Instrument Flight
Aircraft Instrumentation
INSTRUMENT SCAN
During instrument flight, the pilot must divide his attention between the control, performance, and position
instrument/displays. Proper division of attention and the sequence of checking the displays varies
throughout the various phases of flight. There is no one set order for scanning the instrument/displays; it
depends on the type of maneuver to be executed as to which instruments are of prime importance. The
pilot should become familiar with the factors to be considered when dividing his attention between
instrument/displays. The pilot should know the indications which will enable him to identify correct and
incorrect scan techniques. The best way to improve proficiency is through practice. Some common
errors in instrument scanning include the following: having no scan pattern plan, omitting a display
entirely from the scan, fixating on a single or a few display indications, or misusing a display indication.
SCAN TECHNIQUE
A major factor influencing scan technique is the characteristic manner in which instruments respond to
attitude and power changes. Because of signal filtering, raw data processing, and display time, there is
inherent lag in a digital display. The 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/displays assists in
maintaining smooth aircraft control.
For every maneuver, the ADI display is the primary reference 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
display, 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 displays.
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