The Cessna 120-140 Association Forum

Can someone school me on altimeters? My ancient Bulova Watch Co. unit didn't pass a bench test when I questioned it's accuracy (leaks past the adjustment knob). Do I need to replace with a TSO'd unit? If my local avionics guy doesn't have an exchange unit handy then I either send it in for overhaul or get a new unit. My IA is not in town so am doing my own homework (yes, I'm impatient). Pity my old altimeter is on the fritz, I kind of like the idea it was made by Bulova Watch Co.

Absolutely has to be TSO’d if you want to be legal. Then again what you do in the privacy of your own hangar is between you, your god and your insurance company.

And I would definitely have it rebuilt instead of buying brand new.

Roger that. Shipped off to a Wichita instrument shop today. They are curious of the Bulova manufacture but at the least can exchange, hopefully overhaul.

tomreneau wrote: ↑Thu Oct 20, 2022 9:53 am Absolutely has to be TSO’d if you want to be legal.

I'm not saying you're wrong, but, the 120/140 predate the concept of "TSO" so the originals were not "TSO'd". Also, the "Sensitive" altimeter was optional. (The "insensitive" ones had 100 foot graduations.)

The question has been floating round the internet since the beginning, without resolution. My take is the TSO lets the A&P off the hook of deciding if the instrument is acceptable or not.

(BTW, the Bulova part is a military part and doesn't appear to have a TSO tag, nor is it original...)

(BTW, the Bulova part is a military part and doesn't appear to have a TSO tag, nor is it original...)

I found this online, I agree probably not original to the plane but apparently built 3 years before it. The instrument shop says it's probably a Kollsman model made by Bulova, they will cross reference the AN numbers for their paperwork. I like the history.

I'd definitely use it. I was just pointing out that the "requirements" for what constitutes an acceptable altimeter for our planes are somewhat hazy.

Don't agree "it has to be" and I agree this has kicked around here before also. I think the TSO kicks in with us is if you wanted to have an IFR certified panel where I believe all instruments etc, have to be TSO certified. The Bonanza I sold, post heart attack, had an IFR panel. Had two nav/coms, a KX170, non TSO, but had a KX175, same as KX170 but was TSO making the panel legal. Like said, I've heard that some AP/IAs require it just as a COYA, if they are not certain.

PS: There is an interesting write-up on the VAL Avionics page (the radio folks) relative to this topic and also addresses major/minor alterations logic. Little confusing at first, at least to me, but at the end of each segment it ask, NO or Yes, which if you answer Yes' then one has failed one of the previous questions and shouldn't proceed - kinda hard to detail, but I think you will see what I mean.