344 

14 CFR Ch. I (1–1–19 Edition) 

§ 25.1325 

(a) For airplanes certificated in ac-

cordance with § 25.1420(a)(1), the icing 
conditions that the airplane is certified 
to safely exit following detection. 

(b) For airplanes certificated in ac-

cordance with § 25.1420(a)(2), the icing 
conditions that the airplane is certified 
to safely operate in and the icing con-
ditions that the airplane is certified to 
safely exit following detection. 

(c) For airplanes certificated in ac-

cordance with § 25.1420(a)(3) and for air-
planes not subject to § 25.1420, all icing 
conditions. 

[Amdt. 25–140, 79 FR 65527, Nov. 4, 2014] 

§ 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 so that: 

(1) The static pressure system per-

formance is least affected by airflow 
variation, or by moisture or other for-
eign matter; and 

(2) The correlation between air pres-

sure in the static pressure system and 
true ambient atmospheric static pres-
sure is not changed when the airplane 
is exposed to the icing conditions de-
fined in Appendix C of this part, and 
the following icing conditions specified 
in Appendix O of this part: 

(i) For airplanes certificated in ac-

cordance with § 25.1420(a)(1), the icing 
conditions that the airplane is certified 
to safely exit following detection. 

(ii) For airplanes certificated in ac-

cordance with § 25.1420(a)(2), the icing 
conditions that the airplane is certified 
to safely operate in and the icing con-
ditions that the airplane is certified to 
safely exit following detection. 

(iii) For airplanes certificated in ac-

cordance with § 25.1420(a)(3) and for air-
planes not subject to § 25.1420, all icing 
conditions. 

(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

SR

0

with flaps extended and 1.7 

V

SR

1

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 

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