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Old 21st Apr 2015, 23:00
  #9 (permalink)  
NSEU
 
Join Date: Feb 2004
Location: Australia
Posts: 1,300
It is disabled once accelerating through 20 knots and enabled when decelerating through 15 knots so it is for low speed operation only.
On the 747-400, the speed limits are based on wheelspeed information from the Brake System Control Unit (with a backup of IRU groundspeed at 40kts).

The system will still work with the IRUs switched off.
NSEU is offline