Noncombustible Gas Distribution Methods and Systems on Aircraft

A noncombustible gas distribution method comprising:

• opening a first isolation valve to distribute noncombustible gas to a center wing tank of an aircraft during flight each time one or more of the following conditions 1A-1C are met, the center tank being positioned between a left main wing tanks and a right main wing tank of the aircraft and closing the first isolation valve to not distribute the noncombustible gas to the center wing tank during flight when none of the following conditions 1A-1C are met:
• 1A) the center wing tank contains a usable level of fuel;
• 1B) the aircraft is cruising in a pre-descent phase;
• and
• 1C) the aircraft is in a descent phase;
• and
• opening at least a second isolation valve to distribute noncombustible gas to the left and right main wing tanks during flight each time one or more of the following conditions 2A-2D are met and closing the at least the second isolation valve to not distribute the noncombustible gas to the left and right main wing tanks during flight when none of the following conditions 2A-2D are met:
• 2A) the aircraft is climbing;
• 2B) the aircraft is cruising with the left and right main wing tanks' O2% projected to be above an inert limit before fuel decreases below a lower flammability limit;
• 2C) the aircraft is cruising in the pre-descent phase;
• and
• 2D) the aircraft is in the descent phase at an altitude below a selected altitude.

A noncombustible gas distribution system comprising:

• a noncombustible gas source on an aircraft;
• a left main wing tank and a right main wing tank on opposite sides of the aircraft and a center wing tank between the left and right main wing tanks;
• the left and right main wing tanks each having an inboard section and an outboard section each having baffle ribs and other ribs, the sections being defined by baffle ribs between the sections, the baffle ribs defining the sections having less ullage communication area between the sections compared to the ullage communication area of the other ribs within the sections;
• noncombustible gas distribution tubing from the noncombustible gas source to the left and right main wing tanks and the center wing tank;
• a first isolation valve in the noncombustible gas distribution tubing operable to isolate the center wing tank from receiving noncombustible gas;
• at least one second isolation valve in the noncombustible gas distribution tubing operable to isolate the left and right main wing tanks from receiving noncombustible gas;
• and
• a distribution mechanism including first noncombustible gas flow restrictions configured to balance noncombustible gas flow among the left and right main wing tanks and the center wing tank with first isolation valve and the at least one second isolation valve fully open to yield a greater proportion of noncombustible gas flow per tank unit volume distributed to the outboard section of the left and right main wing tanks compared to the inboard section during a climb phase of a flight of the aircraft.