Yes, you are correct. It simply arms the FMS when you hit NAV below 400’, and stays in heading mode until then. (No one I have ever flown with pushes two buttons).
But the original post I made was about turning A/P on below 600’. Was told there was a memo allowing it, but I didn’t remember reading it, that’s why I was asking.
Originally Posted by
FODhopper
Technically it doesn't matter when below 400' you engage NAV mode because it automatically goes to HDG mode IF below 400'. Then it switches to NAV at 400'. If you engage HDG mode first then it requires a second button push, this time NAV mode, at 400' or higher.
At AWAC we departed out of DCA RWY 01 about four times a day and we would engage NAV mode at gear rotation whether using the National Five (using the VOR) or subsequently the RNAV procedures now in use.
BUT, as always, policy is policy so if it says wear out your finger pushing extra buttons, do it.