Hi, can anyone tell me the function of the GPS APR button (highlighted)?
It has two modes: ARM and ACTIVE. I thought it might relate to an RNAV approach, maybe a shortcut for pressing APR on the autopilot but it seems to do nothing during that operation.
No need for a detailed run down of any procedure it’s associated with, just push my thinking in the right direction if you can. It seems to be the only thing not in the manual.
I’m guessing it’ll seem obvious as soon as I’m told but it’s just frustrating me currently…
Thanks.
Switch’s between GPS mode and Radio Mode
Hi, thanks for the answer but I’ve ended up a bit more confused than before (it seems I overestimated my ability to have my thinking “pushed in the right direction”…).
I know that the left button button marked “NAV GPS” changes the HSI from GPS to Radio input but then you’re telling me the right button “GPS APR” does that as well?
Is it used in a certain situation (like if you needed to switch back to the GPS after a missed ILS approach or something like that)?
Sorry for clarification questions. I’ve scoured any youtube vids I can find but haven’t seen anyone even click near it so I’m lost.
I think both button are just duplicate of CDI and APR buttons on GPS.
I still looking for documentation of that
That’s what I’d thought but I’ve tried using the APR GPS button during RNAV landing but ended up having to press APR button on the autopilot in order to catch the glide path. TBH I’m so rusty with all the procedures it may well be me mising something. Luckily it doesn’t seem a crucial bit of equipment so it’s more just a stuborn curiosity for me now.
The help labels list it as GPS approach toggle so I guess I’ll keep fiddling with it on GPS approaches.
Thanks for taking the time to answer o7
I’ve just been using the same plane and also wondered. I’ve actually been wondering for several years! Anyway, AI tells me:
The sequence of “NAV/GPS” and “GPS APR ACTV” buttons refers to controls in aircraft avionics used to select the
navigation source and manage a GPS approach. These are distinct functions typically found on annunciator control units (ACUs), such as the Mid-Continent MD41 series or Bendix/King KLN 89/94 GPS units.
NAV/GPS Button
This button is a switch used to select which source provides the primary navigation data (left/right steering information) to the Horizontal Situation Indicator (HSI) or Course Deviation Indicator (CDI) and potentially the autopilot.
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NAV position: The HSI/CDI uses data from a traditional ground-based navigation receiver (like VOR or ILS).
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GPS position: The HSI/CDI uses data from the GPS receiver, allowing the aircraft to follow a flight plan loaded into the GPS unit.
GPS APR ACTV Button (GPS Approach Arm/Activate)
This is a specific button, often a remote switch/annunciator, used to manage GPS-guided instrument approaches (RNAV approaches).
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ARM mode: Pushing the button arms the GPS for the approach. This is typically done as the aircraft nears the initial approach fix (IAF), usually within 30 nautical miles of the destination airport. The system will annunciate “ARM” (often in white).
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ACTV mode: The system automatically switches from ARM to ACTV (Active) when the aircraft is approximately 2 nautical miles inbound to the final approach fix (FAF), provided all conditions (like RAIM availability and being in the correct flight plan leg mode) are met. The annunciation changes to “ACTV”. In this mode, the navigation scaling on the HSI/CDI becomes much more sensitive (e.g., from ±1.0 nm to ±0.3 nm) to provide the precision required for the final approach segment.
Manually pressing the GPS/APR button cycles between the ARM state (if an approach is in the flight plan) and the ARM canceled state. You cannot manually select ACTV mode; it activates automatically