U.S. patent application number 10/091818 was filed with the patent office on 2002-10-24 for close/intra-formation positioning collision avoidance system and method.
This patent application is currently assigned to L-3 Communications Corporation. Invention is credited to Frazier, James A. JR., Jongsma, Kenneth R., Sturdy, James T..
Application Number | 20020154061 10/091818 |
Document ID | / |
Family ID | 22836922 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020154061 |
Kind Code |
A1 |
Frazier, James A. JR. ; et
al. |
October 24, 2002 |
Close/intra-formation positioning collision avoidance system and
method
Abstract
A passive Traffic Alert and Collision Avoidance System (TCAS)
and method is based on receiving and processing Mode-S transponder
messages without the TCAS computer having to interrogate the
transponders of the respective aircraft flying in formation (i.e.,
a passive TCAS). A TCAS computer and Mode-S transponder are used to
provide distributed intra-formation control among multiple cells of
aircraft flying in formation or close-in. The Mode-S transponder
provides ADS-B Global Positioning System (GPS) squitter data to the
TCAS computer; the TCAS computer receives and processes the data
without having to interrogate the transponders of the multiple
cells of aircraft. The method and system allow a safe separation
between 2 to 250 aircraft flying in formation at selectable
ranges.
Inventors: |
Frazier, James A. JR.;
(Albuquerque, NM) ; Jongsma, Kenneth R.;
(Albuquerque, NM) ; Sturdy, James T.;
(Albuquerque, NM) |
Correspondence
Address: |
SQUIRE, SANDERS & DEMPSEY L.L.P.
40 North Central Avenue, Suite 2700
Two Renaissance Square
Phoenix
AZ
85004-4424
US
|
Assignee: |
L-3 Communications
Corporation
|
Family ID: |
22836922 |
Appl. No.: |
10/091818 |
Filed: |
March 6, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10091818 |
Mar 6, 2002 |
|
|
|
09223533 |
Dec 30, 1998 |
|
|
|
Current U.S.
Class: |
342/455 ;
342/357.32; 342/357.52 |
Current CPC
Class: |
G01S 13/933 20200101;
G01C 23/00 20130101 |
Class at
Publication: |
342/455 ;
342/357.08 |
International
Class: |
G01S 003/02; G01S
005/14 |
Claims
The embodiments of an invention in which an exclusive property or
right is claimed are defined as follows:
1. A passive close formation collision avoidance system for a host
aircraft, the system comprising: data link transponder means, said
transponder means generating and transmitting broadcast data, the
broadcast data comprising aircraft position information of the host
aircraft; and traffic alert and collision avoidance system (TCAS)
computer means in communication with said transponder means for
receiving and processing broadcast data from a second data link
transponder means located onboard other aircraft to determine
relative aircraft position of the host aircraft with respect to the
other aircraft.
2. The system of claim 1, wherein the TCAS computer means is
passive.
3. The system of claim 1 further comprising display means for
displaying data to an operator of the host aircraft.
4. The system of claim 3, wherein the relative velocity of the
other aircraft are displayed on the display means.
5. The system of claim 1, wherein said transponder means is a
mode-select data link transponder.
6. The system of claim 1, wherein the broadcast data is automatic
dependent surveillance broadcast (ADS-B) data.
7. The system of claim 1, wherein the broadcast data is global
positioning system (GPS) data.
8. The system of claim 1, wherein the broadcast data is Mode-S
squitter data.
9. The system of claim 1, wherein the broadcast data is extended
squitter airborne position data.
10. The system of claim 1, wherein the broadcast data is extended
squitter airborne velocity data.
11. The system of claim 1, wherein the broadcast data is
continuously transmitted by the data link transponder means at a
predetermined interval.
12. The system of claim 1, wherein said TCAS computer means
comprises a radio frequency power step attenuator.
13. The system of claim 1 further comprising a mission computer,
and wherein said TCAS computer means comprises an input/output
interface, the input/output interface providing a data interface
from said TCAS computer means to the mission computer.
14. A passive intra-formation positioning collision avoidance
system for a transponder-equipped host aircraft, the system
comprising: a data link transponder, said transponder generating
broadcast data, the broadcast data comprising aircraft position;
and a traffic alert and collision avoidance system (TCAS) computer
in communication with said transponder for receiving and processing
the broadcast data from said transponder; a mission computer unit
in communication with said TCAS computer, wherein said mission
computer unit receives the broadcast data from said TCAS computer
and generates steering commands based on the broadcast data; and a
communication link in communication with said mission computer to
transmit the steering commands to at least one other
transponder-equipped aircraft for processing, the at least one
other transponder-equipped aircraft being responsive to the
steering commands to position itself with respect to the host
aircraft.
15. The system of claim 14, wherein the TCAS computer means is
passive.
16. The system of claim 14, wherein the communication link is a
very high frequency (VHF) data link.
17. The system of claim 14, wherein the communication link is an
ultra-high frequency (UHF) data link.
18. The system of claim 14, wherein the relative velocity of the
plurality of aircraft are displayed on a display means.
19. The system of claim 14, wherein the at least one other
transponder-equipped aircraft is further equipped with station
keeping equipment means for receiving and processing the steering
commands to position the at least one other transponder-equipped
aircraft with respect to the host aircraft, the station keeping
equipment being responsive to the steering commands.
20. The system of claim 14, wherein the at least one other
transponder-equipped aircraft is further equipped with automatic
flight control station means for receiving and processing the
steering commands to position the at least one other
transponder-equipped aircraft with respect to the host aircraft,
the automatic flight control station means being responsive to the
steering commands.
21. The system of claim 14, wherein the steering commands comprise
commands used to maintain horizontal and vertical separation
between the at least one other transponder-equipped aircraft and
the host aircraft within a predefined airspace cell.
22. The system of claim 14, wherein the at least one other
transponder-equipped aircraft is identifiable by a unique Mode-S
address identifier.
23. The system of claim 14, wherein the broadcast data is automatic
dependent surveillance broadcast (ADS-B) data.
24. The system of claim 14, wherein the broadcast data is global
positioning system (GPS) data.
25. The system of claim 14, wherein the broadcast data is Mode-S
squitter data.
26. The system of claim 14, wherein the broadcast data is extended
squitter airborne position data.
27. The system of claim 14, wherein the broadcast data is extended
squitter airborne velocity data.
28. The system of claim 14, wherein said TCAS computer comprises an
input/output interface, the input/output interface providing a data
interface from said TCAS computer means to the mission computer
unit.
29. The system of claim 14 further comprising display means for
displaying informational data to an operator of the host aircraft,
the informational data comprising the relative velocity of the
other aircraft.
30. A passive collision avoidance method for aircraft flying in
formation with respect to one another, the method comprising the
steps of: providing a transponder, the transponder generating and
transmitting broadcast data, the broadcast data comprising aircraft
position; and providing a traffic alert and collision avoidance
system (TCAS) computer onboard a host aircraft, the TCAS being in
communication with said transponder for receiving and processing
the broadcast data from the transponder.
31. The method of claim 30 further comprising the step of
positioning the aircraft with respect to one another while flying
in formation based on the broadcast data.
32. The method of claim 30 further comprising the steps of:
providing a mission computer in communication with the TCAS
computer; transmitting the broadcast data from the TCAS computer to
the mission computer; processing the broadcast data; and
selectively transmitting the processed broadcast data between the
aircraft via a data link.
33. The method of claim 30 further comprising the step of providing
automatic flight means for positioning and separating the aircraft
with respect to one another based on the processed broadcast
data.
34. The method of claim 30 wherein the step of selectively
transmitting comprises the step of selecting a particular aircraft
to receive the processed broadcast data based on a unique flight
identifier of the particular aircraft.
35. The method of claim 30, further comprising the steps of
alerting an operator of the aircraft when an intruder penetrates a
predefined perimeter of aircraft flying in formation.
36. The method of claim 30, further comprising the step of
inhibiting air traffic control radar beacon systems (ATCRBS)
messages from being sent by the transponder.
37. The method of claim 32, wherein the step of processing the
broadcast data comprises the step of calculating target range,
range rate, relative altitude, altitude rate, and bearing from the
broadcast data received from the transponder to determine whether
an aircraft is intruding upon a predefined airspace of the host
aircraft.
Description
I. CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to co-pending application, filed
on even date herewith, entitled "Vertical Speed Indicator/Traffic
Resolution Advisory Display For TCAS."
II. BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to the field of
avionics for collision avoidance systems (CAS). More specifically,
the present invention relates generally to airborne traffic alert
and collision avoidance systems and transponders. The collision
avoidance system described herein has the capability to position
and separate aircraft in a large flight formation in, for example,
night/instrument meteorological conditions.
[0003] Spurred by the collision of two airliners over the Grand
Canyon in 1956, the airlines initiated a study of collision
avoidance concepts. By the late 1980's, a system for airborne
collision avoidance was developed with the cooperation of the
airlines, the aviation industry, and the Federal Aviation
Administration (FAA). The system, referred to as Traffic Alert and
Collision Avoidance System II (TCAS II) was mandated by Congress to
be installed on most commercial aircraft by the early 1990's. A
chronology of the development of airborne collision avoidance
systems can be found in "Introduction to TCAS II," printed by the
Federal Aviation Administration of the U.S. Department of
Transportation, March 1990.
[0004] The development of an effective airborne CAS has been the
goal of the aviation community for many years. Airborne collision
avoidance systems provide protection from collisions with other
aircraft and are independent of ground based air traffic control.
As is well appreciated in the aviation industry, avoiding such
collisions with other aircraft is a very important endeavor.
Furthermore, collision avoidance is a problem for both military and
commercial aircraft alike. In addition, a large, simultaneous
number of TCAS interrogations from close-in formation aircraft
members generate significant radio frequency (RF) interference and
could potentially degrade the effectiveness of maintaining precise
position/separation criteria with respect to other aircraft and
obstacles. Therefore, to promote the safety of air travel, systems
that avoid collision with other aircraft are highly desirable.
[0005] In addition the problems described above, it is desirable
that aircraft, specifically military aircraft, perform precision
airdrops, rendezvous, air refueling, and air-land missions at night
and in all weather conditions, including Instrument Meteorological
Conditions (IMC) with a low probability of detection. Also, it is
desirable that these aircraft be allowed as few as 2 through as
many as 250 aircraft to maintain formation position and separation
at selectable ranges from 500-ft to 100-nm at all Instrument Flight
Rules (IFR) altitudes as described in the Defense Planning
Guidelines. Also, the system is to be compatible (primarily because
of cost issues) with current station keeping equipment (SKE)
systems or they will not be able to fly IMC formation with
SKE-equipped aircraft.
[0006] Referring to FIG. 1, there is shown a block diagram of a
conventional TCAS system. Shown in FIG. 1 are TCAS directional
antenna 10, TCAS omni-directional antenna 11, and TCAS computer
unit 12, which includes receiver 12A, transmitter 12B, and
processor 12C. Also shown are aural annunciator 13, traffic
advisory (TA) display 14, and resolution advisory displays 15.
Alternatively, the TA and RA displays are combined into one display
(not shown). The transponder is comprised of transponder unit 16A,
control panel 16B, and transponder antennas 16C and 16D. The TCAS
and transponder operate together to function as a collision
avoidance system. Those skilled in the art understand that this is
merely illustrative of a conventional TCAS. For example, many other
configurations are possible such as replacing omni-directional
antenna 11 with a directional antenna as is known to those skilled
in the art. The operation of TCAS and its various components are
well known to those skilled in the art and are not necessary for
understanding the present invention.
[0007] In a TCAS system, both the interrogator and transponder are
airborne and provide a means for communication between aircraft.
The transponder responds to the query by transmitting a reply that
is received and processed by the interrogator. Generally, the
interrogator includes a receiver, an analog to digital converter
(A/D), a video quantizer, a leading edge detector, and a decoder.
The reply received by the interrogator consists of a series of
information pulses which may identify the aircraft, or contain
altitude or other information. The reply is a pulse position
modulated (PPM) signal that is transmitted in either an Air Traffic
Control Radar Beacon System (ATCRBS) format or in a Mode-Select
(Mode-S) format.
[0008] A TCAS II equipped aircraft can monitor other aircraft
within approximately a 20 mile radius of the TCAS II equipped
aircraft. (U.S. Pat. No. 5,805,111, Method and Apparatus for
Accomplishing Extended Range TCAS, describes an extended range
TCAS.) When an intruding aircraft is determined to be a threat, the
TCAS II system alerts the pilot to the danger and gives the pilot
bearing and distance to the intruding aircraft. If the threat is
not resolved and a collision or near miss is probable, then the
TCAS II system advises the pilot to take evasive action by, for
example, climbing or descending to avoid a collision.
[0009] In the past, systems in addition to those described above
have been developed to provide collision avoidance for aircraft
flying in formation. One type of system is provided by AlliedSignal
Aerospace and is known as Enhanced Traffic Alert Collision
Avoidance System (ETCAS). The ETCAS provides a normal collision
avoidance and surveillance, and a formation/search mode for
military specific missions.
[0010] The AlliedSignal ETCAS falls short in several ways. First,
once an aircraft joins the formation, the ETCAS does not itself or
in conjunction with any other onboard system maintain aircraft
position and separation within the formation. The ETCAS is simply a
situational awareness tool that designates formation members by
receiving the Mode 3/A code transmitted from the plane's
transponder; the ETCAS does not interface with other aircraft
systems to compensate for formation position errors. The ETCAS is
actually an aircraft formation member identification and rendezvous
system that falls short as a true intra-formation positioning
collision avoidance system. Second, the ETCAS Vertical Speed
Indicator/Traffic Resolution Alert (VSI/TRA) display does not
annunciate relative velocity (range-rate) of the lead formation and
member aircraft. The ETCAS is only marginally effective without
relative velocity of formation aircraft annunciated on the VSI/TRA
display. Hence, the pilot has no relative velocity reference to
maintain formation position with the lead aircraft, especially
during critical turning maneuvers. Third, the ETCAS
formation/search mode technique is wholly based upon active TCAS
interrogations. Transponder interrogations and the resulting Mode-S
transponder replies significantly increase RF reception
interference with a large formation of aircraft and could degrade
the effectiveness of maintaining precise position/separation
criteria. In addition, the increased composite level of RF severely
inhibits a large formation from covertly traversing airspace
undetected.
[0011] Another problem is presented in previous systems wherein
station keeping equipment (SKE) on existing military aircraft can
support a formation of only 16 aircraft.
III. BRIEF SUMMARY OF THE INVENTION
[0012] The following summary of the invention is provided to
facilitate an understanding of some of the innovative features
unique to the present invention, and is not intended to be a full
description. A full appreciation of the various aspects of the
invention can only be gained by taking the entire specification,
claims, drawings, and abstract as a whole.
[0013] The present invention describes a system and method of
maintaining aircraft position and safe separation of a large
aircraft flying formation, such as those types of military
formations to perform a strategic brigade airdrop, although it can
be used for any aeronautical service involving the application of
aircraft formation flying units. The present invention involves the
use of a passive Traffic Alert and Collision Avoidance System
(TCAS) and Mode-S data link transponder to provide distributed
intra-formation control among multiple cells of formation
aircraft.
[0014] In one embodiment, the present invention comprises a data
link Mode-S transponder, which generates and transmits ADS-B
broadcast data. Such ADSB broadcast data contains aircraft position
information of the host aircraft. The present invention also
includes a passive traffic alert and collision avoidance system
(TCAS) computer in communication with the Mode-S transponder. The
TCAS receives and processes broadcast data from another data link
transponder that is located onboard another aircraft (e.g., a
follower aircraft within a cell) to determine relative aircraft
position of the host aircraft with respect to the other
aircraft.
[0015] In a further embodiment of the present invention, a data
link Mode-S transponder is in communication with a TCAS computer.
The TCAS computer receives and processes the broadcast data from
the transponder. The TCAS computer is also in communication with a
flight mission computer, which receives the broadcast data from the
TCAS computer and generates steering commands based on the
broadcast data. The present invention includes a high-speed digital
communication link that is operatively connected to the mission
computer, which is used to transmit the steering commands to one
other transponder-equipped aircraft where the steering commands are
processed by the other aircraft. The other aircraft uses the
steering commands to position itself with respect to the host
aircraft. This can be accomplished either with station keeping
equipment or automatic flight controllers.
[0016] The method of the present invention includes the steps of
providing a transponder (on one or more aircraft), which generates
and transmits ADS-B broadcast data to determine relative aircraft
position, and providing a TCAS computer onboard a host aircraft.
The TCAS is in communication with the transponder and receives and
processes ADS-B broadcast data from the transponder. The method
includes the step of (automatically) positioning and separating the
aircraft with respect to one another while flying in formation
based on the broadcast data using, for example, automatic flight or
station keeping means. The method further includes the steps of
providing a mission computer in communication with the TCAS
computer; transmitting the broadcast data from the TCAS computer to
the mission computer; processing the broadcast data; and
selectively transmitting the processed broadcast data between the
aircraft via a high speed data link. The step of processing further
includes the step of calculating the target aircraft range, range
rate, relative altitude, altitude rate, and bearing from the
broadcast (ADS-B) data received from the Mode-S transponder to
determine whether an aircraft is intruding upon the air space of
the TCAS-equipped aircraft. The step of selectively transmitting is
conducted, for example, using a unique flight identifier of the
particular aircraft. The method also includes the steps of alerting
the pilot of the aircraft when an intruder penetrates a predefined
perimeter of aircraft flying in formation and displaying the range
rate or relative velocity of the aircraft within a predefined cell
or airspace. The method further includes the step of inhibiting air
traffic control radar beacon systems (ATCRBS) messages from being
sent by the Mode-S transponder.
[0017] The present invention is capable of supporting a flight
formation of 250 aircraft through distributed control of multiple
aircraft formation cell units. It uses a passive surveillance
technique for maintaining formation aircraft position within 500-ft
to 100-nm of one another at all Instrument Flight Rules (IFR)
altitudes. Updated aircraft position information is broadcast
periodically (e.g., 2 times per second). These periodic Mode-S
transponder transmissions of Automatic Dependent Surveillance
Broadcast (ADS-B) information are sent to and received by the TCAS
of other TCAS-equipped aircraft. This extended ADS-B data
transmission is also referred to herein as Global Positioning
System (GPS) or Mode-S squitter. Aircraft positions, relative
altitude and velocity are presented on the Vertical Speed
Indicator/Traffic Resolution Advisory (VSI/TRA) display (e.g.,
cathode ray tube or flat panel display) and processed in the
aircraft mission computer's intra-formation positioning collision
avoidance system (IFPCAS) data fusion center. The mission computer
receives data from the TCAS computer, processes the data to obtain,
for example, range and range rate, and then the mission computer
places the data in a format usable by external equipment such as
the station keeping equipment. Steering commands are generated and
disseminated to the various or individual formation aircraft. The
steering commands are executed using on-board station keeping
equipment (which can also be used to maintain helicopter
positioning) or autopilot means. The passive surveillance technique
of the present invention significantly reduces the range upon which
a large aircraft formation can be detected and the resulting lower
RF interference maintains uninterrupted position and separation
correction updates.
[0018] The present invention overcomes several problems, including,
but not limited to: providing a means to position and separate
aircraft in an extremely large flight formation (e.g., 100
aircraft) in night/instrument meteorological conditions utilizing
ADS-B information and high frequency data links (and accompanying
antennas) for disseminating intra-formation steering commands;
utilizing the aircraft mission computer as a data fusion center for
generating steering commands based upon assimilated ADS-B
information received from the TCAS; and reducing the amount of RF
interference resulting from multiple simultaneous TCAS
interrogations and Mode-S transponder replies. The present
invention maintains safe separation between 2 to 100 aircraft, and
up to 250 aircraft, in night and Instrument Meteorological
Conditions (IMC). The present invention enables aircraft
position/separation at selectable ranges from 500-ft to 100-nmi at
all Instrument Flight Rules (IFR) altitudes. The present invention
is an integrated aircraft positioning/separation control
solution.
[0019] The novel features of the present invention will become
apparent to those of skill in the art upon examination of the
following detailed description of the invention or can be learned
by practice of the present invention. It should be understood,
however, that the detailed description of the invention and the
specific examples presented, while indicating certain embodiments
of the present invention, are provided for illustration purposes
only because various changes and modifications within the spirit
and scope of the invention will become apparent to those of skill
in the art from the detailed description of the invention and
claims that follow.
IV. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The accompanying figures, in which like reference numerals
refer to identical or functionally-similar elements throughout the
separate views and which are incorporated in and form part of the
specification, further illustrate the present invention and,
together with the detailed description of the invention, serve to
explain the principles of the present invention.
[0021] FIG. 1 (prior art) is a block diagram of a conventional TCAS
system.
[0022] FIG. 2 is a diagram of the components of an exemplary
aircraft formation.
[0023] FIG. 3 is a block diagram of an embodiment of the collision
avoidance system for close formation flights in accordance with the
present invention.
[0024] FIG. 4 is a block diagram of an alternate embodiment of the
collision avoidance system for intra-formation positioning flights
in accordance with the present invention.
[0025] FIG. 5 is a more detailed block diagram of the embodiment of
FIG. 4 (the intra-formation collision avoidance system
architecture) in accordance with the present invention.
[0026] FIG. 6 is an elevation of a TCAS VSI/TRA display with the
relative velocity (range rate) of formation aircraft displayed in
accordance with the present invention.
[0027] FIG. 7 is a flowchart of the methodology used to display
information to the viewer in accordance with the present
invention.
[0028] FIG. 8 is a flowchart of the methodology used to display
information to the viewer in accordance with the present
invention.
[0029] FIG. 9 is a flowchart of the methodology used to display
information the to viewer in accordance with the present
invention.
[0030] FIG. 10 is a flowchart of the methodology used to display
information to the viewer in accordance with the present
invention.
V. DETAILED DESCRIPTION OF THE INVENTION
[0031] A passive Collision Avoidance System (CAS) is implemented by
the present invention to maintain selectable separation between
formation cells and follower aircraft within each cell using an
integrated control system. The passive CAS is attained by the
present invention using centralized control and decentralized
execution of multiple aircraft formation cells. The present
invention uses TCAS and Global Positioning System (GPS) Squitter
data from a Mode-S transponder. The terms GPS squitter, Mode-S
squitter, and ADS-B mean the same thing and are used
interchangeably throughout the description of the present invention
to describe extended data transmission.
[0032] Assembling a large number of formation aircraft (e.g., for a
massive size military airdrop in IMC and night flying conditions)
is a positioning/separation control problem that is implemented by
the present invention in two parts:
[0033] 1) Modification or augmentation of a conventional TCAS,
e.g., Honeywell TCAS-2000 (product no. RT-951), to permit close
formation flight without unnecessary traffic advisories or
resolution advisories; and
[0034] 2) Use of data from a Mode-S transponder to process aircraft
position, and an external high-frequency (e.g., VHF, UHF) data link
(transmitter and receiver), with accompanying antennas, to pass
data, such as ADS-B and intraformation steering commands, between
aircraft.
[0035] Referring to FIG. 2, there is shown an exemplary aircraft
formation with its members heading towards a drop zone 260 for
which an Intra-Formation Positioning Collision Avoidance System
(IFPCAS) is necessary. Adjacent aircraft flying in close proximity
to one another but not part of the same cell could maintain a safe
separation using passive TCAS detection and processing. A large
formation (master cell) 200 can be split into smaller cells (210,
220, 230, 240) with a cell leader (225, 235, 245) responsible for
maintaining aircraft separation among cell followers (212, 222,
232, 242). A cell is defined as a smaller formation of
approximately 2-50 aircraft. A large formation (up to 250 aircraft)
200 contains many cells within it. A Master Formation Leader (MFL)
250 is responsible for maintaining separation between the multiple
cells (210, 220, 230, 240) that make up the entire formation 200
(the MFL acts as a beacon for the formation followers).
[0036] The MFL 250 maintains cell separation using information that
is periodically broadcast from the cell leader's transponder,
specifically, Global Positioning System (GPS) squitter data. The
MFL 250 receives the data from each cell leader (225, 235, 245)
aircraft. Each cell leader's (225, 235, 245) aircraft is identified
by a unique Mode-S 24-bit address. Precise position location of
formation cells and other multiple formations could be accurately
tracked with GPS squitter data. MFL 250 fuses the data of all cell
positions; such data fusion is accomplished in the MFL's Flight
Management System (FMS) IFPCAS data fusion center as shown and
discussed with respect to FIG. 5. Individual cell steering commands
are transmitted via Mode-S data link to cell leader (225, 235, 245)
aircraft as shown and discussed with respect to FIG. 4. Steering
commands are directed to individual cell leaders by their unique
Mode-S 24-bit address. MFL 250, cell leaders (225, 235, 245), and
cell followers can be identified by their Mode-S 24-bit address
and/or Flight Identification that are assigned to each aircraft and
transmitted as part of the existing Mode-S message types.
[0037] Cell leaders (225, 235, 245) then process steering commands
within their own FMS and disseminate steering commands to their
element aircraft within their cell. Individual cell aircraft act
upon the steering command if they are addressed to do so via their
station keeping system digital datalink with the cell leader. It
should be noted that every Mode-S message contains a cyclic
redundancy check (24-bit error detection code) to prevent erroneous
information from being received by the aircraft.
[0038] GPS squitter would also be used in a similar manner to
enable multiple formations to interfly and maintain
position/separation at selectable distances. In the multiple
formations scenario a Super Master Formation Leader (SMFL) receives
ADS-B information from the MFLs. The SMFL processes the fused data
and disseminates steering commands to formation element master
leaders to maintain position and separation between multiple
formations.
[0039] This distributed formation positioning control approach
prevents single point of failure and provides the flexibility of
passing MFL 250 and cell leader (225, 235, 245) responsibilities to
subordinate formation aircraft.
[0040] Referring to FIG. 3, there is shown a graphical depiction of
the passive surveillance system of the present invention that is
used to attain close formation collision avoidance. Passive
surveillance as used herein means that a close formation collision
avoidance can be attained without active TCAS traffic advisory
interrogations. Conventional TCAS operate with active TCAS traffic
advisory interrogations. Passive surveillance can be achieved
through Mode-S transponder GPS squitter broadcast and subsequent
TCAS reception and processing of that data to display aircraft
position.
[0041] FIG. 3 illustrates an exemplary embodiment of the present
invention. Although only two aircraft systems are illustrated, it
should be clear to those skilled in the art that multiple aircraft
will have a similar relationship to that shown between Aircraft No.
1 and No. 2. In formation, the Aircraft No. 1 would represent the
MFL. The operation of TCAS and each component shown are well known
in the art and need not be described in detail. Certain traffic
control system transponders, such as the Mode-S transponder,
include unique aircraft identifiers so that each message from a
target aircraft can be stamped with the identity of the target
aircraft. ADS-B messages are broadcast from the Mode-S transponder
360 at a predetermined interval, e.g., periodically one or two
times per second, and contain the aircraft's geographic coordinates
(latitude and longitude), magnetic heading, velocity, intended
flight path, barometric altitude, and flight identifier, etc., of
the respective aircraft. Such ADS-B data set is derived from
aircraft's GPS, Inertial Navigation System (INS), and Flight
Management System (FMS) (not shown) via a bus interface, e.g.,
high-speed ARINC 429-bus interface, and provided to the Mode-S
transponder 360. ADS-B data received by the TCAS-equipped aircraft
is processed and displayed in the cockpit to better enable a flight
crew to assess potential conflicts. The TCAS 350 is manipulated by
software to receive the Mode-S squitter information and compute the
positions of target proximity aircraft. Target range, range rate,
relative altitude, altitude rate, and bearing are calculated from
this ADS-B data received from the Mode-S transponder to determine
whether an aircraft is intruding upon the air space of the
TCAS-equipped Aircraft No. 1. In a formation, only the lead
aircraft is permitted to respond to any ground interrogations
because of the radio frequency interference and inability of FAA
Air Traffic Control to decipher multiple returns in a very small
area. From an accuracy point of view, the present invention uses
GPS/INS data that is broadcast by an intruding aircraft, which
permits an exact calculation of position with no more than 10-m
error in most cases instead of a relative positional calculation.
The relative altitude, altitude rate, range, and relative velocity
(range-rate) are all critical to avoiding a collision in the
present invention. Other parameters of the target aircraft are
accounted for to derive intent and closure rate.
[0042] The TCAS 350 of Aircraft No. 1 receives ADS-B data from the
Mode S transponder 360' of Aircraft No. 2 through the Mode-S
transponder datalink at a predetermined frequency, for example,
1090 MHz. Similarly, the Mode-S transponder 360 of Aircraft No. 1
transmits ADS-B data to the TCAS 350' of Aircraft No. 2 through its
Mode-S transponder datalink. The TCAS 350 is in communication with
the Mode-S transponder 360 through bus 370, e.g., ARINC 429-bus
interface. The Mode-S transponder 360 provides the TCAS with
altitude information of the aircraft, which is derived from the ADC
340. ADS-B data 310, such as latitude, longitude, velocity,
intended flight path, etc., are provided from Global Navigation
Satellite System/inertial Navigation System (GNSS/INS) 330 to the
TCAS 350 (through the Flight Management System (FMS), which is not
shown) and to the Mode-S transponder 360. ADS-B data 320, such as
altitude, is provided from the Air Data computer (ADC) 340 to the
Mode-S transponder 360.
[0043] The ADS-B messages referenced herein are comprised of five
"extended length" squitter messages: (1) Extended squitter airborne
position; (2) Extended squitter airborne velocity; (3) Extended
squitter surface position; (4) Extended squitter aircraft
identification; and (5) Event-driven squitter. For formation
flying, the present invention primarily uses message formats (1)
and (2) for passive airborne implementations and are discussed in
the following paragraphs. Additional information regarding these
ADS-B messages can be found in AEEC (Airlines Electronic
Engineering Committee) ARINC (Aeronautical Radio, Inc.),
Circulation of Draft 2 of Project Paper 718A, "MARK 4 AIR TRAFFIC
CONTROL TRANSPONDER (ATCRBS/MODE-S)," Sep. 12, 1997.
[0044] The extended squitter airborne position message is emitted
only when the aircraft is airborne. The extended squitter airborne
position message contains position information derived from the
aircraft navigation aids (GPS and INS). The extended squitter for
airborne position is transmitted as Mode-S Downlink Format Message
17 (DF 017), which is a format known to those skilled in the art.
The message is emitted twice per second at random intervals that
are uniformly distributed over the range 0.4 to 0.6 seconds
relative to the previous extended squitter airborne position
emission.
[0045] The extended squitter airborne velocity message is emitted
only when the aircraft is airborne. The extended squitter airborne
velocity message contains velocity information derived from
aircraft navigation aids (GPS, INS). The extended squitter airborne
velocity message is transmitted as Mode-S Downlink Format Message
17 (DF 017), which is a format known to those skilled in the art.
The message is emitted twice per second at random intervals that
are uniformly distributed over the range 0.4 to 0.6 seconds
relative to the previous extended squitter airborne velocity
emission.
[0046] It is important to note that the TCAS 350 is operating in a
passive mode, i.e., instead of actively interrogating other
aircraft it is receiving and processing data. Under conventional
TCAS operations, the TCAS and Mode-S transponder share resolution
advisory information, or sometimes called coordination messages,
when the TCAS is operating in the active interrogation mode. In the
present invention, the active interrogation of the TCAS is disabled
when in its formation flying mode.
[0047] Broadcast Mode-S squitter data is not only key to tight
formation collision avoidance, but also key to effectively
controlling the relative position of cellular formation units
within the larger formation group. The intra-formation positioning
system presented herein is based upon a distributed formation cell
control scheme that utilizes Mode-S transponder ADS-B squitter,
TCAS ADS-B information processing, mission computer target track
processing, and the resident aircraft SKE. In this approach, a MFL
maintains cell positioning using the ADS-B information that is
periodically broadcast from the cell leader's Mode-S
transponder.
[0048] Referring to FIG. 4, there is shown an alternate embodiment
of the present invention when operating in the IFPCAS mode. A
mission computer 410 and SKE 380 communicate with the TCAS 350 as
had been described earlier with respect to FIG. 3. Suitable SKE
include products AN/APN-169C or AN/APN-240 available from Sierra
Research, a division of Sierra Technologies Inc., although details
of the SKE are not necessary for an understanding of the present
invention. A higher level diagram of this system architecture is
shown in FIG. 5.
[0049] Although only two aircraft are illustrated in FIG. 4, an
extremely large formation (e.g., 250 aircraft) consisting of
multiple formation units would operate in a similar manner. A
passive surveillance approach could be equally effective in
enabling multiple formations to interfly and maintain formation
position/separation at selectable distances from 500 ft to 100 nmi
at all IFR altitudes. In this scenario, a "Super MFL" will receive
MFL ADS-B position information and generate steering commands that
will be disseminated in a hierarchical manner as described
above.
[0050] A Master Formation Leader (see, e.g., MFL of FIG. 2)
communicates with a cell follower. The TCAS 350 provides the
mission computer 410 a full set of ADS-B derived track data. The
mission computer 410 selects formation cell leaders by the
aircraft's unique 24-bit Mode-S address. Cell unit position and
separation information are calculated by the on-board mission
computer 410 with the resultant steering commands disseminated to
the cell formation leaders via high frequency data link 390.
Steering commands are forwarded from the high frequency receive
suite to the cell leader's mission computer 410', which in turn,
forwards them to the SKE 380'. The mission computer 410 provides
aircraft guidance commands to its SKE 380 via bus 385 based on the
data received from the TCAS 350. Follower aircraft then execute the
cell leader's SKE commands, which may involve a variety of commands
such as pitch, roll and thrust to maintain the position in the
formation. The system architecture shown in FIG. 5 is illustrated
with the IFPCAS Controller, Data Fusion, and Control Laws
implemented in the mission computer 410 as software functions or a
separate VME processing card. Multi-function Displays (MFDs) 550
could be used as an alternative to the TCAS VSI/TRA display 600 to
display the formation CAS information. The MFD could display the
TCAS targets displayed on them instead of or in addition to the
VSI/TRA 600.
[0051] It is important to note that the selection of formation
members can be accomplished using the unique 24-bit Mode-S address
that is broadcast at the tail end of each GPS squitter
transmission. In addition, a secondary means of member selection
can be attained using the Flight ID, which is also transmitted as
part of the Mode-S extended length message.
[0052] Non-station keeping aircraft formations (e.g., tanker cell
formations) can be handled in a similar manner. In fact,
TCAS-equipped tankers can utilize Mode-S ADS-B information to
rendezvous with specific formation aircraft using the selective
24-bit address or Flight ID transmitted in the Mode-S squitter
message. Such non-station keeping aircraft could maintain position
and separation within the formation unit by receiving Mode-S
squitter ADS-B data from the MFL and/or cell leader aircraft and
reconfiguring the aircraft's mission data to comply with the Mode-S
squitter ADS-B data. Similarly, rendezvous aircraft guidance
commands could be generated by their mission computers using
serviced aircraft's ADS-B track data. This is another example where
the unique Mode-S address can be used to selectively track a
specific formation member aircraft.
[0053] Referring to FIG. 5, there is shown an embodiment of the
IFPCAS architecture in accordance with the present invention.
Strategic Brigade Airdrop (SBA) carrying aircraft will simply fly
themselves to the VSI/TRA displayed ground target/drop zone using
the positional methodology discussed above. The aircraft mission
computer 410 is comprised of IFPCAS Controller 555 subject to
IFPCAS Control Laws 560, FMS 565, Data Fusion 570, and Display
Processing 575.
[0054] The Data Fusion element 570 interfaces with peripheral
(digital) datalink equipment to collect data available from the
TCAS 350, Mode-S Transponder 360, VHF Data Link Radio 520, SKE 380,
and Zone Marker Receiver 510. The data collected is Automatic
Dependent Surveillance (ADS) data, Station Keeping Equipment (SKE)
data, and Traffic Alert and Collision Avoidance System (TCAS) and
Mode-S data. ADS data is received from other aircraft within line
of sight range of this aircraft as well as from Air Traffic Control
(ATC) ground stations. SKE data is received from other aircraft
currently in formation with this aircraft. TCAS/Mode-S data is
received from other aircraft within line of sight range of this
aircraft as well as from ATC ground stations.
[0055] Because this data is obtained from multiple independent
sources, it represents different views of the position and state of
this aircraft relative to other adjacent aircraft. The total set of
data collected will contain duplicate data and possibly some
contradictory data. Data fusion algorithms (details are not
necessary for understanding the present invention) are used to
correlate this total set of data into logical and consistent
subsets of information that eliminate duplicate data and resolve
contradictory data. Several subsets are involved: a subset for
aircraft currently in formation with this aircraft; a subset for
aircraft in adjacent or joining formations; and a subset for
aircraft in the line of sight range of this aircraft, but not
associated with the intra-formation. Each subset of information
will contain identification data, position data, intent data,
threat priority data, and intra-formation data for each
aircraft.
[0056] The IFPCAS Controller 555 interfaces with peripheral
datalink equipment to determine their current modes of operations.
The IFPCAS Controller 555 element receives crew command inputs and
data fusion information to determine which IFPCAS functions to
activate. During intra-formation operations, the IFPCAS Controller
555 responds to crew inputs and activates Control Laws 560 to fly
the aircraft in formation using data fusion information.
Additionally, the IFPCAS Controller 555 interfaces with the FMS 565
passing it control data for flight plan changes coordinated among
other aircraft in the intra-formation. Also, the IFPCAS Controller
555 responds to crew inputs to enable or minimize RF emissions by
sending control data to the Mode S Transponder 360 and TCAS 350.
This will minimize the ability of enemy forces to detect this
aircraft in or near war zones during military operations.
[0057] The IFPCAS Control Laws 560 are control laws that use the
Data Fusion information and IFPCAS Controller 555 inputs to process
control law algorithms that compute airspeed, altitude, heading,
and throttle targets for the Automatic Flight Control System (AFCS)
530 in a manner apparent to those skilled in the art. Because the
control laws of conventional TCAS are known by those skilled in the
art, the control laws of the present invention are similarly
implemented by those skilled in the art while also accounting for
external equipment such as the SKE. The AFCS 530 is a conventional
aircraft automatic flight control system that provides flight
director, autopilot, and autothrottle control functions. The AFCS
530 receives airspeed, altitude, heading, and throttle targets from
the IFPCAS Control Laws element 560 to control this aircraft within
the intra-formation. These targets are used to keep the aircraft in
formation with other aircraft and to maintain the crew-entered
separation distances.
[0058] The Control Display Units (CDUs) 540 are interfaces used by
an operator to input flight parameters into the FMS 565. The FMS
565 is a conventional aircraft flight management system that
provides flight plan routes, and lateral and vertical guidance
alone those routes. The FMS 565 receives control data from the
IFPCAS Controller 555 to accomplish coordinated flight plan route
changes among all aircraft within the intra-formation.
[0059] The Display Processing 575 element is a conventional display
processing function that presents information to the flight crew
on, for example, multi-function displays (MFDs) 550. The Display
Processing 575 element receives display data from the IFPCAS
Controller 555 and Data Fusion 570 functions. This data is an
integrated set of Cockpit Display of Traffic Information (CDTI)
that provides a clear and concise presentation of the adjacent
traffic for improved situational awareness.
[0060] Non-formation military and civilian aircraft that are
capable of receiving TCAS ADS-B data can see formation aircraft
targets on their VSI/TRA 600 (see FIG. 6). Because formation
aircraft are not passing resolution advisories it will be the
responsibility of the non-formation aircraft to maneuver out of the
way.
[0061] The TCAS 350 receives and processes the ADS-B information
and displays relative aircraft position (range, bearing, and
altitude) on the Vertical Speed Indicator/Traffic Resolution Alert
(VSI/TRA) display 600. When the TCAS of the present invention is
configured for IFPCAS mode, resolution advisories are inhibited
because of the close proximity of aircraft within the cell. Of
course, the prior art systems teach away from this feature of the
present invention because resolution advisory is desired in those
other collision avoidance situations.
[0062] Zone marker receiver 510 emulates GPS squitter broadcasts
from a Mode-S transponder 360, which are key to ensuring precision
airdrops. The TCAS 350 could designate the zone marker with unique
symbology as described herein. Zone marker receiver 510 updates
100-nmi out appear feasible. However, it will be dependent upon the
RF transmit power levels that can be tolerated for various mission
scenarios.
[0063] The Honeywell TCAS-2000 (e.g., RT-951) and Mode-S
Transponder (e.g., XS-950) can meet the unique intra-formation
positional requirements described herein with some modifications to
the TCAS-2000 unit. These changes will be discussed in the
following paragraphs.
[0064] A modified or augmented TCAS-2000 is a preferable TCAS
(being that it is the most recent product) but other TCAS systems
can be adapted and used as well in a manner well known to those
skilled in the art. The TCAS-2000 is a new Traffic Alert and
Collision Avoidance System and is available from Honeywell, the
company that also developed the TCAS II. Standard (i.e., before
modification as described herein) TCAS 2000 features include:
increased display range to 80 nautical miles (nm) to meet
Communication, Navigation, Surveillance/Air Traffic Management
(CNS/ATM) requirements; variable display ranges (5, 10, 20, 40 and
80 nm); 50 aircraft tracks (24 within five nm); 1200 knots closing
speed; 10,000 feet per minute vertical rate; normal escape
maneuvers; enhanced escape maneuvers; escape maneuver coordination;
and air/ground data link.
[0065] By way of illustration and not by limitation, an
input/output (I/O) card 350 is added (in, for example, an existing
spare card slot) in the TCAS-2000 computer in addition to its other
components as shown in FIG. 4. This I/O card 350 provides the ADS-B
data interface from the TCAS-2000 computer to the aircraft mission
computer 410. In addition, the TCAS 350 derives its present
position, altitude, and airspeed from GNS/INS. Such information is
accommodated using this I/O card 352 to interface with the
aircraft's GPS receiver and INS systems (330). The I/O card 352
accommodates an ARINC 429 interface to the GNSS/INS 330 so the TCAS
can establish its own geographical position and airspeed reference.
The TCAS receives altitude data from the Mode-S Transponder via a
high-speed ARINC 429 data bus. These parameters are necessary in
order to precisely calculate exact range, range-rate, bearing and
relative altitude of adjacent cell formation aircraft.
[0066] A modification to the TCAS-2000 Computer Processing Unit
card (not shown) is needed to decrease the average filtered range
error from approximately 72 feet to 50 feet. Also, a modification
to the Control Panel is needed to add the IFPCAS mode selection
option and to add the 0.5 nmi range selection option.
[0067] A preferable Mode-S transponder is the Honeywell Mode-Select
(Mode-S) Data Link Transponder (product no. XS-950), which is a
"full-feature" system implementing all currently defined Mode-S
functions--but with built-in upgradeability for future growth. As
will become apparent to those skilled in the art, other Mode-S
transponders can be used in the present invention. Current Mode-S
transponders are used in conjunction with TCAS and ATCRBS to
identify and track aircraft position, including altitude. The
Mode-S Data Link Transponder XS-950 product transmits and receives
digital messages between aircraft and air traffic control. It meets
all requirements for a Mode-S transponder as described in DO-181A,
including Change 1. The unit also conforms to ARINC Characteristic
718 with interfaces for current air transport applications. The
Mode-S transponder is capable of transmitting and receiving
extended length Mode-S digital messages between aircraft and ground
systems. The data link provides more efficient, positive, and
confirmed communications than is possible with current voice
systems.
[0068] Modifications to the conventional Mode-S transponder are
required by the present invention to inhibit Air Traffic Control
Radar Beacon System (ATCRBS) interrogation replies while in the
IFPCAS operational mode. To further reduce RF emission levels, the
present invention further comprises an external RF power step
attenuator, which requires a change to the TCAS RF board. The
Mode-S RF power transmission level is 640 watts peak pulse, 250
watts minimum. An external attenuator controlled from the pilot's
station reduces emission levels for close proximity aircraft,
contributes to reducing probability of detection, and reduces the
chance of adjacent aircraft L-Band receiver desensitization. Only
the formation cell leader (e.g., 225 in FIG. 2) will transmit at
higher Mode-S squitter power levels to ensure positive formation
positional control with the Master Formation Leader (250 in FIG.
2). No modification to the Honeywell XS-950 Mode-S transponder is
required to broadcast GPS Squitter data because it is already
Mode-S, ICAO Level 4 capable (i.e., transmits and receives
16-segment extended length (112) bit messages).
[0069] In addition to hardware modifications to the
commercially-available TCAS 2000 (or other TCAS product), software
modifications to it and to the Mode-S ADS-B systems are
contemplated for the present invention to reduce the number of
unnecessary evasive maneuvers and allow close formation flying. The
modifications include, for example, a GPS Squitter capability
enhancement to the commercially-available Honeywell Mode-S
transponder product no. XS-950. The IFPCAS mode will be added to
the existing software. This unique TCAS mode of operation will
provide pilot/operator situational awareness when flying in a
formation of multiple TCAS-equipped aircraft. Differences between
the IFPCAS mode of the present invention and the conventional TCAS
operation mode include, but are not limited to: TCAS Interrogation
inhibited; VSI/TRA display of intruders with visual/aural
indication of when an intruder penetrates a protected volume or
meets some closure rate criteria within a protected volume;
centered (or some positioning) VSI/TRA display with approximately
0.5 nmi selection range (see FIG. 6) appropriate sized range ring
(e.g., 500 feet) on VSI/TRA display (see FIG. 6); intruder range
quantization of a predetermined distance (e.g., 70 feet) and
filtered to provide resolution of a predetermined distance (e.g.,
50 feet); additional annunciation of relative velocity and
formation member identification (see FIG. 6); shutoff interference
limiting logic; changes necessary to interface with a GNSS/INS; new
data recorder parameters; and modify Mode-S Transponder software
code to inhibit Air Traffic Control Radar Beacon System (ATCRBS)
response by follower aircraft (only the MFL will have the
transponder enabled). All of these changes are well within the
skill of those skilled in the art and their implementation will be
apparent to them.
[0070] Both TCAS-2000 GPS Squitter data processing and Mode-S
extended length message ADS-B data transmission will be implemented
as part of TCAS-2000 Change 7 software modification in accordance
with the present invention as described above. The existing
commercial TCAS-2000 system can be modified to operate in an IFPCAS
mode while maintaining the normal TCAS mode of operation. Normal
TCAS Traffic Advisory/Resolution Advisory (TA/RA) capability would
be inhibited to prevent aircraft interrogations and resolution
advisory operation.
[0071] Software in the transponder is completed and certified to
DO-178B, the FAA requirement for software development and
certification. Software updates can be completed on-board the
aircraft by means of, for example, an ARINC 615 portable data
loader, which has a data loader port located on the front
connector. All of the foregoing software modifications are well
within the skill of those skilled in the art and their
implementation need not be discussed in detail.
[0072] Referring to FIG. 6, there is shown a Vertical Speed
Indicator/Traffic Resolution Advisory (VSI/TRA) (or Traffic
Advisory/Resolution Advisory) display 600 in accordance with the
present invention. FIG. 6 illustrates an exemplary VSI/TRA display
600 with formation and non-formation members identified, such as
formation cell aircraft (depicted as airplane icons), lead
formation aircraft 250 (depicted as an airplane icon inside a
diamond), and non-formation aircraft (depicted by blue diamonds 620
and an amber circle 630). The VSI/TRA display can also show
different symbology for formation, tanker, non-formation aircraft,
etc.
[0073] As shown in FIG. 6, the TCAS VSI/TRA display of the present
invention not only shows the relative altitude 660 to the
TCAS-equipped aircraft 670 (depicted as an airplane icon inside the
dotted range ring 640) but annunciates the relative velocity 650
(or range-rate) of the TCAS-equipped aircraft 670 with the
formation lead 250 and follower aircraft (610, 680). Own aircraft
position is represented by the aircraft icon 670 at the bottom of
the display headed toward the twelve o'clock position. The number
(-05) on top of the airplane icon 680 represents the relative
velocity (650, 652, 654) in, for example, nmi/hr and the number
below the targets (e.g., 660 pointing to -01) represent the
relative altitude in, for example, thousands of feet. A negative
number indicates that the target aircraft (250, 610, 680) is
traveling at a lower velocity than the TCAS-equipped aircraft 670
while a positive number indicates that the target aircraft (250,
610, 680) is traveling at a higher velocity than the TCAS-equipped
aircraft 670. This enhancement makes the TCAS a value-added
instrument for the pilot flying in tight formation profiles.
Relative velocity annunciation will be particularly useful for
maintaining aircraft relative position within a formation during
turning maneuvers. A conventional TCAS is aware of intruder range
and range-rate but today it displays only color warnings when the
intruder's relative velocity presents a threat. The TCAS display of
the present invention operating in intra-formation mode displays
formation cell aircraft relative velocity (650, 652, 654); relative
velocity is displayed digitally along with the relative altitude
data on the TCAS display 600.
[0074] With instantaneous knowledge of the relative speed of each
aircraft in a formation, any crew can immediately correct their
speed to match the lead aircraft or communicate with an adjacent
aircraft if it is flying off formation speed. Once speed is under
better control, it becomes possible for all the aircraft in
formation to fly coupled to their flight management system, thus
ensuring each aircraft flies the same track. The TCAS display 600
of the present invention, which is augmented with relative
velocity, should eliminate nearly all of the variation in range,
significantly reduce crew workload and enhance safe effective large
cell formations in IMC.
[0075] The method of the present invention follows the above
description of the systems embodiments and is described in the
Summary of the Invention section.
[0076] Referring to FIG. 7 through 9, there is shown flowcharts of
the information processing to determine the manner in which
information is displayed to the aircraft flight crew on the display
600. In step 704, the process of displaying TCAS formation members
is begun. In step 706, the TCAS computer of the lead or host
aircraft receives Mode-S Squitter (ADS-B) message from an intruder
to the protected volume. The VSI/TRA display provides pilots
situational awareness of formation aircraft position and an
audiovisual indication when an intruder penetrates a protected
volume or meets some closure rate criteria within a protected
volume. Intruder range quantization is filtered to provide
resolution of, for example, 50 feet. The VSI/TRA display 600
includes appropriate-sized range ring 640 of approximately 500 feet
and centered display with approximately 0.5-nmi range selection as
shown in FIG. 6. In step 708, the intruder is identified by its
unique 24-bit Mode-S address ID and stored for further processing.
In step 710, the mission computer accesses a look-up table to
determine whether the intruder is a formation member (FMBR) or a
formation leader (FLDR) or non-formation member (NFMBR) or
otherwise. In step 712, a decision is made as to whether the
intruder is a formation member according to the Mode-S address ID.
If the intruder is a FMBR, then certain bits, referred to herein as
FMBR bits, in, for example, the ARINC 429 are set in step 714 and a
TCAS-to-display data label is assigned. In step 720, the relative
altitude, range, range rate, and bearing information are set in the
ARINC 429 and a data label assigned. The intruder data label
assigned in step 720 is then transmitted to the VSI/TRA display 600
in step 722. The information obtained in step 708 is also provided
to step 716, which is a TCAS intruder database that can be arranged
by an aircraft's Mode-S address ID. In step 716, the information is
updated in the TCAS intruder database, specifically, the range,
range rate, relative altitude, altitude rate, and the bearing of
the intruder. The outputs of step 716 are provided to both steps
718 and 720. In step 718, the TCAS closure rate of the intruder is
calculated after which it is sent to step 730 (FIG. 8) for further
processing and presentation on display 600.
[0077] Referring again to step 712, a decision is made as to
whether the intruder is a formation member according to the Mode-S
address ID. If the intruder is not a FMBR, then another decision is
made in step 724 as to whether the intruder is a FLDR. If the
intruder is a FLDR, then the FLDR bits are set in the ARINC 429 in
step 714 for processing in steps 720 and 722 as discussed
earlier.
[0078] If the intruder is not a FLDR, then the non-formation member
(NFMBR) bits are set in the ARINC 429 in step 728. In step 730, the
NFMBR is identified or tagged as a resolution advisory, a traffic
advisory, proximate traffic, or other traffic. These NFMBR bits are
then set as NFMBR intruder traffic type bits in the ARINC 429. Then
the information is processed in steps 720 and 722 as discussed
earlier for transmission to the VSI/TRA display 600.
[0079] Referring to FIG. 9, the TCAS intruder data label
information transmitted in step 722 is received in step 742 by the
mission computer. In step 744, the TCAS intruder data label is
decoded to derive the intruder type (i.e., FMBR, FLDR, NFMBR) in
addition to its relative altitude, range, range rate, and bearing.
The intruder is identified by its unique Mode-S address ID in step
746. The information is processed in step 748 to determine if the
FMBR bit is set and in step 754 to determine if the FLDR bit is
set. If the FMBR bit is set, then the intruder is annunciated on
the display as a FMBR at the correct relative bearing/range
position along with the most recent relative altitude and range
rate in step 750. This information is processed along with
information obtained from the intruder database in step 752. If the
FMBR bit is not set, then a further decision is made in step 754.
If the FLDR bit is set, then the intruder is annunciated on the
display as a FLDR at the correct relative bearing/range position
along with the most recent relative altitude and range rate in step
756 as obtained in part from step 752. This information is
processed along with information obtained from the intruder
database in step 752. If the FLDR bit is not set, then a further
decision is made in step 758. If neither the FLDR bit nor the FMBR
bit is set, then the intruder is a NFMBR. In step 758, if the NFMBR
intruder is a resolution advisory, then the intruder is displayed
on display 600 as, for example, a solid red square. Along with the
solid red square is displayed the correct relative bearing/range
position and the relative altitude in step 762 as obtained in part
from step 752. If the NFMBR intruder is not a resolution advisory,
then a further decision is made in step 764 to determine whether
the NFMBR intruder is a traffic advisory. In step 768, if the NFMBR
intruder is a traffic advisory, then the intruder is displayed on
display 600 as a solid amber circle as shown in FIG. 6 (numeral
630). Along with the solid amber circle is displayed the correct
relative bearing/range position and the relative altitude in step
770 as obtained in part from step 752. If the NFMBR intruder is not
a traffic advisory, then a further decision is made in step 766 to
determine whether the NFMBR intruder is proximate traffic. If the
NFMBR intruder is proximate traffic, then it is displayed as an
intruder in step 772 as a solid cyan diamond as shown in FIG. 6
(e.g., numeral 620). Along with the solid cyan diamond is displayed
the correct relative bearing/range position and the relative
altitude in step 774 as obtained in part from step 752. If the
NFMBR intruder is not proximate traffic, then a symbology is used
in step 776 to display the intruder as other traffic intruder such
as a hollow cyan diamond. Again, along with the hollow cyan diamond
is displayed the correct relative bearing/range position and the
relative altitude in step 778 as obtained in part from step
752.
[0080] Although there are numerous advantages realized by the TCAS
system described herein, there are two major advantages of using
passive surveillance for close formation aircraft separation.
[0081] The first major advantage is that the positional accuracy is
substantially equivalent to the longitude and latitude positional
accuracy associated with the aircraft's GPS navigational source. A
relative aircraft bearing within 2.degree. root mean square (rms)
can be attained with the present invention. This is because TCAS
calculates individual target cell position based upon ADS-B
positional data transmitted from each aircraft. TCAS ADS-B
operations enables processing of at least 50 targets. The number of
targets displayed to the pilot will be based upon a prioritization
scheme of number of aircraft within a specified horizontal range,
bearing relative to the host aircraft, and relative altitude. The
nominal aircraft target processing and display capability is a
formation of 35 TCAS-equipped aircraft. The received TCAS ADS-B
data could be transferred to the aircraft's mission computer via
ARINC 429 data bus interface for further processing and generation
of SKE steering commands to maintain aircraft horizontal and
vertical separation within the cell. Processed ADS-B information
that results in aircraft horizontal and vertical positioning would
be directly or indirectly coupled to the autopilot or SKE via the
Flight Management Computer (FMC).
[0082] The second major advantage is that passive surveillance
reduces RF emissions and contributes to minimizing probability of
detection. TCAS interrogations are not required to establish the
relative position of aircraft squittering ADS-B data. GPS squitter
data is emitted at random intervals uniformly distributed over a
range, for example, from 0.4 to 0.6 seconds. The Honeywell XS-950
transponder contains ARINC 429 interfaces reserved for inputting
longitude, latitude, airspeed, magnetic heading, intended flight
path, and flight number identification. Most of these parameters
are provided via Global Positioning System Navigation Satellite
System (GNSS) and Flight Management System (FMS). Barometric
altitude, however, would be derived by the on-board Air Data
Computer (ADC 340) via the Mode-S transponder interface.
[0083] Other variations and modifications of the present invention
will be apparent to those of skill in the art, and it is the intent
of the appended claims that such variations and modifications be
covered. For example, the antenna mounting technique taught in U.S.
Pat. No. 5,805,111 could be implemented in the present invention to
extend TCAS detection range. The particular values and
configurations discussed above can be varied and are cited merely
to illustrate a particular embodiment of the present invention and
are not intended to limit the scope of the invention. It is
contemplated that the use of the present invention can involve
components having different characteristics as long as the
principle, the presentation of a passive TCAS and Mode-S
transponder in communication is followed. The present invention
applies to almost any CAS system and is not limited to use by TCAS.
It is intended that the scope of the present invention be defined
by the claims appended hereto.
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