Some more info (with sources :-)
From AAIB Bulletins (Feb 96) A340-311, G-VBUS
"... during takeoff is that the changeover between ground mode and flight mode takes place quite rapidly. In pitch, the flight mode is progressively blended in over a period of five seconds which starts when either the aircraft is above 100 feet radio altitude or it has been airborne for 5 seconds and the pitch attitude is above 8 degrees. However, the roll flight mode is blended in over a period of two seconds which begins 0.5 sec after the aircraft becomes airborne."
I can only assume that the changeover from flight mode to ground mode occurs below a given radio altitude and this allows the selection of reverse idle. (Similar to Scando's post above about the 737NG). On the A32x, the transition from Flight Mode to Flare Mode is initiated at 50 ft RA. (
www.airbusdriver.net)
Regards,
Shuttlebus