400A autopilot
 

Having been a big s tec fan in the past, and now acquiring a 73 P337 with a 400A a/p. I'd like to hear some comments about the 400a before jumping to the conclusion that I need to replace it. Any comments are welcome.

Dave Dillehay

My experience has been (and I think that if you do a Search you will find that others agree) that the 400A is a fine autopilot. It is, however, subject to aging, in the sense that with time (35 years for a 1973 model) the electronic components drift/atrophy and service is required. The most common fault is leaking capacitors, which is an easy repair. You can still find shops that fix them, and the equipment can be removed (1/2 is under the throttle/props/mixture levers, the other half is overhead and towards the rear, behind the headliner) and sent out to be serviced.

On this subject, perhaps the most knowledgeable person on this Board is Pete Somers and I hope he'll jump in here with his views. BTW, my Search on autopilot and 400A yielded many threads with good info.

Ernie

Dave
As Ernie has said the 400A is a good A/P and like all things subject to aging, however there is plenty of shops to repair them and still a lot of spares available. It works fine and easy to use.
Stick with it, you will find it an excellent system.

Pete

How about GPSS
 

Has anyone hooked one up to a Garmin 430/530W with a gpss convertor? Does the gpss make it track better on a cross country course and will it fly procedure turns and gps approaches?

I'm curious about the same if I hook an Aspen Pro into the autopilot.

If you hook this system up to the A/P and you have a Course/Heading input and a left/right and operate it in NAV mode should be no problem.

Pete

Pete, I'm no expert on this, but the "if" in your sentence is significant. I think it may be hard to get the two units to "talk" and "handshake" effectively. And lots of luck finding a shop with experience in marrying a modern GPS with a legacy ARC autopilot. Again, I could be wrong, but could you expand on the difficulty in achieving this?

Ernie

Sorry Ernie, I did not take the time to think about this one and put it into something that made some sense. But Ok here we go.

In normal NAV mode the 400A takes heading information which on a HSI is provided by the Course (yellow arrow with the L/R bar in the centre on the King system).

Left/Right is provided by the NAV system to provide track error.

All or most GPS provide a track error signal that can be displayed on a standard CDI for track error, this left/right can be wired through a switch and you will be able to either use NAV or GPS. However you will have to use the No1 NAV system as this supplied the CRS error signal.

Hope this make sense

Regards
Pete

Aspen pro for GPSS autopilot commands
 

I have the Garmin 530W and Aspen Pro installed and should have the 400A installed by April 2. I am expecting hands off waas approaches, but I'll believe it when I see it.

I understand the GPSS should send 'approach' sensitivity to the 400A for more precise tracking even during regular cross country GPS navigation. Do you guys agree?

My experience has been good with a 530/430 (non WAAS) to the ARC unit, although I also have a Flight Director. In NAV mode, it will follow the magenta line quite nicely and even the turns are not bad as the Garmin unit does use anticipation which if I recall correctly is programable anyway in the Garmin. Than with LOC mode armed, when LOC is sensed, it switches to that and with GS armed, when intercepted, the glide slope is also followed.

Works pretty well, but that said I almost always hand fly the approaches for the practice and monitor the entire approach when coupled.

There was a requirement for an adapter box or two so the Garmins would talk to everything as I recall, but that was the top and tail of it.

Peter has seen my set-up so may also be able to comment further.

Regards - Dave

Loc mode is a switched output from the GNS unit which is connected to the A/Pilot, and as Dave says in LOC mode on the A/Pilot the glide slope is armed. However in Nav mode the glide slope is disabled.
The 400A is a very good system and like everything, maintained correctly will give you no problems, and they are easy to repair when they go wrong.

The main problems are-----

1 Pilots overriding the servos and either breaking the shear pin or damaging the clutch.
2. The follow up resistors in the servos go intermittant.

Apart from those, the system is fine, remember the 400A is installed into most Cessna twins until the 400B came out, but the 400B does not differ much from the 400A.

Hello Mr Underwood, all ok?

Regards
Pete

400a autopilot
 

is there anyone out there with technical knowledge of the 400a autopilot-
have an intermittent problem I'd like some opinions

Autopilots Central in Tulsa, OK.

400 autopilots will develop intermittent problems due to their age. This can come from leaking capacitors to corrosion on connectors.

Is there a published procedure for replacing capacitors and cleaning connectors?