Method and apparatus for assisting piloting of an aircraft to respect a required time of arrival
By calculating the effective velocity curve in the flight management computer and using correction coefficients to correct the aircraft's setpoint velocity, the problem of the aircraft's difficulty in complying with RTA constraints is solved, and effective compliance with RTA and consistency of flight strategy are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- AIRBUS OPERATIONS (SAS)
- Filing Date
- 2019-04-10
- Publication Date
- 2026-07-21
Smart Images
Figure CN110400492B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method and system for assisting aircraft piloting, the method and system being designed to assist in adhering to the arrival time required to reach a waypoint during aircraft flight. Background Technology
[0002] The piloting of aircraft, particularly civil or military transport aircraft, is typically conducted along a flight plan comprising a set of waypoints defined in three-dimensional space. The aircraft must be guided along the flight plan by adhering to a maximum margin of positional error relative to the segments connecting the different waypoints. Increasingly, especially in high-traffic areas, some waypoints in the flight plan include required Time-of-Arrival (RTA) constraints mandated by air traffic control to ensure compliant separation between different aircraft. In this case, the aircraft must also be guided along the flight plan by adhering to a maximum margin of time error relative to the RTA constraints of the waypoints that include such constraints.
[0003] Generally, before flight, the aircraft's speed is planned using a cost index. This cost index typically corresponds to a coefficient between 0 and 100, such that when the coefficient equals 100, the planned speed corresponds to the aircraft's maximum operating speed Vmax, and when the coefficient equals 0, the planned speed corresponds to the aircraft's minimum operating speed Vmin. When the cost index equals a value k between 0 and 100, the planned speed is equal to:
[0004] Vmin+k(Vmax-Vmin) / 100.
[0005] Before flight, the pilot inputs a cost index into the aircraft's flight management computer, such as an FMS (Flight Management System) type computer. During flight, the FMS controls the aircraft's guidance computer based on the flight plan and the cost index. If the pilot receives an RTA (Responsible Time of Arrival) constraint from air traffic control at a waypoint on the flight plan, he or she inputs this constraint into the FMS. The FMS then calculates the aircraft's estimated time of arrival at this waypoint by considering the current value of the cost index. This estimated time of arrival is commonly referred to as the ETA. Document US 5.121.325 describes a system that enables the determination of an aircraft's estimated time of arrival at a specific point. The FMS compares this estimated time of arrival (ETA) with the RTA constraint. If the difference between the ETA and RTA exceeds a predetermined time threshold (e.g., 10 seconds), the FMS calculates a new value for the cost index that allows the difference to be reduced below this predetermined time threshold, and then the FMS controls the guidance computer based on this new value of the cost index.
[0006] For some flights of an aircraft, a nominal speed profile comprising several flight segments is defined before the aircraft takes off. A nominal speed is defined for each flight segment. Minimum and maximum speeds are also defined for each flight segment. This speed profile allows for different flight strategies to be defined for different flight segments. Figure 2The diagram illustrates an example of a flight plan including this nominal speed curve 20. This nominal speed curve comprises five segments S1 to S5, with the planned altitude 30 of the aircraft for these segments shown in the attached diagram. Segment S1, named "LONGRANGE," is a cruise flight segment at a constant altitude. The nominal speed for this segment is 250 knots, or approximately 463 km / h. This speed is close to the center of the permissible speed range between Vmin = 180 knots (approximately 333 km / h) and Vmax = 300 knots (approximately 555 km / h), allowing for optimized fuel consumption. Segment S2, named "MAX ENDUR," is a climb flight segment. The nominal speed for this segment is 190 knots, or approximately 352 km / h. This speed falls more in the lower part of the permissible speed range between Vmin = 180 knots (approximately 333 km / h) and Vmax = 300 knots (approximately 555 km / h), allowing the aircraft to maintain flight for as long as possible while ensuring a suitable rate of climb. Segment S3, designated "Long Range," is another cruise segment at constant altitude. The nominal speed for this segment is 235 knots (approximately 435 km / h). This speed is close to the center of the permissible speed range between Vmin = 195 knots (approximately 361 km / h) and Vmax = 290 knots (approximately 537 km / h), allowing for optimized fuel consumption. Segment S4, designated "Maximum Speed (MAX SPD)," is a descent segment. The nominal speed for this segment is 290 knots (approximately 546 km / h). This speed corresponds to the upper limit of the permissible speed range between Vmin = 195 knots (approximately 361 km / h) and Vmax = 290 knots (approximately 546 km / h) to ensure a suitable rate of descent. Segment S5, designated "Long Range," is also a cruise segment at a constant altitude. The nominal speed for this segment is 265 knots, or approximately 490 km / h. This speed is close to the center of the permissible speed range between Vmin = 195 knots (approximately 361 km / h) and Vmax = 295 knots (approximately 546 km / h), allowing for optimized fuel consumption.
[0007] When the flight management computer controls the aircraft's guidance based on a flight plan that includes such a nominal speed profile, if the aircraft's pilot receives an RTA constraint from air traffic control and inputs this RTA constraint into the flight management computer, then, as previously instructed, the flight management computer modifies the speed profile, that is, modifies it by applying the full computational cost index to the flight plan. This has the effect of smoothing speed variations between different segments of the flight plan, and subsequently, the flight plan modified to take the RTA constraint into account no longer considers the strategy selected with respect to the speed profile. Therefore, in a particular instance, for a flight guided by... Figure 2 The speed curves shown, and considering that each segment from S1 to S5 has a length of 100 Nm (approximately 185.2 km), the time t5 corresponding to the aircraft's arrival at the end of segment S5 is, for example, equal to 14 h04. Assuming the pilot receives an RTA constraint of 14 h00 for the waypoint at the end of segment S5 and inputs this constraint into the flight management computer, the flight management computer calculates the cost index that allows arrival at this waypoint at time t5, which is equal to 14 h00. Figure 3 The diagram illustrates a suitably modified flight plan. In this particular instance, the cost index calculated by the flight management computer will be 58. As a result, the speed Vcalc calculated by the flight computer for each segment to comply with RTA constraints will be equal to Vcalc = Vmin + 0.58(Vmax - Vmin). Once the cost index is calculated, these calculated speed values for each segment depend only on the threshold values Vmax and Vmin. They will equal:
[0008] For segment S1: Vcalc = 249.6 kts
[0009] For segment S2: Vcalc = 249.6 kts
[0010] For segment S3: Vcalc = 250.1 kts
[0011] For segment S4: Vcalc = 250.1 kts
[0012] For segment S5: Vcalc = 248.6 kts
[0013] The differences between the calculated speeds corresponding to different flight segments are significantly reduced relative to the differences between the nominal speeds corresponding to these different flight segments. Therefore, the speed profiles of the flight plan modified to comply with RTA constraints are completely different from the nominal speed profiles. It will now be expected that the speed profiles of the modified flight plan conform to the different flight strategies defined for the different flight segments of the flight plan. Summary of the Invention
[0014] The purpose of this invention is to overcome the aforementioned shortcomings. This invention relates to a method for assisting the piloting of an aircraft, the method being designed to assist the piloting of the aircraft in adhering to the arrival time required to reach a waypoint during flight according to a predetermined flight plan, the flight plan including a nominal speed profile of the aircraft, the nominal speed profile comprising at least two distinct flight segments, each flight segment defining a nominal speed, a maximum speed, and a minimum speed of the aircraft.
[0015] It is noteworthy that this method includes the following steps performed by the processing unit of the aircraft's flight management computer:
[0016] a) Determine the effective speed profile of the aircraft, which includes flight segments similar to those of the nominal speed profile. This determination includes the following sub-steps:
[0017] a3) Calculate a correction term for each segment of the nominal speed curve, the correction term corresponding to the product of a correction factor and the difference between: on the one hand, the maximum or minimum speed defined for this segment, and on the other hand, the nominal speed corresponding to this segment; the correction factor is a common correction factor for all segments of the nominal speed curve; and
[0018] a4) Calculate a setpoint speed for each segment of the effective speed curve, wherein the setpoint speed is equal to the sum of the nominal speed defined for the corresponding segment of the nominal speed curve and the correction term calculated for the corresponding segment of the nominal speed curve.
[0019] b) The guidance computer of the aircraft is controlled to guide the aircraft according to the effective speed curve determined in step a).
[0020] Therefore, the effective speed curve that allows adherence to the arrival time required to reach waypoints ensures that the setpoint speed calculated for each flight segment corresponds to the nominal speed of the corresponding flight segment on the nominal speed curve, corrected by a correction term. This correction term corresponds to the product of a common correction factor for all segments and the difference between the speed limit (maximum or minimum) corresponding to this segment and the nominal speed corresponding to this segment. This difference corresponds to the margin between the nominal speed and the speed limit. Thus, the speeds of different segments of the effective speed curve are all based on the nominal speeds of the corresponding segments of the nominal speed curve, and the correction terms corresponding to different segments allow for consistent correction of the speeds of different segments so that the ratios between the speed margins corresponding to different segments of the effective flight plan are similar to the ratios between the speed margins corresponding to different segments of the nominal flight plan. This allows for the acquisition of an effective speed curve consistent with the nominal speed curve from the perspective of the individual speeds corresponding to different flight segments.
[0021] In one embodiment, step a) includes a sub-step a1) of calculating the estimated time of arrival at the waypoint by assuming that the aircraft is flying according to the nominal speed curve, and in step a3), the difference between one of the maximum speed or the minimum speed defined for the segment on one hand and the nominal speed corresponding to this segment on the other hand is selected to be equal to:
[0022] - When the estimated time of arrival at a waypoint is later than the required time of arrival, it is the difference between the maximum speed and the nominal speed defined for this segment; and
[0023] - When the estimated arrival time at a waypoint is earlier than the required arrival time, it is the difference between the minimum speed and the nominal speed required for this segment.
[0024] Advantageously, step a) further includes:
[0025] - Sub-step a2) prior to sub-step a3) selecting the value of the common correction coefficient for all segments of the speed curve; and
[0026] - Sub-step a5) calculates the estimated arrival time to the waypoint by assuming that the aircraft flies according to the effective speed curve including the setpoint speed value calculated in sub-step a4).
[0027] And iteratively execute the sub-steps a2), a3), a4), and a5) until the difference between the estimated arrival time and the required arrival time at the waypoint is lower than a predetermined time threshold.
[0028] Similarly advantageously, in the sub-step a2), the value of the correction coefficient common to all segments of the speed curve is selected by using a dichotomy method.
[0029] Specifically, the dichotomy method is a weighted dichotomy method based on the difference between the estimated arrival time and the required arrival time at the waypoint.
[0030] Preferably, the value of the correction coefficient is between 0 and 1.
[0031] The present invention also relates to a system for assisting aircraft piloting to ensure that the aircraft adheres to the arrival time required to reach a waypoint during flight according to a predetermined flight plan, the flight plan including a nominal speed profile of the aircraft, the nominal speed profile comprising at least two distinct flight segments, for each of the flight segments defining a nominal speed, a maximum speed, and a minimum speed of the aircraft. It is noteworthy that the system includes:
[0032] - A flight management computer, the flight management computer including a processing unit configured to determine the effective speed profile of the aircraft, the effective speed profile including flight segments similar to the nominal speed profile, the determination of the effective speed profile including:
[0033] For each segment of the nominal speed curve, a correction term is calculated, which corresponds to the product of a correction factor and the difference between: on the one hand, the maximum or minimum speed defined for this segment, and on the other hand, the nominal speed corresponding to this segment; the correction factor is a common correction factor for all segments of the nominal speed curve; and
[0034] For each segment of the effective speed curve, a setpoint speed is calculated, the setpoint speed being equal to the sum of the nominal speed defined for the corresponding segment of the nominal speed curve and the correction term calculated for the corresponding segment of the nominal speed curve.
[0035] - The guidance computer of the aircraft, which is configured to guide the aircraft according to the effective speed curve determined by the processing unit of the flight management computer.
[0036] The present invention also relates to an aircraft that includes such a pilot assistance system. Attached Figure Description
[0037] The invention will be better understood by reading the following description and studying the accompanying drawings.
[0038] Figure 1This refers to an aircraft that includes a pilot assistance system according to the present invention;
[0039] As already described, Figure 2 The nominal speed curve of the aircraft's flight plan is shown;
[0040] As already described, Figure 3 A speed curve according to the prior art is shown, which allows for compliance with RTA constraints;
[0041] Figure 4 The speed curves determined by the flight assistance system of the aircraft according to the present invention are shown;
[0042] Figure 5 This is a block diagram of the flight assistance system for an aircraft according to the present invention. Detailed Implementation
[0043] exist Figure 5 The system 10 schematically shown is an embodiment of the present invention. The system is embedded in, for example... Figure 1 The illustrated aircraft 1 (particularly a civil or military transport aircraft) is configured to assist in flying according to a flight plan by adhering to the Time of Arrival (RTA) required to reach the waypoints in the flight plan. This system is installed, for example, in the avionics bay 2 of the aircraft. System 10 includes the aircraft's flight management computer 12, particularly an FMS (Flight Management System) type computer. This flight management system computer includes a processing unit 14. The flight management system computer also includes undisplayed memory, which is provided to store at least one flight plan of the aircraft. The flight management computer 12 is linked at its input to a human-machine interface 16, which is preferably located in the cockpit 3 of the aircraft. This human-machine interface corresponds in particular to components including a screen, keyboard, and / or instruction units (e.g., MCDU (Multipurpose Control and Display Unit) type units). The output of the flight management computer 12 is linked to the input of the aircraft's guidance computer 18, particularly an FG (Flight Guidance) type computer. This guidance computer is provided, for example, to guide the aircraft in either an automatic guidance mode (when the aircraft is engaged with autopilot) or a manual guidance mode (e.g., by means of a flight guide).
[0044] In operation, before the aircraft takes flight, the pilot defines a nominal flight plan for the flight and inputs this plan into the flight management computer 12 via the human-machine interface 16. When applicable to this planned flight, the nominal flight plan includes a nominal speed profile of the aircraft, comprising at least two distinct flight segments, for which a nominal speed, maximum speed, and minimum speed are defined. The flight management computer stores the nominal flight plan and the nominal speed profile in its memory. This nominal speed profile, for example, is described... Figure 2 The nominal speed curve 20 shown allows for different flight strategies to be defined for different flight segments.
[0045] During flight, the flight management computer controls the aircraft's guidance computer 18 to guide the aircraft according to the nominal flight plan and nominal speed profile. Sometimes, air traffic control may need to send the required time of arrival (RTA) associated with waypoints in the flight plan to the aircraft's pilot. If the pilot approves this constraint, he or she inputs it into the flight management computer via the human-machine interface 16. The flight management computer 12 then determines the effective speed profile 21 of the aircraft that allows it to comply with the RTA constraint, and then controls the aircraft's guidance computer 18 to guide the aircraft according to the appropriately determined effective speed profile. This effective speed profile includes flight segments similar to those of the nominal speed profile. The flight management computer 12 determines the effective speed profile by including the following steps:
[0046] a3) Calculate a correction term for each segment of the nominal speed curve, which corresponds to the product of a correction factor and the difference between: on the one hand, the maximum or minimum speed defined for this segment, and on the other hand, the nominal speed corresponding to this segment; this correction factor is a common correction factor for all segments of the nominal speed curve; and
[0047] a4) Calculate the setpoint speed for each segment of the effective speed curve. The setpoint speed is equal to the sum of the nominal speed defined for the corresponding segment of the nominal speed curve and the correction term calculated for the corresponding segment of the nominal speed curve.
[0048] Specifically, in step a1) prior to step a3), the flight management computer 12 calculates the estimated time of arrival (ETA) to the waypoint by assuming the aircraft is flying according to the nominal speed curve. Then, in step a3), the difference between the maximum or minimum speed defined for this segment on one hand and the nominal speed corresponding to this segment on the other hand is selected to be equal to:
[0049] - When the estimated time of arrival at the waypoint is later than the required time of arrival (RTA), it is the difference between the maximum speed and the nominal speed for this segment; and
[0050] - When the estimated arrival time to a waypoint is earlier than the required arrival time (RTA), it is the difference between the minimum speed and the nominal speed required for this segment.
[0051] exist Figure 2 In the example shown, assuming the pilot receives an RTA constraint of 14h00 for the waypoint at the end of segment S5 and inputs this constraint into the flight management computer, the flight management computer calculates the estimated time of arrival (ETA) to this waypoint. This estimated time of arrival corresponds to the time t5 shown in the figure. As previously indicated, this time t5, corresponding to the aircraft's arrival at the end of segment S5, is equal to 14h04. Therefore, the estimated time of arrival (ETA) is later than the required time of arrival (RTA). As a result, in step a3), for each segment of the speed profile, the correction term and correction coefficient correspond to the product of the difference between the maximum speed defined for this segment and the nominal speed corresponding to this segment.
[0052] Advantageously, in step a2) after step a1) and before step a3), the flight management computer selects a value for a common correction factor for all segments of the speed curve, and in step a5) after step a4), the flight management computer calculates the estimated time of arrival (ETA) to the waypoint by assuming that the aircraft is flying according to an effective speed curve including the setpoint speed values calculated in step a4). The flight management computer repeats steps a2), a3), a4), and a5) each time a new value for the correction factor is selected in step a2), until the difference between the ETA and the required time of arrival (RTA) to the waypoint is below a predetermined time threshold. This time threshold is selected such that the difference between the ETA and the RTA to the waypoint is low enough that the RTA constraint is considered satisfactory. This threshold may, for example, be selected to be equal to 10 seconds.
[0053] In a particular embodiment, in step a2), the value of the common correction factor for all segments of the speed curve is selected by using a bisection method. Advantageously, the bisection method weights the values based on the difference between the estimated time of arrival (ETA) and the required time of arrival (RTA) at the waypoint, which reduces the number of iterations in steps a2) to a5) necessary to determine the correction factor.
[0054] In the specific case of the examples considered above, as previously indicated, for each segment of the speed curve, the correction term and correction factor correspond to the product of the difference between the maximum speed defined for that segment and the nominal speed corresponding to that segment. Given the maximum and nominal speed values for different segments, the flight management computer determines the correction factor to be equal to 0.15. Therefore, for each segment of the speed curve, the setpoint speed Vtgt calculated by the flight management computer is equal to Vtgt = Vnom + 0.15(Vmax - Vnom). Figure 4 The setpoint speed of the effective speed curve 21 from segment S1 to segment S5, as shown, is therefore equal to:
[0055] For segment S1: Vtgt = 257.5kts
[0056] For segment S2: Vtgt = 206.5kts
[0057] For segment S3: Vtgt = 243.3kts
[0058] For segment S4: Vtgt = 290.0 kts
[0059] For segment S5: Vtgt = 269.5kts
[0060] Therefore, the relative values of the speeds corresponding to different flight segments S1 to S5 with respect to the nominal speed curves remain basically unchanged.
[0061] Given the formula for calculating the setpoint velocity, the value of the correction coefficient is between 0 and 1.
[0062] According to the first alternative, the nominal speed curve, which uses the nominal speed value, maximum speed value, and minimum speed value to calculate the setpoint speed of the effective speed curve, corresponds to the nominal speed curve of the optimal flight plan defined before the aircraft takes flight. The flight management computer then stores the optimal flight plan and its optimal speed curve on one hand, and the effective flight plan and its effective speed curve on the other. Before flight begins, the flight management computer 12 copies the optimal flight plan and its optimal speed curve to the effective flight plan and its effective speed curve, and controls the guidance computer 18 based on the effective flight plan and the effective speed curve. If, during flight, the pilot inputs RTA constraints into the flight management computer, the flight management computer calculates the setpoint speed value of the effective speed curve as described above (in step a4), and the effective speed curve used to guide the aircraft is thus modified to take the RTA constraints into account. If new RTA constraints are input into the flight management computer during the same flight of the aircraft, the new setpoint speed values of the effective speed curve are calculated based on the nominal speed, maximum speed, and minimum speed of the nominal speed curve that were defined before the flight and stored in the memory of the flight management computer.
[0063] According to the second alternative, the nominal speed curve, which uses the nominal speed value, maximum speed value, and minimum speed value to calculate the setpoint speed of the effective speed curve, corresponds to the speed curve of the aircraft's current flight plan. The flight management computer then stores a single flight plan and its speed curve. Before flight begins, when the pilot inputs the optimal flight plan and its optimal speed curve into the flight management computer 12, this optimal flight plan and its optimal speed curve are directly stored in memory, thus corresponding to the current flight plan and its speed curve. The flight management computer 12 controls the guidance computer 18 based on the current flight plan and its effective speed curve. If, during flight, the pilot inputs a first RTA constraint into the flight management computer, the flight management computer calculates the setpoint speed value of the effective speed curve in step a4) as previously indicated, by assuming that the optimal flight plan and its optimal speed curve correspond to the current flight plan and its speed curve. This speed curve of the current flight plan then corresponds to the nominal speed curve stored before flight begins. The effective speed curve determined by the flight management computer is copied into the speed curve of the current flight plan to allow the aircraft to be guided according to this effective speed curve. If new RTA constraints are input into the flight management computer during the same flight period, a new setpoint velocity value for the effective velocity curve is calculated by again assuming that the optimal flight plan and its optimal velocity curve correspond to the current flight plan and its velocity curve. This velocity curve then corresponds to the effective velocity curve calculated after receiving the previous RTA constraints. This takes into account that the relative values of the setpoint velocities corresponding to different flight segments remain substantially constant when calculating the effective velocity curve from the nominal velocity curve, which is acceptable.
Claims
1. A method for assisting the piloting of an aircraft (1) to comply with the time of arrival (RTA) required to reach a waypoint during flight according to a predetermined flight plan, the flight plan comprising a nominal speed profile (20) of the aircraft, the nominal speed profile comprising at least two distinct flight segments (S1…S5), for each of the flight segments defining a nominal speed (Vnom), a maximum speed (Vmax), and a minimum speed (Vmin) of the aircraft. The method is characterized in that it includes the following steps performed by the processing unit (14) of the flight management computer (12) of the aircraft: a) Determine the effective speed profile (21) of the aircraft, which includes flight segments (S1…S5) similar to those of the nominal speed profile (20), the determination comprising the following sub-steps: a3) Calculate a correction term for each segment of the nominal speed curve, the correction term corresponding to the product of a correction factor and the difference between: on the one hand, the maximum speed (Vmax) or minimum speed (Vmin) defined for this segment, and on the other hand, the nominal speed (Vnom) corresponding to this segment; the correction factor is a common correction factor for all segments (S1…S5) of the nominal speed curve (20); and a4) Calculate the setpoint speed (Vtgt) for each segment of the effective speed curve (21), the setpoint speed being equal to the sum of the nominal speed (Vnom) defined for the corresponding segment of the nominal speed curve (20) and the correction term calculated for the corresponding segment of the nominal speed curve. b) The guidance computer (18) of the aircraft is controlled to guide the aircraft according to the effective speed curve (21) determined in step a).
2. The method according to claim 1, characterized in that, Step a) includes a sub-step a1) of calculating the estimated time of arrival (ETA) to the waypoint by assuming that the aircraft is flying according to the nominal speed curve (20), and in step a3), the difference between one of the maximum speed (Vmax) or the minimum speed (Vmin) defined for the segment on the one hand and the nominal speed (Vnom) corresponding to this segment on the other hand is selected as: - When the estimated time of arrival (ETA) to the waypoint is later than the required time of arrival (RTA), it is equal to the difference between the maximum speed (Vmax) and the nominal speed (Vnom) defined for this segment; and - When the estimated time of arrival (ETA) to the waypoint is earlier than the required time of arrival (RTA), it is equal to the difference between the minimum speed (Vmin) and the nominal speed (Vnom) defined for this segment.
3. The method according to claim 2, characterized in that, Step a) further includes: - Sub-step a2) prior to sub-step a3) selecting the value of the common correction coefficient for all segments of the speed curve; and - Sub-step a5) calculates the estimated time of arrival (ETA) to the waypoint by assuming that the aircraft flies according to the effective speed curve (21) including the setpoint speed value (Vtgt) calculated in sub-step a4). And iteratively execute the sub-steps a2), a3), a4), and a5) until the difference between the estimated time of arrival (ETA) and the required time of arrival (RTA) at the waypoint is lower than a predetermined time threshold.
4. The method according to claim 3, characterized in that, In sub-step a2), the value of the correction coefficient common to all segments of the speed curve is selected by using a bisection method.
5. The method according to claim 4, characterized in that, The dichotomy method is a weighted dichotomy based on the difference between the estimated time of arrival (ETA) and the required time of arrival (RTA) at the waypoint.
6. The method according to any one of the preceding claims, characterized in that, The value of the correction coefficient is between 0 and 1.
7. A pilot assistance system (10) for assisting the piloting of an aircraft (1) in adhering to the time of arrival (RTA) required to reach a waypoint during flight according to a predetermined flight plan, the flight plan comprising a nominal speed profile (20) of the aircraft, the nominal speed profile comprising at least two distinct flight segments (S1…S5), each flight segment defining a nominal speed (Vnom), a maximum speed (Vmax), and a minimum speed (Vmin) of the aircraft, characterized in that, The system includes: - A flight management computer (12), the flight management computer including a processing unit (14) configured to determine the effective speed curve (21) of the aircraft, the effective speed curve including flight segments (S1…S5) similar to the flight segments of the nominal speed curve (20), the determination of the effective speed curve including: A correction term is calculated for each segment of the nominal speed curve, the correction term corresponding to the product of a correction factor and the difference between: on the one hand, the maximum speed (Vmax) or minimum speed (Vmin) defined for this segment, and on the other hand, the nominal speed (Vnom) corresponding to this segment; the correction factor is a common correction factor for all segments (S1…S5) of the nominal speed curve (20); and For each segment of the effective speed curve (21), a setpoint speed (Vtgt) is calculated, the setpoint speed being equal to the sum of the nominal speed (Vnom) defined for the corresponding segment of the nominal speed curve (20) and the correction term calculated for the corresponding segment of the nominal speed curve. - The guidance computer (18) of the aircraft is configured to guide the aircraft according to the effective speed curve (21) determined by the processing unit (14) of the flight management computer (12).
8. An aircraft (1) comprising a pilot assistance system (10) according to claim 7.