303 

Federal Aviation Administration, DOT 

§ 23.1325 

(2) The ground run calibration must 

be determined assuming an engine fail-
ure at the minimum value of V

1

. 

(f) For commuter category airplanes, 

where duplicate airspeed indicators are 
required, their respective pitot tubes 
must be far enough apart to avoid dam-
age to both tubes in a collision with a 
bird. 

[Amdt. 23–20, 42 FR 36968, July 18, 1977, as 
amended by Amdt. 23–34, 52 FR 1834, Jan. 15, 
1987; 52 FR 34745, Sept. 14, 1987; Amdt. 23–42, 
56 FR 354, Jan. 3, 1991; Amdt. 23–49, 61 FR 
5168, Feb. 9, 1996; Amdt. 23–62, 76 FR 75761, 
Dec. 2, 2011] 

§ 23.1325

Static pressure system. 

(a) Each instrument provided with 

static pressure case connections must 
be so vented that the influence of air-
plane speed, the opening and closing of 
windows, airflow variations, moisture, 
or other foreign matter will least af-
fect the accuracy of the instruments 
except as noted in paragraph (b)(3) of 
this section. 

(b) If a static pressure system is nec-

essary for the functioning of instru-
ments, systems, or devices, it must 
comply with the provisions of para-
graphs (b)(1) through (3) of this section. 

(1) The design and installation of a 

static pressure system must be such 
that— 

(i) Positive drainage of moisture is 

provided; 

(ii) Chafing of the tubing, and exces-

sive distortion or restriction at bends 
in the tubing, is avoided; and 

(iii) The materials used are durable, 

suitable for the purpose intended, and 
protected against corrosion. 

(2) A proof test must be conducted to 

demonstrate the integrity of the static 
pressure system in the following man-
ner: 

(i) 

Unpressurized airplanes. Evacuate 

the static pressure system to a pres-
sure differential of approximately 1 
inch of mercury or to a reading on the 
altimeter, 1,000 feet above the aircraft 
elevation at the time of the test. With-
out additional pumping for a period of 
1 minute, the loss of indicated altitude 
must not exceed 100 feet on the altim-
eter. 

(ii) 

Pressurized airplanes. Evacuate 

the static pressure system until a pres-
sure differential equivalent to the max-

imum cabin pressure differential for 
which the airplane is type certificated 
is achieved. Without additional pump-
ing for a period of 1 minute, the loss of 
indicated altitude must not exceed 2 
percent of the equivalent altitude of 
the maximum cabin differential pres-
sure or 100 feet, whichever is greater. 

(3) If a static pressure system is pro-

vided for any instrument, device, or 
system required by the operating rules 
of this chapter, each static pressure 
port must be designed or located in 
such a manner that the correlation be-
tween air pressure in the static pres-
sure system and true ambient atmos-
pheric static pressure is not altered 
when the airplane encounters icing 
conditions. An antiicing 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 read-
ing of the altimeter when on the pri-
mary static system by more than 50 
feet, a correction card must be pro-
vided for the alternate static system. 

(c) Except as provided in paragraph 

(d) 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. 

(d) For unpressurized airplanes, para-

graph (c)(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. 

(e) Each static pressure system must 

be calibrated in flight to determine the 
system error. The system error, in in-
dicated pressure altitude, at sea-level, 
with a standard atmosphere, excluding 
instrument calibration error, may not 
exceed 

±

30 feet per 100 knot speed for 

the appropriate configuration in the 
speed range between 1.3 V

S0

with flaps 

extended, and 1.8 V

S1

with flaps re-

tracted. However, the error need not be 
less than 30 feet. 

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