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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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347 

Federal Aviation Administration, DOT 

§ 25.1331 

from providing guidance or control to 
an unsafe speed. 

(i) The flight guidance system func-

tions, controls, indications, and alerts 
must be designed to minimize 
flightcrew errors and confusion con-
cerning the behavior and operation of 
the flight guidance system. Means 
must be provided to indicate the cur-
rent mode of operation, including any 
armed modes, transitions, and rever-
sions. Selector switch position is not 
an acceptable means of indication. The 
controls and indications must be 
grouped and presented in a logical and 
consistent manner. The indications 
must be visible to each pilot under all 
expected lighting conditions. 

(j) Following disengagement of the 

autopilot, a warning (visual and audi-
tory) must be provided to each pilot 
and be timely and distinct from all 
other cockpit warnings. 

(k) Following disengagement of the 

autothrust function, a caution must be 
provided to each pilot. 

(l) The autopilot may not create a 

potential hazard when the flightcrew 
applies an override force to the flight 
controls. 

(m) During autothrust operation, it 

must be possible for the flightcrew to 
move the thrust levers without requir-
ing excessive force. The autothrust 
may not create a potential hazard 
when the flightcrew applies an override 
force to the thrust levers. 

(n) For purposes of this section, a 

transient is a disturbance in the con-
trol or flight path of the airplane that 
is not consistent with response to 
flightcrew inputs or environmental 
conditions. 

(1) A minor transient would not sig-

nificantly reduce safety margins and 
would involve flightcrew actions that 
are well within their capabilities. A 
minor transient may involve a slight 
increase in flightcrew workload or 
some physical discomfort to passengers 
or cabin crew. 

(2) A significant transient may lead 

to a significant reduction in safety 
margins, an increase in flightcrew 
workload, discomfort to the flightcrew, 
or physical distress to the passengers 
or cabin crew, possibly including non- 
fatal injuries. Significant transients do 
not require, in order to remain within 

or recover to the normal flight enve-
lope, any of the following: 

(i) Exceptional piloting skill, alert-

ness, or strength. 

(ii) Forces applied by the pilot which 

are greater than those specified in 
§ 25.143(c). 

(iii) Accelerations or attitudes in the 

airplane that might result in further 
hazard to secured or non-secured occu-
pants. 

[Doc. No. FAA–2004–18775, 71 FR 18191, Apr. 
11, 2006] 

§ 25.1331

Instruments using a power 

supply. 

(a) For each instrument required by 

§ 25.1303(b) that uses a power supply, 
the following apply: 

(1) Each instrument must have a vis-

ual means integral with, the instru-
ment, to indicate when power adequate 
to sustain proper instrument perform-
ance is not being supplied. The power 
must be measured at or near the point 
where it enters the instruments. For 
electric instruments, the power is con-
sidered to be adequate when the volt-
age is within approved limits. 

(2) Each instrument must, in the 

event of the failure of one power 
source, be supplied by another power 
source. This may be accomplished 
automatically or by manual means. 

(3) If an instrument presenting navi-

gation data receives information from 
sources external to that instrument 
and loss of that information would 
render the presented data unreliable, 
the instrument must incorporate a vis-
ual means to warn the crew, when such 
loss of information occurs, that the 
presented data should not be relied 
upon. 

(b) As used in this section, ‘‘instru-

ment’’ includes devices that are phys-
ically contained in one unit, and de-
vices that are composed of two or more 
physically separate units or compo-
nents connected together (such as a re-
mote indicating gyroscopic direction 
indicator that includes a magnetic 
sensing element, a gyroscopic unit, an 
amplifier and an indicator connected 
together). 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–41, 42 FR 36970, July 18, 
1977] 

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