Preflighting a Cessna 172 revisited

I must have preflighted the 172 over a hundred times now. Every now and so often I take an hour with a CFI for some recurrent training and I usually ask to be observed as I step through my pre-flight. Over the years I've learned that every CFI contributes yet another piece of wisdom that lets me know and understand that machine, which is about to take me aloft, just a little better. Last year it was a mechanic that lubricated a flap push rod that explained how the left flap is tied to the right via cables. By pushing up on the left flap one can test for excessive play in that connection and at the same time observe whether the rollers are actually moving in the tracks. If they don't it leads to excessive wear. Thanks to that same mechanic I now also check for chafing on the top surface of the flaps.

Today's pre-flight was no exception. Tom pointed out three new items that were either new or just not clear to me before.

1) Ever wondered how many static wicks your airplane can be missing and still be flown safely? The Cessna 172 should have 8 of those wicks, 2 on each wing, 2 on the rudder and 2 on the stabilator. They are there to disperse static charge that builds up all around the aircraft and that could interfere with radios. It is safe to fly with a maximum of 3 missing.

2) Tom asked me to explain what I am looking for on the safety wire and what the safety wire is there for. With safety wires you are looking for broken wire, which would indicate that a stop screw has moved or a connection has come loose. On the tail of a 172 one would check for the safety wire to be intact on both sides of the rudder cable connection (that one I knew). You also check for safety wire to be unbroken for the 2 rudder stop screws and the elevator stop screw. A broken wire indicates that the screws have moved and that would allow the rudder or elevator excessive travel.

3) How would you know that the break hydraulic lines are leaking? My answer, look for break fluid next to the tire, missed the point. I had forgotten to set the plane's parking break. The way to get pressure on the hydraulic line so that fluid would be forced out would be to either apply the breaks or in this case just simply set the parking break and then look for leaking. A plane that has set there without a break applied might not show lots of leakage, especially in a training airplane that was just parked. Apparently the hydraulic lines like to fail in the corners where they are bent or where they are rubbing up against the landing gear. Especially when wheel pants are not attached these lines vibrate in the wind against the gear and start chafing over time.

4) I always visually inspect the openings in the plane's cowling to make sure no birds have started nesting. Especially in the fall when nests can appear from on day to the next. What never occurred to me is that the best place for a nest is in between the cylinders where a visual inspection won't find them. If the engine isn't hot, run your hand through that space to make sure no critter built a home there.

Sometimes it takes another pilot or CFI to ask provocative questions to make you think about what to check during pre-flight. Most importantly, always ask yourself "why am I checking this" and "what would this look like had it failed or become damaged".

Off it was to another fun flight. 7 rounds in the pattern. The ceiling lifted to 4000 feet and we headed South for slow flight and stall practice. In March I'm coming up on my first Bi-Annual Flight Review (BFR). I'll be going the Wings route, so look here soon for the next entry on completing the Basic Wings phase in lieu of a BFR.