FAA Federal Aviation Regulations (FARS, 14 CFR)

Static longitudinal stability must be shown as follows:

(a) Climb. The stick force curve must have a stable slope at speeds between 85 and 115 percent of the trim speed, with --

(1) Flaps retracted;

(2) Landing gear retracted;

(3) Maximum continuous power; and

(4) The airplane trimmed at the speed used in determining the climb performance required by §23.69(a).

(b) Cruise. With flaps and landing gear retracted and the airplane in trim with power for level flight at representative cruising speeds at high and low altitudes, including speeds up to VNO or VMO/MMO, as appropriate, except that the speed need not exceed VH --

(1) For normal, utility, and acrobatic category airplanes, the stick force curve must have a stable slope at all speeds within a range that is the greater of 15 percent of the trim speed plus the resulting free return speed range, or 40 knots plus the resulting free return speed range, above and below the trim speed, except that the slope need not be stable --

(i) At speeds less than 1.3 VS1; or

(ii) For airplanes with VNE established under §23.1505(a), at speeds greater than VNE; or

(iii) For airplanes with VMO/MMO established under §23.1505(c), at speeds greater than VFC/MFC.

(2) For commuter category airplanes, the stick force curve must have a stable slope at all speeds within a range of 50 knots plus the resulting free return speed range, above and below the trim speed, except that the slope need not be stable --

(i) At speeds less than 1.4 VS1; or

(ii) At speeds greater than VFC/MFC; or

(iii) At speeds that require a stick force greater than 50 pounds.

(c) Landing. The stick force curve must have a stable slope at speeds between 1.1 VS1 and 1.8 VS1 with --

(1) Flaps in the landing position;

(2) Landing gear extended; and

(3) The airplane trimmed at --

(i) VREF, or the minimum trim speed if higher, with power off; and

(ii) VREF with enough power to maintain a 3 degree angle of descent.

[Doc. No. 27807, 61 FR 5190, Feb. 9, 1996]