306 

14 CFR Ch. I (1–1–14 Edition) 

§ 23.1351 

freeze must have means to allow drain-
age on the ground; 

(4) There must be a means to indicate 

the amount of usable fuel in each tank 
when the airplane is on the ground 
(such as by a stick gauge); 

(5) Tanks with interconnected outlets 

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

(6) No fuel quantity indicator is re-

quired for an auxiliary tank that is 
used only to transfer fuel to other 
tanks if the relative size of the tank, 
the rate of fuel transfer, and operating 
instructions are adequate to— 

(i) Guard against overflow; and 
(ii) Give the flight crewmembers 

prompt warning if transfer is not pro-
ceeding as planned. 

(c) 

Fuel flowmeter system. If a fuel 

flowmeter system is installed, each 
metering component must have a 
means to by-pass the fuel supply if 
malfunctioning of that component se-
verely restricts fuel flow. 

(d) 

Oil quantity indicator. There must 

be a means to indicate the quantity of 
oil in each tank— 

(1) On the ground (such as by a stick 

gauge); and 

(2) In flight, to the flight crew mem-

bers, if there is an oil transfer system 
or a reserve oil supply system. 

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as 
amended by Amdt. 23–7, 34 FR 13096, Aug. 13, 
1969; Amdt. 23–18, 42 FR 15042, Mar. 17, 1977; 
Amdt. 23–43, 58 FR 18976, Apr. 9, 1993; Amdt. 
23–51, 61 FR 5138, Feb. 9, 1996; Amdt. 23–49, 61 
FR 5169, Feb. 9, 1996] 

E

LECTRICAL

S

YSTEMS AND

E

QUIPMENT

 

§ 23.1351

General. 

(a) 

Electrical system capacity. Each 

electrical system must be adequate for 
the intended use. In addition— 

(1) Electric power sources, their 

transmission cables, and their associ-
ated control and protective devices, 
must be able to furnish the required 
power at the proper voltage to each 
load circuit essential for safe oper-
ation; and 

(2) Compliance with paragraph (a)(1) 

of this section must be shown as fol-
lows— 

(i) For normal, utility, and acrobatic 

category airplanes, by an electrical 
load analysis or by electrical measure-

ments that account for the electrical 
loads applied to the electrical system 
in probable combinations and for prob-
able durations; and 

(ii) For commuter category air-

planes, by an electrical load analysis 
that accounts for the electrical loads 
applied to the electrical system in 
probable combinations and for probable 
durations. 

(b) 

Function.  For each electrical sys-

tem, the following apply: 

(1) Each system, when installed, 

must be— 

(i) Free from hazards in itself, in its 

method of operation, and in its effects 
on other parts of the airplane; 

(ii) Protected from fuel, oil, water, 

other detrimental substances, and me-
chanical damage; and 

(iii) So designed that the risk of elec-

trical shock to crew, passengers, and 
ground personnel is reduced to a min-
imum. 

(2) Electric power sources must func-

tion properly when connected in com-
bination or independently. 

(3) No failure or malfunction of any 

electric power source may impair the 
ability of any remaining source to sup-
ply load circuits essential for safe oper-
ation. 

(4) In addition, for commuter cat-

egory airplanes, the following apply: 

(i) Each system must be designed so 

that essential load circuits can be sup-
plied in the event of reasonably prob-
able faults or open circuits including 
faults in heavy current carrying cables; 

(ii) A means must be accessible in 

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

(iii) The system must be designed so 

that voltage and frequency, if applica-
ble, at the terminals of all essential 
load equipment can be maintained 
within the limits for which the equip-
ment is designed during any probable 
operating conditions; 

(iv) If two independent sources of 

electrical power for particular equip-
ment or systems are required, their 
electrical energy supply must be en-
sured by means such as duplicate elec-
trical equipment, throwover switching, 
or multichannel or loop circuits sepa-
rately routed; and 

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