachometer. The tachometer records the revolutions per minute (RPM) of the engine crankshaft. In the 172P, the propeller is attached to the engine crankshaft, so the tachometer records both engine and propeller RPM. Tach time is the total number of hours that the engine has run.

Next up: landing gear, wheels, and brake service