Is there a reference for that information, Euroflyer?
EuroFlyer wrote:
They (Garmin) use GPS altitude information to be more precise on the glideslope.
How can gps be more accurate then the radio beam of an ILS?
Or do you mean the glidepath of an RNP APP, probably not as this wouldn’t work without GPS anyway.
AFAIK it‘s for ‚enhancement‘. Whatever that means.
If you look at ILS rawdata you can see that the signal is actually quite rough. It is one parameter that is measured during the regular ILS calibrations. So GPS might be usefull to straighten that out.
I compared the track of a KFC 150 and a GFC 500 and the GFC was signifcantly better.
Could it use the GPS to ensure it does not fly a false glidescope? The marketing department could categorise that as more accurate…
I think this is all unlikely (GPS altitude especially).
You must be able to fly an ILS to an airport which is not even in the GPS database.
And not every ILS GS is 3 degrees.
So whatever the GFC500 uses the GPS aiding for, it can’t be flying an “approach path” to the airport.
Even if it just used the GPS ground track, how does it know what is the right ground track? It can’t unless the airport and the ILS are in the database and the GPS navigator box sends that data to the autopilot.
I just don’t believe it can be doing something that clever. At least the POH should state clearly it can’t fly an ILS unless the GPS database holds the data, and it doesn’t say that, does it?
The GFC 500 is tied to the G5. The G5 has a built in GPS receiver or it can use a GPS navigator or ADS-B Out transponder with built in GPS.
These are various quotes from the Pilot Guide:
The G5 calculates aircraft attitude using information from its built-in inertial sensors.
The G5 also uses GPS and airspeed data to provide the most accurate attitude
information.
3.3.3.7 GLIDESLOPE MODE (GS)
Glideslope Mode is available for LOC/ILS approaches to capture and track the
glideslope. When Glideslope Mode is armed (annunciated as ‘GS’ in white), LOC
Approach Mode is armed as the lateral flight director mode.
NOTE: Glideslope Mode requires a valid GPS position.
3.3.4.4 NAVIGATION MODE (GPS, VOR, LOC)
NOTE: The G5 must have a valid GPS position for VOR and LOC Modes.
If Navigation Mode is active and either of the following occur, the AFCS reverts to
Roll Hold Mode (wings rolled level):
• Active navigation source manually switched
• Navigation input is lost
• GPS reception is lost
So it is not just an ILS that requires GPS, so does VOR/LOC tracking. Also GPS is used by the G5 to assist with attitude indication.
So whatever the GFC500 uses the GPS aiding for, it can’t be flying an “approach path” to the airport.
It may use it for attitude.
In G1000+GFC700, I can see ILS auto-ident, even for similar ILS frequency, I imagine that’s used to build DTK for GPS-enhancement of the AP in APP mode?
Peter wrote:
Even if it just used the GPS ground track, how does it know what is the right ground track? It can’t unless the airport and the ILS are in the database and the GPS navigator box sends that data to the autopilot.
It knows it to one degree, surely, because it knows what your HSI course pointer (or OBS) is set to?
Perhaps it is just using GPS data to self-critique – i.e. it knows it is supposed to be flying a FAT of 242 degrees and uses it to check whether its wind calculations are having the desired effect. In essence using a second data point (alongside a centered localiser needle) to verify that one is proceeding in the right direction?
Much as someone hand-flying a procedure might, when outbound from the IAF, check their course over ground on the GPS against that noted on the plate.
