Originally Posted by
Intruder
That DE who said "Autobrakes 4 is cooler" needs to get his head examined. The harder the brakes are applied, the more power (i.e., energy dissipation/time) used and the less influence of other factors like air drag, reverse thrust, and mechanical friction. Therefore, Autobrakes 2 and max reverse thrust will cause the least wear.
Autobrakes 1 is not used in the 744/748 because it usually results in multiple brake-release cycles during the landing roll, which increase the wear on carbon brakes. Any time you think Autobrakes 1 might be sufficient (e.g., CVG Rwy 9), simply use idle reverse and Autobrakes OFF instead. On that runway, do a brake check crossing 18R/36L and roll to the end using hardly any brakes at all.
Is there a reference for the statement that AB1 will release the brakes multiple times? That is not my understanding of the AB system - in fact I believe that once the autobrake engages the pressure will modulate to keep the decelaration rate but will in fact not release entirely. The reason for this and also why, with Carbon brakes it is better to keep the brakes on is so that no oxidation occurs which results in an additional brake wear event apart from the shaving effect of the initial brake application. It is far better to have carbon brakes operating in the 200-300 degree range since the carbon will pack more tightly together resulting in less physical brake wear. Above 450 degrees the effect of oxidation really increases compared to lower temps and at temperatures lower than 200 the effect of shaving is greater given the strands of carbon are not tightly packed - almost like "standing up" as opposed to packed down when hot. I have been taught and so teach that AB is reccomended so that you have one continuous brake application - this gets the temps up to the 200 degree range rapidly and allows for minimal oxidation.