Seeing Peter’s photos in the “How high” thread got me thinking. How many of you who fly high performance IFR types with a six pack have the old three needle clock altimeters and how many have a drum and pointer type? I am so out of practice with the three needle type I needed a second or two to read it in the photo.
I asked that here, a long time ago.
My RHS altimeter is a bit sticky, and I have some options
Now that you raised this @Josh I will look into the single pointer as a replacement.
It would need to be the 3.125" size.
If the replacement unit is encoding, maybe one day I could install a switch in the gray code wiring so the aircraft’s pressure altitude can come from two sources. That would be a useful redundancy, because the LHS KEA130A does fail and when it goes you lose the autopilot (for ALT capture and hold).
Digging around US Avionics Ebay I could have one of yours 
I would have thought that the sorts of aircraft going high are gradually and inexorably going over to glass solutions. Aren’t a lot of the drum types as pictured above AC electric powered, and hence unsuitable for light aircraft?
They’re just so much easier to read. Having read the previous thread asking about power, the power is only required for high accuracy as the design range of these altimeters is up to the stratosphere (FL510 on one type I’m rates on). With the lower pressure changes at high altitude, the friction in simple mechanical movement can be enough to prevent a rapid response, so they include a powered vibrator to keep the internals wobbling to increase the accuracy of the response.
I believe without power the accuracy would be sufficient for all practical purposes at lower levels, but you would have to read the specs for that.
Neil – I very much doubt they are AC powered as the Learjet runs on 28V DC and has one installed as the standby.
They are DC with vibrator. On the Meridian the vibrator is an airworthiness item on the standby altimeter.
OK, understood, and I agree about the readability.
We now have Proline 21 but in a previous aircraft we had to replace an altimeter to get an RVSM approval and I was sure the new one needed electricity, but it was probably just DC.
FL510 is a bit spicy if there’s a pressurisation problem, do you have the masks around your neck at that altitude?
An encoding altimeter will need power AFAIK. All IFR certified ones need power for the backlight.
Re glass, I think that trend is a mainly light-GA one. Bigger aircraft get standardised cockpits and they run for years with exactly the same layout, with lots of individual instruments. I also think a part of the reason for that is to minimise AOG time – exactly the reason I stick with separates. AOG with a glass cockpit usually means the dealer rep has to travel to you, with a replacement box and his secret config codes, which is “OK” in light GA if you are not going anywhere important and have lots of time and money to burn.
One thing I wondered about was whether there was some reg prohibiting the two different styles being installed in the same aircraft. I can’t find any reference, but one A&P on a US site got “extremely excited” about the legality of this, saying one needs an aircraft specific approval to fit anything. My understanding is that if the following are met
then on an N-reg, Part 91, you can install most things on the RHS panel. And I have seen countless examples of this, with e.g. engine monitors which are freely installed on the RHS.
Peter wrote:
Re glass, I think that trend is a mainly light-GA one. Bigger aircraft get standardised cockpits and they run for years with exactly the same layout, with lots of individual instruments. I also think a part of the reason for that is to minimise AOG time – exactly the reason I stick with separates. AOG with a glass cockpit usually means the dealer rep has to travel to you, with a replacement box and his secret config codes, which is “OK” in light GA if you are not going anywhere important and have lots of time and money to burn.
I don’t really agree with that. Of course King Airs and Citations are still the light end of aviation but I don’t know anyone doing any sort of upgrade and NOT going to glass. In fact it’s cheaper to upgrade to a dual Garmin 500 than it is to replace the old kit if it goes faulty. It’s the same if a King 55 HSI goes wrong badly, an Aspen is cheaper. At the heavier end of GA there are numerous retrofit schemes, like Garmin G5000 for the Beechjet, Honeywell for Gulfstream, Universal for the HS125, etc.
I also don’t agree with the reliability point. In almost 4000 hours of flight our proline 21 equipped company aircraft have never had an AOG issue with avionics; we have never lost a screen, and the only issue I can recall was an ADF u/s, caused by an incorrectly mated connector, not that we missed the ADF anyway.
The discrete vs integrated avionics battle is over, Peter.
Downtimes are much reduced by the integrated flight decks. It’s a lot easier to identify and swap a faulty box than reverse engineering the 5 in line converter boxes or where the gray code goes wrong due to interference and why the analog DME tuning signal is not working sporadically.
