14 CFR 23.1323 - 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) Each airspeed system must be calibrated in flight to determine the system error. The system error, including position error, but excluding the airspeed indicator instrument calibration error, may not exceed three percent of the calibrated airspeed or five knots, whichever is greater, throughout the following speed ranges:
(1) 1.3 VS1 to VMO/MMO or VNE, whichever is appropriate with flaps retracted.
(2) 1.3 VS1 to VFE with flaps extended.
(c) The design and installation of each airspeed indicating system must provide positive drainage of moisture from the pitot static plumbing.
(d) If certification for instrument flight rules or flight in icing conditions is requested, each airspeed system must have a heated pitot tube or an equivalent means of preventing malfunction due to icing.
(e) In addition, for normal, utility, and acrobatic category multiengine jets of more than 6,000 pounds maximum weight and commuter category airplanes, each system must be calibrated to determine the system error during the accelerate-takeoff ground run. The ground run calibration must be determined -
(1) From 0.8 of the minimum value of V1 to the maximum value of V2, considering the approved ranges of altitude and weight; and
(2) The ground run calibration must be determined assuming an engine failure at the minimum value of V1.
(f) For commuter category airplanes, where duplicate airspeed indicators are required, their respective pitot tubes must be far enough apart to avoid damage to both tubes in a collision with a bird.