Talking recently to a pilot with a Indonesian airline equipped with Boeing 737NG series that have carbon brakes. Company SOP is that autobrake 3 is used for all landings on dry hard runways regardless of length. However, if the runway surface is wet, it is SOP to select autobrake MAX regardless of runway length which could often be as much as 11,000 ft.
Whether or not this SOP is something to do with minimising brake wear with carbon brakes or perhaps a desire to mitigate against those pilots that deliberately float a long way to ensure a smooth touchdown, is anyone's guess.
An extract from an Airbus bulletin explains briefly about the principle of carbon brakes by saying: "Carbon brake wear and tear depends on the number of brake applications and on brake temperature. It does not depend on the applied pressure, or the duration of the braking. The temperature at which maximum brake wear occurs depends on the brake manufacturer. Therefore, the only way the pilot can minimize brake wear is to reduce the number of brake applications"
A further extract from a large SE Asia operator of A330 aircraft states in part: "Autobrake shall be armed for all landings. The use of autobrake is preferable because it minimizes the number of brake applications and thus reduces brake wear.
The use of LO autobrake should be preferred on long dry runways, whereas the use of MED autobrake should be preferred for short or contaminated runways.
The use of MAX autobrake is not recommended. On long dry runways where minimal braking is anticipated, the autobrake may be disengaged after touchdown provided the aircraft has landed in the Touchdown Zone."
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A final point from the Boeing 737 Classic FCTM re use of autobrake. Again, in part it states: "Boeing recommends that whenever runway limited, using higher than normal approach speeds, landing on slippery runways or landing in a crosswind, the autobrake system be used".
This implies that there is no need to use the autobrake system if none of the above conditions apply. Despite this Boeing recommendation is it common for operators to use autobrakes for landing at all times notwith standing landing distances may be well in excess of performance requirements. In real life it is probably rare to be runway limited on most landings.
This gets around to my request for expert opinions (
) of the logic of the 737NG operator in Indonesia whose SOP is autobrake 3 be used for all landings regardless of runway length and autobrake MAX for wet runway landings also regardless of runway length. And what about the A330 operator whose SOP is autobrakes for all landings but then permits the crew to disengage the autobrake after touchdown where minimal braking is anticipated? What is the point of having the autobrake system selected when it will be disengaged after touch down?
In the example of the 737 NG operator with carbon brakes, does it mean that autobrake 3 (which by any standards is fairly heavy braking) reduces the wear on carbon brakes because they get hotter faster? If the aim is to save the cost of brake wear, then surely where excess runway is available then why use autobrakes at all? And to have an SOP requiring MAX autobrake when ever the runway is wet and which may be well in excess of performance limits in the FCOM/QRH, seems to me a massive overkill. Or an indictment of the standard of the crews....
To cap off the discussion on autobrake SOP, it is interesting to note that some of the Gulfstream Global Express series of corporate aircraft are not even fitted with autobrakes!