When the GTN650 starts up it is supposed to allow me to enter fuel on board and fuel flow. It will then use this information to display range rings.

When my starts up, if the 5600 comes up first the GTN650 will not allow me to enter to information. If the GTN650 comes up first I can enter it, but as soon as the 5600 comes up it forgets what I entered. After reading the GTN650 manual it appears the GTN was incorrectly configured for fuel sensors but the manual does not explain how to change this setting. I called Garmin but they just said to take the unit to an authorized dealer and my Tecnam dealer who installed the system claims they can't change it.

I read the 5600 manual again and I notice it shows a GTN configuration screen for the RS-232 port with the name Fuel Format 1. How do I get to this screen?