TR182RG Fresh air vent interacts with altimeters
I've been struggling with my fresh air vents inteacting with altimeters and we are talking by 80 to 100 feet. This started after a visit to the absolute worst avionics shop on the planet (don't let me get started on that story) - anyway. All pitot/static has been tested and there are no leaks. A theory some were putting out there is that opening the fresh air would pressurize the cabin and a leak in the static would thus increase pressure on the static side. But if that were true, then opening (and thus pressurizing) the air vent would cause the altimeters to "think" the aircraft is lower and so would go lower. The reaction is opposite, when opening the vent the altimeters jump up 100 feet, not down. Someone suggested that the air vent door on the copilot side when opened was interfering with airflow past the static port on that side but why then has it not always done that and why then is it not known as a common 182/172 problem. Also, there is a static port on both sides so the pilot side port should equalize, no?
I have an idea to test that idea by covering that side static port with tape and try it, then remove the air intake hose from the forward ducting and plug with a sponge and try it again. Today's Wyoming weather is a no-fly day but I'll try that as soon as I'm able. In the meantime has anyone observed such symptoms before or have any thoughts or troubleshooting ideas?
Comments
OMg, lol.. wow. ok you still have a leak somewhere, and i suspect it could be a instrument glass face seal or similar. even your encoder may be suspect, anything that is inside the aircraft. Unfurtunately the only way to evaulate may be to isolate sections and instruments. make sure if you have the alternate static, it closes well and also see if you have the junk plastic reservoirs at the static ports. if you can t find something easy, its gonna take some creative time. pump the static down and start rapping on gages. i hope you can find something simple. carl
IA 47yr A&P DAL A/C Inspector 172n
Hi Carl, I agree and you beat me on this one. Just a thought: In my Piper I have an alternate static valve. Did the mechanic perchance move the valve to the alternate position and leave it there?
Scott Sherer
Wright Brothers Master Pilot, FAA Commercial Pilot
Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.
Need help? Let me know!
I would check a couple things. I believe that your TR182 is probably equipped with an alternate static valve, right under the pilot yoke. The foam trim around that valve can degrade and both let the valve open and hide the valve from sight.
We had a weird problem with our static system. The encoder was reporting altitude about 300 feet off from the altimeter. Turned out that a previous maintainer plumbed the encoder to the right static port, and left the line that had previously been connected to the right port open. Basically provided cabin pressure for alternate static for the altimeter all the time. It took a couple hours to get that straightened out and the system plumbed properly. The static pressure line goes to the instruments from the back of the valve, and is connected to either the external static ports or the alt static port line depending on valve position. Check ALL the plumbing, and look for cracks in the plastic sump bottles.
Hey HESSAERO, I think you are definatley on to something here. Definately funky plumbing likely at the Alt Static valve. Hopefully the attached video will play OK. Showes very funky behviour between two altimeters when toggling the valve from normal to ALT. Also, check out that air speed. They are obvoiusly not referancing the same static source. I put tape over the right static port and the altimeters behaved correctly.
wierd