Natstrackalpha
72 Kts is only a command to the ground spoilers not the autobrake. The autobrake LO, MED or MAX will not engage if GROUND spoilers do not deploy.
On landing the 72kts is not relevant as spoilers deploy on main wheel compression LO and MED.
For RTO the spoilers only deploy above 72kts.
The 40kts you are getting confused about is irrelevant and I honestly do not understand it as it states that for MAX to engage must have spoiler activation and be above 40kts and nose wheel compressed. Maybe it is GS and the 72kts for spoiler activation is IAS.
if you RTO you want it to stop you - not have a debate with itself as to what speed you are doing
This is incorrect, cleared for immediate take off due aircraft on 5 nm final, after setting thrust and reaching 50kts you have an ECAM relating to a door or similar. The first exit is 3000ft away. Do you really want to stop in 1000ft and then spend a minute figuring out you need to disarm the spoilers whilst the guy behind you has to go around. Its probably due to dirt in the door but as your brakes are now hot you have to wait at the gate for an hour before you can go again.
thats what max is all about, it does not brake harder, it brakes . . sooner.
This is also incorrect. MED and LOW is a deceleration rate target that the computer aims for. If you use max reverse it will apply less braking as can meet its deceleration rate with less. MAX is just as the button says, it supplies maximum braking to the wheels. At MAX autobrake the aircraft for a given speeds stopping distance varies with its weight. For MED and LO as long as the target deceleration can be met the stopping distance for a specific speed remains the same regardless of aircraft weight.