An aircraft and method for controlling an extinguishing agent concentration in a cargo compartment

The invention relates to an aircraft 2 having a cargo hold 4, a first container 6 with a fire-extinguishing agent, a first line section 8 extending from the first fire-extinguishing agent container to the cargo hold. A controllable valve 10 is coupled to the first line section and is operable to control flow therethrough. A concentration sensor 12 is arranged to sense a concentration of the fire-extinguishing agent in the cargo hold, and based on this, a monitoring unit is operable to control the valve, thus maintaining the level of fire-extinguishant in the cargo hold to a predetermined level. In a preferred embodiment, a second line section 32 extends from a second container 30 containing fire-extinguishing agent to the cargo hold for providing an unmonitored flow of fire-extinguishing agent. A method for monitoring a concentration of fire-extinguishing agent in the cargo hold of the aircraft is also disclosed.