CS 25.671 General

(See AMC 25.671)

(a)     Each flight control system must operate with the ease, smoothness, and positiveness appropriate to its function. In addition, the flight control system shall be designed to continue to operate, respond appropriately to commands, and must not hinder aeroplane recovery, when the aeroplane is in any attitude or experiencing any flight dynamics parameter that could occur due to operating or environmental conditions.

(b)     Each element of each flight control system must be designed to minimise the probability of incorrect assembly that could result in the failure or malfunctioning of the system. Distinctive and permanent marking may be used where design means are impractical, taking into consideration the potential consequence of incorrect assembly.

(c)      The aeroplane must be shown by analysis, test, or both, to be capable of continued safe flight and landing after any of the following failures or jams in the flight control system within the normal flight envelope. In addition, it must be shown that the pilot can readily counteract the effects of any probable failure.

(1)     Any single failure, excluding failures of the type defined in CS 25.671(c)(3);

(2)     Any combination of failures not shown to be extremely improbable, excluding failures of the type defined in CS 25.671(c)(3); and

(3)     Any failure or event that results in a jam of a flight control surface or pilot control that is fixed in position due to a physical interference. The jam must be evaluated as follows:

(i)      The jam must be considered at any normally encountered position of the control surface, or pilot controls;

(ii)     The jam must be assumed to occur anywhere within the normal flight envelope and during any flight phase from take-off to landing; and

In the presence of a jam considered under this sub-paragraph, any additional failure conditions that could prevent continued safe flight and landing shall have a combined probability of 1/1 000 or less.

(d)     The aeroplane must be designed so that, if all engines fail at any time of the flight:

(1)     it is controllable in flight;

(2)     an approach can be made;

(3)     a flare to a landing, and a flare to a ditching can be achieved; and

(4)     during the ground phase, the aeroplane can be stopped.

(e)     The aeroplane must be designed to indicate to the flight crew whenever the primary control means is near the limit of control authority.

(f)      If the flight control system has multiple modes of operation, appropriate flight crew alerting must be provided whenever the aeroplane enters any mode that significantly changes or degrades the normal handling or operational characteristics of the aeroplane.

[Amdt 25/18]

[Amdt 25/24]