Pre Take Off Burn Off
The fuel required to be burnt during taxy to allow txfr from tank 11 to tanks 5 & 7 to achieve TO CG (53.5% or 54%).
Used when ramp CG aft of TO CG (ie high fuel load)
Alternative was Pre Take off Transfer when ramp CG ahead of TO CG - fuel txfrd to tank 11. Much quicker and less hassle.