§29.975 Fuel tank vents and carburettor vapour vents

(a) Fuel tank vents. Each fuel tank m ust be vented from the top part of the expansion space so that vent ing i s effect ive under norm al fl ight conditions. In addition: (1) The vents must be arranged to avoid stoppage by dirt or ice formation; (2) The vent arrangem ent must prevent siphoning of fuel during normal operation; (3) The vent ing capaci ty and vent pressure levels m ust m aintain acceptable differences of pressure bet ween the interior and exterior of the tank, during: (i) Norm al flight operation; (ii) Maximum rate o f ascen t an d descent; and (iii) Refuelling an d d efuelling (where applicable); (4) Airspaces of tanks with interconnected outlets must be interconnected; (5) There may be no poi nt i n any vent line where m oisture can accum ulate with the rotorcraft in the ground attitude or the level flight attitude, unless drainage is provided; (6) No vent or drai nage provi sion may end at any point: (i) Where the discharge of fuel from the v ent o utlet wo uld co nstitute a fire hazard; or (ii) From which fumes could enter personnel compartments; and (7) The vent ing sy stem must be designed to m inimise spillage of fuel through the vents to an i gnition source in the event of a rollover during landing, ground operations, or a survivable impact. (b) Carburettor vapour vents. Each carburettor with vapour el imination connect ions must have a vent line to lead vapours back to one of the fuel tanks. In addition – (1) Each vent system m ust have m eans to avoid stoppage by ice; and (2) If there is m ore than one fuel tank, and it is necessary to use the tanks in a d efinite sequence, each vapour vent return line must lead back to the fuel tank used for take-off and landing.