I've been flying using INS+GPS navigation mode and decided to test GPS-only navigation mode to avoid having to deal with INS.

The problem is that I'm having trouble getting the aircraft to recognize the GPS route in this mode. I import the route into the GPS, ensure it's in GPS instead of VLOC, but the aircraft doesn't seem to recognize the route. On the HSI, the indicator of how many miles are left to the next yawpoint shows zero and doesn't point in the direction of the next waypoint. Because of this, the A/P doesn't follow the route.

Curiously, this only happens when I load the aircraft from the gate, in cold & dark mode. If I load the aircraft from the runway, with the engines already running, the aircraft does recognizes the GPS route and follows it normally without any problem. It's as if, when loading from cold & dark, I would have to perform an alignment for the aircraft to know where it is, but how can I do that if ''GPS mode only'' removes the INS?

Can someone tell me what I'm doing wrong?

Hi,

I can't suggest what's wrong - but I've flown all my flights GPS only, and haven't had any issues with the aircraft not following the GPS path. The indicator distances on the HSI only work with the INS, but the arrows follow the gps guidance, at least on my set up.

Sorry this doesn't help you at all, but since you've confirmed you're setting the CDI correctly I can't think of anything else...

Hi

7 hours ago, edu2703 said:

On the HSI, the indicator of how many miles are left to the next yawpoint shows zero and doesn't point in the direction of the next waypoint. Because of this, the A/P doesn't follow the route.

As Bunkie mentioned above, the HSI DIS/TIME Readouts are only driven by the INS Computers. They cannot display data from any other sources such as your GPS or NAV1/2 DME.

To use GPS Navigation, you have to

• Import or manually enter your route into the GPS

• Ensure CDI is set to GPS instead of VLOC
  

• Set the RADIO/INS switch to RADIO
  

• Set FD to ON and use VOR mode for guidance
  

• On your HSI it will also read "GPS" to show you the source driving the HSI needle
  

I've done a number of flights already swapping between VOR, INS and GPS modes frequently across the same flight from C&D and haven't yet come across your issue.

Maybe a video from Cold & Dark till when you notice the issue can help assess if there is some bug or any kind of missed step during setup? You can upload to Youtube/GDrive and share link here in case file size is too large.