497 

Federal Aviation Administration, DOT 

§ 25.1309 

must be based on the direct measure-
ment of thrust or of parameters that 
are directly related to thrust. The indi-
cator must indicate a change in thrust 
resulting from any engine malfunction, 
damage, or deterioration. 

(2) A position indicating means to in-

dicate to the flightcrew when the 
thrust reversing device— 

(i) Is not in the selected position, and 
(ii) Is in the reverse thrust position, 

for each engine using a thrust revers-
ing device. 

(3) An indicator to indicate rotor sys-

tem unbalance. 

(e) 

For turbopropeller-powered air-

planes.  In addition to the powerplant 
instruments required by paragraphs (a) 
and (c) of this section, the following 
powerplant instruments are required: 

(1) A torque indicator for each en-

gine. 

(2) Position indicating means to indi-

cate to the flight crew when the pro-
peller blade angle is below the flight 
low pitch position, for each propeller. 

(f) For airplanes equipped with fluid 

systems (other than fuel) for thrust or 
power augmentation, an approved 
means must be provided to indicate the 
proper functioning of that system to 
the flight crew. 

[Amdt. 25–23, 35 FR 5678, Apr. 8, 1970, as 
amended by Amdt. 25–35, 39 FR 1831, Jan. 15, 
1974; Amdt. 25–36, 39 FR 35461, Oct. 1, 1974; 
Amdt. 25–38, 41 FR 55467, Dec. 20, 1976; Amdt. 
25–54, 45 FR 60173, Sept. 11, 1980; Amdt. 25–72, 
55 FR 29785, July 20, 1990; Amdt. 25–115, 69 FR 
40527, July 2, 2004] 

§ 25.1307

Miscellaneous equipment. 

The following is required miscella-

neous equipment: 

(a) [Reserved] 
(b) Two or more independent sources 

of electrical energy. 

(c) Electrical protective devices, as 

prescribed in this part. 

(d) Two systems for two-way radio 

communications, with controls for 
each accessible from each pilot station, 
designed and installed so that failure of 
one system will not preclude operation 
of the other system. The use of a com-
mon antenna system is acceptable if 
adequate reliability is shown. 

(e) Two systems for radio navigation, 

with controls for each accessible from 
each pilot station, designed and in-

stalled so that failure of one system 
will not preclude operation of the other 
system. The use of a common antenna 
system is acceptable if adequate reli-
ability is shown. 

[Amdt. 25–23, 35 FR 5678, Apr. 8, 1970, as 
amended by Amdt. 25–46, 43 FR 50598, Oct. 30, 
1978; Amdt. 25–54, 45 FR 60173, Sept. 11, 1980; 
Amdt. 25–72, 55 FR 29785, July 20, 1990] 

§ 25.1309

Equipment, systems, and in-

stallations. 

(a) The equipment, systems, and in-

stallations whose functioning is re-
quired by this subchapter, must be de-
signed to ensure that they perform 
their intended functions under any 
foreseeable operating condition. 

(b) The airplane systems and associ-

ated components, considered sepa-
rately and in relation to other systems, 
must be designed so that— 

(1) The occurrence of any failure con-

dition which would prevent the contin-
ued safe flight and landing of the air-
plane is extremely improbable, and 

(2) The occurrence of any other fail-

ure conditions which would reduce the 
capability of the airplane or the ability 
of the crew to cope with adverse oper-
ating conditions is improbable. 

(c) Warning information must be pro-

vided to alert the crew to unsafe sys-
tem operating conditions, and to en-
able them to take appropriate correc-
tive action. Systems, controls, and as-
sociated monitoring and warning 
means must be designed to minimize 
crew errors which could create addi-
tional hazards. 

(d) Compliance with the require-

ments of paragraph (b) of this section 
must be shown by analysis, and where 
necessary, by appropriate ground, 
flight, or simulator tests. The analysis 
must consider— 

(1) Possible modes of failure, includ-

ing malfunctions and damage from ex-
ternal sources. 

(2) The probability of multiple fail-

ures and undetected failures. 

(3) The resulting effects on the air-

plane and occupants, considering the 
stage of flight and operating condi-
tions, and 

(4) The crew warning cues, corrective 

action required, and the capability of 
detecting faults. 

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