AMC 25.1333(b) Instruments systems
ED
Decision 2003/2/RM
1.      Attitude
displays systems. If three displays are used to show compliance with CS 25.1333(b),
the reliability and independence of those displays should be confirmed by a
suitable assessment in accordance with CS 25.1309.
Each display should have independent sensors and power supplies. If a total
failure of the generated electrical power causes the loss of both main
instruments, the power supply to the third (standby) attitude indicator and
its appropriate lighting should be such that the display is usable from each
pilot’s station for a time duration in accordance with AMC 25.1351(d).
Note: the
time for which the display remains usable will be stated in the Aeroplane
Flight Manual (AFM).
2.      Airspeed,
altitude, and direction display systems. The reliability and independence
of the displays used to show compliance with CS 25.1333(b) should be
sufficient to ensure continued safe flight and landing appropriate to the
intended operation of the aeroplane.
Historically,
“sufficient information” to control attitude, airspeed, altitude, and
direction has been provided by specific indicators of the state of each
parameter. However, since control is considered to be the ability to change or
maintain a given parameter to a desired value, it is assumed that these
parameters will be available without flight crew action.
There may be
alternate parameters in the cockpit that provide equivalent means to control
attitude, airspeed, altitude and direction, without displaying those
parameters directly (for example, without display of standby airspeed, by
using a suitable angle-of-attack display). For these alternate cases,
compliance to CS 25.1333(b) must be shown by analysis and flight test.
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