Doors to Automatic “… but even on Med Autobrake the aircraft can be brought to a halt in 3000ft so you have got a hell of a margin ..”
3000ft, who say’s so? Read the small print, what about varying depths of water, different runway surfaces, varying wind, touchdown speed, position, etc, etc. What margin then?
From AC 91-79 Runway Overrun Prevention.
10kts fast on a wet runway, 500ft; float due to shearing wind, 2500ft; 10 ft high at threshold 200ft; and these are before you might have to consider a slick runway due to rubber or even hydroplaning.
Auto brake is only a selection of the deceleration target, and whilst the brakes (or brakes / reverse combination) attempt to meet this target there is no guarantee of achieving it; nor are there particularly good feedback cues for detecting less than desired braking performance, better to use manual brake and get a feel for the landing from the ‘feet & seat’.