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. <EOS>