Aircraft terrain advisory system

Abstract: A terrain advisory system for an aircraft (A) comprises a processor (11) which compares terrain information, accessed from a memory means 13 according to data from a navigation means (12), with dynamic flight parameters from a monitor (14) for the aircraft (A). The processor (11) also generates a trajectory signal and a pull-up signal to indicate, on a display means (15), the current aircraft trajectory relative to a line constructed from notional pull up trajectories for the aircraft (A) which avoid a predetermined clearance height without exceeding a predetermined acceleration acting on the aircraft during a pull up manoeuvre.

Description: This invention relates to an aircraft terrain advisory system, in which terrain information is compared with the dynamic flight parameters for that aircraft to indicate the current aircraft trajectory with respect to clearance heights for a terrain to be avoided by the aircraft without exceeding a predetermined acceleration of the aircraft during a pull up manoeuvre. The invention also related to a method for indicating the current aircraft trajectory with respect to clearance heights for a terrain. It is known, from United Kingdom Patent 1, 062, 530, that an apparatus, to be carried by an aircraft, can provide a warning of the aircraft's approach to an obstacle ahead of it that constitutes a collision hazard and to allow a manoeuvre which can be executed by the aircraft to avoid the obstacle without involving the production of stresses in the aircraft that exceed approved limits. This document also teaches that the obstacle-warning apparatus incorporates equipment arranged to transmit signals in directions within an observation sector ahead of the aircraft, and to detect objects within that sector by means of signal reflection back to the apparatus. This disclosure teaches that an aircraft terrain advisory system (hereinafter termed "of the kind specified"), comprises a navigation means arranged to generate navigational information in respect of the aircraft, and a processor arranged to determine clearance heights above terrain heights within a terrain area which must not be violated when the aircraft overflies the terrain area and without exceeding a maximum predetermined acceleration of the aircraft. Consider an eye position above the ground, and the various lines of sight radiating from that position. Some of these lines of sight will intercept the ground or objects projecting from the ground, while others will not. The boundary between the lines of sight which do and do not intercept the ground is known as the visual horizon from that eye position The operation of the aircraft terrain advisory system can be defined analogously. Consider the position of an aircraft above the ground, and consider the possible trajectories emanating from that point. For each of these trajectories it will be either possible or impossible to pull up from that point without exceeding a predetermine acceleration of the aircraft, given the dynamic flight parameters of that aircraft, such that the trajectory avoids hitting the ground. The region defined by trajectories from which pull up can be achieved is the region the current trajectory of the aircraft must remain in to ensure pull up is possible for a given acceleration of the aircraft. In practice the aircraft is required to avoid violating a clearance level above the ground and not just merely the ground. WO 92 21077A discloses an aircraft terrain and obstacle avoidance system which generates a warning signal when the aircraft is on a potentially hazardous course with respect to terrain to be overflown. This involves the computation of pull-up trajectories which the aircraft could perform, at a point forward of the present location of the aircraft. The pull-up trajectories collectively define a region notionally moving in advance of the aircraft at a spacing which is a function of the aircraft velocity, acceleration, the aircraft's response to pilot commands and the pilot reaction time. The warning signal is produced if at any point on the trajectories there is a predetermined relationship with height data stored in a map storage relating to the region defined by trajectories. It is an object of this invention to provide an aircraft terrain advisory system which will enable a pilot to avoid violating a predetermined terrain clearance level without exceeding a predetermined acceleration of the aircraft. According to a first aspect of the present invention there is provided an aircraft terrain advisory system of the kind specified, comprising a monitor means arranged to generate parameter information representing dynamic flight parameters of the aircraft, and a memory means arranged to store height information of terrain that might be overflown by the aircraft, characterised in that the processor is operably arranged 1. to access and receive the height information for a terrain area ahead of the aircraft dependant on the navigational information and to generate future terrain clearance level signals representing predetermined clearance heights above terrain heights within the terrain area which must not be violated when the aircraft overflies the terrain area, 2. to generate sets of pull-up signals representing notional pull-up trajectories that the aircraft can perform without exceeding a maximum predetermined acceleration of the aircraft determined from the parameter information and without violating the predetermined clearance heights determined from the terrain clearance level signals, and 3. to generate from the parameter information and the navigational information a trajectory signal representing current trajectory of the aircraft, and to indicate the current trajectory with respect to safe and unsafe regions established by the pull-up signals in which the aircraft can fly without exceeding the maximum predetermined acceleration of the aircraft. Preferably, a display means may be operably connected to the processor and arranged to receive the sets of pull-up signals and the trajectory signal, the display means being arranged to display a line corresponding to the sets of pull-up signals, and the display means also being arranged to display a trajectory symbol, corresponding to the trajectory signal, with respect to the line. Conveniently, the line is constructed from a boundary region between a plurality of possible aircraft pull up trajectories which avoid the predetermined clearance heights and a plurality of possible aircraft pull up trajectories which do not avoid the predetermined clearance heights for the maximum predetermined acceleration of the aircraft. The navigation means may comprise an Inertial Navigation System operably connected to a Terrain Referenced Navigation System and may be arranged to receive corrections from the Terrain Referenced Navigation System or alternatively the navigation means may comprise a Global Positioning System Receiver. The processor may be arranged to generate a set of pull-up signals for each of a plurality of maximum predetermined accelerations of the aircraft and the display means may be further arranged to display a line corresponding to each set of pull-up signals. Alternatively the processor may be arranged to generate sets of pull-up signals, which correspond to lines immediately above and immediately below the trajectory symbol and the display means may be further arranged to display each line. As a further alternative, the processor may be arranged to generate sets of pull-up signals corresponding to truncated lines immediately above and immediately below the trajectory symbol and the display means may be further arranged to display each truncated line. Advantageously, an audible means may be operably connected to the processor and arranged to receive the set of pull-up signals and the trajectory signal, and the audible means may be arranged to generate a plurality of audible signals which correspond to the position of the trajectory signal with respect to the sets of pull-up signals. According to a second aspect of the present invention there is provided a method of indicating current aircraft trajectory with respect to terrain clearance levels, including generating navigational information in respect of an aircraft, characterised by including the steps of: accessing height information for a terrain area ahead of the aircraft depending on the navigational information and generating future terrain clearance level signals representing predetermined clearance heights above terrain heights within the terrain area which must not be violated when the aircraft overflies the terrain area, generating sets of pull-up signals dependant on flight parameters of the aircraft and the terrain clearance level signals, the sets of pull-up signals representing notional pull-up trajectories that the aircraft can perform without exceeding a maximum predetermined acceleration of the aircraft and without violating the predetermined clearance heights, generating a trajectory signal using the parameter information and the navigational information, the trajectory signal representing current trajectory of the aircraft, and indicating the current trajectory with respect to safe and unsafe regions established by the pull-up signals in which the aircraft can fly without exceeding the maximum predetermined acceleration of the aircraft. Preferably, the method may further comprise displaying a line corresponding to the sets of pull-up signals, and displaying a trajectory symbol corresponding to the trajectory with respect to the line. The method may further comprise constructing the line by determining the line as a boundary region between a plurality of possible aircraft pull-up trajectories which avoid the predetermined clearance heights, and a plurality of possible aircraft pull-up trajectories which do not avoid the predetermined clearance heights for a maximum predetermined acceleration of the aircraft. The invention is further described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a block diagram of an aircraft terrain advisory system according to the present invention, Figure 2 illustrates a plurality of possible heading trajectories, for the system of the present invention, in a terrain area ahead of an aircraft in the azimuth plane; Figure 3 illustrates a plurality of possible dive/climb trajectories in a terrain area ahead of an aircraft in the elevation plane compared with a terrain and a clearance height, and Figure 4 illustrates a plurality of possible pull-up trajectories for an aircraft, having a system of the present invention, for a single set of possible trajectories for a given heading across the terrain area. Referring to Figure 1, an aircraft terrain advisory system 10 of the present invention, carried by an aircraft comprises a processor 11 operably connected to a navigation means 12 and a memory means 13. The navigation means 12 maybe an Inertial Navigation System which is operably connected to receive slowly varying corrections from a Terrain Referenced Navigation System 16 to update an estimate of navigation corrections with terrain measurements, or a Global Positioning System Receiver or any other high precision navigation instrument. The memory means 13 is arranged to store height information, in the form of terrain heights, for a terrain area which might be overflown by the aircraft and may be a terrain database or any suitable device for storing height information. The processor 11 is arranged to receive navigational information, in respect of the aircraft, from the navigational means 12, and to access the memory means 13 and receive the stored height information for a terrain area ahead of the current position of the aircraft according to the received navigational information. The processor 11 is also operably connected to a monitor means 14 which generates parameter information representing dynamic flight parameter of the aircraft. The processor 11 is arranged to generate a future terrain clearance level signal which corresponds to predetermined clearance heights above the terrain heights, within the terrain area. The clearance heights represent a clearance margin above the terrain heights. The processor 11 is arranged to compare received parameter information from the monitor means 14 with the terrain clearance level signal and to generate sets of pull-up signals representing notional pull-up trajectories that the aircraft can perform without violating the clearance heights and without exceeding a maximum predetermined acceleration of the aircraft. The processor 11 is also arranged to generate a trajectory signal, from the received parameter information and navigational information, which represent the current trajectory of the aircraft. A display means 15, operably connected to the processor (11), is arranged to display a line indicating notional pull-up trajectories using the pull-up signals and to display a trajectory symbol corresponding to the trajectory signal as the current trajectory of the aircraft with respect to the line on the display means 15. Hence, a pilot or operator of the aircraft can determine, by observation of the current trajectory relative to the line, if evasive action is necessary for the aircraft to avoid the terrain area ahead of the aircraft without passing below the predetermined clearance heights and without exceeding the predetermined acceleration of the aircraft. The pull-up signal for the displayed line above which the displayed current trajectory is to be maintained is determined in the following manner. Referring to Figure 2, an aircraft A following a current trajectory 17 across a terrain area ahead of the aircraft has a plurality of possible heading trajectories 18 in the azimuth plane corresponding with the heading angle 19 of the aircraft A. Figure 3, shows that for each possible heading trajectory in the terrain area ahead of the aircraft there are also a plurality of possible dive/climb trajectories 20 in the elevation plane for variations of only the dive/climb angle 21. Therefore there are a plurality of possible trajectories radiating from the aircraft A which can be divided into sets of dive/climb trajectories 20 each set having a similar heading angle 19, as illustrated in Figure 4. Referring to Figure 3, for each set of dive/climb trajectories, a set of notional pull-up trajectories 22 can be determined using the dynamic flight parameters of the aircraft such that a predetermined acceleration acting on the aircraft A is not exceeded and such that the notional pull-up trajectories 22 avoid violating a clearance level 23 above a terrain height 24. Any point on the line can be determined by considering possible heading trajectory and finding a boundary region between dive/climb trajectories 20 where the aircraft A would, or would not, avoid violating the clearance heights 23 given the dynamic flight parameters of the aircraft A and without exceeding a predetermined acceleration of the aircraft A. More particularly the point can be found by determining, for an initial pair of dive/climb trajectories 20, the first trajectory set at the minimum dive/climb angle and the second trajectory set at the maximum dive/climb angle, if the point lies somewhere between the initial pair of dive/climb trajectories 20. If the point is determined to exist between the initial pair of dive/climb trajectories 20 then a central value is considered to determine which half the point lies in. This binary search is continued until the point has been determined to the required resolution. This is the boundary region. This is illustrated by the pair of pull up trajectories 25 and 26, from which it will be seen that the first trajectory 25 does not avoid violating the clearance heights 23 but the second trajectory 26 does. A point can be determined for each possible heading trajectory 18 so as to construct a line indicating a horizon of the safe and unsafe regions in which the aircraft A can fly without necessitating a manoeuvre which will infringe either the predetermined clearance height or the predetermined acceleration of the aircraft. By displaying the current trajectory 17 with respect to this line of safe and unsafe regions, the pilot can observe if the aircraft A is flying within a safe or unsafe region and adjust the position of the current trajectory 17 of the aircraft A with respect to the line accordingly. Figure 4 illustrates the pull up trajectories 22 for a plurality of dive/climb angles 19 for a given heading across the terrain area. A time delay 27 to allow for the reaction time of the pilot or operator and the aircraft A is included in the determination of the boundary region for each heading trajectory and hence built into the line. The pilot can also enter parameters such as the clearance height 23 and the acceleration of the aircraft which should not be exceeded via a keypad 28 as indicated in Figure 1 or the parameters may be stored in a suitable memory device. The line can also be determined for a range of accelerations of the aircraft, so that a ladder of lines can be displayed on the display means 15 together with the current trajectory 17 of the aircraft so that the pilot can observe the pull up acceleration required to safely pull up on any heading across the line. If processing power is limited, the ladder can be restricted to a small portion displaying only the. lines immediately above and immediately below the current trajectory 17 on the display means 15. Alternatively, only a section of the lines immediately above and immediately below the current trajectory 17 can be displayed on the display means 15, for example in the form of an icon. The current trajectory 17 need not be displayed in this instance as it will lie between the lines above and below the current trajectory and can be followed with the change from one vertical acceleration level to another on the ladder. The display may be any suitable display or instrument that is capable of indicating to a pilot or operator the current trajectory of the aircraft with respect to a line, for instance a head up display, head down display, visor projected display or retina projected display. The display may also be remote from the aircraft for use by an operator. In an alternative embodiment an audible means may be operably connected to the processor to receive the pull-up signal and the trajectory signal and arranged to generate a series of audible signals corresponding to the position of the trajectory signal with respect to the pull-up signal.

Claims: An aircraft terrain advisory system, comprising a navigation means (12) arranged to generate navigational information in respect of the aircraft (A), a processor (11) arranged to determine clearance heights (23) above terrain heights (24) within a terrain area which must not be violated when the aircraft (A) overflies the terrain area and without exceeding a maximum predetermined acceleration of the aircraft (A), a monitor means (14) arranged to generate parameter information representing dynamic flight parameters of the aircraft (A), and a memory means (13) arranged to store height information of terrain that might be overflown by the aircraft (A), with the processor (11) being arranged to receive the navigational information and the parameter information characterised in that the processor (11) is operably arranged 1. to access and receive the height information for a terrain area ahead of the aircraft dependant on the navigational information and to generate future terrain clearance level signals representing predetermined clearance heights (23) above terrain heights (24) within the terrain area which must not be violated when the aircraft (A) overflies the terrain area, 2. to generate sets of pull-up signals representing notional pull-up trajectories (22) that the aircraft (A) can perform without exceeding a maximum predetermined acceleration of the aircraft (A) determined from the parameter information and without violating the predetermined clearance heights (23) determined from the terrain clearance level signals, and 3. to generate from the parameter information and the navigational information a trajectory signal representing current trajectory (17) of the aircraft, and to indicate the current trajectory with respect to safe and unsafe regions established by the pull-up signals in which the aircraft can fly without exceeding the maximum predetermined acceleration of the aircraft. An aircraft terrain advisory system, as in Claim 1, including a display means (15) operably connected to the processor (11) and arranged to receive the sets of pull-up signals and the trajectory signal, the display means (15) being arranged to display a line corresponding to the sets of pull-up signals, and the display means (15) also being arranged to display a trajectory symbol, corresponding to the trajectory signal, with respect to the line. An aircraft terrain advisory system, as claimed in Claim 2, wherein the line is constructed from a boundary region between a plurality of possible aircraft pull up trajectories (26) which avoid the predetermined clearance heights (23) and a plurality of possible aircraft pull up trajectories (25) which do not avoid the predetermined clearance heights (23) for the maximum predetermined acceleration of the aircraft (A). An aircraft terrain advisory system, as claimed in any preceding claim, wherein the navigation means (12) comprises an Inertial Navigation System operably connected to a Terrain Referenced Navigation System (16) and arranged to receive corrections from the Terrain Referenced Navigation System (16). An aircraft terrain advisory system, as claimed in any one of Claims 1 to 3, wherein the navigation means (12) comprises a Global Positioning System Receiver. An aircraft terrain advisory system, as claimed in any one of Claims 2 to 5, wherein the processor (11) is arranged to generate a set of pull-up signals for each of a plurality of maximum predetermined accelerations of the aircraft and the display means (15) is further arranged to display a line corresponding to each set of pull-up signals. An aircraft terrain advisory system, as claimed in any one of Claims 2 to 5, wherein the processor (11) is arranged to generate sets of pull-up signals, which correspond to lines immediately above and immediately below the trajectory symbol and the display means (15) is further arranged to display each line. An aircraft terrain advisory system, as claimed in any one of Claims 2 to 5 wherein the processor (11) is arranged to generate sets of pull-up signals corresponding to truncated lines immediately above and immediately below the trajectory symbol and the display means (15) is further arranged to display each truncated line. An aircraft terrain advisory system, as claimed in Claim 1, including an audible means operably connected to the processor (11) and arranged to receive the set of pull-up signals and the trajectory signal, and the audible means is arranged to generate a plurality of audible signals which correspond to the position of the trajectory signal with respect to the sets of pull-up signals. A method of indicating current aircraft trajectory with respect to terrain clearance levels including generating navigational information in respect of an aircraft (A), characterised by including the steps of: accessing height information for a terrain area ahead of the aircraft (A) depending on the navigational information and generating future terrain clearance level signals representing predetermined clearance heights (23) above terrain heights (24) within the terrain area which must not be violated when the aircraft (A) overflies the terrain area, generating sets of pull-up signals dependant on flight parameters of the aircraft (A) and the terrain clearance level signals, the sets of pull-up signals representing notional pull-up trajectories (22) that the aircraft (A) can perform without exceeding a maximum predetermined acceleration of the aircraft (A) and without violating the predetermined clearance heights (23), generating a trajectory signal using the parameter information and the navigational information, the trajectory signal representing current trajectory (17) of the aircraft, and indicating the current trajectory with respect to safe and unsafe regions established by the pull-up signals in which the aircraft can fly without exceeding the maximum predetermined acceleration of the aircraft. A method, as claimed in Claim 10, further comprising displaying a line corresponding to the sets of pull-up signals, and displaying a trajectory symbol corresponding to the trajectory signal, with respect to the line. A method, as claimed in Claim 11, comprising constructing the line by determining the line as a boundary region between a plurality of possible aircraft pull-up trajectories (26) which avoid the predetermined clearance heights (23), and a plurality of possible aircraft pull-up trajectories (25) which do not avoid the predetermined clearance heights (23) for a maximum predetermined acceleration of the aircraft (A).

Inventors: HENLEY ANTHONY JOHN MICHAEL, HENLEY, ANTHONY JOHN MICHAEL
Applicants: BAE SYS ELECTRONICS LTD, BAE SYSTEMS ELECTRONICS LTD.
Application year: 1997
Main classification: G01C23
IPC codes: G01C23, G08G5, G05D1