[Code of Federal Regulations]

[Title 14, Volume 1]

[Revised as of January 1, 2006]

From the U.S. Government Printing Office via GPO Access

[CITE: 14CFR25.255]



[Page 368-369]

 

                     TITLE 14--AERONAUTICS AND SPACE

 

CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION

 

PART 25_AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES--Table 

of Contents

 

                            Subpart B_Flight

 

Sec. 25.255  Out-of-trim characteristics.



    (a) From an initial condition with the airplane trimmed at cruise 

speeds up to VMO/MMO, the airplane must have satisfactory maneuvering 

stability and controllability with the degree of out-of-trim in both the 

airplane nose-up and nose-down directions, which results from the 

greater of--

    (1) A three-second movement of the longitudinal trim system at its 

normal rate for the particular flight condition with no aerodynamic load 

(or an equivalent degree of trim for airplanes that do not have a power-

operated trim system), except as limited by stops in the trim system, 

including those required by Sec. 25.655(b) for adjustable stabilizers; 

or

    (2) The maximum mistrim that can be sustained by the autopilot while 

maintaining level flight in the high speed cruising condition.

    (b) In the out-of-trim condition specified in paragraph (a) of this 

section, when the normal acceleration is varied from +1 g to the 

positive and negative values specified in paragraph (c) of this 

section--

    (1) The stick force vs. g curve must have a positive slope at any 

speed up to and including VFC/MFC; and

    (2) At speeds between VFC/MFC and 

VDF/MDF the direction of the primary longitudinal 

control force may not reverse.

    (c) Except as provided in paragraphs (d) and (e) of this section, 

compliance with the provisions of paragraph (a) of this section must be 

demonstrated in flight over the acceleration range--

    (1) -1 g to +2.5 g; or

    (2) 0 g to 2.0 g, and extrapolating by an acceptable method to -1 g 

and +2.5 g.

    (d) If the procedure set forth in paragraph (c)(2) of this section 

is used to demonstrate compliance and marginal conditions exist during 

flight test with regard to reversal of primary longitudinal control 

force, flight tests must be accomplished from the normal acceleration at 

which a marginal condition is found to exist to the applicable limit 

specified in paragraph (b)(1) of this section.

    (e) During flight tests required by paragraph (a) of this section, 

the limit maneuvering load factors prescribed in Sec. Sec. 25.333(b) 

and 25.337, and the maneuvering load factors associated with probable 

inadvertent excursions beyond the boundaries of the buffet onset 

envelopes determined under Sec. 25.251(e), need not be exceeded. In 

addition, the entry speeds for flight test demonstrations at normal 

acceleration values less than 1 g must be limited to the extent 

necessary to accomplish a recovery without exceeding VDF/

MDF.

    (f) In the out-of-trim condition specified in paragraph (a) of this 

section, it must be possible from an overspeed condition at 

VDF/MDF to produce at



[[Page 369]]



least 1.5 g for recovery by applying not more than 125 pounds of 

longitudinal control force using either the primary longitudinal control 

alone or the primary longitudinal control and the longitudinal trim 

system. If the longitudinal trim is used to assist in producing the 

required load factor, it must be shown at VDF/MDF 

that the longitudinal trim can be actuated in the airplane nose-up 

direction with the primary surface loaded to correspond to the least of 

the following airplane nose-up control forces:

    (1) The maximum control forces expected in service as specified in 

Sec. Sec. 25.301 and 25.397.

    (2) The control force required to produce 1.5 g.

    (3) The control force corresponding to buffeting or other phenomena 

of such intensity that it is a strong deterrent to further application 

of primary longitudinal control force.



[Amdt. No. 25-42, 43 FR 2322, Jan. 16, 1978]