346 

14 CFR Ch. I (1–1–24 Edition) 

§ 25.1326 

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 airplanes, para-

graph (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. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–5, 30 FR 8261, June 29, 
1965; Amdt. 25–12, 32 FR 7587, May 24, 1967; 
Amdt. 25–41, 42 FR 36970, July 18, 1977; Amdt. 
25–108, 67 FR 70828, Nov. 26, 2002; Amdt. 25– 
140, 79 FR 65527, Nov. 4, 2014] 

§ 25.1326

Pitot heat indication systems. 

If a flight instrument pitot heating 

system is installed, an indication sys-
tem must be provided to indicate to 
the flight crew when that pitot heating 
system is not operating. The indication 
system must comply with the following 
requirements: 

(a) The indication provided must in-

corporate an amber light that is in 
clear view of a flight crewmember. 

(b) The indication provided must be 

designed to alert the flight crew if ei-
ther of the following conditions exist: 

(1) The pitot heating system is 

switched ‘‘off’’. 

(2) The pitot heating system is 

switched ‘‘on’’ and any pitot tube heat-
ing element is inoperative. 

[Amdt. 25–43, 43 FR 10339, Mar. 13, 1978] 

§ 25.1327

Magnetic direction indicator. 

(a) Each magnetic direction indicator 

must be installed so that its accuracy 
is not excessively affected by the air-
plane’s vibration or magnetic fields. 

(b) The compensated installation 

may not have a deviation, in level 
flight, greater than 10 degrees on any 
heading. 

§ 25.1329

Flight guidance system. 

(a) Quick disengagement controls for 

the autopilot and autothrust functions 
must be provided for each pilot. The 

autopilot quick disengagement con-
trols must be located on both control 
wheels (or equivalent). The autothrust 
quick disengagement controls must be 
located on the thrust control levers. 
Quick disengagement controls must be 
readily accessible to each pilot while 
operating the control wheel (or equiva-
lent) and thrust control levers. 

(b) The effects of a failure of the sys-

tem to disengage the autopilot or 
autothrust functions when manually 
commanded by the pilot must be as-
sessed in accordance with the require-
ments of § 25.1309. 

(c) Engagement or switching of the 

flight guidance system, a mode, or a 
sensor may not cause a transient re-
sponse of the airplane’s flight path any 
greater than a minor transient, as de-
fined in paragraph (n)(1) of this section. 

(d) Under normal conditions, the dis-

engagement of any automatic control 
function of a flight guidance system 
may not cause a transient response of 
the airplane’s flight path any greater 
than a minor transient. 

(e) Under rare normal and non-nor-

mal conditions, disengagement of any 
automatic control function of a flight 
guidance system may not result in a 
transient any greater than a signifi-
cant transient, as defined in paragraph 
(n)(2) of this section. 

(f) The function and direction of mo-

tion of each command reference con-
trol, such as heading select or vertical 
speed, must be plainly indicated on, or 
adjacent to, each control if necessary 
to prevent inappropriate use or confu-
sion. 

(g) Under any condition of flight ap-

propriate to its use, the flight guidance 
system may not produce hazardous 
loads on the airplane, nor create haz-
ardous deviations in the flight path. 
This applies to both fault-free oper-
ation and in the event of a malfunc-
tion, and assumes that the pilot begins 
corrective action within a reasonable 
period of time. 

(h) When the flight guidance system 

is in use, a means must be provided to 
avoid excursions beyond an acceptable 
margin from the speed range of the 
normal flight envelope. If the airplane 
experiences an excursion outside this 
range, a means must be provided to 
prevent the flight guidance system 

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