GB2375748A

GB2375748A - System and method for monitoring the performance of an aircraft during a take-off run

Info

Publication number: GB2375748A
Application number: GB0112545A
Authority: GB
Inventors: David Zammit-Mangion; Martin Ewart Eshelby
Original assignee: Cranfield University
Current assignee: Cranfield University
Priority date: 2001-05-24
Filing date: 2001-05-24
Publication date: 2002-11-27
Anticipated expiration: 2021-05-24
Also published as: GB2375748B; CA2447638A1; AU2002310689A1; WO2002097764A2; US7158052B2; WO2002097764A3; GB0112545D0; US20040260434A1; EP1393284A2

Abstract

A system for monitoring the performance of an aircraft during a take-off run comprises data acquisition means, a data processing device and a display device. During a take-off run, the data acquisition means records values of acceleration and relays these values to the data processing means. The data processing means then performs calculations to determine the performance of the aircraft during the run and compares the results with predetermined standard levels of performance. Predictions of future performance during the run are also made, and the results are displayed to give the pilot guidance as to whether the take-off run can be safely completed or should be aborted.

Description

A METHOD AND SYSTEM FOR MONITORING THE PERFORMANCE OF AN AIRCRAFT DURING THE TAKE-OFF MANOEUVRE The present invention relates to a method and system for monitoring the performance of an aircraft during the take-off manoeuvre.

The performance of an aircraft during take-off is critical to safety. The aircraft must of course reach the required take-off speed before it reaches the end of the runway in order to become airborne. If, however. it under-performs, for example because it suffers an engine failure early in the take-off manoeuvre, it may be unable to reach the take-off speed in the distance available. The pilot would then have to abort the take-off and bring the aircraft to a halt on the remaining runway.

As the aircraft accelerates down the runway, the distance to the end of the runway decreases and the distance needed to stop the aircraft increases. There is therefore a point during the take-off run, where these distances become equal, beyond which the aircraft will not be able to stop in the remaining distance available if the run is aborted. This defines a point of no return on the runway to which the decision speed, V,, is linked. The allowable distance from brake release in which V, is to be achieved is herein referred to as the Critical Distance, D,,,,, Once past the critical distance, the pilot is required to complete the take-off manoeuvre. even if the aircraft suffers an engine failure. On the other hand, if the aircraft is seriously under-performing, and will not achieve V, within Dent'the pilot should be advised and have the option to abort the take-off before reaching the point of no return.

In practice, pilots have no objective means for assessing directly how far they have travelled down the runway. In current procedure, they base their decision whether or not to continue with a take-off on the basis of the aircraft's speed relative to V,. This implicitly assumes that the aircraft is performing normally and, on reaching V,, it will have travelled no more than the critical distance.

This procedure is generally satisfactory for situations where the aircraft performs normally up to V,. since in such cases the acceleration of the aircraft will be adequate and reasonably consistent. It is also satisfactory for situations where the aircraft suffers a sudden reduction

of performance, such as that caused by an engine failure, since aircrew are trained to recognise and respond in an appropriate manner to such failures. However, subtle underperformance such as may be caused, for example, by dragging brakes, a burst tyre, mis-set flaps, or overloading, may not be noticeable. In this case, the acceleration of the aircraft would be less than normal, with the result that the aircraft may have passed the critical distance before it reaches V,. In these circumstances, the safety of the aircraft may be compromised.

There is, therefore, a need for a system for monitoring the performance of an aircraft during take-off, which can inform the pilot of the progress of the run and alert him or her to any significant under-performance. In this way, the pilot would be better and more objectively informed of such under-performance at a relatively early stage in the take-off run and be able to take appropriate action.

Various methods of monitoring the take-off performance of an aircraft have been proposed previously. These include methods that are non-predictive, which compare achieved performance instantaneously with a predetermined model describing threshold performance. Such methods can produce only a limited warning of any deterioration of performance. Predictive methods, which are capable of foreseeing the situation at a future point in the take-off, are therefore preferable. However, past attempts of predictive take-off monitoring have usually included aircraft equations of motion that need to be defined under the specific conditions of the take-off being monitored. The difficulty in defining the coefficients of those equations during the take-off run may seriously compromise the accuracy of the prediction.

Prior art monitoring systems have also frequently failed to provide the pilot with information regarding the aircraft's performance in a way that is appropriate and easily assimilated. In some cases, the information has been displayed in an over-complicated

manner that is difficult to interpret whilst engaged in the high workload environment of the 1- z : l L- take-off manoeuvre. In other cases, the information may not translate unequivocally to a particular situation and may, therefore, be misleading. In yet other cases, the information has been reduced to a simple stop/go indication, which denies the pilot any discretion and fails to provide sufficient quantitative information.

It is an object of the present invention to provide a method and system for monitoring the performance of aircraft during the take-off manoeuvre that mitigates at least some of the aforesaid disadvantages.

According to the present invention there is provided a method of monitoring the performance of an aircraft during the take-off manoeuvre. The method includes the following steps: monitoring the progress of the take-off run, extrapolating from the monitored progress to predict the future progress of the run, comparing the predicted progress with a predetermined standard and providing an indication of the performance based on that comparison.

By predicting the future progress of the run, using an extrapolation based on the history of the run to that moment, the method is able to provide an early indication of circumstances that might assist in the decision to abandon the take-off attempt. These include the subtle effects of under-performance, which might not otherwise be apparent to the crew. Such information allows the crew time in which to assess the take-off situation before the aircraft reaches the critical distance Dent. This method is sufficiently robust that transient fluctuations in the acceleration of the aircraft, such as may be caused, for example, by running through standing water on the runway, do not seriously affect the prediction. The method, therefore, is more reliable than those relying on instantaneous measurement and provides an effective real-time indication of the performance of the aircraft to significantly enhance the safety of the take-off manoeuvre.

Advantageously. the progress of the take-off run is monitored by collecting data representing the speed of the aircraft and either the distance travelled from the start of the run or the time of measurement. Preferably, the speed of the aircraft and the distance travelled from the start of the run are determined by sensing the acceleration of the aircraft and integrating accordingly with respect to time. The acceleration and/or speed may be sensed using the aircraft s existing inertial navigation system. thereby avoiding the need for additional measuring devices. Alternatively. some other quantity may be sensed directly, such as the ground speed. the airspeed or the distance travelled, or other devices used to measure the acceleration.

Advantageously, the data set is extrapolated to predict the distance the aircraft will have travelled by the time it reaches a predetermined speed, and the predicted distance is compared with a predetermined distance. Preferably, the predetermined speed is the decision speed V, and the predetermined distance is the critical distance Durit.

The achieved performance of the run may be measured by a process of curve-fitting using, for example, the least-squares method. Preferably, a second order polynomial function is fitted to data representing the monitored progress of the run. However, higher order polynomial functions or other functions may also be fitted to the curve.

Preferably, predetermined limits are placed on the coefficients of the polynomial function, to prevent excessive fluctuations in the predicted performance being caused by any transient effects.

Compensation may be applied to the polynomial function to adjust its curvature, so as to take account of known speed-dependent effects, for example the speed-dependent reduction in thrust of a propeller-driven aircraft.

The data representing the monitored progress of the run may be weighted to increase the dependence of the curve-fitting function on more recently acquired data. The prediction of performance will then be influenced more by the recent performance than the earlier performance, and so will reflect more rapidly any changes in performance. Further, the data representing an initial portion of the run may be disregarded during calculation of the curve-fitting function, so that the prediction is not unduly influenced by inconsequential data collected at the start of the run. before the aircraft's motion and the thrust of the engines have stabilised.

Advantageously, the uncertainty in the predicted progress of the take-off run is calculated. zn The uncertainty calculation may be used to control the performance indication: for example, the display may be cancelled if the prediction is too uncertain to be meaningful.

Alternatively, the degree of uncertainty may be shown in the display.

The indication of the aircraft's performance preferably includes indicia representing the magnitude and sign of the comparison of the predicted progress with the predetermined standard. The indication of the aircraft's performance may be displayed in association with

an indication of the aircraft's airspeed and any other parameter that may be considered relevant. This makes the information easy to assimilate, and provides the crew with vital information concerning the performance of the aircraft, without placing excessive demands on their ability to process data.

Data collected during the monitoring process may be recorded for later analysis, so allowing ground staff to assess the performance of the aircraft and to identify any anomaly or trend, so that any necessary remedial action can be taken. The data may also be used to monitor the performance of the crew.

According to a further aspect of the invention there is provided a system for monitoring the performance of aircraft during take-off, the system including data acquisition means, a data processing device and a display device, the system being constructed and arranged to operate according to a method as defined by the preceding statements of invention.

According to a further aspect of the invention there is provided a system for monitoring the performance of aircraft during take-off, the system including data acquisition means, a data processing device and a display device, the system being constructed and arranged to collect data representing the progress of the take-off run, to predict the future progress of the run by a process of extrapolation using the collected data, to compare the predicted progress with a predetermined standard and to provide an indication of the performance based on that comparison.

The data acquisition means may include an accelerometer. an airspeed measurement means and preferably includes the aircraft's inertial navigation system.

The display device may include an analogue-or digitally-generated visual display and is preferably associated with the aircraft's airspeed indicator.

The system may include a data recording device for recording data collected during the monitoring process.

An embodiment of the invention will now be described with reference to the accompanying

drawings, in which : z : l Figure I illustrates schematically some of the key speeds and distances in a typical take-off manoeuvre :

Figures 2 is a plot of speed against distance during take-off for aircraft with different performance characteristics ; Figure 3 illustrates schematically the main components of a monitoring system according to the present invention ; Figures 4 and 5 are flow diagrams illustrating the main steps of a monitoring method according to the invention : Figures 6a to 6d show a cockpit display for use in a system according to the invention.

Some of the key speeds and distances in a typical take-off manoeuvre are shown schematically in Fig. 1. The aircraft starts at rest at the beginning 1 of the runway 2. Takeoff thrust is set, the brakes are released and the aircraft starts to accelerate 3 down the runway.

The aircraft continues to accelerate down the runway, eventually reaching the rotation speed V at which the nose of the aircraft is raised to the take-off attitude, followed moments later by the lift-off speed V LOF- when the aircraft lifts off the ground and starts to climb 4. Obviously, the aircraft must leave the ground before it reaches the end 5 of the runway.

If the aircraft suffers an engine failure or some other problem that might jeopardise safety of the flight, the pilot may decide to abandon the take-off. However, the take-off can only be abandoned during the first part of the take-off run, before the aircraft has passed the critical distance Db, defined by the decision speed, V l'Once the aircraft has passed that point it will be travelling too fast and will have too little distance available to stop before reaching the end of the runway 5, and the take-off must therefore be continued.

In the present invention, it is assumed that if the aircraft is to achieve the lift-off speed VLOF before it reaches the end 5 of the runway, it must have attained the decision speed V, by the time it reaches the critical distance D,,. If it is apparent that the aircraft will not attain the decision speed V, before it has travelled the critical distance Dent'the crew need to be informed as early as possible so that they can take the appropriate action. Normally. the aircraft will attain the decision speed V, well before it has travelled the critical distance Durit.

In the present invention the performance of the aircraft is monitored continuously during the take-off run, by monitoring the speed and the distance it has travelled from the beginning of the runway. These measurements are then used to predict. by a process of extrapolation. the distance the aircraft will have travelled by the time it reaches the decision speed V,. The predicted distance D, is then compared with the critical distance Dent and the difference information is presented to the pilot.

The process described above is illustrated in Fig. 2. Fig. 2 is a graph of the aircraft's airspeed V against the distance D it has travelled down the runway. The decision speed V, and the critical distance Dent are marked.

The central line 6 represents a performance curve that is just sufficient to achieve the decision speed V, at the critical distance Dew assuming that the performance of the aircraft remains constant throughout the take-off run. This is referred to as the'net'performance curve. It can be seen that the speed increases from V=0 at D=0 to V, at Den !' The net curve 6 therefore represents a minimum acceptable performance of the aircraft during take-off.

The graph includes a second line 7 that represents the typical or'gross'performance of an aircraft during a normal take-off. It can be seen that the gross performance curve is significantly better than the net performance curve 6, since'net'performance is'gross' performance factored by a statistical factor of safety.

In this example, the first part 7a of the curve. which is shown as a solid line, represents a set of measurements of V and D made during a take-off run. up to a moment 8 that, in this example. represents the present position and speed of the aircraft. The second part 7b of the curve, shown as a broken line, is an extrapolation (prediction), which represents the future progress of the aircraft as it accelerates up to the decision speed V,. It can be seen that according to the extrapolation, the decision speed V, will be reached at a predicted distance D, where D, < Dmt. This implies that the performance is satisfactory.

The graph in Fig. 2 also includes a third line 9 that represents the progress of an aircraft that is under-performing and has reduced acceleration. It can be seen that the curve is significantly less than the net performance curve 6.

In this example, the first part 9a of the curve, which is shown as a solid line, again represents a set of measurements of V and D made during the take-off run, up to a moment 10 that represents the present position and speed of the aircraft. The second part 9b of the curve, shown as a broken line, is an extrapolation (prediction), which represents the future progress of the aircraft as it accelerates towards the decision speed V,. It can be seen that according to the extrapolation, the decision speed V, will be reached at a predicted distance D/where D,' > Dc,,t.

The extrapolation therefore provides an indication that the aircraft will be unable to achieve the decision speed V, before it reaches the critical distance Dent. This implies that there would be insufficient distance available either to continue to a safe take-off or to stop from the decision speed. V,. It should be noted that because under-performance is detected well before the aircraft reaches the critical distance D,,,,, the decision can be taken to abandon the take-off while there is still a sufficient length of runway available for the aircraft to be brought to a standstill.

The main components of a monitoring system according to the present invention are shown schematically in Figure 3. The system includes a data acquisition unit 20, a data processing unit 22. a display device 24 and optionally a data recording device 26, the data processing unit 22 being connected to the other three components. The data acquisition unit 20 may be connected to motion sensing devices. for example accelerometers, which may be part of the aircraft's existing inertial navigation system. The data acquisition unit 20 may also be connected to other sensors for detecting variables such as airspeed. engine thrust and so on. Output data from the data acquisition unit is transmitted to the data processing unit 22 for analysis.

The data processing unit 22 consists of a computer or dedicated digital processor. It uses information received from the data acquisition unit 20 to determine the speed and the distance of the aircraft from the start of the take-off run. This may be done for example by integrating the acceleration data to determine the aircraft's speed, and integrating the speed data again to determine the distance travelled. These are routine mathematical processes. which will not be described further. The additional data required by the data processing

unit 22 includes the values of the critical distance D, and the decision speed V That I , t information is input into the unit before the take-off run commences.

The data processing unit 22 applies a curve fitting function to the sets of distance and speed data, and then extrapolates from that function to predict the distance D, the aircraft will have travelled by the time it reaches the decision speed V,. This predicted distance D, is compared with the predetermined critical distance D,,,, and the result of that comparison is displayed on the display device 24. This procedure is repeated at predetermined time intervals using new data collected by the data acquisition unit 20, the display being modified according to the revised prediction of D 1 until the speed reaches V,. After that speed is reached, the pilot is committed to the take-off and the display is therefore cancelled.

Preferably, the curve-fitting routine uses the least-squares method and fits a second order polynomial in the form Ax + Bx + C to the collected data. Other functions may also, of course, be used. The least-squares method may be weighted to give extra weight to data from the more recent section of the run. This allows the system to react better to changes in the performance of the aircraft, taking less account of data from the earlier and less significant parts of the run. The weighting is preferably based on an exponential function, although other weighting methods might be used. The first few moments of the run, which usually contain transients while the engines are still building up to full thrust, might be ignored entirely.

In the first few seconds of the take-off run an alternative method of performance monitoring is used to provide a display of performance where the predictive algorithm, presented herein, is not yet operational. This enables a continuous display to be provided from the start of the run. A process of integrating the output of the two methods is a part of the algorithm.

As a further refinement compensation might be applied to the extrapolation, to increase or decrease the curvature of the fitted curve, so as to reflect the performance characteristics

of the aircraft's engines. This may be necessary when, for example, modelling the t : l I performance of propeller-driven aircraft, the thrust characteristics of which decrease significantly with increased airspeed. The fitted polynomial, on extrapolation. may not be

capable of reflecting this effect on performance further down the run and compensation z : l may therefore be necessary for an accurate prediction. The use and amount of compensation depends on the performance characteristics of the aircraft on which the fit is performed. A process for applying compensation to the extrapolation is described below.

Third or higher order coefficients are introduced, or bias is added to the second order coefficient, to alter the curvature of the predicted curve. The coefficients or bias introduced would typically be derived from theory. When modelling the speed profile of the aircraft with a second order polynomial of the form A + Bx + Cx2 for example, a third order coefficient D may be introduced as a function of any of the coefficients A, B and C.

Typically, for a Jetstream-100 aircraft, the coefficient D needs to be numerically 1.6 x 10-4 times the value of B. It should be understood, however. that different ratios and compensation techniques would be appropriate to different aircraft types.

Furthermore, the amount of compensation necessary may need to be varied as the run progresses. This again depends on aircraft type and for the Jetstream-100 would have the form:

rry-y /v 1'' [ target tnstamaneous)/V targetJ The system may also include means for estimating the uncertainty in the prediction of D, This can be achieved through the use of standard statistical tools and specifically derived equations. The estimated degree of uncertainty may be used by the algorithms to discount predictions that fall below a predetermined confidence level, or an indication of the confidence level may be included in the pilot's display.

The optional data recording device 26 records the data generated by the data processing unit c 22 for post-flight analysis. This data may be useful for monitoring the performance of the aircraft.

The steps of a computer program for measuring the performance of an aircraft during takeoff are illustrated in Figs. 4 and 5. The steps of the main routine are shown in Fig. 4. The routine begins 30 and it then waits 32 for the run to start. This may be indicated automatically by response to one or more of a variety of parameters such as: release of the

brakes, the engine power being above a predetermined level or the acceleration being 0 greater than a predetermined figure. Alternatively, it may be indicated by a manual signal.

Once the start of the run has been detected, a sub-routine 34 is repeated continuously, for example, every 0. 1 sees, until either the speed exceeds V, or the pilot has abandoned the take-off 36. The sub-routine 34 includes the steps: fetching data 38 from the data acquisition system, estimating 40 the performance of the aircraft and displaying the result 41. When the sub-routine 34 ends as determined by the afore-mentioned conditions, the main routine ends 42.

The steps of the performance estimation sub-routine 40 are shown in Fig. 5. As mentioned previously, this sub-routine is repeated until a termination condition is detected. The subroutine begins 50 and the distance travelled since the last pass is calculated 52. This is preferably achieved by means of a software algorithm that uses a standard integration technique. That distance is then added to the sum of the previous distance calculations to give the total distance travelled since the start of the run.

The first few seconds of the run are not normally used for curve-fitting since this period contains transients associated with rapid rates of change of acceleration, which could compromise the accuracy of the prediction. The sub-routine 40 therefore includes a decision step 54. which will inhibit the curve fitting process until stable conditions are sensed. During this time. and until a valid prediction is achieved, an alternative means of monitoring replaces the predictive monitor. This alternative monitoring method may for example be based simply on monitoring the acceleration of the aircraft and comparing that acceleration with a predetermined standard.

Once stable conditions are sensed, the sub-routine applies the curve-fitting algorithm to the captured sets of data 56 and extrapolates the curve to V,, applying compensation if necessary. Next. the expected distance-to-go to V, is calculated from the compensated extrapolated curve. This distance-to-go is added to the distance gone to generate the predicted value of D,. The predicted value of D, is compared to the critical distance D to provide an indication of performance 58. The uncertainty of the prediction is then calculated 60 in terms of the upper and lower expected limits of D, This process is repeated typically ten times per second.

The data thus calculated is stored 62 in the data recording device 26, after which the subroutine ends 64.

A cockpit display device for indicating the performance of an aircraft is shown in Figs.

6a to 6d. In this example, the display device is a computer-driven digital display generated using, for example, a cathode ray tube or flat screen display. It should be understood, however, that separate discrete instruments may also be used.

Typically. the performance display device 80 is located alongside a conventional airspeed indicator 82, which may include a digitally generated airspeed'tape'84 carrying airspeed markings 86. Typically, the tape moves vertically past a stationary pointer 88 as the speed increases or decreases, the pointer 88 indicating the current speed. A small arrow 90 is normally provided to indicate the direction in which the speed is changing (an arrow pointing upwards indicating that the speed is increasing). t : l The proposed performance display device 80 displays the performance information in the form of a bar 94. This typically extends upwards or downwards from a reference mark 96, associated with minimum acceptable (net) performance and aligned with pointer 88, on the airspeed tape. Also included is a graduated scale 92 that extends vertically, alongside the bar 94. the scale providing a means of assessment of the performance of the current run. Advantageously, this allows the pilot to compare the current performance with the performance distribution expected of aircraft of that type operating under the same conditions. Comparison is made by reference to the length and colour of the bar 94, according to the comparison of the predicted distance D, to the critical distance Dent. When D < Dc, the bar will be green and will extend upwards. and when 01 > Dcnt the bar will be red and will extend downwards. The length of the bar is proportional to the difference between D, and Den !' Alternative graduations to those depicted in Fig. 6 may be used.

When the aircraft is performing normally and average (gross) performance is predicted, the bar 94 will be green in colour and will extend upwards from the reference centre graduation 96 to the next major graduation 98 on the scale, as shown in Fig. 6a. If the performance is less than gross performance, but better than net performance. a small green bar 94 is displayed as shown in Fig. 6b. This indicates that the aircraft is predicted to perform below gross performance, but still within regulation. Should the performance be less than net

performance the bar 94 is coloured red and it extends downwards from the reference graduation 96, Fig 6c. This shows that the predicted performance is below the regulatory minimum (net) and the aircraft is not accelerating sufficiently rapidly to achieve V, before

it reaches Dent. A longer red bar 94 as shown in Fig. 6d would indicate that the crit'zn t-- performance is further below regulation. The red indications would inform the pilot that the performance is below regulatory minimum acceptable standard and that he or she should take the appropriate action.

Advantageously, as well as indicating the present performance of the aircraft, the indication also allows the crew to monitor any change or trend in the performance, by observing the direction and rate of change of the indicator bar 94. Thus, for example, if the floating edge of the bar 94 is moving upwards, the performance is improving, whilst a downward trend shows a decreasing performance.

Further options in colour and colour changes and in the graduations of the monitor display might be introduced depending on operational and regulatory issues and experience.

Other indicia, such as that indicating the speed that will be attained at the critical distance, may also be included in forms appropriate to current practice.

Further, instead of predicting the distance gone at V,, it is possible to use the inverse of this approach by predicting the speed at the critical distance D and comparing the predicted speed with a predetermined speed (for example, V,).

Claims

CLAIMS I. A method of monitoring the performance of an aircraft during a take-off

manoeuvre. the method including the steps of monitoring the progress of the taket- t=l off run and extrapolating from the monitored progress to predict the future progress of the run.
2. A method according to claim 1, including comparing the predicted progress with a predetermined standard and providing an indication of the performance based on that comparison.

-off
3. A method of monitoring the performance of an aircraft during a take-off manoeuvre, the method including the steps of predicting the progress of the take-off run, comparing the predicted progress with a predetermined standard and providing an indication of the performance based on that comparison.
4. A method according to any one of the preceding claims, in which the progress of tD t- the take-off run is monitored by collecting data representing the speed of the aircraft and the time from the start of the run.
5. A method according to claim 4, in which the speed of the aircraft is determined by sensing the acceleration of the aircraft and integrating with respect to time.
6. A method according to any one of the preceding claims, in which the progress of the take-off run is monitored by collecting data representing the distance the aircraft has travelled from the start of the run.
7. A method according to claim 6, in which the distance the aircraft has travelled is

determined by integrating the speed of the aircraft with respect to time. t=l c
8. A method according to any one of the preceding claims. in which the collected data set is stored following successive measurements and used to determine by curve fitting the achieved performance of the aircraft.
9. A method according to claim 8. in which the fitted curve is extrapolated to predict future performance.

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10. A method according to claim 9, in which the distance the aircraft will have travelled by the time it reaches a predetermined speed is predicted, and the predicted distance is compared with a predetermined distance.
11. A method according to claim 9, in which the speed that will be achieved by the time it reaches a predetermined distance is predicted, and the predicted speed is compared with a predetermined speed.
12. A method according to claim 10 or claim 11, in which the predetermined speed is the decision speed V, and the predetermined distance is the critical distance Dmt.
13. A method according to any one of claims 8 to 12, in which the achieved

performance is obtained by a process of curve-fitting using the least squares Z=l method.
14. A method according to any one of claims 8 to 13, in which a second order

polynomial function is fitted to data representing the monitored progress of the run. z : l
15. A method according to claim 14, in which predetermined limits are placed on the coefficients of the polynomial function.
16. A method according to any one of claims 13 to 15, in which compensation is applied to the curve-fitting function to adjust its curvature.
17. A method according to any one of claims 13 to 16, in which the data representing the monitored progress of the run is weighted to increase the dependence of the curve-fitting function on recently acquired data.
18. A method according to any one of claims 8 or 13 to 17, in which the data representing an initial portion of the run is disregarded during calculation of the curve-fitting function.
19. A method according to any one of the preceding claims. in which an alternative t : l t : l method of monitoring the performance is employed during an initial part of the take-off run.

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20. A method according to claim 19, in which the alternative method includes z : l monitoring the acceleration of the aircraft and comparing the monitored acceleration with a predetermined standard.
21. A method according to claim 19 or claim 20, in which the result of the alternative monitoring method is merged with the result of the predictive monitoring method after an initial part of the take-off run has been completed.
22. A method according to any one of the preceding claims, in which the uncertainty z in the predicted progress of the take-off run is calculated.
23. A method according to claim 22, in which the uncertainty calculation is used to control the performance indication.
24. A method according to any one of the preceding claims. in which the indication of Z=l the aircraft's performance includes indicia representing the magnitude and sign of the comparison of the predicted progress with the predetermined standard. zn
25. A method according to any one of the preceding claims, in which the indication includes the predicted speed of the aircraft at the predetermined distance.
26. A method according to claim 25, in which the predetermined distance is the critical distance Dz
27. A method according to any one of the preceding claims, in which the indication of the aircraft's performance is displayed in association with an indication of the aircraft's airspeed.
28. A method according to any one of the preceding claims, in which data collected t=l during the monitoring process is recorded for later analysis.
29. A system for monitoring the performance of an aircraft during the take-off manoeuvre, the system including data acquisition means. a data processing device and a display device, the system being constructed and arranged to operate

according to the method as defined by any one of claims 1 to 28. tn

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30. A system for monitoring the performance of an aircraft during the take-off manoeuvre. the system including data acquisition means. a data processing device Z-1 and a display device, the system being constructed and arranged to collect data representing the progress of the take-off run, and to predict the future progress of the run by a process of extrapolation using the collected data.
31. A system according to claim 30, the system being constructed and arranged to compare the predicted progress with a predetermined standard and to provide an indication of the performance based on that comparison.
32. A system for monitoring the performance of an aircraft during the take-off manoeuvre, the system including data acquisition means, a data processing device and a display device. the system being constructed and arranged to compare the predicted progress with a predetermined standard and to provide an indication of the performance based on that comparison.
33. A system according to any one of claims 29 to 32, in which the data acquisition t means includes an accelerometer.
34. A system according to claim 33, in which the accelerometer comprises part of the aircraft's inertial navigation system.
35. A system according to any one of claims 29 to 34. in which the display device includes a digital or analogue optical display.
36. A system according to any one of claims 29 to 35, in which the display device is associated with the aircraft's airspeed indicator.
37. A system according to any one of claims 29 to 36, including a data recording device for recording data collected during the monitoring process.
38. A system according to any one of claims 29 to 37, in which following successive measurements the collected data sets are stored and used to determine by curve

fitting the achieved performance of the aircraft. Z=l

38. A method of monitoring the performance of an aircraft during the take-off manoeuvre, in which a collected data set is stored following successive measurements and used to determine by curve fitting the achieved performance of the aircraft.

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39. A method of monitoring the performance of an aircraft during the take-off manoeuvre, the method being substantially as described herein with reference to the accompanying drawings.

40. A system for monitoring the performance of an aircraft during the take-off r manoeuvre, the system being substantially as described herein with reference to the accompanying drawings.

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Amendments to the claims have been filed as follows

CLAIMS 1. A method of monitoring the performance of an aircraft during a take-off manoeuvre, the method including the steps of monitoring the progress of the take-off manoeuvre by acquiring data representing the motion of the aircraft at a plurality of points during the manoeuvre, generating a function that best fits the acquired data, and using the generated function to predict the future progress of the manoeuvre.

2. A method according to claim 1, including comparing the predicted progress with a 0 t t, predetermined standard and providing an indication of the performance based on that comparison.

3. A method according to claim 2, including providing a quantitative indication of the performance.

4. A method according to any one of the preceding claims, in which the progress of the take-off manoeuvre is monitored by collecting data representing the speed of the aircraft and the time from the start of the manoeuvre.

5. A method according to claim 4, in which the speed of the aircraft is determined by sensing the acceleration of the aircraft and integrating with respect to time.

6. A method according to any one of the preceding claims, in which the progress of the take-off manoeuvre is monitored by collecting data representing the distance the aircraft has travelled from the start of the manoeuvre.

7. A method according to claim 6, in which the distance the aircraft has travelled is determined by integrating the speed of the aircraft with respect to time. t : l 8. A method according to any one of the preceding claims, in which following successive measurements the collected data sets are stored and used to determine by curve fitting the achieved performance of the aircraft.

9. A method according to claim 8, in which the fitted curve is extrapolated to predict ZD future performance.

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10. A method according to claim 9, in which the distance the aircraft will have travelled I by the time it reaches a predetermined speed is predicted, and the predicted distance is compared with a predetermined distance.

11. A method according to claim 9, in which the speed that will be achieved by the time it reaches a predetermined distance is predicted, and the predicted speed is compared with a predetermined speed.

12. A method according to claim 10 or claim 11, in which the predetermined speed is z the decision speed V, and the predetermined distance is the critical distance D,,,,.

13. A method according to any one of claims 8 to 12, in which the achieved t performance is obtained by a process of curve-fitting using the least squares method.

14. A method according to any one of claims 8 to 13, in which a second order polynomial function is fitted to data representing the monitored progress of the manoeuvre.

15. A method according to claim 14, in which predetermined limits are placed on the coefficients of the polynomial function.

16. A method according to any one of claims 13 to 15, in which compensation is applied to the curve-fitting function to adjust its curvature.

17. A method according to any one of claims 13 to 16, in which the data representing

the monitored progress of the manoeuvre is weighted to increase the dependence of 0 the curve-fitting function on recently acquired data.

18. A method according to any one of claims 8 or 13 to 17, in which the data representing an initial portion of the manoeuvre is disregarded during calculation of

the curve-fitting function. z : l 19. A method according to any one of the preceding claims, in which an alternative I method of monitoring the performance is employed during an initial part of the takeoff manoeuvre.

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20. A method according to claim 19, in which the alternative method includes monitoring the acceleration of the aircraft and comparing the monitored acceleration with a predetermined standard.

21. A method according to claim 19 or claim 20, in which the result of the alternative z : l monitoring method is merged with the result of the predictive monitoring method after an initial part of the take-off manoeuvre has been completed.

22. A method according to any one of the preceding claims, in which the uncertainty in the predicted progress of the take-off manoeuvre is calculated.

23. A method according to claim 22, in which the uncertainty calculation is used to control the performance indication.

24. A method according to any one of the preceding claims, in which the indication of the aircraft's performance includes indicia representing the magnitude and sign of

the comparison of the predicted progress with the predetermined standard.

Z7, 25. A method according to any one of the preceding claims, in which the indication includes the predicted speed of the aircraft at the predetermined distance.

26. A method according to claim 25, in which the predetermined distance is the critical distance Dent.

27. A method according to any one of the preceding claims, in which the indication of the aircraft's performance is displayed in association with an indication of the aircraft's airspeed.

28. A method according to any one of the preceding claims, in which data collected during the monitoring process is recorded for later analysis.

29. A system for monitoring the performance of an aircraft during the take-off manoeuvre, the system including data acquisition means, a data processing device and a display device, the system being constructed and arranged to operate

according to the method as defined by any one of claims 1 to 28.

1

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30. A system for monitoring the performance of an aircraft during the take-off manoeuvre, the system including data acquisition means, a data processing device and a display device, the system being constructed and arranged to monitor the progress of the take-off manoeuvre whereby, during operation, the data acquisition means acquires data representing the motion of the aircraft at a plurality of points during the manoeuvre, the data processing device generates a function that best fits the acquired data, and the data processing device uses the generated function to predict the future progress of the manoeuvre.

31. A system according to claim 29 or claim 30, the system being constructed and arranged to compare the predicted progress with a predetermined standard and to provide an indication of the performance based on that comparison.

32. A system according to claim 31, in which the system provides a quantitative indication of the performance.

33. A system according to any one of claims 29 to 32, in which the data acquisition means includes an accelerometer.

34. A system according to claim 33, in which the accelerometer comprises part of the aircraft's inertial navigation system.

35. A system according to any one of claims 29 to 34, in which the display device includes a digital or analogue optical display.

36. A system according to any one of claims 29 to 35, in which the display device is associated with the aircraft's airspeed indicator.

37. A system according to any one of claims 29 to 36, including a data recording device tn for recording data collected during the monitoring process.