[Code of Federal Regulations]
[Title 14, Volume 1]
[Revised as of January 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 14CFR25.255]

[Page 362-363]
 
                     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 Secs. 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 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:

[[Page 363]]

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