4.1 General
4.1.1 Craft should be provided with means for directional, attitude and altitude control
of adequate strength and suitable design to enable the craft's attitude, altitude,
heading and direction of travel to be effectively controlled to the maximum extent
possible in the prevailing conditions and craft speed without undue physical effort at
all speeds and in all conditions for which the craft is to be certificated. The
performance should be verified through trials conducted in accordance with chapter 16
and annex 8.
4.1.2 Directional, attitude and altitude control may be achieved by means of air or
water rudders, foils, flaps, propellers or jets which may be steerable, yaw control
ports or side thrusters, differential propulsive thrust, variable geometry of the craft
or its lift-system components or by a combination of these devices.
4.1.3 For the purpose of this chapter, a directional, attitude and altitude control
system includes any propulsion, lift or steering devices, any mechanical linkages and
all power or manual devices, controls and actuating systems.
4.1.4 Attention is drawn to the possibility of interaction between directional, attitude
and altitude control systems and stabilization systems. Where such interaction occurs or
where dual-purpose components are fitted, the provisions of 11.5 and chapters 15 and 16
should also be observed with, as applicable.
4.2 Reliability
4.2.1 The probability of total failure of all directional, attitude and altitude control
systems should be extremely remote when the craft is operating normally, i.e. excluding
emergency situations such as grounding, collision or a major fire.
4.2.2 A design incorporating a power drive or an actuation system employing powered
components for normal directional, attitude and altitude control should provide a
secondary means of actuating the device unless a redundant system or an alternative
system is provided.
4.2.3 Any secondary means of actuating a directional, attitude and altitude control
device may be manually driven when the Administration is satisfied that this is
adequate, bearing in mind the craft's size and design and any limitations of speed or
other parameters that may be necessary.
4.2.4 Directional, attitude and altitude control systems should be constructed so that a
single failure in one drive or system, as appropriate, will not render any other control
system inoperable or prevent the craft from being brought to a safe situation. The
Administration may allow a short period of time to permit the connection of a secondary
control device when the design of the craft is such that such delay will not, in its
opinion, hazard the craft.
4.2.5 The SSA conducted under part C should include the directional, attitude and
altitude control system.
4.2.6 If necessary to bring the craft to a safe condition, power drives for directional,
attitude and altitude control devices, including those required to change propulsion
thrust direction, should become operative automatically, and respond correctly, within a
time that ensures that the safety of the craft is not prejudiced following power or
other failure. Transitional arrangements may be used for this purpose.
4.2.7 Directional, attitude and altitude control devices involving variable geometry of
the craft or its lift system components should, so far as is practicable, be so
constructed that any failure of the drive linkage or actuating system will not
significantly hazard the craft.
4.3 Demonstrations
4.3.1 The limits of safe use of any of the control system devices, should be based on
demonstrations and a verification process in accordance with chapter 16 and annex 8.
4.3.2 Demonstration in accordance with chapter 16 and annex 8 should determine any
adverse effects upon safe operation of the craft in the event of any possible
uncontrollable total deflection of any one control device or hard-linked series of
devices. Any limitation on the operation of the craft as may be necessary to ensure that
the redundancy or safeguards in the systems provide equivalent safety should be included
in the craft operating manual.
4.4 Control Position
4.4.1 All directional, attitude and altitude control systems should be operated from the
craft's operating station.
4.4.2 Adequate indications should be provided at the operating station to provide the
person controlling the craft with verification of the correct response of the control
devices, and also to indicate any abnormal responses or malfunction. The indications of
directional, attitude and altitude response or rudder angle indicator should be
independent of the system for directional, attitude and altitude control. The logic of
such feedback and indications should be consistent with the other alarms and indications
so that in an emergency operators are unlikely to be confused.