Aircraft Instrumentation
Instrument Flight
SCAN TECHNIQUE
A major factor influencing scan technique is the characteristic manner in which instruments respond to
attitude and power changes. The control instruments provide a direct and immediate indication of attitude
and power changes, but indications on the performance instruments have an inherent lag. Lag will not
appreciably affect the tolerances within which the pilot controls the aircraft; however, at times, a slight
unavoidable delay in knowing the results of attitude and/or power changes will occur.
When the attitude and power are smoothly controlled, the lag factor is negligible and the indications on the
performance instruments will stabilize or change smoothly. Do not make abrupt control movements in
response to the lagging indications on the performance instruments, without first checking the control
instruments. Failure to do so leads to erratic aircraft maneuvers which will cause additional fluctuations
and lag in the performance instruments. Frequent scanning of the control instruments assists in
maintaining smooth aircraft control.
For every maneuver, the ADI is the primary reference instrument that should be scanned most frequently.
The majority of the pilot’s time should be spent on the control of the aircraft attitude by referencing the
ADI, supported by the control instruments. The remainder of the pilot’s time should be spent confirming
the desired performance and position by quickly scanning those instruments.
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