Patent ID: 8386097

Claim:
A method for assisting guidance of an aircraft, the method comprising the steps of: entering into a time constraint entry unit at least one time constraint relating to a passage time at a check-point in a flight of the aircraft; determining, by an information source, values of first flight parameters relating to the flight of the aircraft; determining, by a flight management system, guidance instructions including speed instructions to guide the aircraft to said check-point at said passage time, wherein said guidance instructions are determined from said values of first flight parameters and the at least one time constraint entered into the time constraint entry unit; generating, by an accuracy generating unit, an accuracy level for complying with said time constraint, said accuracy level representing a maximum allowable difference between a required passage time and an actual passage time at said check-point and at least one error level for at least one of said first flight parameters; determining, by a margin determining unit, an operating margin for at least one second parameter, which is representative of air speed level of the aircraft, said operating margin representing a range of air speed criterion values of the aircraft, wherein the operating margin is determined from said accuracy level and from said at least one error level; determining, by a range determining unit, whether the operating margin representing the range of air speed criterion values is within an air speed envelope of the aircraft, said air speed envelope comprising air speeds at which the aircraft can fly between its current position and said check-point; modifying said speed instructions, by a speed modifier, when said range of air speed criterion values is not within said air speed envelope, said speed instructions being modified to be within said air speed envelope; determining a reliable time domain, by the flight management system, which corresponds to a passage time domain that the aircraft can observe at said check-point with said accuracy level, including a probability level; and presenting, on a display screen, to a pilot of the aircraft at least one of the following: a graph illustrating the reliable time domain; and information that said reliable time domain cannot be attained.