TangoWhiskey
Touchdown! Greaser!
This thread from another forum (Beech Owners) was interesting. Thought it might generate some discussion here about the subleties of using your Autopilot on approaches:
Another thought expressed in this thread was the advantage of using the Approach mode is that (most? all?) autopilots will not capture the Glideslope (if they are capable of doing so in the first place!) unless it is in approach mode; and, since the 430 will autocycle to VLOC if it sees a localizer frequency, then if you're already in "Approach mode" on the autopilot, you're all set up to capture and fly the full approach... no need to remember to switch from NAV mode to APPROACH mode on your A/P.
Troy
You always use *approach* mode when coupling to the GPS. Goes for all the autopilots. KFC types, too.
Reason: The *approach* dynamics are much more suited to GPS type needle indications than NAV mode.
NAV mode has all sorts of patches to deal with VOR coupling, such as limiting rate of turns to give a decent ride when dealing with VOR scalloping and needles flopping around when going over the VOR stations. These patches interfere with crisp coupling to GPS needles when changing to a new heading.
If you couple to a VOR with Approach mode, you will quickly see why the NAV mode was invented. The ride is pretty bad.
The GPS needle is so solid that approach mode can be used with no problem. And since the needle sensitivity remains relatively constant, the autopilot coupling is really effective.
Try it. Approach mode. Even without a Sandel, you will find that in the worst case of a T - shape GPS approach that you can manually feed the new headings to the HSI as cued by the GPS and the coupling will be flawless. You do not need to decouple the approach mode as you go from one segement to the next--just dial in the new heading.
So if you use approach mode, with the sandel, it WILL be as good as a real gpss!! Or almost.
Another thought expressed in this thread was the advantage of using the Approach mode is that (most? all?) autopilots will not capture the Glideslope (if they are capable of doing so in the first place!) unless it is in approach mode; and, since the 430 will autocycle to VLOC if it sees a localizer frequency, then if you're already in "Approach mode" on the autopilot, you're all set up to capture and fly the full approach... no need to remember to switch from NAV mode to APPROACH mode on your A/P.
Troy