14 CFR § 23.2125

The applicant must determine climb performance at each weight, altitude, and ambient temperature within the operating limitations—

For all single-engine airplanes;

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

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.

The applicant must determine the glide performance for single-engine airplanes after a complete loss of thrust.