GB2189448A - Balanced risk director - Google Patents

Abstract

A balanced risk director is used in situations where rapid decisions have to be made between alternative courses of action, on the basis of minimising risk. It is particularly useful in dynamic situations where the risks are changing quickly and are very sensitive to changes in the conditions being experienced. A balanced risk director consists of a computations unit programmed to calculate and compare, in real time or near real time, appropriate risks, both with one another and with generally acceptable standards, with a sampling rate appropriate to the application. The results of the calculations are displayed in a form readily usable to a human operator, and/or in a form suitable for controlling an automatic system, again with an update rate appropriate to the application. An aeroplane take-off monitor is described, in which aeroplane take-off and braking performance are stored in a database, aeroplane weight, runway and ambient conditions are fed in prior to take-off, and transducers measure acceleration, distance gone, ground and air speeds, and brake-pressure. Calculated information displayed to the pilot advises him of the advisability of continuing or abandoning take-off. <IMAGE>

Description

SPECIFICATION Balanced risk director This invention relates to a balanced risk director.

Situations often arise where decisions have to be made between two or more alternative courses of action, on the basis of minimising risks. In quasi-static situations the risks can be estimated or calculated before making the decision but in some dynamic situations (eg. controlling vehicles, systems or machinery) the risks can be changing too rapidly forthis approach to be practical. In such dynamic situations the risks are often pre-calculated on the basis of assumed conditions, in orderto derive some simple criterion or 'rule of thumb' on which the decision can then be based.

This approach works quite well when actual conditions match those assumed but it can easily lead to wrong decisions when the actual conditions experienced depart significantly from the assumptions.

The balanced risk director is intended as an aid to decision making in such dynamic situations, in thatit permits such decisions to be based on real time, or rear real time, risk calculations using the actual conditions being experienced as the situation develops as the basis for the calculations.

The balanced risk director is shown in schematic in figure 1 and consists of a computation unit which when programmed in accordance with this invention: -will accept inputs from input means, -will accept signals from transducers appropriate to the application, either directly or via a signal conditioning unit, - will carry out repetitive real time, or near real time, calculation and recalculation ofthe risks associated with appropriate alternative courses of action, as those risks vary throughout a dynamic situation, and -will outputthe results of those calculations in an appropriate form to a utilisation means appropriateto the application.

Specific example of one application of the invention is described with reference to the accompanying figures: The example quoted is that of a balanced risk director intended for use on an aeroplane during take-off. Its' purpose is to provide the pilot with current i nformation throug hout the take-off on: (a) whether the risks involved in continuing the take-off are acceptable by comparison with those generally regarded as being acceptable, and compared with the risks involved in attempting to stop from the current speed and position, and (b) whether it would be safertotry and continue the take-offorto abandon it and try to stop if, at any time, a failure that might hazard the aeroplane (eg. engine failure) were detected.

In this application a database is needed to store the following information aboutthe aeroplane's performance and aboutthe runwaysfrom which it will operate: Aircraftperformance model: -acceleration in normal conditions, - acceleration on a contaminated runway, - lift-off speeds, - braked deceleration on a dry runway, - braked deceleration on a wet runway, - braked deceleration on a contaminated runway, - braked deceleration on an icy runway, - anti-skid inorperative deceleration effect, - one brake inoperative deceleration effect, and - reversers inoperative deceleration effect.

Runwayinformation: - runway length, and - runway slope.

Apre-take-offinput is required through an input means, to includethefollowing information: -aircraft weight, -take-off configuration (if not availablefrom a system interface), -thrustsetting (if not available from a system interface), - runway in use, - runway state (ie. dry, wet, contaminated or icy), -depth ofcontaminant (if any), -pressure altitude (if not available from a system interface), - outside airtemperature (if not available from a system interface), and - maximum permitted thrust setting (if not availablefrom a system interface).

Transducers are required to measure: - acceleration, - distance gone, - groundspeed, - airspeed, - wheel-brake pressure, and to detect engine failure, to supply information on these parameters to the computation unit continuously throughout the take-off, via a signal conditioning unit as necessary.

Once a take-off begins the computation unit uses the above information in conjunction with pre-programmed models ofthe likelyvariability of the aeroplane's performance and of the reliability of its engines, wheels and tyres, to make real time, or near real time, calculations of: (a) the probability that a fatal accident would result if an engine were to fail at that instant andthetake-off was continued (Probability = PT).

(b) the probability that a fatal accident would result if an engine were to fail at that instant and thetake-off was abandoned (Probability = Ps).

(c) the probability that a fatal accident would result if the take-off was continued with all engines remaining operating throughout (Probability = PA).

(d) the probability that a fatal accidentwould result ifthe take-offwas continued, but tasking into accountthe probability of a subsequentfailure before lift-off, giving rise to the need to either continue the take-offwith thefailureorto abandonthetake-offand stop (Probability= Pc).

Note: PC PA + SV (PFXPo)+VvEL (PEXPG) Where: VE = the speed above which the risk involved in attempting to stop exceeds the risk involved in continuing, V = thecurrentspeed, VL = lift-off speed, PF = probability of a failure atany point leading to a decision to stop, PE = probability of an engine failure at any point where it would lead to a decision to continue the take-off, PD = probability of a fatal overrun resulting from a decision to stop from any point, and PG = probability that a fatal overrun would result from a decision to continue the take-off with one engine inoperative, from any point.

The calculation procedure and output logic are shown in figure 2,3 and 4. An acceleration signal derived from an inertial reference system is used to calculate groundspeed and position and to correctthe preprogrammed model of the aeroplanes performance to reflect the level of performance actually being achieved. This corrected model is then used to predictthe aeroplanes performance throughoutthe remaining part of the take-off and for any abandoned take off, and hence to calculate the fatal overrun probabilities defined above, assuming the aeroplanes performance to be normally distributed.

The sources of variability in the aeroplanes performance needing to be taken into account are:- Acceleration distances: - aircraft weight, - engine th rust, - drag (aerodynamic and contaminant), - rolling friction, - errors in recognition of rotation speed (where appropriate), and - runway slope.

The corresponding sources of variability in stopping distances are: - aircraft weight, - recognition and action times, - braking friction, - reverse thrust, -drag,and - runway slope.

One further source of variability that must be taken into account is that arising from sensing errors (position, acceleration, speed etc.) The decision making information available to the pilot as a resultofthese calculations is shown in figures3 and 4. The means of display will varyfrom one application to another, depending on the particular instrumentation fit of each aircraft.

The 'Warning Threshold' referred to in figure 4 has to be set at a level such that it will give a warning ifthe risk level becomes unacceptably high, but also such that it will not give rise to an unacceptably high rate of nuisance warnings. The exact setting will need to be the subject of a development programme to determine an optimum setting, but this is likely to be ofthe orderofa calculated fatal overrun probability of 1.75 x 10-5.

After lift-off and if a take-off is abandoned the balanced risk directorwill disarm automatically and present an 'Off' indication to the pilot.

The computation speed is such that the calculated risks and the outputs two the pilot's display and/orthe automatic systems are updated at least once per second throughoutthetake-off.

Claims (11)

1. A balanced risk director comprising a computation unit programmed in accordance with this invention: - to accept in puts from input means, - to accept signa Is from transducers via a signal conditioning unit, as necessary, - to carry out a repetitive real time, or near real time, calculation and re-calculation of the risks associated with adopting various appropriate alternative courses of action, as those risks vary in a dynamic situation, and - to pass the results of those calculations to appropriate utilisation means.

2. A balanced riskdirector as claimed in claim 1 designed and programmed to acceptinputsfrom keyboard, in addition to the inputs and signals described in claim 1.

3. A balanced risk director as claimed in claim 1 or claim 2 designed and programmed to accept inputs from a pre-recorded recording medium, in addition to the input and signals described in claim 1 and claim 2.

4. A balanced riskdirectoras claimed in claim 1, claim 2 orciaim 3 designed and programmed to accept input fro a pre-programmed electronic memory unit in addition to the inputs and signals described in claims 1,2 and 3.

5. A balanced riskdirectoras claimed in claim 2, claim 2 orclaim 3 designed and programmed to accept inputs from a pre-programmed ROM cartridge in addition to the inputs described in claims 1,2 or3.

6. A balanced risk director as claimed in claims 1,2, 3, 40r 5 designed and programmed to presentthe results of its calculations on a display unit.

7. A balanced risk director as claimed in claims 1,2,3,4,5 or 6 designed and programmed to supply control signals to an automatic control system.

8. A balanced risk director substantially as described herein with reference to figure 1.

9. A balanced risk director as claimed in claim 8when used as an aircrafttake-offmonitor.

10. A balanced riskdirector as claimed in claim 8orclaim 9when used as an aircraft landing approach monitor.

11. Abalanced riskdirectoras claimed in claims 8, 9, or 10when used as an aircraft cruise diversion monitor.