Patent Description:
ICAO and other regulators envision three kinds of aircraft tracking: <NUM>) Aircraft Tracking Normal Operations ("Normal Tracking"); <NUM>) Aircraft Tracking Abnormal Operations ("Abnormal Tracking"); and <NUM>) Autonomous Distress Tracking ("ADT"). The Aircraft Tracking Normal Operations is a possible subset of Air Traffic System ("ATS") surveillance used for airline operational functions. Normal Tracking occurs continuously from takeoff to landing and tracks where the airplane travels. Information pertaining to a position of the airplane is transmitted at least once every fifteen minutes via a position report. The position report can include information, such as latitude, longitude, altitude, and heading information. If available, surveillance can be substituted for Normal Tracking. The Abnormal Tracking and ADT are triggered by an abnormal event and provide flight location data at least once per minute in response to a trigger. Abnormal Tracking can be triggered when the airplane is in the air or on the ground. If available, surveillance can be substituted for Abnormal Tracking. ADT can be triggered by a very specific set of conditions being defined, for example, by Special Committee SC-<NUM>. The ADT is a formal distress signal that initiates SAR protocols. The ADT is independent of aircraft power loss and continues to transmit after a loss of aircraft power for the duration of the flight. It is required that the ADT provides a crash site location within six nautical miles of the crash site (or a one minute minimum update rate). Furthermore, the ADT system cannot be isolated and should be independent of Normal and Abnormal Tracking. However, because all three kinds of aircraft tracking are controllable by the flight crew, or another person, the systems can be disabled or tampered with. Thus, there is a need for a tamperproof avionics system by which an aircraft could be located and/or tracked down in case of an abnormal or distress event.

<CIT> describes a system that includes an aircraft secondary radar transponder activity detector that monitors an aircraft's transponder transmissions and activates an emergency locator transmitter to begin transmitting should the aircraft transponder transmission cease to help locate an aircraft that may have become undetectable by conventional aircraft surveillance and tracking systems.

This section provides a general summary of the present disclosure and is not a comprehensive disclosure of its full scope or all of its features, aspects, and objectives.

The present invention is defined in appended independent claim <NUM>. The invention relates to an autonomous distress tracking system for an aircraft which includes a first transponder configured to transmit radio frequency (RF) emissions and an RF detector unit configured to detect the RF emissions. The system further includes an alert system that is in communication with the RF detector unit and comprising a distress radio beacon. The system further includes a second transponder, wherein the transponder is installed at a first location and the second transponder is installed at a second location. The first transponder and the second transponder function independently. The alert system is configured to activate the distress radio beacon if no RF emissions from the first and the second transponders are detected within a predetermined period of time.

Also disclosed herein, but not part of the invention, are exemplary implementations of a method for activating a locator beacon for global aircraft tracking. An exemplary method includes detecting aircraft operations and identifying an abnormal event based on the aircraft operations. The method further includes determining if the abnormal event was intentional and activating the locator beacon if the abnormal event was not intentional.

Also disclosed herein are exemplary implementations of a system for activating a radio beacon on an aircraft, which is not part of the invention. An exemplary system includes a transponder and an RF detector. The transponder is installed on the aircraft at a first location and the RF detector installed on the aircraft at a second location. The transponder is configured to transmit coded information readable by the RF detector and the RF detector is configured to trigger activation of the radio beacon based on the coded information.

The following description is merely exemplary in nature and is not intended to limit the disclosure in its application or uses. For purposes of clarity, the same reference numbers are used in the description and drawings to identify similar elements.

The present disclosure relates generally to an avionics system by which an aircraft can be located and/or tracked down in the event of an abnormal event, such as a distress event, a catastrophic emergency, hijacking, etc. The avionics system can use electronic and/or visual signals. The avionics system can be installed inside or outside of the aircraft and away from the cockpit and passenger/cargo compartments to eliminate access to external controls that could otherwise be tampered with.

<FIG> illustrates an avionics system <NUM> of an aircraft <NUM> for activating a radio beacon through an aircraft transponder in accordance with aspects of the present disclosure. The avionics system <NUM> can include additional and/or fewer components and is not limited to those illustrated in <FIG>. As shown above by way of example, the avionics system <NUM> can include and/or communicate with at least the following components: a first satellite <NUM>, a transponder <NUM> that can include trigger logic for transmitting an Automatic Dependent Surveillance - Broadcast ("ADS-B") out <NUM> via a first antenna <NUM>, an Automatic Direction Finder Recorder ("ADFR") <NUM> that can include trigger logic, an ELT/RF module <NUM> that can include an Emergency Locator Transmitter-Distress Tracking ("ELT-DT") unit and an RF detector, and a second antenna <NUM> for transmitting a wireless distress trigger <NUM>, for example, to a second satellite <NUM>.

The aircraft <NUM> can also include a first communication system <NUM> and a second communication system <NUM>. The first communication system <NUM> can include the transponder <NUM>, which can transmit ADS-B out <NUM> to the first satellite <NUM>. The first satellite <NUM> can be a space-based ADS-B-capable satellite. The aircraft <NUM> can determine its position via satellite navigation or any other desired means and periodically broadcast the information to the transponder <NUM> for transmission, which enables the aircraft <NUM> to be tracked via ADS-B out <NUM>. In this way, the transponder <NUM> can be used as a part of the aircraft's surveillance system. The information from the transponder <NUM> can be received by air traffic control (ATC) ground stations or other aircraft. In other words, the transponder <NUM> can periodically (e.g. every second or any other desired periodicity) broadcast real-time information about the aircraft <NUM> through the transponder <NUM> located on the aircraft <NUM>. Such transmissions of information, for example, position and velocity data, make the aircraft <NUM> visible in real-time to the ATC and other appropriately equipped aircraft.

The transponder <NUM> can also include trigger logic, such as distress trigger logic. The distress trigger logic can monitor the aircraft's performance to determine whether a distress event has occurred. If a distress event has occurred, then the transponder <NUM> can be activated and a distress signal can be sent to the first satellite <NUM>. The transponder <NUM> can also send coded information to a matched RF detector located on the same aircraft to wirelessly activate a beacon or locator. The RF detector is identified in the second communication system <NUM> in more detail below. The distress trigger logic can be hosted inside the transponder <NUM>. When the distress trigger logic is hosted in the transponder <NUM>, there is no impact to the aircraft wiring or to a Line-Replaceable Unit ("LRU") count. Alternatively, the distress trigger logic can be hosted external from the transponder <NUM> and wired to the transponder <NUM> to detect any distress events.

The second communication system <NUM> can include the ELT/RF module <NUM>. The ELT/RF module <NUM> can be configured to function as an alert system. The ELT/RF module <NUM> can include the RF detector and the ELT-DT unit for detecting information and transmitting the information, respectively, to the second satellite <NUM>. The second satellite <NUM> can be a COSPAS SARSAT or any other suitable satellite type. The COSPAS SARSAT is a system that can detect and locates radio beacons, such as distress beacons that are activated, for example, by aircraft, ships, and people in remote areas. After an activated distress beacon is detected, the COSPAS SARSAT can send the distress alerts to SAR authorities.

The RF detector monitors transmissions, such as <NUM> transmissions, sent by the transponder <NUM>. The RF detector can be located in the ELT/RF module <NUM>, an RF detector unit <NUM>, the ELT-DT unit, or in any other desired location, such as a stand-alone unit. For example, the RF detector can be installed in-line between the transponder <NUM> and the first antenna <NUM> or in any other desired location, such as in a separate LRU. The RF detector could be integrated into any LRU, such as an LRU for the ELT or any other LRU, given that the ELT/RF module <NUM> cannot be disabled.

When the transponder <NUM> sends a distress bit or the transponder <NUM> stops sending any RF transmissions (i.e. all RF transmissions cease), the RF detector can activate the ELT-DT unit. The avionics system <NUM> can then activate a radio beacon, such as the wireless distress trigger <NUM>, for global aircraft tracking. The wireless distress trigger <NUM> can be received by the second satellite <NUM>, such as the COSPAS SARSAT, or another satellite, aircraft, organization, or device.

The second communication system <NUM> can also include the ADFR <NUM> with optional trigger logic. The distress trigger logic can be hosted externally. The external system can be wired to the ADFR <NUM> and used to detect any distress events. The ADFR <NUM> can record flight information from the aircraft's navigation system. For example, the ADFR <NUM> can record information from the aircraft's position report, aircraft avionics systems and sensor data, and other information. The flight information can be downloaded for post-flight analysis. The trigger logic can be activated if it detects an abnormal event, such as a distress event or when the aircraft <NUM> enters into a distress tracking mode. For example, if the trigger logic determines that a distress event has occurred, such as an emergency of the aircraft <NUM> or that no RF transmissions are being sent from the aircraft <NUM> (i.e., all or both transponders failed or are in an OFF state) within a specified period of time, the wireless distress trigger <NUM> via the ELT-DT unit can be activated. Additionally, the transponder <NUM> can transmit dedicated information to a compatible or matched RF detector on the same aircraft to activate the wireless distress trigger <NUM>. The ELT-DT unit can also inform the SAR authorities that the aircraft <NUM> is in distress.

<FIG> illustrates a global aircraft tracking radio beacon activation system, or system <NUM> in accordance with aspects of the present disclosure. The system <NUM> can include aircraft avionics systems and sensor data <NUM>. The aircraft avionics systems and sensor data <NUM> can include a weather radar system ("WXR") <NUM>, a distance measuring equipment ("DME") <NUM>, a flight management system ("FMS") <NUM>, an air data computer ("ADC") <NUM>, an inertial reference system ("IRS") <NUM>, a flight control computer ("FCC")/mode control panel ("MCP") <NUM>, and a global positioning system ("GPS")/global navigation satellite system ("GNSS") <NUM>. The system <NUM> can include a sensor or another device or form of communication for detecting, receiving, and/or transmitting data to/from the aircraft avionics systems.

The aircraft avionics systems and sensor data <NUM> can transmit aircraft avionics systems and sensor data separately to a first transponder unit <NUM> and to a second transponder unit <NUM>. The aircraft avionics systems and sensor data <NUM> can include, for example, information contained in a position report; position, velocity, acceleration, airspeed, altitude, orientation data, or any other desired parameter of the aircraft <NUM>; transponder mode and/or status data; aircraft control surface position and flight control system data; distress mode configuration data; in-air/on ground and phase of flight data; weather radar data; or any other desired data concerning the aircraft <NUM>.

The transponder units <NUM>, <NUM> can each include a Mode S function <NUM>, a distress mode function <NUM>, and distress mode configuration data <NUM>. The Mode S function <NUM> can be a secondary surveillance radar process that allows selective surveillance of the aircraft <NUM> according to a unique <NUM>-bit address assigned to the aircraft <NUM>. The Mode S function <NUM> transmits information to the distress mode function <NUM>. The distress mode function <NUM> can be configured to increase communication when the aircraft <NUM> is in a distress mode, including the activation of the distress beacon (ELT, recorder, etc.) under a predefined set of criteria. The distress mode configuration data <NUM> can also send information, for example, configuration data to the distress mode function <NUM>.

The transponder units <NUM>, <NUM> can be connected to a first antenna <NUM> and a second antenna <NUM> via a first cable <NUM> and a second cable <NUM>, respectively. The antennas <NUM>, <NUM> can be L-band antennas, or another type of antenna used for receiving and/or transmitting information, such as transponder RF transmissions <NUM>, <NUM>, respectively. The cables <NUM>, <NUM> can be RF coaxial cables, or any other desired cables or wiring. The transponder units <NUM>, <NUM> can also be wirelessly connected to the antennas <NUM>, <NUM>. The antennas <NUM>, <NUM> can be located inside or outside of the aircraft fuselage <NUM> (i.e. the main body section of the aircraft <NUM>). The antennas <NUM>, <NUM> can also be located internally as part of the transponder units <NUM>, <NUM> (i.e. integrated within the transponder units <NUM>, <NUM>).

The transponder units <NUM>, <NUM> can separately communicate to an air traffic control ("ATC")/traffic collision avoidance system ("TCAS") System Control (hereinafter, ATC/TCAS <NUM>). The ATC/TCAS <NUM> can include an ATC control function <NUM> and a TCAS <NUM>. The communication between the transponder units <NUM>, <NUM> and the ATC/TCAS <NUM> can include TCAS/transponder coordination data, traffic advisory (TA) and resolution advisory (RA) information, distress mode configuration data, or any other desired data.

The transponder units <NUM>, <NUM> can also communicate directly to a distress beacon system <NUM>. The distress beacon system <NUM> can include a flight recorder <NUM> and an ELT <NUM>. The flight recorder <NUM>, such as the ADFR <NUM>, can be configured to record flight information from the aircraft's navigation system. The flight information can include a variety of information, such as location, heading, elevation, ascent/decent, banking, airspeed, acceleration/deceleration, or any other desired flight information. The flight information can be downloaded for post-flight analysis. The ELT <NUM> can be configured to transmit a radio beacon. For example, the ELT <NUM> can function as an alert system to transmit a distress radio beacon. The distress beacon system <NUM> can be connected to a distress beacon system antenna, or antenna <NUM> via a cable <NUM>, such as an RF coaxial cable. Alternatively, the distress beacon system <NUM> can communicate wirelessly to the antenna <NUM> or communicate using another type of connection. The transponder units <NUM>, <NUM> can be configured to send distress mode and trigger data to the distress beacon system <NUM>. If either of the transponder units <NUM>, <NUM> send a distress mode and/or trigger data to the distress beacon system <NUM>, the distress beacon system <NUM> can evaluate the information and when appropriate, activate a radio beacon <NUM>, such as a distress beacon, to a satellite <NUM>. In this configuration, the activation of the distress beacon (ELT, recorder, etc.) under a predefined set of criteria can be automated, and thus, tamperproof.

The transponder units <NUM>, <NUM> can also communicate via the antennas <NUM>, <NUM> to an RF detector unit <NUM>. The RF detector unit <NUM> can be connected to an antenna <NUM>, such as an RF detector antenna, via a cable <NUM>, such as an RF coaxial cable. Alternatively, the RF detector unit <NUM> can communicate wirelessly to the antenna <NUM> or communicate using another type of connection. The antenna <NUM> can receive information from antennas <NUM>, <NUM> and transmit the information to the RF detector unit <NUM>.

The RF detector unit <NUM> can be configured to measure transponder RF transmissions <NUM>, <NUM> and/or other RF emissions to/from the aircraft <NUM>. As transponder units <NUM>, <NUM> can be required to transmit information or data periodically, the RF detector unit <NUM> can be used to determine any time there is a lack of transmissions. If the RF detector unit <NUM> does not detect RF transmissions from the aircraft <NUM> (e.g., transmitted from either transponder unit <NUM>, <NUM>), the system <NUM> can similarly activate the radio beacon <NUM> (e.g. the distress beacon). In doing so, the RF detector unit <NUM> can be configured to transmit RF activity status/trigger data to the distress beacon system <NUM>. The distress beacon system <NUM> can then, when appropriate, activate the radio beacon <NUM> as a distress or locator beacon.

The RF detector unit <NUM> can be a separately installed device. The RF detector unit <NUM> can be installed on the skin of the aircraft next to the TCAS <NUM>, on one of the transponder antennas <NUM>, <NUM>, or any other desired location. For example, the RF detector unit <NUM> can be installed in-line between the transponder unit <NUM> and the antenna <NUM>, between the transponder unit <NUM> and the antenna <NUM>, in any other desired location as a separate LRU. The RF detector unit <NUM> can also be integrated into any LRU, such as an LRU for the ELT <NUM> or any other LRU, given that the integrated unit cannot be disabled. Furthermore, the RF detector unit <NUM> can be powered through an internal battery to ensure that the RF detector unit <NUM> cannot be disabled during flight, as well as keeping the RF detector unit <NUM> powered during a complete loss of aircraft power. The RF detector unit <NUM> can be powered, for example, by 28VDC or <NUM> V <NUM> from the aircraft <NUM>.

As shown above by way of example, leveraging a satellite payload, such as an Aireon ADS-B satellite payload on the Iridium constellation, airlines can use the ADS-B system to meet the normal and other tracking needs worldwide. However, a potential challenge with this ADS-B space-based solution is to address the automated distress tracking mode. To address this, several solutions may be possible, among them being moving the transponder breakers or transponder units out of the cockpit. Pursuant to embodiments of the present invention, the system <NUM> can be activated when it detects that the aircraft <NUM> strayed from perceived normal operation as described above. According to the invention, the ELT unit can be activated if neither of the transponder units <NUM>, <NUM> detect any transponder RF transmissions <NUM>, <NUM> from the aircraft <NUM> (i.e., all transponders have failed or are in an OFF state). By incorporating a radio beacon <NUM> into the ADS-B system or systems <NUM>, a full complement of distress conditions can be addressed without the need to move either of the transponder units <NUM>, <NUM>.

<FIG> illustrates an avionics system <NUM> using a stand-alone RF detector, such as the RF detector unit <NUM> in accordance with aspects of the present disclosure. The transponder unit <NUM> can be a Mode-S transponder unit or another transponder device. The transponder unit <NUM> transmits transponder RF transmissions <NUM> to the RF detector unit <NUM>. The transponder RF transmissions <NUM> travel from the transponder unit <NUM> through the cable <NUM> and then can be transmitted from the antenna <NUM> to the antenna <NUM> to travel through the cable <NUM> to the RF detector unit <NUM>. The RF detector unit <NUM> can be configured to send RF activity status or trigger data to the ELT <NUM>. The ELT <NUM> can activate the radio beacon <NUM> by sending a transmission (e.g. an RF transmission) through the cable <NUM> to an ELT antenna, or antenna <NUM>. The radio beacon <NUM> can be transmitted via the antenna <NUM>, for example, to the ATC or the SAR via a satellite. The antennas <NUM>, <NUM>, and <NUM> can be located within the aircraft fuselage <NUM> (i.e. within the aircraft's main body section) or external or outside of the aircraft fuselage <NUM>. The antennas <NUM>, <NUM>, and <NUM> can also be located internally of the transponder unit <NUM>, the RF detector unit <NUM>, and the ELT <NUM>, respectively. For example, the RF detector unit <NUM> can have an internal antenna for the electronic beacon to prevent tampering. An external antenna port can also be configured. Furthermore, the antennas <NUM>, <NUM>, and <NUM> can be any of a variety of antennas types, including, but not limited to, an L-Band antenna, an RF detector antenna, and an ELT antenna, respectively. Additionally, the avionics system <NUM> can transmit <NUM>-<NUM> watts or any other desired range to allow for the electronic signal to penetrate through areas, such as deep water, dense foliage, etc..

<FIG> illustrates an avionics system <NUM> using an RF detector module integrated into an ELT module in accordance with aspects of the present disclosure. The avionics system <NUM> is similar to the avionics system <NUM> described above, with a few exceptions. More specifically, the transponder unit <NUM> transmits transponder RF transmissions <NUM> to the RF detector unit <NUM> via an RF integrated unit <NUM>. The RF integrated unit <NUM> can include the RF detector unit <NUM> and the ELT <NUM>. The RF detector unit <NUM> and the ELT <NUM> can be integrated to allow for internal communication <NUM>, such as RF activity status or trigger data, to travel internally from the RF detector unit <NUM> to the ELT <NUM>. The ELT <NUM> can activate the radio beacon <NUM> by sending a transmission through the cable <NUM> to the antenna <NUM> as described above.

<FIG> illustrates an avionics system <NUM> using an RF detector integrated into a LRU in accordance with aspects of the present disclosure. The avionics system <NUM> is similar to the avionics system <NUM> described above, with a few exceptions. More specifically, the transponder unit <NUM> transmits transponder RF transmissions <NUM> to the RF detector unit <NUM> via a non-RF integrated unit <NUM>. The non-RF integrated unit <NUM> can include the RF detector unit <NUM> and a non-ELT device <NUM>. The non-ELT device <NUM> can be a LRU or another device that does not have RF functions. The RF detector unit <NUM> and the non-ELT device <NUM> can be integrated to allow for internal communication, transfer of power, or any other function. The RF detector unit <NUM> can transmit RF activity status or trigger data to the ELT <NUM>. The ELT <NUM> can activate the radio beacon <NUM> by sending a transmission through the cable <NUM> to the antenna <NUM> as described above. The systems <NUM>, <NUM>, <NUM> can include additional and/or fewer components and configurations and are not limited to those illustrated in <FIG>.

<FIG> illustrates an exemplary method <NUM> for activating a radio beacon (e.g. locator beacon) from any of the exemplary systems illustrated in and described with respect to <FIG> or any variations thereof. At step <NUM>, the system detects aircraft operations.

At decision step <NUM>, the system determines if some other abnormal event has occurred (e.g. that the aircraft strayed form a perceived normal operation). Abnormal events can include, but are not limited to the following situations: <NUM>) the aircraft suddenly ascends/descends out of a range of normal operation for the aircraft; <NUM>) the aircraft suddenly banks in a manner that is out of range of normal operation for the aircraft; <NUM>) the aircraft suddenly changes in airspeed beyond a predefined acceptable airspeed change, at any time during the flight but typically when the aircraft <NUM> is at a greater than predetermined distance from an airport; or <NUM>) any or all installed transponders are determined as not operating or not functioning properly. If the system does not detect an abnormal event, then the system proceeds back to step <NUM>. If the system determines that an abnormal event has occurred, then the system proceeds to step <NUM>.

At step <NUM>, the system can monitor at least one information system. Some exemplary information systems can include any of the systems identified above in the aircraft avionics systems and sensor data <NUM>, the TCAS, transponder busses, or any other desired system that provides sensor data, avionics data, or any other desired information. The TCAS can be an aircraft collision avoidance system used for reducing the incidence of mid-air collisions between aircraft. The TCAS may issue a traffic advisory ("TA"), a resolution advisory ("RA"), or by the absence of a TA and an RA, indicate that the aircraft is clear of conflict. The system can monitor the TCAS for current traffic conditions and alerts. The system can monitor transponder busses to detect whether each transponder is in an ON state or an OFF state. Furthermore, the transponder busses can be monitored for proper function (i.e., whether each transponder is working properly). The system can also monitor a weather radar system, such as WXR <NUM> for weather conditions. For example, the system can monitor if there is a change in weather pattern, type of weather condition, wind speed, temperature, or any other desired weather condition.

At decision step <NUM>, the system determines if various factors, such as changes in elevation, heading, or speed was initiated intentionally. The system can determine this from the data or information collected by monitoring the information system(s) in step <NUM>. For example, the system can determine if a TAIRA event was occurring, if the transponders were turned off, or if a weather event or condition was occurring that would cause the aircraft <NUM> to suddenly or drastically change its flight pattern, such as elevation, heading, or speed. If the system determines that the abnormal event was not intentional, then the system proceeds to step <NUM>. If the system determines that the abnormal event was intentional, then the system proceeds to decision step <NUM>.

At decision step <NUM>, the system determines if a specific event occurred. The specific event can be any one of a number of events, such as if a TAIRA event has occurred, if both or all of the transponders are in an OFF state, if at least one transponder is in an OFF state but was properly functioning before entering the OFF state (i.e., at least one transponder was properly functioning when exiting the ON state), or a weather condition or event occurred outside of a set of normal parameters. In the situation of no transmissions being detected or a properly functioning transponder being turned off, the system determines that the transponder may have been tampered with and can activate the locator beacon, informing proper authorities of the location of the aircraft <NUM> or that the aircraft <NUM> has an emergency. If the system determines that no specific event detected, then the system proceeds to step <NUM>. If the system determines that the specific event was detected, then the system proceeds to step <NUM>.

At step <NUM>, the system enters into a monitor mode. For example, if the system detects that a TAIRA event is occurring, it reverts to the monitor mode for a period of time (e.g., several seconds) to allow the other aircraft to complete the necessary maneuvers. As described above, the system can monitor transponder busses to determine whether the transponders have been turned off and whether the transponders were functioning properly when the transponders were turned off (e.g. entered into an OFF state). If the transponders have been turned off but were not functioning or working properly when they were turned off, then the system enters into a monitor mode. As described above, the system can monitor the weather radar to determine if a specific event was occurring that would require the aircraft to change elevation, heading, or speed. If the system determines that such a specific event was occurring at the time of the aircraft maneuver, it can revert to a "monitor" mode for a period of time (e.g., several seconds) to allow the aircraft <NUM> to complete the necessary maneuver. The system then proceeds back to step <NUM>. The system may exit the monitor mode before proceeding to step <NUM>, remain in the monitor mode for a period of time, and/or remain in the monitor mode while detecting aircraft operations in step <NUM>.

At step <NUM>, the system can activate the locator beacon. The locator beacon can be used to assist authorities in locating the aircraft <NUM>. By incorporating a beacon into the system, such as the ADS-B system, a full complement of distress conditions can be addressed without the need to move transponder breakers. The methods described in <FIG> can include additional and/or fewer components and/or steps in an alternative order and are not limited to those illustrated in this disclosure.

Claim 1:
An autonomous distress tracking system (<NUM>, <NUM>, <NUM>, <NUM>) for an aircraft (<NUM>), comprising:
a first transponder (<NUM>) configured to transmit radio frequency (RF) emissions (<NUM>);
an RF detector unit (<NUM>) configured to detect the RF emissions; and
an alert system (<NUM>) in communication with the RF detector unit (<NUM>) and comprising a distress beacon system (<NUM>),
a second transponder (<NUM>), wherein the first transponder (<NUM>) is installed at a first location and the second transponder (<NUM>) is installed at a second location,
characterized in that
the transponder (<NUM>) and the second transponder (<NUM>) function independently, and in that
wherein the alert system (<NUM>) is configured to activate the distress radio beacon (<NUM>) if no RF emissions from both the first and second transponders (<NUM>, <NUM>) are detected by the RF detector (<NUM>) within a predetermined period of time.