What type Altimeter is an SA-91? It has three pointers 100, 1000, 10000. Don't know if it is Kollsman. I can't find any info as far as repairing unit.enter image description here

  • $\begingroup$ Are you asking who the manufacturer is, or its principle of operation? I'm guessing you want to know who makes it? What aircraft is this from? $\endgroup$
    – Ron Beyer
    Apr 15 '16 at 14:59
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    $\begingroup$ are there any markings on the back? A picture of the back might be helpful. $\endgroup$
    – FreeMan
    Apr 15 '16 at 17:02
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    $\begingroup$ It does appear to be a sensitive altimeter with a kollsman type adjustment, though the kollsman window is blacked out—perhaps the adjustment knob has been turned down too far. In other ways it does appear to be a Kollsman brand altimeter, markings, shape, and milling. Kollsman brand often had the name stamped into the metal at the back of the instrument as well as a tag, also on the back. Additional photos would be very helpful. $\endgroup$
    – J Walters
    Apr 15 '16 at 21:04

It seems to be a C-12 or C-13 sensitive altimeter (SA) from Kollsman Instrument Division / Square D Company, manufactured circa 1940:

enter image description here

The only difference seems to be the marking "ALTITUDE" replaced by "SA-91". As this is the 39th in the series, this could be the initial marking, later replaced by the more standard one. I don't see what could be "91" for.

The Kollsman window is black (as commented) because the setting dial has been turned past maximum pressure reference, as indicated by the bug between 7 and 8. The window value and this bug are linked.

The brown color seem to be related to phosphorescent markings and needles.

The C-12 has apparently many variants, likely designed on demand, especially for the USAF, like this one with alternate colors for the marks:

enter image description here
C-12 manufactured by C.G. Conn Ltd., (source)

C.G. Conn Ltd. is a music instruments company (saxophones), but at war time they provided aircraft instruments to the USAF (flying on instruments finally explained!).

Kollsman published handbooks about their instruments. Here is one from 1938. It doesn't cover this model of altimeter, but can be helpful though:

enter image description here

  • $\begingroup$ Someone just gave me a Kollsman C-12 with the alternating white/blue number markings that looks almost identical to the C. G. Conn you linked to, but mine is manufactured by Square D Company and "KOLLSMAN" is embossed on the back. Per the deatails on a spec place screwed to the back, it's a Type C-12, MFRS Part NO 671 BK-010, CONTR NO AF-33186 and SER NO (serial) 43[unreadable]. My co-worker gave it to me, and supposedly his dad's friend, who was a WWII pilot (deceased) gave it to him. I'd love to know what AC it came out of. Do you know which AC used the White/Blue variant like that? $\endgroup$
    – elrobis
    May 14 '19 at 15:53
  • $\begingroup$ FWIW I thought I could look up the coworker's dad's friend and assume it came out of an AC he flew in the war, but unfortunately his last name, "Young" is a terrible search term. Also the first name "Larry" isn't getting me anywhere, either, but it may be short for Lawrence. (It also may be a middle name..) $\endgroup$
    – elrobis
    May 14 '19 at 15:55
  • $\begingroup$ @elrobis: 43 is the year of manufacturing. From here: "The C-12 Altimeter was used across all aircraft of the Air Corps US Army, including heavy bombers B-17 and B-24, medium bombers, B-25 and B-26, Fighters P-38, P-39, P-40, P-47, and P-51, and transports C-46 and C-47, according to the Maintenance Interchangeability Chart dated Dec 1943." $\endgroup$
    – mins
    May 14 '19 at 20:57

Of interest is the serial number on the face of the instrument. Yes it appears to be the Kollsman type but lacks the barometric readout in the "Kollsman window".

I suspect that you have an early prototype of the Kollsman. At least that is my best guess. I'm not an expert on antique altimeters but just a knowledgeable pilot and aviation enthusiast.


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