Originally Posted by
Skyjob
Think to poster's airline makes a valid point in its restriction, as it means NAV is not allowed below the obstacle critical altitude being MSA.
Once above MSA, obstacles are no longer assessed, thus NAV is safe to be used.
It ensures crew restrict themselves from overbanking and obstacle proximity by using Selected Guidance with its imposed bank angle limits.
I believe the restriction on using NAV below MSA for pilot's created waypoints is primarily due to CFIT prevention. The "overbanking" is not really an issue in Airbus FBW in both Hdg/Trk and NAV mode.