552 

14 CFR Ch. I (1–1–24 Edition) 

§ 27.1353 

(4) Each electric power source control 

must allow the independent operation 
of each source. 

(c) 

Generating system. There must be 

at least one generator if the system 
supplies power to load circuits essen-
tial for safe operation. In addition— 

(1) Each generator must be able to 

deliver its continuous rated power; 

(2) Generator voltage control equip-

ment must be able to dependably regu-
late each generator output within 
rated limits; 

(3) Each generator must have a re-

verse current cutout designed to dis-
connect the generator from the battery 
and from the other generators when 
enough reverse current exists to dam-
age that generator; and 

(4) Each generator must have an 

overvoltage control designed and in-
stalled to prevent damage to the elec-
trical system, or to equipment supplied 
by the electrical system, that could re-
sult if that generator were to develop 
an overvoltage condition. 

(d) 

Instruments. There must be means 

to indicate to appropriate crew-
members the electric power system 
quantities essential for safe operation 
of the system. In addition— 

(1) For direct current systems, an 

ammeter that can be switched into 
each generator feeder may be used; and 

(2) If there is only one generator, the 

ammeter may be in the battery feeder. 

(e) 

External power. If provisions are 

made for connecting external power to 
the rotorcraft, 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 rotorcraft’s electrical system. 

(Secs. 313(a), 601, 603, 604, and 605 of the Fed-
eral Aviation Act of 1958 (49 U.S.C. 1354(a), 
1421, 1423, 1424, and 1425); and sec. 6(c) of the 
Dept. of Transportation Act (49 U.S.C. 
1655(c))) 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–11, 41 FR 55470, Dec. 20, 
1976; Amdt. 27–13, 42 FR 36972, July 18, 1977] 

§ 27.1353

Energy storage systems. 

Energy storage systems must be de-

signed and installed as follows: 

(a) Energy storage systems must pro-

vide automatic protective features for 
any conditions that could prevent con-
tinued safe flight and landing. 

(b) Energy storage systems must not 

emit any flammable, explosive, or 
toxic gases, smoke, or fluids that could 
accumulate in hazardous quantities 
within the rotorcraft. 

(c) Corrosive fluids or gases that es-

cape from the system must not damage 
surrounding structures, adjacent equip-
ment, or systems necessary for contin-
ued safe flight and landing. 

(d) The maximum amount of heat 

and pressure that can be generated dur-
ing any operation or under any failure 
condition of the energy storage system 
or its individual components must not 
result in any hazardous effect on rotor-
craft structure, equipment, or systems 
necessary for continued safe flight and 
landing. 

(e) Energy storage system installa-

tions required for continued safe flight 
and landing of the rotorcraft must 
have monitoring features and a means 
to indicate to the pilot the status of all 
critical system parameters. 

[Amdt. 27–51, 88 FR 8738, Feb. 10, 2023] 

§ 27.1357

Circuit protective devices. 

(a) Protective devices, such as fuses 

or circuit breakers, must be installed 
in each electrical circuit other than— 

(1) The main circuits of starter mo-

tors; and 

(2) Circuits in which no hazard is pre-

sented by their omission. 

(b) A protective device for a circuit 

essential to flight safety may not be 
used to protect any other circuit. 

(c) Each resettable circuit protective 

device (‘‘trip free’’ device in which the 
tripping mechanism cannot be over-
ridden by the operating control) must 
be designed so that— 

(1) A manual operation is required to 

restore service after trippling; and 

(2) If an overload or circuit fault ex-

ists, the device will open the circuit re-
gardless of the position of the oper-
ating control. 

(d) If the ability to reset a circuit 

breaker or replace a fuse is essential to 
safety in flight, that circuit breaker or 
fuse must be located and identified so 
that it can be readily reset or replaced 
in flight. 

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