altitude hold problem w/ altimatic IIIB

[N8632Y]

[MillenniumFlight]

[N8632Y]

[Scott Ducey]

[Zach Grant L1011jock]

[N8632Y]

[Kristin Winter]

Another thing to check with the IIIB is whether the cable which runs from the control head in the panel, to the computer box under the panel, really works properly. I recently had one of the receptacle ears break off, which meant that no matter how I adjusted the altitude, it did not change the setting in the computer, because the cable turned, but didn't engage.

[MillenniumFlight]

I agree with the other posts in this thread that connector integrity is a likely culprit, particularly after having work done on the panel. The Altimatic IIIB has multiple units -- controller, altitude unit, nav radio interface, autoflight system, amplifier and servos -- interfaced with each-other and with the artificial horizon and HSI / DG through a birds-nest of wiring. Plenty there that could go wrong!

No question, the STEC 55X is the unit of choice, if money is available. Because I fly single-pilot hard IFR, having an inoperative autopilot did not seem to be a sensible option for me. I looked into the S-Tec system 30, which had most of the 55X functionality but at lower cost: but I was quoted $18K installed, by the local instrument shop, and over $20K from the nearest Piper dealer. That's when I got interested in rehabilitating the Altimatic.

With the repair of the pitot / static lines, and some tweaking, I now have an excellent state-of-the-art-in-the-1970's autopilot, capable of climbs, descents, holds, heading-bug navigation, VOR Navigation, GPS navigation (though not yet GPSS equipped)...... it will intercept, capture and follow the ILS reliably, and I have flown several GPS approaches without incident (no WAAS yet, though the autopilot would be capable enough, I think, if I had the correct navigator!)

There's an art to flying the Altimatic smoothly. I use the pitch selector for climbs and descents, rather than changing the altitude selector. Before engaging pitch hold, make sure the needle is centered to avoid abrupt pitch changes. Once the pitch is selected, I adjust the altitude preselector to the approximate target altitude. As we get close (say 200 feet to go), I progressively adjust pitch towards level flight, and tweak the preselect (using the indicator needle as a guide), switching back to altitude hold once the needle is centered at the chosen altitude. One of the advantages of the IIIB unit is the auto-trim feature, which works beautifully, leaving the trim near-perfect any time you choose to revert to hand-flying.

Although it's certainly more complex to use than a modern digital unit, it's actually fairly easy to master after a few hours of practice.... and it's certainly MUCH better than not having an autopilot, for a tiny fraction of the cost.

It will have to do me for a year or two until I can save up my pennies for something fancier!

Bryan McIver
1969 PA-30
N8807Y

[N8632Y]

Bryan,
I agree, the altimatic has been a very capable SIC, and I was very comfortable with course reversals, capturing glideslope, climbs, etc, I had GPSS installed with the 530W and the racetrack is picture perfect, holds are easy, etc.
I do like to hand fly as much as possible and use the autopilot when i'm busy, and then I can monitor the aircraft systems, review approach plates, follow maps, etc.
The 530W and autopilot can make you lazy, something I never want to be. In charge, ahead of the plane, ahead of ATC, weather and prepared for the unexpected.
I'd like to fix the old autopilot, cause 20K can buy alot of fuel!
Cold weather, I'll be looking at her over the weekend, and all the posts.
Thanks to everyone.
steve

[Hansmeister]

Brian,

You may want to talk to John van Bladeren about an autopilot quote. This is not the time of year to be going to Portland, but his expertise and competitive pricing is worth the trip.

JvB put in the Century 2000 for me, and it is every bit as good as the STEC 60-2. The GPSS is built-in to the Aspen 1000 Pro. Both for a little more than your Piper quote.

[AlanBreen]