Altimeter replacement?

Briar Rabbit

Briar Rabbit

Line Up and Wait
Joined
Mar 22, 2017
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626
Location
Albion, Nebraska
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Display name:
Rob
I was told today my old original equipment altimeter does not pass the static test. The shop quoted me $1,400 + for a new United. Seems high but that actually appears to be a reasonable price for a new one of that brand which I was told is the best. Or a cheaper brand for about $980 new. Still I decided to shop around and have found two shops in Wichita offering rebuilt Uniteds for around $600 and about $400 exchange. Less than that for an overhaul of my old Bendix. I need a 3 1/8” 20,000 foot unit without internal lighting. I have a gps transponder with ADS-B in and out so do not need the mode C connection to the transponder. We do use the bird for IFR occasionally.

Any advice? What would you do? Any pireps on Century Instruments or Aircraft Quality Instruments?
 
Don’t you still need the encoder even with ADS-B out? I thought mode C was based on pressure altitude and not GPS?
 
take it up to 5000’, cap the fittings tightly, paint all the seams, glass face edges & fitting edges with RTV; when you descend the sealant will be forced into the leaks, making it good again!
Or....use it for a household barometer/conversation piece. Yeah, that would be better.
 
Tom-D said:
why. where is it leaking?
Click to expand...
Tom, not sure it was leaking but think it might have been another issue internal to the altimeter. It was off by 150 feet and the needle movement was a bit erratic. I had noticed during takeoffs
it seemed the reading would jump about that same error amount at rotation recently.
 
Briar Rabbit said:
Tom, not sure it was leaking but think it might have been another issue internal to the altimeter. It was off by 150 feet and the needle movement was a bit erratic. I had noticed during takeoffs
it seemed the reading would jump about that same error amount at rotation recently.
Click to expand...

Altimeters are calibratable in place.
turn the knob to that places altitude, disconnect the kholsman window, set altimeter setting for that day. reconnect kohlman window.

This is not a repair, it is an adjustment, allowed by the rules.

Jerkey movement, probably water in static system.
 
When this happened to me, I bought a new United for about $1300 and my old one is sitting on my desk as a barometer .
 
Some times these static systems simply need to be blown out, but first disconnect all instruments and cap the instrument, then blow the system with compressed air.

you'd be surprised what comes out of these old systems. dead bugs, water, mud, grime, old hose interior lining
 
needle jumping 150 feet on take off,, ? just the air bubble finally get thru the water.
 
sent mine in to QAA and had them do an IRAN....(inspect and repair as necessary). I think it was around $300.
 
aggie06 said:
Don’t you still need the encoder even with ADS-B out? I thought mode C was based on pressure altitude and not GPS?
Click to expand...

Absolutely need a pressure altitude encoder for mode C / ADS-B out.

My guess is that an old encoding altimeter was disconnected from the transponder and a new blind encoder was installed when the transponder was replaced.
 
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