(a) Fuel tank vents. Each fuel tank must be vented from the top
part of the expansion space so that venting is effective under normal
flight conditions. In addition --
(1) The vents must be arranged to avoid stoppage by dirt or ice
formation;
(2) The vent arrangement must prevent siphoning of fuel during normal
operation;
(3) The venting capacity and vent pressure levels must maintain
acceptable differences of pressure between the interior and exterior of
the tank, during --
(i) Normal flight operation;
(ii) Maximum rate of ascent and descent; and
(iii) Refueling and defueling (where applicable);
(4) Airspaces of tanks with interconnected outlets must be
interconnected;
(5) There may be no point in any vent line where moisture can
accumulate with the rotorcraft in the ground attitude or the level flight
attitude, unless drainage is provided;
(6) No vent or drainage provision may end at any point --
(i) Where the discharge of fuel from the vent outlet would constitute a
fire hazard; or
(ii) From which fumes could enter personnel compartments; and
(7) The venting system must be designed to minimize spillage of fuel
through the vents to an ignition source in the event of a rollover during
landing, ground operations, or a survivable impact.
(b) Carburetor vapor vents. Each carburetor with vapor
elimination connections must have a vent line to lead vapors back to one
of the fuel tanks. In addition --
(1) Each vent system must have means to avoid stoppage by ice; and
(2) If there is more than one fuel tank, and it is necessary to use the
tanks in a definite sequence, each vapor vent return line must lead back
to the fuel tank used for takeoff and landing.