Mutt:
herewith is your psalm and verse.... FAR 25.121 Airworthiness
In the U.S. that transfers to the applicable commercial flight operations regulations. But, for the non-commercial operator flying a Part 25 aircraft it does not. Part 91 does require the non-commercial operator to calculate the balanced field for takeoff but once airborne there is no specific requirement to make good the Part 25 takeoff flight path, all engines operating or OEI. With all engines operating he is bound, though, by a SID climb gradient as I would be in my Part 23 bugsmasher.