(a) Each instrument with static air case connections must be vented to
the outside atmosphere through an appropriate piping system.
(b) Each vent must be located where its orifices are least affected by
airflow variation, moisture, or foreign matter.
(c) Each static pressure port must be designed and located in such
manner that the correlation between air pressure in the static pressure
system and true ambient atmospheric static pressure is not altered when
the rotorcraft encounters icing conditions. An anti-icing means or an
alternate source of static pressure may be used in showing compliance with
this requirement. If the reading of the altimeter, when on the alternate
static pressure system, differs from the reading of altimeter when on the
primary static system by more than 50 feet, a correction card must be
provided for the alternate static system.
(d) Except for the vent into the atmosphere, each system must be
(e) Each pressure altimeter must be approved and calibrated to indicate
pressure altitude in a standard atmosphere with a minimum practicable
calibration error when the corresponding static pressures are applied.
(f) Each system must be designed and installed so that an error in
indicated pressure altitude, at sea level, with a standard atmosphere,
excluding instrument calibration error, does not result in an error of
more than ±30 feet per 100 knots speed. However, the error need not be
less than ±30 feet.
(g) Except as provided in paragraph (h) of this section, if the static
pressure system incorporates both a primary and an alternate static
pressure source, the means for selecting one or the other source must be
designed so that --
(1) When either source is selected, the other is blocked off; and
(2) Both sources cannot be blocked off simultaneously.
(h) For unpressurized rotorcraft, paragraph (g)(1) of this section does
not apply if it can be demonstrated that the static pressure system
calibration, when either static pressure source is selected, is not
changed by the other static pressure source being open or blocked.
(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), Dept. of
Transportation Act (49 U.S.C. 1655(c)))