Critical Altitude

The maximum altitude at which, in standard atmosphere, it is possible to maintain, a specified power or a specified manifold pressure at a specified rotational speed. Unless otherwise stated, the critical altitude is the maximum altitude at which it is possible to maintain, at the maximum continuous rotational speed, one of the following: 1) The maximum continuous power, in the case of engines for which this power rating is the same at sea level and at the rated altitude; 2) The maximum continuous rated manifold pressure, in the case of engines, the maximum continuous power of which is governed by a constant manifold pressure. (14CFR1)