AIRSPEED IN-FLIGHT ACCURACY
CHECK. The following procedure for airspeed calibration is offered for evaluation:
a. A measured course should be chosen with readily identifiable landmarks at each end. The land-
marks should be a known distance apart, and the length of course should be at least 1 to 2 miles long.
b. The pilot must fly a precision course maintaining a constant altitude (e.g., 1,000 feet), constant
airspeed, constant magnetic heading, and constant engine rpm. The pilot must record the tempera-
ture, altitude, indicated airspeed and the time over each landmark for both directions. The average of
these speeds is the ground speed of the aircraft. An E6B computer will convert the temperature,
altitude, and ground speed into True Indicated Airspeed for the tests.
NOTE: The difference between the E6B computer readings and the aircraft’s ground speed readings
is the error in the instrument and the error caused by the installation of the system in the aircraft.
c. The airspeed calibrations runs should be made several times in opposite headings for each
of the selected airspeeds the pilot wants to check. Such accuracy test runs should start at the lowest
safe airspeed and work up to cruise speed using 10 mph/knot increments.
d. Most errors will be found at the low end of the speed range due to the angle of the pitot mast
to the relative wind and/or the location of the static ports. Using a Global Positioning Satellite (GPS)
hand held receivers to check airspeed accuracy is also acceptable.
e. Retractable Flaps
Test the accuracy of the airspeed indicator with the flaps up and down.
Note:
Any calibration procedure needs to correct back to standard day temperature. A means to
measure actual outside air temperature is required to allow proper correction.
When using a GPS to determine pitot-static errors, a highly recommended procedure is
that of the National Test Pilot School, which can be downloaded from:
http://www.ntps.edu/HTML/Downloads/
Appendix 1 NOV 09
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