Section 27.1323 - Airspeed indicating system(a) Each airspeed indicating instrument must be calibrated to indicate true airspeed (at sea level with a standard atmosphere) with a minimum practicable instrument calibration error when the corresponding pitot and static pressures are applied.(b) The airspeed indicating system must be calibrated in flight at forward speeds of 20 knots and over.(c) At each forward speed above 80 percent of the climbout speed, the airspeed indicator must indicate true airspeed, at sea level with a standard atmosphere, to within an allowable installation error of not more than the greater of- (1) ±3 percent of the calibrated airspeed; orDoc. No. 5074, 29 FR 15695, Nov. 24, 1964, as amended by Amdt. 27-13, 42 FR 36972, July 18, 1977 Secs. 313(a), 601, 603, 604, and 605 of the Federal Aviation Act of 1958 (49 U.S.C. 1354(a) , 1421 , 1423 , 1424 , and 1425 ) ; and sec. 6(c) of the Dept. of Transportation Act (49 U.S.C. 1655(c)