(a) VSO and VS1 are the stalling speeds or the minimum steady flight speeds, in knots (CAS), at which the airplane is controllable with --

(1) For reciprocating engine-powered airplanes, the engine(s) idling, the throttle(s) closed or at not more than the power necessary for zero thrust at a speed not more than 110 percent of the stalling speed;

(2) For turbine engine-powered airplanes, the propulsive thrust not greater than zero at the stalling speed, or, if the resultant thrust has no appreciable effect on the stalling speed, with engine(s) idling and throttle(s) closed;

(3) The propeller(s) in the takeoff position;

(4) The airplane in the condition existing in the test, in which VSO and VS1 are being used;

(5) The center of gravity in the position that results in the highest value of VSO and VS1; and

(6) The weight used when VSO and VS1 are being used as a factor to determine compliance with a required performance standard.

(b) VSO and VS1 must be determined by flight tests, using the procedure and meeting the flight characteristics specified in §23.201.

(c) Except as provided in paragraph (d) of this section, VSO and VS1 at maximum weight must not exceed 61 knots for --

(1) Single-engine airplanes; and

(2) Multiengine airplanes of 6,000 pounds or less maximum weight that cannot meet the minimum rate of climb specified in §23.67(a) (1) with the critical engine inoperative.

(d) All single-engine airplanes, and those multiengine airplanes of 6,000 pounds or less maximum weight with a VSO of more than 61 knots that do not meet the requirements of §23.67(a)(1), must comply with §23.562(d).

[Doc. No. 27807, 61 FR 5184, Feb. 9, 1996]