Traffic alert and collision avoidance system enhanced surveillance system and method

[0001] Conventionally, avionics, engineers and certification bodies are improving and providing pilots and flight crews with information necessary to identify in-flight traffic. An approach has been to provide the flight crew with information on the location of other aircraft in the area. One exemplary system which is capable of providing this information, is known as a traffic alert and collision avoidance system (TCAS). The systems are required for all airliners flying the United States air space today. TCAS devices have been designed to interrogate transponders of other aircrafts, sometimes referred to as intruder aircraft. The TCAS system evaluates the threat of collision with other aircraft and coordinates an avoidance maneuver for the aircraft.

[0002] Recently, the aviation industry has worked to define a new standard of performance for Mode S transponders which are the communication devices used in most TCAS systems. The extension of the function of Mode S transponders is to provide more information about the state and plans of aircraft which are under surveillance. This extended information may collectively be called “enhanced surveillance”. The feature is designed to provide ground-based aircraft control and additional information to enable improved management of air traffic. Although this information is provided from Mode S transponders to ground-based air traffic control, it may be desirable and useful for a first aircraft to be able to interrogate a Mode S transponder and receive enhanced surveillance information from a Mode S transponder on a second aircraft.

[0003] Accordingly, there is a need for a system and method in which the first aircraft may request and receive enhanced surveillance information from other airborne Mode S transponders. Further, there is a need for a system and method in which the first aircraft may request and receive enhanced surveillance information from a second aircraft Mode S transponder and provide integrity checking of the position of the aircraft. Further still, there is a need for a airborne system onboard a first aircraft which may interrogate a second aircraft's Mode S transponder at a variable rate, the rate dependent upon the determined dynamics of particular requested data.

[0004] It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.

[0005] What is provided is a traffic alert and collision and avoidance system (TCAS). The TCAS comprises a first interrogator associated with a first aircraft, the first transponder sending an interrogation request. The TCAS system also comprises a second transponder associated with a second aircraft, the second transponder responding to the interrogation request. The response comprises enhanced surveillance data that was asked for in the request.

[0006] What is also provided is a method of providing air traffic information from a first aircraft to a second aircraft. The method comprises receiving an interrogation request from a first aircraft. The request includes a request for enhanced surveillance data. The method also comprises responding by a second aircraft transponder a message comprising enhanced surveillance data that was asked for in the request.

[0007] Further, what is provided is a method of integrity checking the position of a second aircraft. The method comprises interrogating an aircraft transponder including a request for enhanced surveillance data including the position of the second aircraft. The method also comprises receiving a reply to the interrogation request by the first aircraft. Further, the method comprises calculating the position of the second aircraft based on the message response time and its bearing. Further still the method comprises comparing the calculated position with the received position. Yet further still, the method comprises determining the integrity of the received position.

[0008] Further still, what is provided is a method of interrogating the traffic alert and collision avoidance system transponder. The method comprises interrogating an aircraft transponder including a request for enhanced surveillance data. The method also comprises determining based on the enhanced surveillance data received, whether the rate of interrogation should be changed. Further, the method comprises changing the rate of interrogation if it is determined that the rate should be changed.

[0009] Alternative examples and other exemplary embodiments relate to other features and combinations of features as may be generally recited in the claims.

[0016] Before describing in detail the particular improved system and method, it should be observed that the invention includes, but is not limited to a novel structural combination of conventional data/signal processing elements and communication circuits, and not in the particular detailed configurations thereof. Accordingly, the structure, methods, functions, control and arrangement of conventional components and circuits have, for the most part, been illustrated in the drawings by readily understandable block representations and schematic diagrams, in order not to obscure the disclosure with the structural details which will be readily apparent to those skilled in the art, having the benefit of the description herein. Further, the invention is not limited to the particular embodiments depicted in the exemplary diagrams, but should be construed in accordance with the language in the claims.

[0017] Referring now to FIG. 1, a first aircraft 100 is depicted. First aircraft 100 may be any of a variety of aircrafts including but not limited to airplanes and helicopters. Aircraft 100 may have an onboard TCAS system 110 which may include a transponder 120 and an interrogator. As depicted in FIG. 1, the interrogator may be a part of TCAS block 110 or may alternatively be a separate interrogator unit. Transponder 120 may be a Mode S transponder or other type of applicable transponder. Similarly, a second aircraft 130 is in the vicinity of aircraft 100. Aircraft 130 also has a TCAS system 150 including a transponder 140 which may be a Mode S or other transponder. In operation, as aircraft 130 comes into the local vicinity of aircraft 100, aircraft 100 transmits an interrogation signal 160 to aircraft 130. Transponder 140 interprets the interrogation signal and provides the requested information over the air to aircraft 100. In an exemplary embodiment, the requested information includes enhanced surveillance information, that is information which is beyond the typical position and identification information used in conventional TCAS systems.

[0018] Table 1 is an exemplary embodiment of the registers identified in a Mode S transponder and the register parameter contents that may be extracted from the transponder by an interrogator according to the ground-initiated COMM-B protocol (GICB). The information shown corresponds with enhanced surveillance data.

[0019]

TABLE 1
Register Allocation and Parameters as per ICAO Annex 10,
Volume III, Chapter 5, Appendix.
GICB (BDS)		Register Parameter
Register #	Register Name	Contents
0.5	Extended Squitter	Format Type Code
	Airborne Position	Surveillance Status
		Single Antenna Flag Bit
		Altitude
		Time Tag Bit
		Compact Position
		Reporting Format Bit
		Encoded Latitude
		Encoded Longitude
0.6	Extended Squitter	Format Type Code
	Surface Position	Movement
		Ground Track Status Bit
		Ground Track (True)
		Time Tag Bit
		Compact Position
		Reporting Format Bit
		Encoded Latitude
		Encoded Longitude
0.7	Extended Squitter Status	Transmission Rate Sub-
		field (TRS)
		Altitude Type Subfield
		(ATS)
0.8	Extended Squitter Air-	Format Type Code
	craft Identification and	Aircraft Category
	Category	Aircraft Identification
		Character 1 through 8
0.9	Extended Squitter Airborne	Format Type Code
	Velocity - Subtype 1 and 2	Subtype
	(Velocity over Ground)	Intent Change Flag Bit
		IFR Capability Flag Bit
		Navigation Uncertainty
		Category - Velocity
		East/West Velocity
		North/South Velocity
		Vertical Rate
		GNSS Altitude
		Difference from
		Barometric Alt.
0.9	Extended Squitter Airborne	Format Type Code
	Velocity - Subtype 3 and 4	Subtype
	(Airspeed and Heading)	Intent Change Flag Bit
		IFR Capability Flag Bit
		Navigation Uncertainty
		Category - Velocity
		Magnetic Heading
		Airspeed (True or
		Indicated)
		Vertical Rate
		GNSS Altitude
		Difference from
		Barometric Alt.
0.A	Extended Squitter Event	Used to multiplex
	Driven Messages	transmission of messages
		contained in registers
		6.1–through- 6.f
0.B	Aircraft State Information 1	True Airspeed
	(Aircraft State)	Heading
		True Track Angle
		Ground Speed
0.C	Aircraft State Information 2	Level Off Altitude
	(Aircraft Intent)	Next Course (True
		Ground Track)
		Time to Next Waypoint
		Vertical Velocity
		Roll Angle
0.D–0.E	Reserved for Air/Air State
	Information
0.F	Reserved for ACAS
1.0	Data Link Capability	Various Datalink and
	Report	TCAS Capability
		Annunciations
1.7	Common Usage GICB	Used to declare common
	Capability Report	usage GICB register
		services currently being
		supported
1.8–through- 1.C	Mode-S Specific Services	Used to declare GICB
	GICB Capability Reports	services that are installed
1.D–through- 1.F	Mode-S Specific Services	Used to indicate Modes
	MSP Capability Reports	S Specific Protocol
		services that are installed
		and require servicing.
2.0	Aircraft Identification	Aircraft Identification
		Character 1–through- 8
2.1	Aircraft and Airline	Aircraft Registration
	Registration	Number, Character 1–
		through- 7
		ICAO Airline Registra-
		tion Marking, Character
		1 and 2
2.2	Antenna Positions	Antenna 1 Position
		Antenna 2 Position
		Antenna 3 Position
		Antenna 4 Position
2.5	Aircraft Type	Aircraft Type
		Number of Engines
		Engine Type
		Model Designation,
		Character 1–through- 5
		Wake Turbulence
		Category
3.0	ACAS Active Resolution	Active Resolution
	Advisory	Advisories
		Resolution Advisory
		Complement Record
		Resolution Advisory
		Terminated Bit
		Multiple Threat
		Encounter Bit
		Threat-Type Indicator
		Threat Identity Data
4.0	Selected Vertical Intention	MCP/FCU Selected
		Altitude
		FMS Selected Altitude
		Barometric Pressure
		Setting - minus 800 mb
		Status of MCP/FCU
		Mode Bits
		VNAV Mode Bit
		Altitude Hold Bit
		Approach Mode Bit
		Status of Target Altitude
		Source Bits
		Target Altitude Source
		Bits (2)
4.1	Next Waypoint Details -	Characters 1–through- 9
	Identity
4.2	Next Waypoint Details -	Waypoint Latitude
	Position	Waypoint Longitude
		Waypoint Crossing
		Altitude
4.3	Next Waypoint Details -	Bearing to Waypoint
	Nav	Time-to-Go
		Distance-to-Go
4.4	Meteorological Routine Air	FOM/Source
	Report	Wind Speed
		Wind Direction (True)
		Static Air Temperature
		Average Static Pressure
		Turbulence
		Humidity
4.5	Meteorological Hazard	Turbulence
	Report	Wind Shear
		Microburst
		Icing
		Wake Vortex
		Static Air Temperature
		Average Static Pressure
		Radio Height
4.6	Reserved for Flight
	Management System
	Mode 1
4.7	Reserved for Flight
	Management System
	Mode 2
4.8	VHF Channel Report	VHF 1
		VHF 1 Audio Status
		VHF 2
		VHF Audio Status
		VHF 3
		VHF 3 Audio Status
5.0	Track and Turn Report	Roll Angle
		True Track Angle
		Ground Speed
		Track Angle Rate
		True Airspeed
5.1	Position Report - Course	Latitude - Coarse
		Longitude - Coarse
		Pressure Altitude
5.2	Position Report - Fine	Latitude - Fine
		Longitude - Fine
		Pressure Altitude or
		GNSS Height (HAE)
5.3	Air Referenced State	Magnetic Heading
	Vector	Indicated Airspeed (IAS)
		Mach Number
		True Airspeed (TAS)
		Altitude Rate
5.4	Waypoint 1 Information	Status
		Waypoint Identifier,
		Character 1–through- 5
		Estimated Time of
		Arrival (Normal Flight)
		Estimated Flight Level
		(Normal Flight)
		Time-to-Go (Direct
		Route)
5.5	Waypoint 2 Information	Status
		Waypoint Identifier,
		Character 1–through- 5
		Estimated Time of
		Arrival (Normal Flight)
		Estimated Flight Level
		(Normal Flight)
		Time-to-Go (Direct
		Route)
5.6	Waypoint 3 Information	Status
		Waypoint Identifier,
		Character 1–through- 5
		Estimated Time of
		Arrival (Normal Flight)
		Estimated Flight Level
		(Normal Flight)
		Time-to-Go (Direct
		Route)
5.F	Quasi-Static Parameter	Selected Altitude
	Monitoring	Monitor_2 bits
		Selected Heading
		Monitor_2 bits
		Selected Mach Number
		Monitor_2 bits
		Selected Altitude Rate
		Monitor_2 bits
		Next Waypoint
		Monitor_2 bits
		FMS Horizontal Mode
		Monitor_2 bits
		VHF Channel Report
		Monitor_2 bits
		Meteorological Hazards
		Monitor_2 bits
		Target Altitude
		Monitor_2 bits
6.0	Heading and Speed	Magnetic Heading
	Report	Indicated Airspeed
		Mach
		Barometric Altitude Rate
		Inertial Vertical Velocity
6.1	Emergency/Priority Status	Format Type Code = 28
		Subtype Code = 1
		Emergency/Priority
		Status
6.2	Reserved for Trajectory
	Change Point
6.3	Reserved for Trajectory
	Change Point
6.4	Reserved for Aircraft
	Operational Coordination
	message
6.5	Reserved for Aircraft
	Operational Status
6.6–6.F	Reserved for Extended
	Squitter
7.0–7.5	Reserved for Future
	Aircraft Downlink
	Parameters
E.1–E.2	Reserved for Mode-S Byte
F.1	Reserved for Military
	Applications
F.2	Reserved for Military
	Applications

[0020] Referring to FIG. 2, aircraft 200 which includes TCAS system 220, including a transponder 215 and an interrogator 210 sends an interrogation signal 230 to a transponder 235 which has an interrogation interpreter and a plurality of data registers 245 including, but not limited to registers having altitude information 250, identification information 260, heading information 270, roll attitude information 280, pitch attitude information 290, and trajectory information 295. Registers 235 are simply illustrative and are not limited by the types of information depicted. As interrogation interpreter receives the interrogation signal 230, interrogation interpreter 240 determines what data registers should be reported in a reply to aircraft 200's request. For example, in the figure, heading information 270 is reported via a communication 275. Pitch attitude 290 is reported in a communication 285, and trajectory information is communicated in a communication 298 back to interrogator transponder 210. Accordingly, the benefits of enhanced surveillance to airborne interrogators is extended. Currently, only ground-based air traffic control interrogators may utilize this capability. An airborne interrogator makes the benefits of enhanced surveillance available to aircraft. In one exemplary embodiment, the airborne interrogator may be a TCAS. In current applications, TCAS simply interrogates the transponder of another intruder aircraft to obtain its range and altitude. Given the small amount of information, the TCAS system decides if the intruder is a collision threat. Utilizing enhanced surveillance information, a TCAS can make interrogation of the intruder's transponder. This provides TCAS with significantly more information (enhanced surveillance data) than range and altitude. This includes items like intruder's aircraft's heading, pitch and roll angles, the aircraft's velocities and position, and many other items including intended flight path trajectories (see Table 1).

[0021] As an example, an operational enhancement that may occur using enhanced surveillance data is an opportunity to avoid collisions and/or reduce the number of false alarms by utilizing information of the intended trajectory of a second aircraft. In past applications of TCAS, the inability to obtain the intended trajectory information has been a significant limitation to TCAS applications.

[0022] TCAS must provide decisions to avoid collisions with enough warning to allow the pilot of the aircraft to react. The period is typically 30 to 45 seconds. Without intent information, TCAS may only be used to project the trajectory of the intruder based on the past behavior of that aircraft. If the intruder does not intend to continue “doing what it's been doing”, this projection may be in error. This may result in unnecessary alarms or alarms that come without comfortable warning. In the case that enhanced surveillance information is available to the aircraft and the intended trajectory is known, alarms can be deferred without the potential for a collision. One such situation, for example, is called a “bump up.” This occurs when a first aircraft is level at a given altitude and an intruder aircraft is climbing to level off at an altitude 1,000 feet below the first aircraft. In today's TCAS systems, TCAS does not know that the intruder intends to level off and issues an alarm, advising the pilot of the first aircraft to climb to avoid the intruder. However, the alarm, in this case, is unnecessary and could be avoided if TCAS had known that the intruder was going to level off.

[0023] The implementation of the system utilizes existing hardware on aircraft. TCAS interrogates Mode S transponders for the purpose of obtaining range and altitude. Enhanced surveillance transponders have the capability to respond to an interrogation requesting the enhanced information discussed above. The Mode S transponder responds with the enhanced surveillance information requested by an interrogator by processing the content of the interrogation. TCAS needs only to change the data content of its existing interrogation to request the data information in this way. Only minor changes to the content of the TCAS interrogation and no changes to the enhanced surveillance Mode S transponder are necessary to make the new information available for use by TCAS. The airborne interrogator may use the ground-initiated comm-B protocol (GICB) to extract the information from other aircraft. The protocol has already been standardized internationally in the Mode S minimum operational performance standard (ICAO annex 10).

[0024] Referring now to FIG. 3, an exemplary process of the interrogation for enhanced surveillance information is depicted. Process 300 begins with the information determined (step 310). The first aircraft interrogator then interrogates the second aircraft's transponder (step 320). The second aircraft's transponder interprets the interrogation request (step 330). The second aircraft's transponder retrieves the requested information (step 340). The second aircraft's transponder then transmits the requested information via the transponder to the first aircraft (step 350).

[0025] As a result of the use of an interrogation to obtain enhanced surveillance information from an intruder aircraft, a further benefit may be obtained. If the information requested is the other aircraft's position based on its on-board navigation system (such as a GPS system or other on-board navigation systems), the result may be verified by comparing it to its own aircraft's position. The difference in position should agree within some tolerance level with the range and bearing measured directly as a result of the interrogation. This check provides a level of integrity to the position information that cannot be achieved by a system where the position of the other aircraft is merely broadcast.

[0026] An exemplary process in which integrity of another aircraft's position is checked by a first aircraft is depicted by process 400 of FIG. 4. A second aircraft's transponder is interrogated, including a request for position information (step 410). A reply is received from the second aircraft by the first aircraft (step 420). The range and bearing are determined based on the time travel of the reply and request (step 430). Position based on the range and bearing are then calculated (step 440). A comparison is then made of the communicated position with the calculated position (step 450). At that stage then a determination of whether the integrity of the broadcast position has been compromised is made.

[0027] Additionally, a system where interrogation is used to obtain enhanced surveillance data from another aircraft provides benefits in that the interrogator may vary its rate of interrogation to satisfy the needs of a dynamic situation. For example, if the data is changing fast and the situation demands attention, the interrogator can increase the rate of interrogation, allowing the data to closely follow the situation of the other aircraft. If the situation is changing slowly and does not demand close attention, the interrogator can reduce its interrogation rate to minimize channel loading. A further benefit of the interrogation system may be that if the data is not received the first time, a retry can occur to insure the information is obtained.

[0028] Having the enhanced surveillance data available to an aircraft may allow an aircraft to maintain spacing with another aircraft very precisely in addition to all of the other benefits described above with regards to the communication of enhanced surveillance data.

[0029] While the detailed drawings, specific examples, and particular formulations given describe preferred and exemplary embodiments, they serve the purpose of illustration only. The inventions disclosed are not limited to the specific forms shown. For example, the methods may be performed in any of a variety of sequence of steps. The hardware and software configurations shown and described may differ depending on the chosen performance characteristics and physical characteristics of the computing and communication devices. For example, the type of computing and communications devices, communications bus, or processor used may differ. The systems and methods depicted and described are not limited to the precise details and conditions disclosed. Furthermore, other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the invention as expressed in the appended claims.