Text in force at CS27-10: from CS27-0, effective 14 Nov 2003.
(a) Each fuel system for multi-engine rotorcraft must allow fuel to be supplied to each engine through a system independent of those parts of each system supplying fuel to other engines. However, separate fuel tanks need not be provided for each engine.
(b) If a single fuel tank is used on a multi-engine rotorcraft, the following must be provided:
(1) Independent tank outlets for each engine, each incorporating a shut-off valve at the tank. This shut-off valve may also serve as the firewall shut-off valve required by CS 27.995 if the line between the valve and the engine compartment does not contain a hazardous amount of fuel that can drain into the engine compartment.
(2) At least two vents arranged to minimise the probability of both vents becoming obstructed simultaneously.
(3) Filler caps designed to minimise the probability of incorrect installation or in-flight loss.
(4) A fuel system in which those parts of the system from each tank outlet to any engine are independent of each part of each system supplying fuel to other engines.
ED Decision 2003/015/RM · Source