Rotary wing aircraft provided with a transmission system comprising an emergency electric motor

An aircraft provided with a rotary airfoil and a power plant, said power plant comprising a power transmission box provided with a main output shaft rotating said rotary airfoil, said power plant comprising at least one heat engine connected by a mechanical input link to an input shaft of said power transmission box, said aircraft comprising at least one accessory which is set in motion by a secondary output shaft of the power transmission box,

• said aircraft comprising an assistance system provided with a mechanical connection module having a connection shaft which is connected to the secondary output shaft, said assistance system having a first connection member connected to said at least one accessory and connected by a first mechanical link internal to the connection shaft, said mechanical connection module having a second connection member connected to an electric motor and connected by a second mechanical link internal to the connection shaft,
• wherein said electric motor is an irreversible motor operating only in motor mode, said electric motor being requested to set said main output shaft in motion in the event of failure of at least one heat engine via the mechanical connection module.