More G1000 findings

Each flight with the G1000 avionics teaches me more about them. My most recent flight was no exception.

This time I tested how the G1000 handles switching over to the alternate static air source.

Static air pressure is used to determine altitude, air speed, and vertical speed in the airplane - when you switch to the alternate source (maybe because ice formed over the normal port, or it was otherwise clogged) you switch to reading the pressure of the air in the cabin of the airplane. This cabin air is at a slightly lower pressure than the outside air due to aerodynamic forces sucking air out of the tiny gaps in the cabin (around the doors, windows, and other places).

So when you switch to the alternate source, the airplane thinks you are climbing momentarily. I wanted to see how the autopilot and the G1000 would react when this was done in flight.

The first time I tried it I switched to the alternate source and saw the autopilot start to correct altitude as I expected. I quickly switched back to the normal source and the autopilot seemed to recover, again as expected. However, a few moments later the autopilot decided we needed to descend rather aggressively and started pointing the nose down. I turned off the autopilot and corrected the situation. Then I turned the autopilot back on and it behaved normally.

Trying the static source switching again later, this time I kept using the alternate source for a minute or so - in real life you would probably keep using it until you landed, assuming the normal port stayed clogged. This time when I switched back to the normal static air source the autopilot responded to the change in static pressure and continued to operate normally. I came away thinking I had just confused it by switching to alternate and back to normal so quickly the first time.

As an aside, that it actually how I test the alternate static source selector when doing my preflight - I move it on and then off quickly and watch that the altimeter needle reacts.

The other thing I learned was that creating a user waypoint has some weirdness to it. I wanted to create one based on a lat/lon point I had, but it apparently would only allow me to create one based on the bearing and distance from a nav aid (or other item known to the G1000's database).

I am sure you can create one based on a lat/lon but couldn't figure it out in the air after 5 or so minutes of trying. I didn't consult the pilot's guide as I probably should have, but I just refused to believe that it could be so tricky that I'd need the manual.

I'll have to try that out on the sim to see what I was missing.

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