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14 CFR Ch. I (1–1–24 Edition) 

§ 25.1333 

§ 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 

(c) Additional instruments, systems, 

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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