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a. Substituting a second attitude indicator (with a power source independent from the
primary attitude indicator) for the rate-of-turn indicator will provide an increased
level of safety. It will replace a gyro that only indicates direction and rate of turn
with one instrument that presents turn direction, bank angle, and pitch attitude
information. Also, a second attitude indicator will be less confusing during partial
panel operations because it presents pitch and bank information in the same manner as
the primary attitude indicator. The pilot's scan and instrument interpretation during
partial panel operations becomes easier because pilots will still be able to rely on
an attitude indicator for pitch and bank reference just as they did during full panel
operations. Recognition time that a failure condition exists will be equivalent to
current system configurations.
b. Replacing the rate-of-turn indicator will mean losing an easy reference for standard
rate turns. However, in today's air traffic control system, there is little need for
precisely measured standard rate turns or timed turns based on standard rate. Maintaining
a given bank angle on the attitude indicator for a given speed will result in a standard
rate turn. Pilots using this AC to substitute an attitude indicator for their rate-of-turn
indicator are encouraged to know the bank angle needed for a standard rate turn.
NOTE: The FAA preamble language for the 1970 amendment to section 91.33,
re-codified to section 91.205, states: "[T]he FAA believes, and all other commenters
apparently agree...the rate-of-turn indicator is no longer as useful as an instrument
which gives both horizontal and vertical attitude information."
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