Federal Aviation Administration, DOT § 23.672
to the speed specified for the selected § 23.659 Mass balance. method. The supporting structure and the at- [Amdt. 23–23, 43 FR 50592, Oct. 30, 1978, as tachment of concentrated mass bal- amended by Amdt. 23–31, 49 FR 46867, Nov. 28, ance weights used on control surfaces 1984; Amdt. 23–45, 58 FR 42164, Aug. 6, 1993; 58 must be designed for— FR 51970, Oct. 5, 1993; Amdt. 23–48, 61 FR 5148, (a) 24 g normal to the plane of the Feb. 9, 1996] control surface; WINGS (b) 12 g fore and aft; and (c) 12 g parallel to the hinge line. § 23.641 Proof of strength. CONTROL SYSTEMS The strength of stressed-skin wings must be proven by load tests or by § 23.671 General. combined structural analysis and load (a) Each control must operate easily, tests. smoothly, and positively enough to allow proper performance of its func- CONTROL SURFACES tions. § 23.651 Proof of strength. (b) Controls must be arranged and identified to provide for convenience in (a) Limit load tests of control sur- operation and to prevent the possi- faces are required. These tests must in- bility of confusion and subsequent in- clude the horn or fitting to which the advertent operation. control system is attached. (b) In structural analyses, rigging § 23.672 Stability augmentation and loads due to wire bracing must be ac- automatic and power-operated sys- counted for in a rational or conserv- tems. ative manner. If the functioning of stability aug- mentation or other automatic or § 23.655 Installation. power-operated systems is necessary to (a) Movable surfaces must be in- show compliance with the flight char- stalled so that there is no interference acteristics requirements of this part, between any surfaces, their bracing, or such systems must comply with § 23.671 adjacent fixed structure, when one sur- and the following: face is held in its most critical clear- (a) A warning, which is clearly dis- ance positions and the others are oper- tinguishable to the pilot under ex- ated through their full movement. pected flight conditions without re- (b) If an adjustable stabilizer is used, quiring the pilot’s attention, must be it must have stops that will limit its provided for any failure in the stability range of travel to that allowing safe augmentation system or in any other flight and landing. automatic or power-operated system that could result in an unsafe condi- [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as tion if the pilot was not aware of the amended by Amdt. 23–45, 58 FR 42164, Aug. 6, failure. Warning systems must not ac- 1993] tivate the control system. § 23.657 Hinges. (b) The design of the stability aug- mentation system or of any other auto- (a) Control surface hinges, except matic or power-operated system must ball and roller bearing hinges, must permit initial counteraction of failures have a factor of safety of not less than without requiring exceptional pilot 6.67 with respect to the ultimate bear- skill or strength, by either the deacti- ing strength of the softest material vation of the system or a failed portion used as a bearing. thereof, or by overriding the failure by (b) For ball or roller bearing hinges, movement of the flight controls in the the approved rating of the bearing may normal sense. not be exceeded. (c) It must be shown that, after any [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as single failure of the stability aug- amended by Amdt. 23–48, 61 FR 5148, Feb. 9, mentation system or any other auto- 1996] matic or power-operated system—
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(1) The airplane is safely controllable must be visible to the pilot and must when the failure or malfunction occurs be located and designed to prevent con- at any speed or altitude within the ap- fusion. The pitch trim indicator must proved operating limitations that is be clearly marked with a position or critical for the type of failure being range within which it has been dem- considered; onstrated that take-off is safe for all (2) The controllability and maneuver- center of gravity positions and each ability requirements of this part are flap position approved for takeoff. met within a practical operational (b) Trimming devices must be de- flight envelope (for example, speed, al- signed so that, when any one con- titude, normal acceleration, and air- necting or transmitting element in the plane configuration) that is described primary flight control system fails, in the Airplane Flight Manual (AFM); adequate control for safe flight and and landing is available with— (3) The trim, stability, and stall char- (1) For single-engine airplanes, the acteristics are not impaired below a longitudinal trimming devices; or level needed to permit continued safe (2) For multiengine airplanes, the flight and landing. longitudinal and directional trimming [Doc. No. 26269, 58 FR 42164, Aug. 6, 1993] devices. (c) Tab controls must be irreversible § 23.673 Primary flight controls. unless the tab is properly balanced and Primary flight controls are those has no unsafe flutter characteristics. used by the pilot for the immediate Irreversible tab systems must have control of pitch, roll, and yaw. adequate rigidity and reliability in the portion of the system from the tab to [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as the attachment of the irreversible unit amended by Amdt. 23–48, 61 FR 5148, Feb. 9, to the airplane structure. 1996] (d) It must be demonstrated that the § 23.675 Stops. airplane is safely controllable and that the pilot can perform all maneuvers (a) Each control system must have and operations necessary to effect a stops that positively limit the range of safe landing following any probable motion of each movable aerodynamic powered trim system runaway that surface controlled by the system. reasonably might be expected in serv- (b) Each stop must be located so that ice, allowing for appropriate time wear, slackness, or takeup adjustments delay after pilot recognition of the will not adversely affect the control trim system runaway. The demonstra- characteristics of the airplane because tion must be conducted at critical air- of a change in the range of surface plane weights and center of gravity po- travel. sitions. (c) Each stop must be able to with- stand any loads corresponding to the [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as design conditions for the control sys- amended by Amdt. 23–7, 34 FR 13091, Aug. 13, tem. 1969; Amdt. 23–34, 52 FR 1830, Jan. 15, 1987; Amdt. 23–42, 56 FR 353, Jan. 3, 1991; Amdt. 23– [Amdt. 23–17, 41 FR 55464, Dec. 20, 1976] 49, 61 FR 5165, Feb. 9, 1996]
§ 23.677 Trim systems. § 23.679 Control system locks. (a) Proper precautions must be taken If there is a device to lock the con- to prevent inadvertent, improper, or trol system on the ground or water: abrupt trim tab operation. There must (a) There must be a means to— be means near the trim control to indi- (1) Give unmistakable warning to the cate to the pilot the direction of trim pilot when lock is engaged; or control movement relative to airplane (2) Automatically disengage the de- motion. In addition, there must be vice when the pilot operates the pri- means to indicate to the pilot the posi- mary flight controls in a normal man- tion of the trim device with respect to ner. both the range of adjustment and, in (b) The device must be installed to the case of lateral and directional limit the operation of the airplane so trim, the neutral position. This means that, when the device is engaged, the
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