Federal Aviation Administration, DOT

Section 121.243
(c) Flexible connections in lines that
may be under pressure and subject to
axial loading must use flexible hose assemblies rather than hose clamp connections.
(d) Flexible hose must be of an acceptable type or proven suitable for the
particular application.

contained in any one compartment, either during the time it is being extinguished, or thereafter, unless the extinguishing system floods those compartments simultaneously.
Section 121.225 Propeller deicing fluid.
If combustible fluid is used for propeller deicing, the certificate holder
must comply with Section 121.255.

Section 121.233 Fuel lines and fittings in designated fire zones.
Fuel lines and fittings in each designated fire zone must comply with
Section 121.259.

Section 121.227 Pressure cross-feed arrangements.
(a) Pressure cross-feed lines may not
pass through parts of the airplane used
for carrying persons or cargo unless - 
(1) There is a means to allow crewmembers to shut off the supply of fuel
to these lines; or
(2) The lines are enclosed in a fuel
and fume-proof enclosure that is ventilated and drained to the exterior of the
airplane.

Section 121.235 Fuel valves.
Each fuel valve must - 
(a) Comply with Section 121.257;
(b) Have positive stops or suitable
index provisions in the  - on -  and  - off - 
positions; and
(c) Be supported so that loads resulting from its operation or from accelerated flight conditions are not transmitted to the lines connected to the
valve.

However, such an enclosure need not be
used if those lines incorporate no fittings on or within the personnel or
cargo areas and are suitably routed or
protected to prevent accidental damage.
(b) Lines that can be isolated from
the rest of the fuel system by valves at
each end must incorporate provisions
for relieving excessive pressures that
may result from exposure of the isolated line to high temperatures.

Section 121.237 Oil lines and fittings in designated fire zones.
Oil line and fittings in each designated fire zone must comply with
Section 121.259.
Section 121.239 Oil valves.
(a) Each oil valve must - 
(1) Comply with Section 121.257;
(2) Have positive stops or suitable
index provisions in the  - on -  and  - off - 
positions; and
(3) Be supported so that loads resulting from its operation or from accelerated flight conditions are not transmitted to the lines attached to the
valve.
(b) The closing of an oil shutoff
means must not prevent feathering the
propeller, unless equivalent safety provisions are incorporated.

Section 121.229 Location of fuel tanks.
(a) Fuel tanks must be located in accordance with Section 121.255.
(b) No part of the engine nacelle skin
that lies immediately behind a major
air outlet from the engine compartment may be used as the wall of an integral tank.
(c) Fuel tanks must be isolated from
personnel compartments by means of
fume- and fuel-proof enclosures.
Section 121.231 Fuel system lines and fittings.
(a) Fuel lines must be installed and
supported so as to prevent excessive vibration and so as to be adequate to
withstand loads due to fuel pressure
and accelerated flight conditions.
(b) Lines connected to components of
the airplanes between which there may
be relative motion must incorporate
provisions for flexibility.

Section 121.241 Oil system drains.
Accessible drains incorporating either a manual or automatic means for
positive locking in the closed position,
must be provided to allow safe drainage
of the entire oil system.
Section 121.243 Engine breather lines.
(a) Engine breather lines must be so
arranged that condensed water vapor

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