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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§ 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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