§ 25.1323 14 CFR Ch. I (1–1–12 Edition)

§ 25.1323 indicating system. (h) Each system must be arranged, so For each airspeed indicating system, far as practicable, to prevent malfunc- the following apply: tion or serious error due to the entry of (a) Each airspeed indicating instru- moisture, dirt, or other substances. ment must be approved and must be (i) Each system must have a heated calibrated to indicate (at or an equivalent means of sea level with a standard atmosphere) preventing malfunction due to icing. with a minimum practicable instru- (j) Where duplicate airspeed indica- ment calibration error when the cor- tors are required, their respective pitot responding pitot and static pressures tubes must be far enough apart to are applied. avoid damage to both tubes in a colli- (b) Each system must be calibrated sion with a bird. to determine the system error (that is, [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as the relation between IAS and CAS) in amended by Amdt. 25–57, 49 FR 6849, Feb. 23, flight and during the accelerated take- 1984; Amdt. 25–108, 67 FR 70828, Nov. 26, 2002; off ground run. The ground run calibra- Amdt. 25–109, 67 FR 76656, Dec. 12, 2002] tion must be determined— (1) From 0.8 of the minimum value of § 25.1325 Static pressure systems. V1 to the maximum value of V2, consid- (a) Each instrument with static air ering the approved ranges of altitude case connections must be vented to the and weight; and outside atmosphere through an appro- (2) With the flaps and power settings priate piping system. corresponding to the values determined (b) Each static port must be designed in the establishment of the takeoff and located in such manner that the path under § 25.111 assuming that the static pressure system performance is critical engine fails at the minimum least affected by airflow variation, or value of V1. by moisture or other foreign matter, (c) The airspeed error of the installa- and that the correlation between air tion, excluding the pressure in the static pressure system instrument calibration error, may not and true ambient atmospheric static exceed three percent or five knots, pressure is not changed when the air- whichever is greater, throughout the plane is exposed to the continuous and speed range, from— intermittent maximum icing condi- (1) VMO to 1.23 VSR1, with flaps re- tions defined in appendix C of this part. tracted; and (c) The design and installation of the (2) 1.23 VSR0 to VFE with flaps in the static pressure system must be such landing position. that— (d) From 1.23 VSR to the speed at (1) Positive drainage of moisture is which stall warning begins, the IAS provided; chafing of the tubing and ex- must change perceptibly with CAS and cessive distortion or restriction at in the same sense, and at speeds below bends in the tubing is avoided; and the stall warning speed the IAS must not materials used are durable, suitable for change in an incorrect sense. the purpose intended, and protected (e) From VMO to VMO + 2/3 (VDF ¥ against corrosion; and VMO), the IAS must change perceptibly (2) It is airtight except for the port with CAS and in the same sense, and at into the atmosphere. A proof test must higher speeds up to VDF the IAS must be conducted to demonstrate the integ- not change in an incorrect sense. rity of the static pressure system in (f) There must be no indication of the following manner: airspeed that would cause undue dif- (i) Unpressurized airplanes. Evacuate ficulty to the pilot during the takeoff the static pressure system to a pres- between the initiation of rotation and sure differential of approximately 1 the achievement of a steady climbing inch of mercury or to a reading on the condition. altimeter, 1,000 feet above the airplane (g) The effects of airspeed indicating elevation at the time of the test. With- system lag may not introduce signifi- out additional pumping for a period of cant takeoff indicated airspeed bias, or 1 minute, the loss of indicated altitude significant errors in takeoff or accel- must not exceed 100 feet on the altim- erate-stop distances. eter.

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