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Federal Aviation Administration, DOT 

§ 23.679 

skill or strength, by either the deacti-
vation of the system or a failed portion 
thereof, or by overriding the failure by 
movement of the flight controls in the 
normal sense. 

(c) It must be shown that, after any 

single failure of the stability aug-
mentation system or any other auto-
matic or power-operated system— 

(1) The airplane is safely controllable 

when the failure or malfunction occurs 
at any speed or altitude within the ap-
proved operating limitations that is 
critical for the type of failure being 
considered; 

(2) The controllability and maneuver-

ability requirements of this part are 
met within a practical operational 
flight envelope (for example, speed, al-
titude, normal acceleration, and air-
plane configuration) that is described 
in the Airplane Flight Manual (AFM); 
and 

(3) The trim, stability, and stall char-

acteristics are not impaired below a 
level needed to permit continued safe 
flight and landing. 

[Doc. No. 26269, 58 FR 42164, Aug. 6, 1993] 

§ 23.673

Primary flight controls. 

Primary flight controls are those 

used by the pilot for the immediate 
control of pitch, roll, and yaw. 

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as 
amended by Amdt. 23–48, 61 FR 5148, Feb. 9, 
1996] 

§ 23.675

Stops. 

(a) Each control system must have 

stops that positively limit the range of 
motion of each movable aerodynamic 
surface controlled by the system. 

(b) Each stop must be located so that 

wear, slackness, or takeup adjustments 
will not adversely affect the control 
characteristics of the airplane because 
of a change in the range of surface 
travel. 

(c) Each stop must be able to with-

stand any loads corresponding to the 
design conditions for the control sys-
tem. 

[Amdt. 23–17, 41 FR 55464, Dec. 20, 1976] 

§ 23.677

Trim systems. 

(a) Proper precautions must be taken 

to prevent inadvertent, improper, or 
abrupt trim tab operation. There must 

be means near the trim control to indi-
cate to the pilot the direction of trim 
control movement relative to airplane 
motion. In addition, there must be 
means to indicate to the pilot the posi-
tion of the trim device with respect to 
both the range of adjustment and, in 
the case of lateral and directional 
trim, the neutral position. This means 
must be visible to the pilot and must 
be located and designed to prevent con-
fusion. The pitch trim indicator must 
be clearly marked with a position or 
range within which it has been dem-
onstrated that take-off is safe for all 
center of gravity positions and each 
flap position approved for takeoff. 

(b) Trimming devices must be de-

signed so that, when any one con-
necting or transmitting element in the 
primary flight control system fails, 
adequate control for safe flight and 
landing is available with— 

(1) For single-engine airplanes, the 

longitudinal trimming devices; or 

(2) For multiengine airplanes, the 

longitudinal and directional trimming 
devices. 

(c) Tab controls must be irreversible 

unless the tab is properly balanced and 
has no unsafe flutter characteristics. 
Irreversible tab systems must have 
adequate rigidity and reliability in the 
portion of the system from the tab to 
the attachment of the irreversible unit 
to the airplane structure. 

(d) It must be demonstrated that the 

airplane is safely controllable and that 
the pilot can perform all maneuvers 
and operations necessary to effect a 
safe landing following any probable 
powered trim system runaway that 
reasonably might be expected in serv-
ice, allowing for appropriate time 
delay after pilot recognition of the 
trim system runaway. The demonstra-
tion must be conducted at critical air-
plane weights and center of gravity po-
sitions. 

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as 
amended by Amdt. 23–7, 34 FR 13091, Aug. 13, 
1969; Amdt. 23–34, 52 FR 1830, Jan. 15, 1987; 
Amdt. 23–42, 56 FR 353, Jan. 3, 1991; Amdt. 23– 
49, 61 FR 5165, Feb. 9, 1996] 

§ 23.679

Control system locks. 

If there is a device to lock the con-

trol system on the ground or water: 

(a) There must be a means to— 

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