Dual circuit lubrication method and device with increased reliability for a main power transmission gearbox of an aircraft

A dual circuit method of lubricating a mechanical system that includes a tank containing a lubrication liquid, the method comprising:

• using the lubrication liquid to lubricate the mechanical system simultaneously via a first lubrication circuit and a second lubrication circuit, the second lubrication circuit having a second suction point situated below a limit depth in the tank, the first lubrication circuit including at least one first suction point that can be situated below the second suction point;
• detecting a drop in the level of the lubrication liquid in the tank to below the limit depth;
• stopping the flow of the lubrication liquid in the first lubrication circuit;
• measuring the pressure of the lubrication liquid in the second lubrication circuit;
• detecting a drop of the pressure of the lubrication liquid in the second lubrication circuit;
• reestablishing the flow of the lubrication liquid in the first lubrication circuit;
• and
• stopping the flow of the lubrication liquid in the second lubrication circuit.