On the B737 NG the autopilot can be engaged at 400' agl. Engaging the autopilot will change pitch mode from TOGA to MCP SPD (=LVL CHANGE) and the roll mode will default to HDG SEL unless LNAV has been previously armed (a roll mode should be called for/confirmed at 400' agl).
Engaging the autopilot has no effect on thrust. Thrust will change from takeoff thrust to climb thrust when N1 is selected OR the height entered in TAKE OFF REF 2/2 is reached - UNLESS a low altitude is captured in which the thrust will maintain the commanded speed.
Last edited by Jet Man; 19th Apr 2006 at 22:53.