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This has been a pretty rough week, as I came down with a very nasty cold Monday night. I’m still not quite recovered, but I am feeling a lot better than I did a couple of days ago.

Saturday a week ago I had my biannual check down on the transponder and altitude encoder. Dan from Canadian Airmotive Avionics came by the hangar after lunch to do his magic. The altitude encoder and transponder passed, with one small adjustment on the encoder to put it bang in the middle of the tolerance - it would have passed without the tweak, but it was reading about 75 ft out.

The quick disconnect fittings in the pitot and static system caused hell though. I had done leak checks on both systems the weekend before, found small leaks, and fiddled with the fittings until both were leak free. But on Saturday, a week later, both systems had small leaks again, but within tolerance. Then as he was applying vacuum to bring the altitude up to 14,800 ft for the last check, one of the fittings in the static system developed a huge leak. He slowly released the vacuum, to stop the test. We broke into the system to isolate the altimeter and altitude encoder from the rest of the plumbing, and finished the test with only that portion of the system under vacuum.

After the test, I reconnected everything and did pitot and static leak checks again - both systems had very small leaks, well within tolerance. I suspect that those quick disconnect fittings are perhaps not rated to take the over 6 psi of vacuum that is present during the transponder checks.

On Sunday I went for a flight, and was dismayed to see that the analog airspeed indicator was reading about 30 kt high. I discussed this with Dan on Tuesday, and he pointed out that the ASI would have been subjected to excessive pressure differential between the pitot and static sides when that fitting developed a massive leak. Vacuum is applied to both the pitot and static systems during that test, otherwise the large pressure differential would damage it (14,800 ft on the static system with no vacuum on the pitot system would be equivalent to 485 kt - my ASI is only good to 250 kt). Worse, the pressure differential during that leak would be like a negative airspeed, as that static input to the ASI would see a higher pressure than the pitot side.

I’ve ordered a new ASI. I’ll also remove the quick disconnect fittings and return to the tried and true Nylo-Seal fittings.

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