For the technically minded, and for myself as I am old and easily confused. From the 744 Tech manual or as it is now known... B747 FCOM Vol 2.
During takeoff prior to lift–off:
• with speed less than 50 KIAS, pushing a TO/GA switch activates the
autothrottle in thrust reference (THR REF) and advances thrust levers to
the selected reference thrust limit. If the autothrottle is not active by 50
knots, it cannot be activated until above 400 feet
• at 65 knots, autothrottle annunciation changes to HOLD
After lift–off:
• if an engine failure occurs, the pitch command target speed is:
• V2, if airspeed is below V2
• existing speed, if airspeed is between V2 and V2 + 10
• V2 + 10, if airspeed is above V2 + 10
• if a TO/GA switch is pushed before the reference thrust limit changes to
climb:
• takeoff derates are removed
• A/T in HOLD, autothrottle annunciation is THR REF
• at 50 feet, LNAV activates when armed. Roll commands bank to track the
active route
• at 400 feet, VNAV activates when armed. Pitch commands the current
airspeed. Autothrottle sets the selected reference thrust and annunciates
THR REF