An assistance device for navigation and guidance of an aircraft, said device comprising: - first calculation means for determining a consolidated position of the aircraft; - second calculation means for determining deviations between said position of the aircraft and a current segment of a flight trajectory; and - transmission means for transmitting such deviations to a guidance calculator, - at least one calculator being on board the aircraft, into which said first and second calculation means (6, 7) and said transmission means are integrated, and which further comprises at least the following integrated means: • first reception means (3A, 3B) for receiving a set of successive segments of a flight trajectory to be followed by the aircraft; • memorization means for recording said segments; and • second reception means (5A, 5B, 5C) for receiving, repeatedly, respectively from at least three independent sources of information (36, 37, 38), current position information for the aircraft; - said first calculation means are formed so as to determine, repeatedly, a consolidated position of the aircraft, from said current position information; - said second calculation means are formed so as to determine, repeatedly, the deviations between said consolidated position and a current segment of the flight trajectory, being recorded in said memorization means; and - said device is replicated on at least three different and independent channels so that all the processings performed by said device are simultaneously carried out on said at least three channels, characterized in that said device comprises means for determining delays in a navigation and guidance chain of said device, said means for determining delays determining a transit time between the arrival of a piece of information in a navigation source and the triggering of an action, being related to this piece of information, by a guidance function. - first calculation means for determining a consolidated position of the aircraft; - second calculation means for determining deviations between said position of the aircraft and a current segment of a flight trajectory; and - transmission means for transmitting such deviations to a guidance calculator, - at least one calculator being on board the aircraft, into which said first and second calculation means (6, 7) and said transmission means are integrated, and which further comprises at least the following integrated means: • first reception means (3A, 3B) for receiving a set of successive segments of a flight trajectory to be followed by the aircraft; • memorization means for recording said segments; and • second reception means (5A, 5B, 5C) for receiving, repeatedly, respectively from at least three independent sources of information (36, 37, 38), current position information for the aircraft; • first reception means (3A, 3B) for receiving a set of successive segments of a flight trajectory to be followed by the aircraft; • memorization means for recording said segments; and • second reception means (5A, 5B, 5C) for receiving, repeatedly, respectively from at least three independent sources of information (36, 37, 38), current position information for the aircraft; - said first calculation means are formed so as to determine, repeatedly, a consolidated position of the aircraft, from said current position information; - said second calculation means are formed so as to determine, repeatedly, the deviations between said consolidated position and a current segment of the flight trajectory, being recorded in said memorization means; and - said device is replicated on at least three different and independent channels so that all the processings performed by said device are simultaneously carried out on said at least three channels,