An Evolution Pressurization Mystery

frankblair's picture

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An Evolution Mystery

 

Dear Fellow EVOT’ers, I have had a mystery with my EVOT since last November and I wanted to share it with you all, perhaps as a March puzzle, or just to laugh at me how long it took to solve.

 

My plane is EVOT #17 and I have about 1750 hours on her, N401CH. I built her with Aaron Brook, now head of Advanced Aviation in Bend. Last fall we did the Annual after the Bend fly-in training and update. Among other minor updates, we replaced the door seals with the new better ones.

 

On return home to Bar Harbor, Maine, everything seemed perfect until I stopped to refuel in Michigan. The leg from Boulder to the refueling spot showed normal pressurization at 25,000’ but leaving, it was zero, and I hobbled home at 9,000.

 

So I tried the obvious things first. Since the door seals were new, I tested them, but they pumped up fine and kept the pressure easily with no signs of leaks. I then suspected the squat switch, but it tested out at a Portland, ME shop.

 

The Portland shop suggested that I should replace the Enviro Controller, which I had installed about 1000 hours previously, to replace the troublesome Dukes Controller that originally came with the plane. Only $12,000 and a month’s work……

 

I hoped that it was something else, so after a bit of other troubleshooting, I put together a fun trip from Maine to Charleston to Santa Fe to Oakland to McMinnville to Bend, OR. I thought it might be the Bleed Air because the cabin was cold as well as not pressurized.

 

Aaron and his team at Advanced Aviation thought it would be only an hour’s work, but it took three days. His guys poked at everything. His top computer and systems guy wired up the plane to fly it and test everything out, connected to the Enviro Controller. It came across as garbage and I was fearing that the Maine FBO might be right that the Controller had gone stupid.

 

Finally, on the fourth or fifth test hop, I flew with their top electronics guy with his computer plugged into the system in the copilot seat and a technician in the back, with one rear seat out and full access to the Enviro. The computer was still reading garbage, but the technician in the back said that it was really breezy, where it shouldn’t be.

 

They found that when the Dukes was taken out, some of the small pressure lines that the Enviro didn’t need were capped off with little half inch clear plastic caps, and one had come off after 1000 hours flight time. Total cost of the part, maybe $0.01.

 

The line was sealed off at the bulkhead, in a fashion that will never, ever leak again and the plane now pressurizes perfectly.

 

I shoulda, coulda found the part when I was poking around, but then I wouldn’t have had a fun trip, one lap around the country!

donsak's picture

Thanks for sharing, Frank. 

Thanks for sharing, Frank.  In AMU's (Aviation Monetary Units)  the total expense for the $.01 part was only about 3 or 4 units.

Pretty cheap if you look  at it that way/

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