14 CFR §23.2125

1. (a)The applicant must determine climb performance at each weight, altitude, and ambient temperature within the operating limitations—
   1. (1)For all single-engine airplanes;
   2. (2)For levels 1 and 2 high-speed multiengine airplanes and level 3 multiengine airplanes, following a critical loss of thrust on takeoff in the initial climb configuration; and
   3. (3)For all multiengine airplanes, during the enroute phase of flight with all engines operating and after a critical loss of thrust in the cruise configuration.
2. (b)The applicant must determine the glide performance for single-engine airplanes after a complete loss of thrust.