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