Even the KAP140 has roll steering in NAV mode when connected to a GPS.
Only via a roll steering converter which fakes a heading bug, afaik.
I doubt that because the heading bug is disregarded in NAV mode.
OK; I wonder what the wiring is. Does the KAP140 have ARINC429?
Don’t know. I guess the G1000 which drives the KAP140 can have a software roll steering converter which works by faking the course and/or course deviation signals to the autopilot.
Just one more remark regarding my original question.
I’ve flown the ILS9 and ILS27 at EDVK from several IAPs by now. I typically start by using the GPS overlay to get me onto the localizer. Once the aircraft is heading towards to last GPS waypoint, which happens to be the FAF, the R9 switches automatically from GPS to VLOC. With the exception of the northern entry to ILS27 out of LUXUX the turn towards the FAF GPS waypoint happens in time and there is no overshooting.
So my question was about how these things might be encoded. I will try to contact Jeppesen this week to maybe learn about it.
I fully understand that an ILS should not be flown with GPS – obviously. My intention is to better understand the limits and abilities of what I’ve got and the why behind of what I can observe. Better to try and learn about the automation available on CAVOK days – right?
I have to say that with that high level of automation one, as the human pilot, feels like the pilot monitoring in a 2-crew situation with the system being the pilot flying :-) … and yes, I know about the potential risk of becoming a child of the magenta line! …
Is this “GPS to ILS” issue the one concerning the automatic detection of the “final” and “real” localiser? That issue is difficult to solve automatically, because you can have fake localiser radiation.
The KAP140 does not have roll steering inputs to NAV.
NAV or APR mode on the GFC700 are dependent on the selected source for navigation. With VOR or Localizer as the source, the tracking logic and operation is old school, selected heading sets the intercept angle and selected course selects the tracking course. CDI deflections left or right and the rate of change are used to track the ILS or VOR. When GPS is the selected course, roll steering is used for the course guidance. This can be demonstrated on a day when there is a crosswind and the runway is served by both an ILS and an LPV approach along the identical path. Typically the winds at GS intercept altitude are stronger and 90 degrees to the surface winds, and most of this change occurs in the last 500 feet. The autopilot tracks the final approach course to the FAF and then starts the descent when the GS is intercepted. By the time the aircraft reaches the FAF, the wind correction has been established and the autopilot reduces its tracking sensitivity. As you descend, the direction and velocity of the cross wind changes and the autopilot usually gets behind the change and has to S turn back to reestablish the WCA. Often near 500 feet AGL, I find myself taking over manually under these circumstances. The GFC700 exibits this S turn tendency with the best of autopilots. I then fly the LPV. It is a thing of beauty. The track holds steady the entire way without a hint of an S turn as the heading is continuously adjusted by the roll steering to maintain a constant track to the runway. The CDI remains stuck in the center and never moves off center, but the heading smoothly and continuously adjusts to hold a constant track. Under identical conditions, I have had to take over for the ILS and could let the LPV continue without touching the controls until just before the flare.
In the case of the Garmin GNS430W/530W or GTN navigators, the GPS units will output label 121 on an ILS up until the FAF and then they will suspend sending the roll steering label. This causes an aftermarket GPSS to command wings level from that point as it is no longer receiving the label it needs. For this reason, one can’t use roll steering on the final approach leg of an ILS. Some installations also disable the roll steering anytime the navigation source is changed from GPS to VLOC. Many autopilots could take advantage of the roll steering to provide better lateral navigation on an ILS, but would have to fly the vertical GS manually. The G500/600 enforces the source must be GPS in order for it to supply GPSS, the Aspen does not and neither will some of the after market roll steering adapters.
I find it hard to get my head around how this works… do you mean NCYankee that, on an ILS, the Garmins will fly using GPS LNAV till the FAF and only then use the LOC signal?
That would produce very poor guidance.
In my plane, I press APR when approaching the LOC so the system is tracking the LOC from much earlier. There is zero “snaking” although it can take a while to take out a strong wind drift.
Re the KAP140 roll steering, has there ever been a roll steering converter which instead of faking a heading bug it fakes the course pointer + deviation bar signals, allowing the AP to remain in NAV mode? In principle it could be done. Basically you would fake the outputs of a KI525 HSI.
The KAP140 does not have roll steering inputs to NAV.
Ok, but then the G1000 has work some magic, because in the G1000+KAP140 combination it behaves like it does.
Re the KAP140 roll steering, has there ever been a roll steering converter which instead of faking a heading bug it fakes the course pointer + deviation bar signals, allowing the AP to remain in NAV mode?
Well, I only know that with the KAP140 in NAV mode it will follow the G1000 flight plan, including turn anticipation. It will also do holds and racetracks.
In principle it could be done. Basically you would fake the outputs of a KI525 HSI.
The HSI is of course done entirely with software in an EFIS/FMS system like the G1000, so that should be a simple matter.
