GB2373658A - Collision avoidance system - Google Patents

Abstract

Aircraft transmit their location (latitude and longitude) possibly derived from a global positioning system, their altitude derived from a barometric sensor their type, weight and registration in turn onto a common radio network. All aircraft and ground stations receive the positions and altitudes of all other aircraft from the network. Current and historic positions can be plotted, possibly superimposed over a moving map, giving a "radar like" display of position and speed of other traffic that pilots can use for collision avoidance (Figure 1). Alarms can draw attention to impending collisions and near misses. Pilots can "see" aircraft at 20nm or more (range is set by radio range and network bandwidth available). Ground stations transmit base pressures (QNH's and QFE's), kept constantly updated, onto the network. These base pressures are the basis of the system altimetry. All altitudes displayed within any given aircraft are expressed above the same base, vital for collision avoidance.

Description

Collision Avoidance System This invention relates to a collision avoidance system.

Aircraft pilots have to avoid collision with other aircraft. This is done by visual scanning, as well as technical aids such as radar. Cockpit workload, the speed of conflicting aircraft, and low visibility of conflicting aircraft and the position of the sun may limit the success of visual scanning. Currently the main technical aid that facilitates collision avoidance is radar. Ground based radars can only deal with a certain number of aircraft, beyond which air traffic controllers become overloaded. Radar is not available in all environments, due to expense and range. The current invention ensures separation in all environments. It enables pilots to see all other aircraft that are fitted with the collision avoidance unit, and they can take avoiding action independently in accordance with the rules of the air.

According to the present invention there is provided a digital communications network, for example a radio network, upon which data from aircraft instruments and controls and ground station instruments and controls is presented in turn so that the data from each aircraft and ground station on the network is available to some or all other aircraft and stations on the communications network.

An example of the invention would be a digital communications network, for example a radio network, upon which location data from aircraft global positioning systems, external static barometric pressures measured at aircraft, aircraft registration, aircraft type and aircraft weight code are presented in turn by aircraft. Static barometric pressures measured at ground stations are presented to the communications network in turn by ground stations, so that the data from each aircraft and ground station on the. network is available to some or all other aircraft and ground stations on the communications network.

There is provided a computing system on board each aircraft to store the data from the digital communications network as it is received, together with the time of reception and transmission. This data is stored in records in the computer's memory which are ordered by the aircraft that the data relates to.

The above computing system calculates altitudes for all aircraft on the network, from data received from the network, with respect to any altitude base pressure or datum level. The external static barometric pressure at other aircraft, together with the ground barometric pressure in use at our pilot's aircraft enables the altitude of any other aircraft to be calculated above that base. All of these barometric pressures are received via the network. This calculated altitude to be stored in the ordered aircraft records in the computer memory on board our aircraft.

The above computing system optionally selects aircraft details for display according to criteria set by the pilot.

The above computer to have a display system to plot the present positions and details of aircraft, possibly superimposed upon a moving map display, so that the pilot can see the position, details and altitude of other aircraft relative to his own position.

The above computing system to be able to use the weight code in the aircraft record in the computer memory to optionally display heavier aircraft as a larger spot on the display.

The above computer display system to plot the present position and details of aircraft, and also plot (possibly at reduced intensity) the previous positions of those same aircraft over a selectable time frame, so that the pilot can see the speed and direction of all other traffic relative to his own aircraft's speed and direction.

The computer display system specified above optionally to be able to remove the positions and details of other aircraft easily, possibly at a single touch, so as to leave the plain moving map display un-obscured to facilitate navigation.

The computer display system as described above optionally to replace the positions and details of other aircraft easily.

The computing system described above to calculate range and relative bearing of all other traffic in turn, and add that data to the ordered aircraft records in the computer memory The computing system described above to examine the historic range and relative bearings stored in aircraft records in turn, and any aircraft that are holding the same relative bearing, and whose range is reducing, and that are at the same altitude as our pilot's aircraft to have their position spot (optionally) emphasised on the display, because they represent a collision risk.

According to the present invention location information from an aircraft's global positioning system, and external static barometric pressure is collected, digitally encoded and made available on a radio communications network. Similarly ground stations make the ground barometric pressures available to the same radio communications network. Ground barometric pressures available would include the sea level pressures for altimeter setting regions (regional QNH), airfield field elevation pressures (airfield QFE), and sea level pressures at airfields (Airfield QNH). Aircraft or ground stations transmit their information in turn, and they receive continuously. At every aircraft and ground station data from the network is filed in ordered records in a computer memory as it is received, together with the time of transmission and reception. The result is that every aircraft and ground station on the network has in the memory of its computer current and historic information on every other aircraft and ground station on the network.

From the ground barometric pressures available on the network, and that are stored in the computer memory, and the external barometric pressure at other aircraft, the system can calculate altitudes of all aircraft with respect to any chosen base. At any one time, all altitudes within the computer system of a particular aircraft are displayed with respect to the same altitude base. This calculated altitude information is added to the ordered aircraft records in the computer system on board our aircraft.

From the positions of other aircraft obtained from the network it is possible to calculate range and bearing of all other aircraft relative to ones own aircraft. This information is added to the aircraft records in the computer system on board our aircraft.

GPS systems often feature a moving map display. Aircraft positions can be plotted superimposed upon this. The current position is plotted as a bright spot, and historic positions are plotted as a faded trail. Historic positions may be plotted over the same time frame for each aircraft, so that the length of the faded trail gives a measure of the speed of other traffic.

Most flying is done in straight lines and at constant altitude. It is possible to specify altitude limits over which aircraft are displayed. For example it is possible to display only those aircraft that are within two thousand feet of ones own altitude. This simplifies the display.

Direct plotting requires very little computer power. Other aircraft show up well on the display, it is possible to spot impending collisions very easily. Orbiting aircraft show up well.

Aircraft that are holding the same relative bearing to our aircraft and whose range is decreasing are a collision risk. If range and bearing have been calculated, the computer can examine the historic records for all other traffic, and call attention to those that represent a collision risk.

The collision avoidance display is best plotted as a layer, so that it can be removed from the map display at a single touch to facilitate navigation if required. It can of course also be replaced at a single touch if required.

To take a simple example of the invention. Figure 1 illustrates the pilot's eye view of the display unit. The pilot has already put such details as his aircraft's registration, type, and weight code into non volatile memory in the system in his aircraft. This makes this information available for transmission on the network. The pilot is flying the aircraft with registration G-MEME, whose position is indicated by the miniature aeroplane on the display.

The pilot has set the system to show historic position points over a one minute time frame, and to show other aircraft at his altitude plus or minus one thousand feet, so he can see all other aircraft flying between 4000ft and 2000ft on his display. The lower left hand window shows that altitudes on G-MEME's system are all expressed above the sea level pressure of the Portland altimeter setting region. G-MEME's altitude is 3000ft, and this is shown at the top of the window. The Portland QNH pressure was received from the communications network, and is'updated every 30 seconds. Should the aircraft climb above 3050ft above mean sea level, the altitude display would change to 3100ft. The pilot has set the display to round altitudes to the nearest 100ft to prevent the lower figures racing. Aircraft flown by hand wander a little in both altitude and heading.

The altitude displayed is calculated from the external static barometric pressure measured at the aircraft and the altitude base pressure in use. The altitudes of the other two aircraft on the display, G-BGGT and G-PACE are calculated from the external static barometric pressure measured at those aircraft and presented via the network, and the base pressure in use in G-MEME. In other words all altitudes on G-MEME's collision avoidance display are expressed as altitudes above the same base datum level.

The other window at the bottom of the display shows scale, track made good, and position. It is fairly typical of any moving map display.

The present plotted position of G-MEME is where the wings cross the fuselage of the miniature aircraft on the display. The positions are stored approximately every 10 seconds, so six previous positions are available. Two are obscured by the miniature aircraft, but a trail of four previous positions is visible. This gives the pilot a reference of his speed G-PACE and G-BGGT have presented their positions and other information to the network every 10 seconds, and their present (black dots) and previous (grey dots) positions have been plotted over the same one minute time frame. This gives a measure of their speed. Clearly from the visible trend there is going to be a collision or near miss between these aircraft in about five minutes time. Note that interpolation can be used to join the position dots to form a continuous trace if required.

The positions have been plotted from latitude and longitude information received from each aircraft's GPS system via the communications network, and held in the aircraft records in the computer memory in G-MEME. Aircraft registration details, aircraft type, aircraft weight code and static barometric pressure are transmitted in the same packets. On portable systems, which might be used in several aircraft, registration and type are programmed into non-volatile memory before flight so as to be available for transmission on the network.

Very little computing power is required to receive data, store it, calculate and store altitude, and plot position points. Such a basic display has just the position points and aircraft registration, aircraft type and altitude shown-it is a fairly easy addition to a GPS moving map display system.

From latitude and longitude of both G-MEME and G-PACE it is possible to calculate range and relative bearing of G-PACE. The mathematics is simple, the range and bearings are stored in aircraft records in the computer memory in G-MEME after calculation. The previous range and bearing can be examined in these aircraft records. Any aircraft that is at our altitude, that has held the same relative bearing (within limits) and whose range is steadily decreasing represents a collision risk. On the colour display fitted to G-MEME the alarm is set to be flashing red. Both G-PACE, which has had a relative bearing of 88 degrees for some time, and G-BGGT which has had a relative bearing of 360 degrees plus or minus five degrees for some time, are raising this alarm.

Aircraft flown by hand wander a little from their course. Averaging is necessary to get a steady course made good. Limits of relative bearing are adjustable by the pilot, and have to be set to balance the need to avoid false alarms with the accuracy with which one can comfortably fly the aircraft. For hand flown aircraft the basic system without alarms is quite adequate. The pilot can see situations developing-the system is a great aid to visual scans.

The system has records on all aircraft within range, but only those of interest have been selected for display. Display criteria can be changed by the pilot at any time.

The aircraft G-BGGT is doing a 2 minute turn. It has done half of the turn in the one minute time frame.

The basic system can be made into a very economical self contained portable instrument. Aerials should be fitted with sockets so that they can be extended if required.

System performance is improved by fitting external aerials for both GPS and transceiver.

Likewise even on un-pressurised aircraft altimetry is improved if the external static barometric pressure is derived from a properly installed static pressure port. With a pressurised aircraft the port is mandatory of course. The system can run on batteries, but a connection to the aircraft's power means that the system can run for unlimited time. Required bandwidth for the network transceiver is quite low, with compression it is possible to fit the information from 500 aircraft onto a 20kbps network.

Figure 2 is a block diagram of the hardware. The computer, display, and data entry system could be a laptop computer. However, better ergonomics are possible if a special unit is made. The Global Positioning System (GPS) engine is just reporting location, typically latitude and longitude, this could be fed into a laptop computer via a serial port. The barometric sensor produces a digital output and has a pressure resolution equivalent to typically ten feet of altitude. It is read by the computer every ten seconds or so.

Aircraft packets are transmitted approximately every ten seconds. This enables adequate position points to be plotted, and keeps network bandwidth as low as possible There is a direct trade off between frequency of packet transmission and network bandwidth required. It is possible to change frequency of packet transmission if required, and there is no necessity for aircraft to transmit at the same rate of course. Ground stations transmit their packets approximately every thirty seconds, to enable aircraft starting up to have up to date pressure data within a maximum of thirty seconds.

The range over which the system has to collect data defines both the network transceiver range, and the required network bandwidth. Assuming a closing speed of 600 kt, a

range of 20 run gives 2 minutes to impact. Even on a clear day it is difficult if not impossible to spot a small aircraft at 20 nm. This gives a ground area of 1260 square nautical miles. The system has to be used over water and at all altitudes, so direct aircraft to aircraft communication is desirable. 500 aircraft on the network require a bandwidth of about 20 Kbit/second. Bandwidth required rises linearly with increasing aircraft numbers. Prototyping can be done using about 10 watts power on VHF, with Ethernet networking technology However, there are a number of better technologies and frequencies available. Standards have to be set with some care before the invention enters full production.

The data input enables the pilot to put information such as aircraft registration, aircraft type and weight code into the system. If the system was based on a high powered laptop computer the keyboard or a floppy disk could be used for this. If the invention had been implemented as a special instrument then such data can be put in via a special port on the instrument. That port would be temporarily connected to a personal computer during preflight planning. Existing GPS systems with moving map displays already have all of the items except barometric pressure sensor and the transceiver. They can have collision avoidance added by adding these two pieces of hardware, and modifying the process running within the computer of the unit.

Claims (1)

1. CLAIMS 1) A digital communications network, for example a radio network, upon which data from aircraft instruments and controls and ground station instruments and controls is presented in turn so that the data from each aircraft and ground station on the network is available to some or all other aircraft and stations on the communications network 2) A digital communications network, for example a radio network, upon which location data from aircraft global positioning systems, external static barometric pressures measured at aircraft, aircraft registration, aircraft type and aircraft weight code are presented in turn by aircraft; and upon which static barometric pressures measured at ground stations are presented in turn by ground stations, so that the data from each aircraft and ground station on the network is available to some or all other aircraft and ground stations on the communications network.

   3) A computing system on board each aircraft to store the data from the digital communications network as claimed in Claim 1 or Claim 2 as it is received, together with the time of reception and transmission, in records in the computer's memory ordered by the aircraft that the data relates to.

   4) A computing system as claimed in Claim 3 to calculate altitudes for all aircraft presenting data on the network, from external static barometric pressure data received from those aircraft via the network, and from static barometric pressure measured at ground stations received via the network, and to store these calculated altitudes in the ordered aircraft records referred to in Claim 3.

   5) A computing system as claimed in Claim 3 or Claim 4 to optionally select aircraft details for display according to criteria set by the pilot.

   6) A computing system as claimed in Claim 3 or Claim 4 or Claim 5 to have a display system to plot the present positions and details of aircraft, possibly superimposed upon a moving map display, so that the pilot can see the position, details and altitude of other aircraft relative to his own position.

   7) A computer display system as claimed in Claim 6 to be able to use the weight code in the aircraft record in the computer memory to optionally display heavier aircraft as a larger spot on the display.

   8) A computer display system as claimed in Claim 6 or Claim 7 to plot the present position and details of aircraft, and also plot (possibly at reduced intensity) the previous positions of those same aircraft over a selectable time frame, so that the pilot can see the speed and direction of all other traffic relative to his own aircraft's speed and direction.

   9) A computer display system as claimed in Claim 6 or Claim 7 or Claim 8 optionally to remove the positions and details of other aircraft easily, so as to leave the plain moving map display un-obscured to facilitate navigation.

   10) A computer display system as claimed in Claim 9 optionally to replace the positions and details of other aircraft easily.

   11) A computing system as claimed in any preceding claim to calculate range and relative bearing of all other traffic in turn, and add that data to the ordered aircraft records referred to in Claim 3.

   12) A computing system as claimed in any preceding claim to examine the historic range and relative bearings stored in aircraft records in turn, and any aircraft that are holding the same relative bearing, and whose range is reducing, and that are at the same altitude as our pilot's aircraft to raise an alarm, for example to have their position spot (optionally) emphasised on the display, because those aircraft represent a collision risk.