Many airlines choose to ignore the manufacturers recommendations and operating proceedures and instead develop their own, oftentimes derived from other equipment or at the Chief Pilots' misguided insistance.
The manufacturer designed, built, test flew, designed operating proceedures for, and sold their aircraft and expects it to be operated accordingly. But no, some dorks in airlines think that they "know better". It has been proven time and again that the most efficient and logical way to operate an
aircraft is to do so as designated by the builder.
