Federal Aviation Administration, DOT
Section 25.1333

Section 25.1337

Instrument systems.

For systems that operate the instruments required by Section 25.1303(b) which are
located at each pilot-s station - 
(a) Means must be provided to connect the required instruments at the
first pilot-s station to operating systems which are independent of the operating systems at other flight crew
stations, or other equipment;
(b) The equipment, systems, and installations must be designed so that
one display of the information essential to the safety of flight which is provided by the instruments, including attitude, direction, airspeed, and altitude
will remain available to the pilots,
without additional crewmember action, after any single failure or combination 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 instruments 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]

spaschal on DSK3GDR082PROD with CFR

Section 25.1337

Powerplant instruments.

(a) Instruments and instrument lines.
(1) Each powerplant and auxiliary
power unit instrument line must meet
the requirements of SectionSection 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
Section 25.959;
(2) Tanks with interconnected outlets
and airspaces may be treated as one
tank and need not have separate indicators; and
(3) Each exposed sight gauge, used as
a fuel quantity indicator, must be protected 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 severely 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 indicator. Required turbopropeller blade
position indicators must begin indicating 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 connection; and
(2) If a connection is required under
paragraph (f)(1) of this section, the
gauge balance lines must be independently 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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