A system for monitoring the operational state of an aircraft crew comprising: - a first interface for receiving first crew monitoring data, the first monitoring data having a high design assurance level; - a second interface for receiving second crew monitoring data, the second monitoring data having a lower design assurance level than the first monitoring data; - a unit for determining at least one pilot state based on the first high design assurance monitoring data received from the first receiving interface, and on the second lower design assurance monitoring data received from the second receiving interface, characterised in that the determination unit comprises, for the or each monitored pilot state: • a first high-level evaluation module, adapted to implement a first deterministic algorithm to obtain a high-level pilot state from the first high design assurance level monitoring data, regardless of the second lower design assurance level monitoring data; • a second lower-level evaluation module, suitable for determining a low-level pilot state, from at least the second lower design assurance level monitoring data; • a consolidation module for determining a consolidated pilot state, wherein the consolidated pilot state is obtained in an active configuration of the second lower-level evaluation module as a function of the high-level pilot state and the low-level pilot state, and is obtained in an inactive configuration of the second lower-level evaluation module as a function of the high-level pilot state, without taking the low-level pilot state into account. - a first interface for receiving first crew monitoring data, the first monitoring data having a high design assurance level; - a second interface for receiving second crew monitoring data, the second monitoring data having a lower design assurance level than the first monitoring data; - a unit for determining at least one pilot state based on the first high design assurance monitoring data received from the first receiving interface, and on the second lower design assurance monitoring data received from the second receiving interface, characterised in that the determination unit comprises, for the or each monitored pilot state: • a first high-level evaluation module, adapted to implement a first deterministic algorithm to obtain a high-level pilot state from the first high design assurance level monitoring data, regardless of the second lower design assurance level monitoring data; • a second lower-level evaluation module, suitable for determining a low-level pilot state, from at least the second lower design assurance level monitoring data; • a consolidation module for determining a consolidated pilot state, wherein the consolidated pilot state is obtained in an active configuration of the second lower-level evaluation module as a function of the high-level pilot state and the low-level pilot state, and is obtained in an inactive configuration of the second lower-level evaluation module as a function of the high-level pilot state, without taking the low-level pilot state into account. • a first high-level evaluation module, adapted to implement a first deterministic algorithm to obtain a high-level pilot state from the first high design assurance level monitoring data, regardless of the second lower design assurance level monitoring data; • a second lower-level evaluation module, suitable for determining a low-level pilot state, from at least the second lower design assurance level monitoring data; • a consolidation module for determining a consolidated pilot state, wherein the consolidated pilot state is obtained in an active configuration of the second lower-level evaluation module as a function of the high-level pilot state and the low-level pilot state, and is obtained in an inactive configuration of the second lower-level evaluation module as a function of the high-level pilot state, without taking the low-level pilot state into account.