Final APP
G'day gbotley,
Welcome to the wonderful world of Airbus. Check out:
Auto Flight - Flight Guidance
AP/FD Common Modes - APPROACH
DSC-22_30-80-30-20 p3/10 (in my FCOM, but may be slightly different in yours)
For all non- ILS app
ARMING CONDITIONS
A/C above 400ft AGL
Flight plan is valid (Lat and Vert)
Active FLT PLAN has non ILS approach selected
GA mode not engaged
then a little further on
ENGAGEMENT Conditions
FINAL APP will engages when:
NAV or APP NAV is engaged
FINAL is armed
Predictions in FMGS
APPROACH Phase active
*the a/c is in the capture zone
LAT - +/- 1.5nm from FDP
VERT - +150ft abc FDP
*A/C intercepts a descending leg of the Vert flt path (this is a big one, we can't press the APP button now until the active WPT is the one with a coded vertical path, otherwise it does some funky stuff)
A BLUE arrow is displayed on the ND to show where the FINAL APP conditions are met and where final descent will begin
If a WHITE arrow is displayed, at least one engagement condition isn't met, FINAL APP won't engage and the a/c will not descend automatically.
So while you have FINAL APP in Blue on the FMA, if you don't have the blue arrow, then it won't descend. On the line we tend to activate the APP PHASE a little early, this gives the a/c time to slow down and you can get configured, plus it gives you time to check for the blue Arrow.
So, if you are in a HOLD, once turning inbound, IMM EXIT, then if the next WPT is the FDP you can press APP.
I hope that helps.