ED Decision 2003/15/RM
(a) Each control and control system must operate with the ease, smoothness, and positiveness appropriate to its function.
(b) Each element of each flight control system must be designed, or distinctively and permanently marked, to minimise the probability of any incorrect assembly that could result in the malfunction of the system.
CS 27.672 Stability augmentation, automatic, and power-operated systems
ED Decision 2003/15/RM
If the functioning of stability augmentation or other automatic or power-operated systems is necessary to show compliance with the flight characteristics requirements of this CS-27, such systems must comply with CS 27.671 and the following:
(a) A warning which is clearly distinguishable to the pilot under expected flight conditions without requiring the pilot’s attention must be provided for any failure in the stability augmentation system or in any other automatic or power-operated system which could result in an unsafe condition if the pilot is unaware of the failure. Warning systems must not activate the control systems.
(b) The design of the stability augmentation system or of any other automatic or power-operated system must allow initial counteraction of failures without requiring exceptional pilot skill or strength by overriding the failure by movement of the flight controls in the normal sense and deactivating the failed system.
(c) It must be shown that after any single failure of the stability augmentation system or any other automatic or power-operated system:
(1) The rotorcraft is safely controllable when the failure or malfunction occurs at any speed or altitude within the approved operating limitations;
(2) The controllability and manoeuvrability requirements of this CS-27 are met within a practical operational flight envelope (for example, speed, altitude, normal acceleration, and rotorcraft configurations) which is described in the Rotorcraft Flight Manual; and
(3) The trim and stability characteristics are not impaired below a level needed to permit continued safe flight and landing.
CS 27.673 Primary flight control
ED Decision 2003/15/RM
Primary flight controls are those used by the pilot for immediate control of pitch, roll, yaw, and vertical motion of the rotorcraft.
CS 27.674 Interconnected controls
ED Decision 2003/15/RM
Each primary flight control system must provide for safe flight and landing and operate independently after a malfunction, failure, or jam of any auxiliary interconnected control.
ED Decision 2003/15/RM
(a) Each control system must have stops that positively limit the range of motion of the pilot’s controls.
(b) Each stop must be located in the system so that the range of travel of its control is not appreciably affected by:
(1) Wear;
(2) Slackness; or
(3) Take-up adjustments.
(c) Each stop must be able to withstand the loads corresponding to the design conditions for the system.
(d) For each main rotor blade:
(1) Stops that are appropriate to the blade design must be provided to limit travel of the blade about its hinge points; and
(2) There must be means to keep the blade from hitting the droop stops during any operation other than starting and stopping the rotor.
CS 27.679 Control system locks
ED Decision 2003/15/RM
If there is a device to lock the control system with the rotorcraft on the ground or water, there must be means to:
(a) Give unmistakable warning to the pilot when the lock is engaged; and
(b) Prevent the lock from engaging in flight.
CS 27.681 Limit load static tests
ED Decision 2003/15/RM
(a) Compliance with the limit load requirements of this CS-27 must be shown by tests in which:
(1) The direction of the test loads produces the most severe loading in the control system; and
(2) Each fitting, pulley, and bracket used in attaching the system to the main structure is included.
(b) Compliance must be shown (by analyses or individual load tests) with the special factor requirements for control system joints subject to angular motion.
ED Decision 2003/15/RM
It must be shown by operation tests that, when the controls are operated from the pilot compartment with the control system loaded to correspond with loads specified for the system, the system is free from:
(a) Jamming;
(b) Excessive friction; and
(c) Excessive deflection.
CS 27.685 Control system details
ED Decision 2003/15/RM
(a) Each detail of each control system must be designed to prevent jamming, chafing, and interference from cargo, passengers, loose objects or the freezing of moisture.
(b) There must be means in the cockpit to prevent the entry of foreign objects into places where they would jam the system.
(c) There must be means to prevent the slapping of cables or tubes against other parts.
(d) Cable systems must be designed as follows:
(1) Cables, cable fittings, turnbuckles, splices and pulleys must be of an acceptable kind.
(2) The design of the cable systems must prevent any hazardous change in cable tension throughout the range of travel under any operating conditions and temperature variations.
(3) No cable smaller than 2.4 mm (3/32 inch) diameter may be used in any primary control system.
(4) Pulley kinds and sizes must correspond to the cables with which they are used.
(5) Pulleys must have close fitting guards to prevent the cables from being displaced or fouled.
(6) Pulleys must lie close enough to the plane passing through the cable to prevent the cable from rubbing against the pulley flange.
(7) No fairlead may cause a change in cable direction of more than 3°.
(8) No clevis pin subject to load or motion and retained only by cotter pins may be used in the control system.
(9) Turnbuckles attached to parts having angular motion must be installed to prevent binding throughout the range of travel.
(10) There must be means for visual inspection at each fairlead, pulley, terminal and turnbuckle.
(e) Control system joints subject to angular motion must incorporate the following special factors with respect to the ultimate bearing strength of the softest material used as a bearing:
(1) 3.33 for push-pull systems other than ball and roller bearing systems.
(2) 2.0 for cable systems.
(f) For control system joints, the manufacturer’s static, non-Brinell rating of ball and roller bearings must not be exceeded.
ED Decision 2003/15/RM
(a) Each control system spring device where failure could cause flutter or other unsafe characteristics must be reliable.
(b) Compliance with sub-paragraph (a) must be shown by tests simulating service conditions.
CS 27.691 Autorotation control mechanism
ED Decision 2003/15/RM
Each main rotor blade pitch control mechanism must allow rapid entry into autorotation after power failure.
CS 27.695 Power boost and power-operated control system
ED Decision 2003/15/RM
(a) If a power boost or power-operated control system is used, an alternate system must be immediately available that allows continued safe flight and landing in the event of:
(1) Any single failure in the power portion of the system; or
(2) The failure of all engines.
(b) Each alternate system may be a duplicate power portion or a manually operated mechanical system. The power portion includes the power source (such as hydraulic pumps), and such items as valves, lines, and actuators.
(c) The failure of mechanical parts (such as piston rods and links), and the jamming of power cylinders, must be considered unless they are extremely improbable.