As I mentioned previously, I had ordered the ADS-B transponder, new radios and a wiring harness from Eagle Avionics in Parry Sound. Chris and I moved DKX to his heated hangar last week and the tear down began!
Everything in the radio stack had to come out, along with all the associated wiring, connectors, fuses and components. Plus most of the interior to facilitate running the wires for the 4 place intercom as well as the GPS antenna on the cabin roof. I've had the headliner out once before (to repair a frayed aileron cable) and it's a pile of work. Virtually all the interior panels ahead of the baggage compartment need to come out so the headliner can be lowered and removed.
It took me 1/2 day to remove the interior. Then Chris and I started ripping things out in earnest under the panel. There are basically two wiring harnesses in the a/c. The first is the basic Cessna harness that came from the factory that connects all the electrics. The second is the avionics harness that connects all the radios including all the antenna coax. The goal is to remove the latter without seriously screwing up the former.
Chris did most of the wire cutting and pulling. There was no way I was going to take a pair of wire cutters to anything. It was amazing the amount of stuff that came out of that plane. By end of the day, we had a pile of components and wire that would have filled a shopping cart.
It was actually a fun process. Sort of like demoing a kitchen with the expectation of the new one in mind. We ripped out a lot of stuff that had been installed at the factory but never used. For example there was a large relay above the glove compartment that was there to isolate the electronic bus when an external power supply was used. I don't have that option on the plane, so out came the relay.
"First simplify, then add lightness". The classic dictum by Lotus’ Colin Chapman was perfect here.
Day one was complete. The poor plane looked like it's heart had been ripped out.
The winter weather had delayed the arrival of the wiring harness by a day, so Chris suggested that we might as well go ahead and test the static system and repair any leaks (if any) since the pitot/static system would have to be re certified once the project was completed.
So let me tell you a story...about the static system leak that never was...
Chris gave me a brief run down on how to run the system tester. Basically, it's a box that applies a vacuum to the static system and pressure to the pitot system. A little complicated but not a big deal to operate. Chris explained how to hook it up the plane (which I did) including plugging the open line to the altitude encoder (which we had removed in the tear down) with a screw.
We ran the test. Bummer. The pitot system was fine, but the static system was showing a steady leak of about 500 ft/min descent. That's a relatively big leak and I was surprised because the system had been tested a year previously and everything was fine.
So where was this annoying leak? "Use a system of elimination and go from there. Look for any loose connections. Good luck", said Chris and walked away.
Great. Where do I start? The static line is relatively complicated. It connects the alternate static, the airspeed, the altimeter, the VSI, the altitude encoder and the autopilot. There are a number of T's connections as well. The leak could be anywhere.
The VSI was at the end of the line, so that was the obvious place to start. It was fine. Next was the ASI and ALT at the top of the panel. There was no way to get access to the ASI from behind the panel. The panel had to come off. This was turning into a big freaking job.
I had never removed the instrument panel before. It sits on 8 rubber mounts that had to be disconnected. As I did so, several broke off as they are old and brittle. Great. Now I was into a panel repair as well.
The ASI and ALT were fine. I was starting to sweat. Each time I tightened something I crawled back from under the panel, pumped up the machine and ran the test. No change.
I tested everything. I removed the autopilot from the system. I bypassed the alternate static, No freaking change. It was still leaking. But from where? The only thing left was the altitude encoder line which we had plugged with a screw. Ah ha! It had to be the T fitting at the line! Maybe it had a hairline crack! I was certain I had found the culprit. It couldn't be anything else.
I quickly replaced the T with a new one. Ran the test. No joy. What the #%^&&???!!!
And then in a BFO (Blinding Flash of the Obvious), I realized that the freaking screw (which Chris had told me to use) was the problem. It hadn't plugged the hole! The air was leaking past the threads!
I isolated that line, ran the test and voila!!! NO LEAKS!!
Needless to say, I had a few words with Chris. 2 1/2 hours for nothing!! But I must admit I now know that static system like the back of my hand. So I was thankful for that.
Now let's hope things stay good and tight once the installation of all the new equipment is complete!
