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Title:
IMPROVED TRACKING SYSTEM, DEVICE AND METHOD
Document Type and Number:
WIPO Patent Application WO/2012/011825
Kind Code:
A1
Abstract:
A system for detecting if an aircraft being tracked is involved in an incident including a receiver for receiving transmissions of location information from an aircraft being tracked, and a computer system for monitoring the location information, wherein the computer system is configured to detect that the aircraft is involved in an incident when received location information indicates the aircraft has been substantially stationary for more than a threshold length of time.

Inventors:
BARTLEY, Bruce Howard (13 Cameron Drive, RD1Taupo, 3377, NZ)
Application Number:
NZ2011/000142
Publication Date:
January 26, 2012
Filing Date:
July 22, 2011
Export Citation:
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Assignee:
SPIDER TRACKS LIMITED (117A The Square, Palmerston NorthWellington, 4410, NZ)
BARTLEY, Bruce Howard (13 Cameron Drive, RD1Taupo, 3377, NZ)
International Classes:
G08G5/00; G01S19/17
Foreign References:
EP1190408B12004-07-14
US20030065428A12003-04-03
Attorney, Agent or Firm:
ADAMS, Matthew, D et al. (A J Park, 6th Floor Huddart Parker BuildingPO Box 94, Wellington 6015, NZ)
Download PDF:
Claims:
CLAIMS

1. A system for detecting if an aircraft being tracked is involved in an incident comprising: a receiver for receiving transmissions of location information from an aircraft being tracked, and

a computer system for monitoring the location information,

wherein the computer system is configured to detect that the aircraft is involved in an incident when received location information indicates the aircraft has been substantially stationary for more than a threshold length of time.

2. A system according to claim 1 wherein the location information comes from a tracldng device on the aircraft.

3. A system according to claim 1 or 2 wherein the computer system is further configured to identify the location of the aircraft from the location infotmation.

4. A system according to any preceding claim wherein the computer system is further configured to provide an alert indicating the occurrence of an incident and preferably the location of the aircraft.

5. A system according to any one of claims 2 to 4 wherein the system comprises the tracking device.

6. A system according to any preceding claim wherein the threshold is at least 5 minutes, and preferably the threshold is at least 10 minutes but not more dian 30 minutes.

7. A system according to any preceding claim wherein the computer system is further configured to detect diat the aircraft is involved in an incident when receipt of transmissions of location information cease or otherwise do not keep to an expected regime.

8. A system according to any preceding claims wherein the aircraft is a general aviation or light aircraft.

9. A method for detecting if an aircraft being tracked is involved in an incident comprising: receiving transmissions of location in ormation from an aircraft being tracked, monitoring the location information, and detecting that the aircraft has been involved in an incident when the received location information indicates the aircraft has been substantially stationary for more than a threshold length of time. 10. A method according to claim 9 wherein the location information comes from a tracking device on the aircraft.

11. A method according to claim 9 or 10 method further comprises identifying the location of the aircraft from the location information.

12. A method according to any one of claims 9 to 11 furtlier comprising providing an alert indicating the occurrence of an incident and preferably the location of the aircraft.

13. A metliod according to any one of claims 9 to 12 wherein the threshold is at least 5 minutes, and preferably the threshold is at least 10 minutes but not more than 30 minutes.

14. A metliod according to any one of claims 9 to 13 wherein the aircraft is a general aviation or light aircraft. 15. A tracking device for an aircraft used to assist in detecting if the aircraft is involved in an incident, the tracking device configured to transmit location information to a computer system that is configured to receive and monitor the location information, and to detect that the aircraft is involved in an incident when received location information indicates the aircraft has been substantially stationary for more than a threshold length of time.

16. A tracking device according to claim 15 wherein the tracking device is a GPS device.

17. A tracking device according to claim 15 or 16 wherein the computer system is further configured to identify the location of the aircraft from the location information.

18. A tracking device according to any one of claims 15 to 17 wherein the computer system is further configured to provide an alert indicating the occurrence of an incident and preferably the location of the aircraft. 19. A tracking device according to any one of claims 15 to 18 wherein the threshold is at least 5 minutes, and preferably the threshold is at least 10 minutes but not more than 30 minutes.

20. A tracking device according to any one of claims 15 to 19 wherein the computer system is further configured to detect that the aircraft is involved in an incident when receipt of transmissions of location information cease or otherwise do not keep to an expected regime.

21 A tracking device according to any one of claims 15 to 19 wherein the aircraft is a general aviation or light aircraft

22. A system for detecting if an aircraft being tracked is involved in an incident comprising: a receiver for receiving transmissions of location information from an aircraft being tracked, and

a computer system for monitoring the location information, wherein the computer system is configured to detect that the aircraft is involved in an incident when either:

received location information indicates the aircraft has been substantially stationary for more than a threshold length of time, or

receipt of transmissions of location information cease or otherwise do not keep an expected regime.

Description:
IMPROVED TRACKING SYSTEM, DEVICE AND METHOD FIELD OF THE INVENTION

The present invention relates to aircraft tracking systems comprising tracking devices and their monitoring systems, and in particular, although not solely, to tracking systems using GPS tracking devices and monitoring systems.

BACKGROUND TO THE INVENTION

Traditionally, emergency location transmitters (ELTs) have been used in aircraft to assist emergency services to locate the aircraft when an accident or other emergency or incident occurs. When the aircraft crashes, the ELT is activated, and transmits a signal which allows emergency services to determine the aircraft position. They can then send assistance. The difficulty with ELTs is that sometimes they malfunction, especially due to the accident impact. In this case, the ELT will be useless.

Tracking devices are commonly used to track the position of aircraft. Typically, a tracking device comprises a GPS receiver that receives signals from a GPS satellite network. From the signals, the tracking device can calculate its location, and therefore the current location of the aircraft in which it is installed. The device can have an output that indicates to a user the current position of the device and also historical position information. This information can be monitored.

It is an object of the present invention to utilise location information to indicate detect an aircraft involved in an incident. SUMMARY OF INVENTION

In one aspect the present invention may be said to consist in a system for detecting if an aircraft being tracked is involved in an incident comprising: a receiver for receiving transmissions of location information from an aircraft being tracked, and a computer system for monitoring the location information, wherein the computer system is configured to detect that the aircraft is involved in an incident when received location information indicates the aircraft has been substantially stationary for more than a threshold length of time.

Preferably the location information comes from a tracking device on the aircraft. Preferably the computer system is further configured to identify the location of the aircraft from the location information. Preferably the computer system is further configured to provide an alert indicating the occurrence of an incident and preferably the location of the aircraft. Preferably the system comprises the tracking device.

Preferably the threshold is at least 5 minutes, and preferably the threshold is at least 10 minutes but not more than 30 minutes. Preferably the computer system is further configured to detect that the aircraft is involved in an incident when receipt of transmissions of location information cease or othervvise do not keep to an expected regime.

Preferably the aircraft is a general aviation or light aircraft.

In another aspect the present invention may be said to consist in a method for detecting if an aircraft being tracked is involved in an incident comprising: receiving transmissions of location information from an aircraft being tracked, monitoring the location information, and detecting that the aircraft has been involved in an incident when the received location information indicates the aircraft has been substantially stationary for more than a threshold length of time.

Preferably the location information comes from a tracking device on the aircraft.

Preferably the method further comprises identifying the location of the aircraft from the location information.

Preferably the method further comprises providing an alert indicating the occurrence of an incident and preferably the location of the aircraft. Preferably the threshold is at least 5 minutes, and preferably the threshold is at least 10 minutes but not more than 30 minutes.

Preferably the aircraft is a general aviation or light aircraft. In another aspect the present invention may be said to consist in a tracking device for an aircraft used to assist in detecting if the aircraft is involved in an incident, the tracking device configured to transmit location information to a computer system that is configured to receive and monitor the location information, and to detect that the aircraft is involved in an incident when received location information indicates the aircraft has been substantially stationary for more than a threshold length of time.

Preferably the tracking device is a GPS device.

Preferably the computer system is further configured to identify the location of the aircraft from the location information.

Preferably the computer system is further configured to provide an alert indicating the occurrence of an incident and preferably the location of the aircraft.

Preferably the threshold is at least 5 minutes, and preferably the threshold is at least 10 minutes but not more than 30 minutes.

Preferably the computer system is further configured to detect that the aircraft is involved in an incident when receipt of transmissions of location information cease or otherwise do not keep to an expected regime.

Preferably the aircraft is a general aviation or light aircraft.

In another aspect the present invention may be said to consist in a system for detecting if an aircraft being tracked is involved in an incident comprising; a receiver for receiving transmissions of location information from an aircraft being tracked, and a computer system for monitoring the location information, wherein the computer system is configured to detect that the aircraft is involved in an incident when either: received location information indicates the aircraft has been substantially stationary for more than a threshold length of time, or receipt of transmissions of location information cease or otherwise do not keep an expected regime.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art. It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7).

The term "comprising" as used in this specification means "consisting at least in part of. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner. To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described with reference to the following drawings, of which:

Figure 1 is a schematic diagram of a tracking system in accordance with one embodiment of the invention,

Figure 2 is a block diagram of the tracking device,

Figure 3 is a schematic diagram showing a monitoring system output displaying an aircraft's journey path,

Figure 4 is a schematic diagram of the monitoring system,

Figure 5 is a schematic diagram showing a monitoring system output displaying an aircraft's journey path using the system in an active tracking mode,

Figure 6 is a flow diagram of the tracking system's operation.

Figure 7 is a flow diagram showing more detail of the tracking system's active tracking and overtime alert modes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

System overview

Figure 1 shows a tracking system 1 in accordance with one embodiment of the invention. The tracking system comprises a tracking device 11 that can determine its position (location). The tracking device 1 is installed in an aircraft, and thus can track the position of the aircraft. The tracking device 11 receives signals from location stations e.g. 10, and from those signals can determine its position. In a preferred embodiment, the tracking device 11 is a GPS tracking device that receives signals from the GPS navigation satellite system 10. From the GPS signals, the tracking device 10 can calculate or otherwise determine its position, in the manner known to those skilled in the art It will be appreciated however it is not essential for the tracking device to use GPS technology, and other tracking technology could be used.

The tracking device 11 is adapted to, as and when required, transmit data indicating its location/position (also called location information) to a monitoring system 14/15. It does this when certain conditions are met indicating that the aircraft has taken off or is otherwise operational. Such conditions might comprise distance from last positions report, cumulative distance travelled since last position report, changes in altitude, changes in velocity (either direction or speed), impact detection, requests for position report by an external source (e.g. button on device, request from web server). The monitoring system comprises a computer system 14 that receives the position data and utilises software to log and process the position data. The computer system 14 can present tracking information to a user via an output 15. Typically, monitoring system 14/15 provides output to the user over a website or other network, but any type of monitoring system used in any type of network could be employed.

Preferably, the tracking device 11 transmits data indicating is position to the monitoring system 14/15 via a satellite communications network 12. This could be, for example the existing IRIDIUM satellite network. This comprises a satellite network 12 to which data can be transmitted and a base station 13 that receives a relayed version of the data transmitted to the satellite network 12. The base station 13 then communicates the information to the monitoring site via standard terrestrial or other communication means. While the tracking system 1 preferably utilises satellite

communications to transmit position data from the tracking device 11 to the monitoring system 14/15, tins is not essential. Any sort of communications channel could be used, another example being a mobile telephone network.

The tracking system 1 in its simplest form comprises the monitoring system 14/15 and at least one tracking device 11 installed in the aircraft. However, the tracking system could also be considered to also comprise the GPS satellite network and/or communications channel. These, however, are typically operated by third parties and are not considered part of the tracking system per se. It will also be appreciated that the tracking system 1 could comprise more than one tracking device 11, each device being installed in a aircraft. This enables the monitoring system to monitor a range of tracldng devices 11 and more particularly the vehicles, vessels or aircraft in which they are installed. It should be noted that because in use a tracking device is installed in a aircraft, reference to the device's position will also imply a reference to the position of the aircraft in which it is installed. Figure 2 shows a block diagram of the tracking device 11 in further detail. The tracking device preferably comprises a GPS antenna 20 connected to a GPS receiver 21. The GPS receiver 21 feeds the received data into a processor 22, which can determine the device's position from the received signals. The processor 22 is connected to a satellite transceiver 23 and antenna 24 that enables the processor 22 to transmit data indicating the device's position via the satellite network 12 to a monitoring system 14/15. The processor 22 is connected to a user interface 25, which comprises buttons 26 or other input means that enables a user to operate the device 11. The user interface 25 might also comprise an output screen and/ or other output means such as LEDs or audio signals to indicate various operational states of the device and to output information. Further, there might be a remote user interface 27, such as a keyboard or control panel or the like wirelessly connected to the device or wired to the device 11. The device also comprises a power source 28 that might be internal (such as a battery) or connectable to an external power source such as a cigarette lighter of a vehicle.

The device 11 can determine its position at any particular instant based on the incoming signals received from the GPS satellite network 12. The device might continuously receive GPS signals and use the processor 22 to determine the device's position. Alternatively, it might continuously receive signals, but only periodically determine its position. Alternatively, the device 11 might only periodically receive signals and periodically determine its position. After determining the device's position, the processor might continuously or periodically transmit its determined location to the monitoring system 14/15. It might do this in real-time, i.e. as it determines the current position. This means the position data that is transmitted indicates the current position of the device.

Alternatively, the processor 22 might store the determined position at each instant for transmission at a later date. This means that the position data transmitted might not relate to the current device position. Other arrangements are possible. In general terms, the device 11 is capable of receiving signals at various time instants, and from those, determining the device's position at those time instants. The device can then transmit data indicating the determined position at those time instants in accordance with a suitable regime, based on its mode of operation.

Typically, when the device 11 transmits data at a particular instant, this data will indicate and relate to a single position that was determined at a time instant just prior to transmission (or some time before). However, data could be batch transmitted, indicating a number of positions of the device at various time instants detennined prior to transmissions.

Figure 4 shows the monitoring system 14/15 in more detail. It comprises a transceiver (comprising one or more receivers and transmitters) 40 and antenna 41 for receiving transmissions of location information from the tracking device 11, and for communicating back to the device 11 and sending alerts, location and other information to relevant authorities. The monitoring system also comprises a computer system 42 configured with software to receive and monitor the location information from the transceiver 40, and process this to detect incidents, and perform the other tracking functions of the monitoring system. A user interface 43 (which can comprise monitor 15) and storage 44 is also provided.

Figure 3 shows in schematic form an example of the output screen 15 of the monitoring system 14/15 when the tracking device 11 transmitting location information. The screen shows the general path 33 of an aircraft being monitored. The tracking device in the aircraft periodically determines its position and periodically transmits data indicating its position at a number of time instants. The periodic transmission of data will preferably relate to its current determined position, altliough this is not essential At each time instant when the device 11 determines its position, data indicating that position is transmitted. This position data is received by the monitoring system 14/15. which then stores and processes the data and also uses the data to generate a display 15 of the path 33 of travel of the aircraft. In particular, the monitoring system display a series of dots e.g. 31a, 31b, 31c superimposed on a map 30 of the area in which the device 11 is located, each dot relating to a position of the device at that time. Preferably, dots are added to the display as further position data is received, indicating updated positions of the device in real-time. It will be appreciated that there might be some inherent delay in the system, so the use of the term "real-time" should be taken in its technological context, and not be considered in a limiting manner. A tracking line 32 interpolating the movement of the device between those dots is also superimposed on the map.

As can be seen in Figure 3, the aircraft being tracked has approached land 30 from the west and then has travelled up in a north-east direction up to the top 33 of the region indicated by the map. The aircraft, then returns generally along the same path in a south-west direction and then leaves the land 30 as indicated by path 34. Each dot represents the location of the device at a particular time in accordance with data that is transmitted. The data is transmitted from the tracking device periodically, so not every position of the device/ ircraft is necessarily transmitted. Rather, it may be transmitted every minute or other period of time. Preferably, the data indicating the position is transmitted substantially in real-time.

However, in an alternative the device may delay transmission if necessary. This means that the display in the monitoring system may not be updated in real-time. In this case, the time at which a particular position was determined could be transmitted along with the location data, so this could be determined from looking at the monitor output.

Active tracking mode

The active tracking mode of the tracking device and tracking system enables the monitoring system to determine whether an anomaly/incident/emergency has occurred with the aircraft, such as an accident. The monitoring system 14/15 can then provide an alert if this occurs. Figure 5 shows in schematic form an example of the output of the monitoring device when the active tracking mode is in operation. During the active tracking mode, the tracking device 11 determines its position and transmits data indicating its position in the usual manner, such as described in relation to Figure 3. In the active tracking mode, the data indicating position will be transmitted in relation to a particular regime or pattern. For example, it may be that the data indicating determined position is transmitted periodically, for example every minute. Another transmission regime might be used instead.

The monitoring system 14/15 stores data specifying the regime, and therefore expects to receive position data from the tracking device 11 in accordance with the regime. For example, if the regime is periodic transmission of data every one minute, then the monitoring system 14/15 expects to receive transmitted position data from the tracking device 11 every one minute. The monitoring system 14/15 receives this data, logs it and generates a display on the output in accordance with the data in the usual manner. This comprises displaying dots for every position location received, e.g. 51, and showing a tracking path 52 overlayed a map 53. However, if the monitoring system detects an anomaly in the received data (e.g. loss of data 54), it then determines that an incident has occurred, such as an accident. A general example is that when the monitoring system stops receiving location information, it infers that the aircraft has crashed because the tracking device has stopped t ansmitting due to damage from the impact. An incident is them deemed to have occurred.

The active tracking mode method is shown in Figure 6. The device 11 transmits in normal mode initially, step 70. Active tracking mode is then activated, step 71. The monitoring system 14/15 then checks for anomalies, i.e. that the received data is received in accordance with the known regime, step 72. If there is an anomaly, step 73, then an alert is sent/output to an interested party - such as to a search and rescue authority, step 74. Otherwise, the monitoring system 14/15 keeps checking for anomalies. The checking for anomalies is shown in more detail in Figure 7. Referring to step 72b, if the transmissions cease (or otherwise do not keep to the expected regime), then an incident is detected, step 72d. More particularly, for example, if the regime is to transmit data every one minute, and more than one minute elapses 54 since the last received transmission, the monitoring system will detect that an anomaly has occurred, and infer that a crash or other emergency (incident) has occurred with the aircraft in which the device is installed. This might be due to the transmissions from that device ceasing. The monitoring system 14/15 can then send out an alert, in the form of a text message, email, pre-recorded phone message, pager message or some other communication to an interested party. The alert can indicate that an incident has occurred and provide the last known location of the aircraft.

It should be noted that a pilot can manually cancel tracking and monitoring in the active mode, such as when they have landed, to prevent a false trigger of an alert when they power down the aircraft and transmissions of location information stop. In an alternative, the tracking device might not send position data. Rather, it might send signals or other data. This would enable the monitoring system to monitor the transmissions, and determine if an anomaly in transmission had occurred, even if the tracking device position is not known.

Overtime alert mode

The active tracking mode provides a more reliable alternative to an ELT. As it detects an incident when receipt of transmissions of location information cease (or otherwise do not keep to an expected regime), the mode is relatively failsafe as incidents are detected even if the tracking device is not working due to the incident. However, there is a possibility that an aircraft could crash and disable the pilot (meaning rescue is required), but the tracking device remains operational. In this case, data could still be transmitted according to the regime, and the active tracking mode would not detect an accident has occurred at step 72b of Figure 7. Therefore the computer/monitoring system 14/15 has an additional overtime alert mode, which can detect an accident, even if the tracking device in the aircraft remains operational and transmits according to the expected regime.

Referring to Figure 7, in this overtime alert mode, the computer system 14/15 will detect that an incident has occurred if the received location information indicates that the aircraft has not moved (i.e. is stationary) for a direshold length of itme. The system 14/15 is configured to monitor the incoming location information, step 72a, and determine when the location information suggests the aircraft has not moved for more than a specified time, step 72c. This provides a good indication tliat the aircraft has crashed or otherwise been involved in an incident that has immobilised the aircraft and requires emergency services. Therefore, upon determining that the aircraft has not moved for the threshold time, the computer system infers/ detects an incident has occurred, step 72d, and sends an alert to a suitable party (step 74 Figure 6), which might also comprise the current location information of the aircraft. The aircraft might only have to be substantially stationary for the computer system to infer an incident— that is, small movements of the aircraft might be ignored.

Therefore, the present invention exploits this to use stationary location information as an alternative means to detect an incident. But, the tracking system does not detect an overtime alert incident as soon as it detects that the aircraft is stationary— as the aircraft might be stationary for a deliberate reason that is not indicative of an incident. Rather the tracking system waits a threshold length of time of the aircraft being stationary before triggering the overtime alert. It is the combination of detecting that the aircraft is still stationary after a certain period of time that provides a useful indication of an incident.

An aircraft might be stationary, and transmit location information that indicates it is stationary, even if no incident has occurred. For example, an aircraft might be refuelling, awaiting take-off, ground checks or boarding or unboarding passengers etc. If the tracking device 11 of the aircraft transmits location information that indicates it is stationary, this could cause the monitoring computer system 42 to detect an incident, even when no incident has occurred. This is why a threshold length of time is used before an incident is triggered for a stationary aircraft. The threshold time can be determined as follows.

Due to low battery /power capacity of aircraft, it is abnormal to keep the aircraft instruments powered-up and operating for more than a few minutes when the aircraft is left deliberately stationary under normal circumstances. Usually, instruments (including the tradring device) are powered-down after a few minutes to conserve power. This means that it would be unusual for an aircraft to keep transmitting location information from its tracking device for more than a few minutes while stationary, as normally the tracking device is powered-down (along with other aircraft equipment) after a period.

Preferably, the threshold time (before the overtime alert is triggered) is set to a suitable time corresponding to the usual operation of and the nature of the aircraft. The overtime alert generally relates to tracking of general aviation/light aircraft for which power issues are important, unlike, for example, airliners which receive power from an external power source when grounded. For light aircraft, it would be unusual for the aircraft to remain stationary (for refuelling etc. ) and powered-up for more than 10-12 minutes. Normally by this time the instruments (including the tracking device) will be powered down by the pilot. It would be very unusual to stay powered up for more than 30 minutes, as this comes close to the lifetime of the battery supplies. Possibly, a pilot could get diverted on to another task, which might mean the plane is stationary and powered up for more than 12 minutes, but usually if this occurs, the pilot would still power down the aircraft because of the short batter)' life. Therefore, being powered up and stationary for between 12 to 30 minutes is unusual, and being powered up and stationary for over 30 minutes is very unusual. Therefore, the threshold can be set in view of the likely operation of the aircraft.

Typically the system or aircraft operator will set a default threshold for detecting when a stationary vehicle should trigger an alert. This direshold is likely to be at least 12 minutes. The threshold is unlikely to be more than 30 minutes. For example, if the aircraft is usually powered-down after a few minutes when stationary, then the tracking/ monitoring system could be configured to detect an incident has occurred when it receives information indicating the aircraft has been stationary for, say, 12 minutes or longer. Alternatively, if the aircraft is usually powered-down after a longer time when stationary, say 30 minutes, then the monitoring system could be configured to detect an incident has occurred when it receives information indicating the aircraft has been stationary for 30 minutes or longer. However, the threshold could be less than 12 minutes and more than 30 minutes. This prevents false alarms whereby an aircraft is deliberately stationary but has not yet been powered-down. Clearly, depending on the aircraft and nature of its use, other direshold times could be set. The thresholds mentioned are exemplary only, and should not be considered limiting.

Note, as part of aircraft power-down when the aircraft is deliberately stationary, the tracking system will be alerted (e.g. by the pilot) that operation of the aircraft is over, so the active and overtime alert tracking modes will no longer be implemented by the tracking system. This means diat once power down occurs, data is no longer transmitted and is no longer being monitored by the tracking system so the overtime alert (nor the active tracking alert) will not be triggered by the tracking system. In summary, and with reference to Figure 7, the computer monitoring system 1 /15 can detect anomalies that indicate an aircraft incident by using the active tracking mode and overtime alert mode. This comprises, receiving transmitted location information, step 72a, checking if

transmissions have ceased or otherwise do not keep to the expected regime, step 72b, and if so detecting an incident, step 72d, and checking if the aircraft is stationary for a specified length of time, step 72c, and if so detecting an incident, step 72d. So, an incident is detected if either the transmitted location information does not keep to the expected regime or if the aircraft transmits location information to the expected regime, but that location information indicates that the aircraft has been stationary for more than a direshold length of tirae. It will be appreciated that checking steps 72b and 72c could happen in any order or concurrendy - Figure 6 just shows one possible example.