Mutt:
Considering that FAR91 was written for FAR 23 and FAR 25 aircraft, it stands to reason that they didn't cite climb gradients, however for those of us operating FAR 25 large aircraft, with safety management systems, safety factors, oversight authorities, noise requirements and SAFA, we cannot operate as per the letter of FAR91, it just isn't acceptable. We have takeoff performance issues with SAFA while in full compliance with FAR121
The standard of care in the performance arena required from a regulatory standpoint is simply different for commercial and private flight operations. And, you are right, even with Part 121 operators who meet the
minimum standards set forth in 121.189 can easily have a CFIT with OEI. The industry has been spared most of this in the turbine era because of the fantastic reliability of the powerplants.