29.967—Fuel tank installation.
(a)
Each fuel tank must be supported so that tank loads are not concentrated on unsupported tank surfaces. In addition—
(3)
If flexible tank liners are used, they must be supported so that they are not required to withstand fluid loads; and
(4)
Each interior surface of tank compartments must be smooth and free of projections that could cause wear of the liner, unless—
(b)
Any spaces adjacent to tank surfaces must be adequately ventilated to avoid accumulation of fuel or fumes in those spaces due to minor leakage. If the tank is in a sealed compartment, ventilation may be limited to drain holes that prevent clogging and that prevent excessive pressure resulting from altitude changes. If flexible tank liners are installed, the venting arrangement for the spaces between the liner and its container must maintain the proper relationship to tank vent pressures for any expected flight condition.
(d)
No rotorcraft skin immediately adjacent to a major air outlet from the engine compartment may act as the wall of an integral tank.