GFC500 on a DA42
You mean GFC700…
@NCYankee I will scan my AFMS and check. It has old style ICAO upset attitude definitions as a limitation in pitch (plus 25 degrees minus 15 degrees), these limitations
since discontinued by the ICAO, which I interpret as CWS mode related limitations. The UP/DN trim wheel is limited to 800 fpm RoD, but this is a guidance not a limitation.
In terms of vectoring onto the GS, either at platform altitude and the FAF, or on a when established descend with the glide slope clearance, my point, perhaps not well made, is that a busy ATC will literally vector you onto the GS with no, or virtually no run in. They are required to give you a 2nm run in to establish, but in a jet rush hour environment they will squeeze you on with no run in. In this scenario the KFC200 presumably will not arm GS capture as it hasn’t had time to confirm LOC established, aircraft still turning to intercept? Even biggish iron Honeywell Apex suite struggles when vectored onto the GS directly.
In a slam-dunk approach, it should still arm in APPR mode, even if not in time for the GS to capture. If you are quick or anticipate the slam-dunk, turn off altitude hold and when the GS does not annunciate, use the DN trim button to descend through the GS from above, it should capture. If you dilly dally, it might take more descent rate than your AP is willing to provide.
I have not found any RoD documentation in the POH, AFMS, IM or MM that specifies 800 FPM, just a pitch limitation, so I assume it is what you actually observe.
Hi John dug out the AFMS and copied the relevant section related to ALT mode. My unit doesn’t have altitude pre select. Also note the limitations are +/- 15 degrees in pitch and +/- 25 degrees in roll.
My confusion may be a mis reading of NOTE in section 8 (d), as I also note the Pitch Trim NOTE in 8 (c) FD mode talks of trimming attitude at 1 degree per second, however in FD mode not AP.
Gear DN Flaps UP, 100 KIAS and 700 fpm RoD I would estimate to be around minus 1 to 2 degrees pitch attitude, and am guessing the pitch trim will go beyond this if desired?
My understanding is that you need to be in HDG (on an intercept) and ALT mode, with ALT stable before the APPR will couple both to LOC and GS. Therefore if ALT mode with AP engaged restricts pitch trim operation to 500 to 700 fpm, in a roundabout way you have another limitation?
The 8(d) note only applies to ALT mode. If you are not in ALT mode, then the vertical trim commands a pitch angle at a rate of change of 1 degree per second, so 5 seconds of down gets you – 5 degrees down if you start out level. My understanding is that the pitch angle is then held until you either command a new pitch using the switches, use the CWS to command a new pitch, ALT is selected, or GS is intercepted. The pitch angles are limited to +/- 15 degrees.
Although ALT mode is normally engaged when selecting APPR mode, it is not required to be. If you turn off ALT mode by pressing the ALT button, the AP goes into a pitch hold vertical mode. Anytime the KFC 200 is engaged, it is using a pitch mode (ALT, pitch, GS). Pitch mode is not annunciated, it is the mode the vertical is in when ALT is not selected.
This is what the Pilot Guide has to say regarding conditions for setting APPR mode (Note that being in ALT mode is not one of the requirements):
Operation of the APPR mode requires
the pilot to:
1. Set the NAV receiver frequency.
2. Set the PNI course pointer to the inbound runway heading or the front course in case of ILS precision approach. Do this even on back course approach.
3. Set the HDG SEL “bug” on the PNI to the desired intercept angle and activate HDG” mode.
4. Depress the ”APPR“ button on the mode controller
And this is what the Pilot Guide has to say regarding GS capture. I added bolding and underlining for emphasis.
The Glideslope mode is armed for automatic capture if LOC front course capture has occurred. Automatic Glideslope capture occurs as the aircraft approaches the glide path from above or below.
Upon interception of the Glideslope, capture occurs and “GS is lighted on the Annunciator Panel. A smooth capture pitch command is displayed by the Command V-bar. The pilot (or Autopilot) controls the aircraft to satisfy the Command V-bar. Slewing ALT at time of GS centering will inhibit GS capture. Upon GS capture, the ALT HOLD mode (if active) is cancelled. However, ALT HOLD may be manually reselected to maintain altitude upon reaching MDA if visual contact is not established
@NCYankee I noticed the comment on Beechtalk that the KFC200 is happier capturing the glide slope if it is in ALT mode for around 20 to 30 seconds. I agree that the AFMS and the booklet instructions don’t have ALT as a condition for arming APPR, only stating that if in ALT mode this will disengage when the GS couples.
In the instruction booklet what do they mean by Slewing ALT at time of GS centering will inhibit GS capture? Is it a typo for selecting?
Knowledge of how the modes work, or inhibit other modes, clearly requires some practice.
I think the BeechTalk is an OWT (Old Wives Tale). However, in discussing with the Bendix King engineer many moons ago, the normal mode to join the approach was using heading mode until the localizer was captured. The analog computer projects an intercept point for the localizer and does not start tracking the localizer until past that point, using HDG instead. This made some localizer joins that were very shallow, particularly those that had after market GPSS, because pilots would use heading mode to align with the final approach course localizer and then press APPR, making the join point past where the GS transitioned from fly up to fly down, thus missing the GS capture because of a late localizer capture. The sequence is press HDG then APPR and the annunciation is first APPR/ARM and HDG annunciated, followed by HDG being extinguished and APPR/CPLD being annunciated. Only then will the GS be captured.
To avoid this, it was stressed that APPR should be pressed while there was still a substantial angle to the final approach course, allowing an earlier localizer capture. Many of the BeechTalk commenters have GPSS in one form or another and misinterpret what the autopilot is actually doing. I recall you saying you do not have a GPSS, so as long as you use a normal intercept angle when you press APPR, it should capture fine. The King engineer assured me that if the basic conditions were met, including localizer capture, the GS capture is strictly a function of the KFC 200 computer detecting a transition in the GS from high to low or low to high and nothing else. There is no 30 second delay with the KFC 200 and it does not matter if the AP is in ALT or not when the GS is captured.
I could not find the term Slewing used anywhere else in the Pilot Guide, but I am guessing they mean when in ALT mode and using the up/down switches to adjust the altitude. If you are doing this while close to the GS intercept point, you can miss the intercept.
I’ve merged some threads because the discussion got diffused across multiple autopilot types 
the normal mode to join the approach was using heading mode until the localizer was captured
Indeed, and that is how one usually flies an ILS. I ought to try the KFC225 one day approaching the LOC in NAV mode. This is very unusual anyway but sometimes at LFAT one gets a DCT TUKVI and then it would make sense.
I also found that one should not press APR too soon, because the KFC225 picks up what looks like false LOC signals.
Many of the BeechTalk commenters have GPSS in one form or another and misinterpret what the autopilot is actually doing.
The original thread subject makes more and more sense
@NCYankee many thanks and thank you Peter for moving the thread.
I haven’t found a decent YT on using the KFC150/200/225 family, there are a few flight videos but nothing showing the system in different modes.
One needs to borrow an ILS and do a video One could do all this 1000-2000ft above the platform, at a Class G airport, but it would be common courtesy to tell them in advance.
I don’t currently have a cockpit camera though.
