ED Decision 2003/15/RM
Each auxiliary rotor, each fixed or movable stabilising or control surface, and each system operating any flight control must meet the requirements of CS 27.395, 27.397, 27.399, 27.411 and 27.427.
ED Decision 2003/15/RM
(a) The part of each control system from the pilot’s controls to the control stops must be designed to withstand pilot forces of not less than –
(1) The forces specified in CS 27.397; or
(2) If the system prevents the pilot from applying the limit pilot forces to the system, the maximum forces that the system allows the pilot to apply, but not less than 0.60 times the forces specified in CS 27.397.
(b) Each primary control system including its supporting structure, must be designed as follows:
(1) The system must withstand loads resulting from the limit pilot forces prescribed in CS 27.397.
(2) Notwithstanding sub-paragraph (b)(3), when power-operated actuator controls or power boost controls are used, the system must also withstand the loads resulting from the force output of each normally energised power device, including any single power boost or actuator system failure.
(3) If the system design or the normal operating loads are such that a part of the system cannot react to the limit forces prescribed in CS 27.397, that part of the system must be designed to withstand the maximum loads that can be obtained in normal operation. The minimum design loads must, in any case, provide a rugged system for service use, including consideration of fatigue, jamming, ground gusts, control inertia and friction loads. In the absence of rational analysis, the design loads resulting from 0.60 of the specified limit pilot forces are acceptable minimum design loads.
(4) If operational loads may be exceeded through jamming, ground gusts, control inertia, or friction, the system must withstand the limit pilot forces specified in CS 27.397, without yielding.
ED Decision 2023/001/R
This AMC supplements FAA AC 27-1B, § AC 27.395 and should be used in conjunction with that AC when demonstrating compliance with CS 27.395.
The design reaction loads prescribed in CS 27.395 for the flight control system should apply to the part of the control system from the pilot cockpit control sticks/pedals to the main/tail rotor servo-actuators. The remaining part of the flight control systems located between the attachment of the servo-actuators and the (main/tail) blades (i.e. rotating parts, servo-actuators and their attachments) should be substantiated to the highest of:
— maximum loads expected in service (limit loads) as per CS 27.301, CS 27.305 and CS 27.547 (nominal conditions);
— maximum loads for a single failure of the hydraulic system leading to an operating hydraulic overpressure;
— the maximum loads due to a jamming of the flight control system (rotating parts).
The maximum pilot loads from CS 27.397 to CS 27.399 should be added to these loads appropriately.
[Amdt 27/10]
CS 27.397 Limit pilot forces and torques
ED Decision 2003/15/RM
(a) Except as provided in sub-paragraph (b) the limit pilot forces are as follows:
(1) For foot controls, 578 N (130 lbs).
(2) For stick controls, 445 N (100 lbs) fore and aft, and 298 N (67 lbs) laterally.
(b) For flap, tab, stabiliser, rotor brake, and landing gear operating controls, the following apply:
(1) Crank, wheel, and lever controls, (25.4 + R) x 2.919 N, where R = radius in millimetres (
x 50 lbs, where R = radius in inches), but not less than 222 N (50 lbs) nor more than 445 N (100 lbs) for hand-operated controls or 578 N (130 lbs) for foot-operated controls, applied at any angle within 20° of the plane of motion of the control.
(2) Twist controls, 356 x R Newton-millimetres, where R = radius in millimetres (80 x R inch-pounds where R = radius in inches).
ED Decision 2003/15/RM
Each dual primary flight control system must be designed to withstand the loads that result when pilot forces of 0.75 times those obtained under CS 27.395 are applied –
(a) In opposition; and
(b) In the same direction.
CS 27.411 Ground clearance: tail rotor guard
ED Decision 2003/15/RM
(a) It must be impossible for the tail rotor to contact the landing surface during a normal landing.
(b) If a tail rotor guard is required to show compliance with sub-paragraph (a):
(1) Suitable design loads must be established for the guard; and
(2) The guard and its supporting structure must be designed to withstand those loads.
ED Decision 2003/15/RM
(a) Horizontal tail surfaces and their supporting structure must be designed for unsymmetrical loads arising from yawing and rotor wake effects in combination with the prescribed flight conditions.
(b) To meet the design criteria of sub-paragraph (a), in the absence of more rational data, both of the following must be met:
(1) 100% of the maximum loading from the symmetrical flight conditions acts on the surface on one side of the plane of symmetry and no loading acts on the other side.
(2) 50% of the maximum loading from the symmetrical flight conditions acts on the surface on each side of the plane of symmetry but in opposite directions.
(c) For empennage arrangements where the horizontal tail surfaces are supported by the vertical tail surfaces, the vertical tail surfaces and supporting structure must be designed for the combined vertical and horizontal surface loads resulting from each prescribed flight condition, considered separately. The flight conditions must be selected so the maximum design loads are obtained on each surface. In the absence of more rational data, the unsymmetrical horizontal tail surface loading distributions described in this paragraph must be assumed.
AMC1 27.427 Unsymmetrical loads
ED Decision 2023/001/R
This AMC supplements FAA AC 27-1B, § AC 27.427 and should be used in conjunction with that AC when demonstrating compliance with CS 27.427.
In case of load distribution deviating from CS 27.427(b), the applicant should provide the rationale justifying that the selected load distribution conservatively addresses the limit flight load conditions of Subpart C. Dedicated flight load and/or wind tunnel measurements should be performed to confirm the suitability of the proposed criteria.
[Amdt 27/10]