A system of fuel cells for an aircraft including a plurality of fuel cells, a hydrogen circuit, a cooling circuit and a first air circuit configured to supply oxygen to a first subset of fuel cells having at least two cells. The first air circuit includes an air flow restrictor at each fuel cell inlet of the first subset and configured to distribute the air between the fuel cells of the first subset, and an outlet valve connected to the outlet of the fuel cells of the first subset, the opening of the outlet valve being controlled by a computer as a function of an electrical power that is to be produced by the fuel cells of the first subset. The use of the same air circuit to supply oxygen to several fuel circuits makes it possible to limit the bulk of the fuel cells system.