Cornish,
B744 - HOLD mode for the autothrottle is activated at 65 KIAS, not 80.
It would have to be one bitchin wind for the power not to have reach the thrust reference limit by 65 knots!
Timbotch, yes that is what the TOGA buttons are for. Standard practice is to manually advance the thrust levers slightly to get the thrust coming up symmetrically. For Rolls-Royce engines thrust is advanced to 1.1 - 1.2 EPR, GEs I can't remember, but around 55% N1 sounds familiar. Once you are happy you push the TOGA button and the thrust levers advance to the thrust reference limit, which can be different for every takeoff depending on environmental conditions, runway and whether de-rated thrust is used.
To prevent what radarcontact alluded to with the autothrottle doing strange things (such as bringing thrust back to idle
) at really critical stages of the takeoff, another autothrottle mode activates at 65 KIAS (B744). This is called HOLD mode and the autothrottle does not actually control thrust and the thrust levers can be positioned manually (not usually necessary). I can't remember exactly when HOLD mode is de-activated and THR REF re-activated, it may be when VNAV arms or it may be one of those nosewheel extension +25 seconds or 400 feet whichever happens first things. Can anyone clarify that?