title-14-part-25-sec25-1337

348

14 CFR Ch. I (1–1–24 Edition)

§ 25.1333

Instrument systems.

For systems that operate the instru-

ments required by § 25.1303(b) which are
located at each pilot’s station—

(a) Means must be provided to con-

nect the required instruments at the
first pilot’s station to operating sys-
tems which are independent of the op-
erating systems at other flight crew
stations, or other equipment;

(b) The equipment, systems, and in-

stallations must be designed so that
one display of the information essen-
tial to the safety of flight which is pro-
vided by the instruments, including at-
titude, direction, airspeed, and altitude
will remain available to the pilots,
without additional crewmember ac-
tion, after any single failure or com-
bination of failures that is not shown
to be extremely improbable; and

or equipment may not be connected to
the operating systems for the required
instruments, unless provisions are
made to ensure the continued normal
functioning of the required instru-
ments in the event of any malfunction
of the additional instruments, systems,
or equipment which is not shown to be
extremely improbable.

[Amdt. 25–23, 35 FR 5679, Apr. 8, 1970, as
amended by Amdt. 25–41, 42 FR 36970, July 18,
1977]

§ 25.1337

Powerplant instruments.

(a)

Instruments and instrument lines.

(1) Each powerplant and auxiliary
power unit instrument line must meet
the requirements of §§ 25.993 and 25.1183.

(2) Each line carrying flammable

fluids under pressure must—

(i) Have restricting orifices or other

safety devices at the source of pressure
to prevent the escape of excessive fluid
if the line fails; and

(ii) Be installed and located so that

the escape of fluids would not create a
hazard.

(3) Each powerplant and auxiliary

power unit instrument that utilizes
flammable fluids must be installed and
located so that the escape of fluid
would not create a hazard.

(b)

Fuel quantity indicator. There

must be means to indicate to the flight
crewmembers, the quantity, in gallons

or equivalent units, of usable fuel in
each tank during flight. In addition—

(1) Each fuel quantity indicator must

be calibrated to read ‘‘zero’’ during
level flight when the quantity of fuel
remaining in the tank is equal to the
unusable fuel supply determined under
§ 25.959;

(2) Tanks with interconnected outlets

and airspaces may be treated as one
tank and need not have separate indi-
cators; and

(3) Each exposed sight gauge, used as

a fuel quantity indicator, must be pro-
tected against damage.

(c)

Fuel flowmeter system. If a fuel

flowmeter system is installed, each
metering component must have a
means for bypassing the fuel supply if
malfunction of that component se-
verely restricts fuel flow.

(d)

Oil quantity indicator. There must

be a stick gauge or equivalent means
to indicate the quantity of oil in each
tank. If an oil transfer or reserve oil
supply system is installed, there must
be a means to indicate to the flight
crew, in flight, the quantity of oil in
each tank.

(e)

Turbopropeller blade position indi-

cator. Required turbopropeller blade
position indicators must begin indi-
cating before the blade moves more
than eight degrees below the flight low
pitch stop. The source of indication
must directly sense the blade position.

(f)

Fuel pressure indicator. There must

be means to measure fuel pressure, in
each system supplying reciprocating
engines, at a point downstream of any
fuel pump except fuel injection pumps.
In addition—

(1) If necessary for the maintenance

of proper fuel delivery pressure, there
must be a connection to transmit the
carburetor air intake static pressure to
the proper pump relief valve connec-
tion; and

(2) If a connection is required under

paragraph (f)(1) of this section, the
gauge balance lines must be independ-
ently connected to the carburetor inlet
pressure to avoid erroneous readings.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–40, 42 FR 15044, Mar. 17,
1977]

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§ 25.1353

LECTRICAL

YSTEMS AND

QUIPMENT

§ 25.1351

General.

(a)

Electrical system capacity. The re-

quired generating capacity, and num-
ber and kinds of power sources must—

(1) Be determined by an electrical

load analysis; and

(2) Meet the requirements of § 25.1309.
(b)

Generating system. The generating

system includes electrical power
sources, main power busses, trans-
mission cables, and associated control,
regulation, and protective devices. It
must be designed so that—

(1) Power sources function properly

when independent and when connected
in combination;

(2) No failure or malfunction of any

power source can create a hazard or
impair the ability of remaining sources
to supply essential loads;

(3) The system voltage and frequency

(as applicable) at the terminals of all
essential load equipment can be main-
tained within the limits for which the
equipment is designed, during any
probable operating condition; and

(4) System transients due to switch-

ing, fault clearing, or other causes do
not make essential loads inoperative,
and do not cause a smoke or fire haz-
ard.

(5) There are means accessible, in

flight, to appropriate crewmembers for
the individual and collective dis-
connection of the electrical power
sources from the system.

(6) There are means to indicate to ap-

propriate crewmembers the generating
system quantities essential for the safe
operation of the system, such as the
voltage and current supplied by each
generator.

(c)

External power. If provisions are

made for connecting external power to
the airplane, and that external power
can be electrically connected to equip-
ment other than that used for engine
starting, means must be provided to
ensure that no external power supply
having a reverse polarity, or a reverse
phase sequence, can supply power to
the airplane’s electrical system.

(d)

Operation without normal electrical

power. It must be shown by analysis,
tests, or both, that the airplane can be
operated safely in VFR conditions, for
a period of not less than five minutes,

with the normal electrical power (elec-
trical power sources excluding the bat-
tery) inoperative, with critical type
fuel (from the standpoint of flameout
and restart capability), and with the
airplane initially at the maximum cer-
tificated altitude. Parts of the elec-
trical system may remain on if—

(1) A single malfunction, including a

wire bundle or junction box fire, can-
not result in loss of both the part
turned off and the part turned on; and

(2) The parts turned on are elec-

trically and mechanically isolated
from the parts turned off.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–41, 42 FR 36970, July 18,
1977; Amdt. 25–72, 55 FR 29785, July 20, 1990]

§ 25.1353

Electrical equipment and in-

stallations.

(a) Electrical equipment and controls

must be installed so that operation of
any one unit or system of units will
not adversely affect the simultaneous
operation of any other electrical unit
or system essential to safe operation.
Any electrical interference likely to be
present in the airplane must not result
in hazardous effects on the airplane or
its systems.

(b) Storage batteries must be de-

signed and installed as follows:

(1) Safe cell temperatures and pres-

sures must be maintained during any
probable charging or discharging con-
dition. No uncontrolled increase in cell
temperature may result when the bat-
tery is recharged (after previous com-
plete discharge)—

(i) At maximum regulated voltage or

power;

(ii) During a flight of maximum dura-

tion; and

(iii) Under the most adverse cooling

condition likely to occur in service.

(2) Compliance with paragraph (b)(1)

of this section must be shown by test
unless experience with similar bat-
teries and installations has shown that
maintaining safe cell temperatures and
pressures presents no problem.

(3) No explosive or toxic gases emit-

ted by any battery in normal oper-
ation, or as the result of any probable
malfunction in the charging system or
battery installation, may accumulate
in hazardous quantities within the air-
plane.