Method of validating a flight plan constraint
View Patent ↗An FMS flight management computer equipping an aerodyne, complies with a constraint, in particular an altitude constraint, of the flight plan (Dpv) at an imposed waypoint close to the position of the aerodyne at the moment of instigation of its automatic flight plan following function. It consists in validating, in advance, such a constraint by projecting itself into a near future by way of a forecast (Pt) of the displacement of the aerodyne taking account of the motion of the aerodyne during the transition between the instances of application of the flight presets prevailing before the instigation of the automatic following function and those newly provided by the FMS flight computer ( 30 ) during this instigation.
1. A method of validating a flight plan constraint, at an imposed waypoint, for a flight computer, comprising the steps of:
delivering flight presets to an aerodyne during a resumption of automatic following of a flight plan after a piloted flight phase,
making a forecast of the displacement of the aerodyne up to the imposed waypoint for a validation of said constraint by an FMS flight computer, taking account of the transition between the instances of application by the aerodyne of the flight presets prevailing before the resumption of the automatic following of the flight plan and those newly provided by the flight computer during this same resumption, and validating said constraint in the case where it would not be complied with by the aerodyne if it reached the imposed waypoint by following said forecast of displacement, doing so in order that it remains taken into account in subsequent automatic following of the flight plan.
2. The method as claimed in claim 1 , wherein the forecast of displacement of the aerodyne up to the imposed waypoint, taking account of the transition between the instances of application by the aerodyne of the flight presets prevailing before the resumption of the automatic following of the flight plan and those newly provided by the flight computer during the same resumption is made according to a first order variation model.
3. The method as claimed in claim 1 , applied to the validation of an altitude constraint, wherein the forecast of displacement of the aerodyne up to the imposed waypoint taking account of the transition between the instances of application by the aerodyne of the flight presets prevailing before the resumption of the automatic following of the flight plan and those newly provided by the flight computer during the same resumption is limited to a vertical trajectory forecast.
4. The method as claimed in claim 3 , wherein the vertical trajectory forecast is made by assuming that the aerodyne has, during the vertical speed transition between its initial value Vz 0 before the automatic following of the flight plan by the computer ( 30 ) and its final value Vz f imposed by the flight computer, a constant ground speed and a vertical speed Vz according to a first order variation model complying with the relation:
Vz =( Vz 0 −Vz f ) e −t/τ) +Vz f
t being the time variable and τ a constant characteristic of the aerodyne steered by its automatic pilot or its flight director, according to a law of acquisition of a vertical speed preset Vz f .
5. The method as claimed in claim 3 , comprising:
estimating the date t seq of passage of the aerodyne at the constrained waypoint on the basis of the distance Δdist 0 between the position of the aerodyne upon the instigation of the automatic following of the flight plan and the position of the constrained waypoint by assuming that the aerodyne has a constant ground speed GrdSpd and by applying the relation:
t
seq
=
Δ
dist
0
GrdSpd
estimating the difference in altitude ΔZ seq of the aerodyne between the predicted altitude at the constrained waypoint and the value of the altitude constraint, by assuming that the vertical speed of the aerodyne changes, from its initial value Vz 0 before the automatic following of the flight plan by the flight computer to its final value Vz f corresponding to the flight plan and imposed by the computer, by following a first order variation model complying with the relation:
Δ
z
seq
=
-
τ
(
Vz
0
-
Vz
f
)
(
1
-
ⅇ
(
-
t
seq
τ
)
)
+
Vz
f
·
t
seq
τ being a constant characteristic of the aerodyne steered by its automatic pilot or its flight director, according to a law of acquisition of a vertical speed preset Vz f , and
validating the taking into account of the altitude constraint in the case of compliance with the inequality:
|Δ z seq |>|Δz 0 |−Δz marg
Δz marg being a safety altitude margin.
6. The method as claimed in claim 4 , wherein the initial value V z0 of the speed of descent of the aerodyne at the moment of the resumption of the automatic following of the flight plan by the flight computer, taken into consideration by the validation system, is measured, at the moment of the instigation of the automatic following of the flight plan, by vertical speed sensors equipping the aerodyne.
7. The method of claim 1 , wherein the flight computer is a Flight Management System (FMS) computer.