501 

Federal Aviation Administration, DOT 

§ 25.1325 

(f) There must be no indication of 

airspeed that would cause undue dif-
ficulty to the pilot during the takeoff 
between the initiation of rotation and 
the achievement of a steady climbing 
condition. 

(g) The effects of airspeed indicating 

system lag may not introduce signifi-
cant takeoff indicated airspeed bias, or 
significant errors in takeoff or accel-
erate-stop distances. 

(h) Each system must be arranged, so 

far as practicable, to prevent malfunc-
tion or serious error due to the entry of 
moisture, dirt, or other substances. 

(i) Each system must have a heated 

pitot tube or an equivalent means of 
preventing malfunction due to icing. 

(j) Where duplicate airspeed indica-

tors are required, their respective pitot 
tubes must be far enough apart to 
avoid damage to both tubes in a colli-
sion with a bird. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–57, 49 FR 6849, Feb. 23, 
1984; Amdt. 25–108, 67 FR 70828, Nov. 26, 2002; 
Amdt. 25–109, 67 FR 76656, Dec. 12, 2002] 

§ 25.1325

Static pressure systems. 

(a) Each instrument with static air 

case connections must be vented to the 
outside atmosphere through an appro-
priate piping system. 

(b) Each static port must be designed 

and located in such manner that the 
static pressure system performance is 
least affected by airflow variation, or 
by moisture or other foreign matter, 
and that the correlation between air 
pressure in the static pressure system 
and true ambient atmospheric static 
pressure is not changed when the air-
plane is exposed to the continuous and 
intermittent maximum icing condi-
tions defined in appendix C of this part. 

(c) The design and installation of the 

static pressure system must be such 
that— 

(1) Positive drainage of moisture is 

provided; chafing of the tubing and ex-
cessive distortion or restriction at 
bends in the tubing is avoided; and the 
materials used are durable, suitable for 
the purpose intended, and protected 
against corrosion; and 

(2) It is airtight except for the port 

into the atmosphere. A proof test must 
be conducted to demonstrate the integ-

rity of the static pressure system in 
the following manner: 

(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 airplane 
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. 

(d) Each pressure altimeter must be 

approved and must be calibrated to in-
dicate pressure altitude in a standard 
atmosphere, with a minimum prac-
ticable calibration error when the cor-
responding static pressures are applied. 

(e) Each system must be designed and 

installed so that the error in indicated 
pressure altitude, at sea level, with a 
standard atmosphere, excluding instru-
ment calibration error, does not result 
in an error of more than 

±

30 feet per 100 

knots speed for the appropriate con-
figuration in the speed range between 
1.23 

V

SR0

with flaps extended and 1.7 

V

SR1

with flaps retracted. However, the 

error need not be less than 

±

30 feet. 

(f) If an altimeter system is fitted 

with a device that provides corrections 
to the altimeter indication, the device 
must be designed and installed in such 
manner that it can be bypassed when it 
malfunctions, unless an alternate al-
timeter system is provided. Each cor-
rection device must be fitted with a 
means for indicating the occurrence of 
reasonably probable malfunctions, in-
cluding power failure, to the flight 
crew. The indicating means must be ef-
fective for any cockpit lighting condi-
tion likely to occur. 

(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 

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