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"Enable A/P Approach" message - WHY?

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mvgossman View Drop Down

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mvgossman Quote  Post ReplyReply Direct Link To This Post Topic: "Enable A/P Approach" message - WHY?
    Posted: 31 Mar 2019 at 12:27pm
On page 5-17 of the IFD440 Pilot Guide there is this "Enable A/P Approach" section, see screenshot. Apparently it applies to the King KAP140 and KFC225 autopilots, and only those, and you have to be configured in your IFD440/550 to display it if you have one of those autopilots. There is a similar section in the Garmin 430W manual for the same autopilots. This message is displayed as an LSK button (not a Caution Advisory System alert) but evidently you don't have to act on it, such as pressing it, which means that it's just a warning, message, reminder, or annunciation, however you choose to call at it.

What is special about these two specific autopilots that doesn't apply to others, such as my KAP150 that is similar in operation to the KAP140 (referring to its manual, I've never flown with one)? It must be something in the electronics going on specific to the KAP140/KFC225. I've never received this message since it's not so-configured to display it (via the setting available in maintenance mode). I've never felt I needed a reminder to press the NAV or APR button, although it couldn't hurt to get a tap on the shoulder to switch when established on the intermediate approach segment or on a vectored intercept to it, so why so important for the KAP140? Is there something electronic going on? I don't see how since you don't have to act on this message at all except to change your autopilot mode which you will do on the KAP150 as well. I have an uneasy feeling that I'm lacking a deeper understanding of this and wondering if there are any implications for the KAP150 and other autopilots. I've asked multiple very experienced IFDxxx pilots, waiting to hear from Avidyne's support email, a direct inquiry to an Avidyne tech support expert, and my own avionics installer.


Mooney M20J Aspen EFD1000 Pro IFD440
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Catani View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Catani Quote  Post ReplyReply Direct Link To This Post Posted: 31 Mar 2019 at 1:41pm
With some autopilots (DFC90 for example) the IFD automatically puts the autopilot into the correct mode (course arm and capture, glideslope arm and capture).  It is something a pilot should check to make sure it happens, but it's not something the pilot must activate by pushing buttons to make sure the autopilot flies the approach correctly. The IFD will even tune and identify an ILS freq for you.  Like John Glenn complained about the Mercury capsule, the whole thing is so automated a monkey could fly it (until something goes wrong).

Apparently, the autopilots mentioned in the excerpt you are referring to are not capable of receiving input from the IFD to make the mode changes necessary to fly an approach.  So instead, the pilot receives prompts as reminders that he needs to push some buttons.  Very considerate of the system to do that.

Since your autopilot is not mentioned, you are in no-mans land.  Perhaps your autopilot is neither capable of receiving IFD prompts, nor is the IFD able to determine what kind of autopilot you have.  In which case, just keep flying like you would a steam gauge airplane:  navigate, and if you want autopilot help, control it yourself and don't forget to push the right buttons at the right time.  We did that safely for decades, and we can still do it if so equipped.

Edited by Catani - 31 Mar 2019 at 1:43pm
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paulr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote paulr Quote  Post ReplyReply Direct Link To This Post Posted: 01 Apr 2019 at 8:31am
There's a third possibility: the autopilot might not *have* an approach mode, as most legacy autopilots do not. You BendixKing AP customers are all fancy :)
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