Satellite based aircraft traffic control system

A satellite based air traffic control (ATC) system includes an aircraft unit on an aircraft and an ATC facility. The aircraft unit includes an AARTS processor, GPS receivers or other satellite receivers, a comparator for comparing the GPS data, a two-way radio, and a transmitter and receiver for communicating information and data over a data link with the ATC facility. The ATC facility includes an ATC computer, a two-way radio, a display for displaying aircraft, and a transmitter and receiver for communicating information and data over the data link. The aircraft transmits aircraft identification information, GPS data, aircraft status information, and a transmit detect code to the ATC facility to allow the ATC to track the aircraft and identify the aircraft communicating on two-way radio. The traffic control system and a flight control system utilizing GPS may be used for aircraft in the air and on the ground, and may be used for ships, boats, automobiles, trains or railroads, and aircraft.

BACKGROUND OF THE INVENTION 
The invention relates to a system for the tracking and control of aircraft 
and other vehicles and the communication between aircraft and traffic 
controllers, and specifically to a satellite based system for tracking, 
guiding, controlling and communicating with aircraft and vehicles in the 
air, in the water and on the ground. 
Present air traffic control systems consist of a network of terminal area 
and enroute surveillance radar systems. These systems consist of both 
primary and secondary radar systems and computers that display usable data 
for the control of air traffic in the national and international airspace 
systems. 
The basic radar system consists of Primary Radar which operates by 
transmitting a pulsed radio signal at a known azimuth (direction, in 
degrees from North) from the radar antenna and measures the time it takes 
to receive the reflected signal from an object (aircraft) in space back to 
the point of transmission. This time factor determines the range in 
nautical miles from the radar site and the direction is determined by the 
azimuth from which the signal is received. The limitations of using only 
this system result in the loss of targets because of the difficulty in 
detecting weak reflected radar return signals attenuated by atmospheric 
conditions. 
Secondary radar, known as the Air Traffic Control Radar Beacon System 
(ATCRBS), utilizes cooperative equipment in the form of radio 
receiver/transmitter (Transponder). Radar pulses transmitted from the 
searching radar transmitter interrogate the airborne transponder. In 
response to receiving the interrogating signal from the radar, the 
Transponder transmits a distinctive signal back to the Radar Beacon 
System's antenna. For example Delta flight 195 to Dallas (Dal195) is 
requested to squawk "4142," resulting in the aircraft transponder being 
dialed to code "4142." The computer at the air traffic control (ATC) 
facility is preprogrammed to understand that transponder code "4142" 
corresponds to Dal195. The signal transmitted by the Transponder is 
typically coded to provide both aircraft altitude and aircraft 
identification data (4142) for processing by the air traffic controller's 
computer for display on the air traffic controller's radar scope. The 
aircraft's transponder is connected to an altitude encoder which encodes 
altitude data based on the altitude of the aircraft as determined from the 
aircraft altimeter. In addition, the aircraft's speed is presently 
determined by the ATC computer by measuring the time and distance 
differences from subsequent transmissions of the Transponder. The aircraft 
transponder code, altitude, and speed may be displayed on the controller's 
radar screen. 
However, present radar-based air traffic control systems suffer from a 
number of disadvantages and drawbacks. Radar systems, even when used in 
conjunction with secondary radar, provide limited range and accuracy in 
the determination of the location and altitude of an aircraft. The range 
of radar is inherently limited due to obstacles in the line of sight of 
the radar, curvature of the earth, atmospheric conditions, etc. Search 
radar has a range of approximately 300 to 350 nautical miles, while 
terminal radar is utilized only for about 30 nautical miles. Radar 
coverage is not available in many areas of the world, and is not available 
at all altitudes in the United States. 
Presently, radar is also used to track and determine the location of 
aircraft on the ground One current system is known as the Airport Surface 
Detection Equipment (ASDE), which is a high resolution radar system with a 
tower mounted radar antenna that "looks" down on the airport surface. This 
system tracks aircraft on the surface to a given altitude, for example 
from the surface to an altitude of 185 feet. This type of surface 
detection system has a number of disadvantages, including: a prohibitively 
high cost, aircraft targets are not tagged (location of aircraft is 
identified only by radio communications), the system produces split 
(ghost) targets, buildings and hangars restrict the view of some portions 
of the airport surface, high sensitivity of the system resulting in long 
periods of downtime for maintenance, and the system is not interfaced with 
departure controllers requiring the landing aircraft to be off the 
parallel runway before the departing aircraft can be released. Keeping 
track of the exact location of aircraft is important in low visibility 
conditions and enables controllers to expedite the flow of traffic. 
In addition, the present communication process between aircraft and air 
traffic controllers is standardized, however, it is inherently subject to 
errors or miscommunications. Presently, air traffic controllers and 
aircraft exchange information and communicate orally (verbally) via 
two-way radio. Therefore, with the exception of information obtained via 
primary and secondary radar, all information from the aircraft regarding 
the aircraft's status (i.e., aircraft is okay, emergency condition, 
equipment malfunction), the aircraft's speed, heading, and identification 
of the aircraft, and instructions from the air traffic controller are 
communicated verbally via two-way radio. Thus, the exchange of accurate 
information between the air traffic controller and the aircraft is 
dependent upon hearing, understanding and recording a clear verbal 
communication via two-way radio. This reliance upon human hearing and 
interpretation during the communications process provides an inherent 
opportunity for errors or miscommunication and complicates the air traffic 
controller's job, particularly in light of the background and engine noise 
present on aircraft, poor radio performance or unclear speech. 
Such miscommunication between flight crews and air traffic controllers can 
lead to serious problems. A controller may be giving instructions to the 
pilot of one aircraft on his radar screen and obtain an acknowledgement of 
the instructions from a pilot of another aircraft with a similar call sign 
or flight number. The only true verification that the correct aircraft 
received the instructions is a verbal verification of the correct call 
sign, or by observance by the controller that the aircraft called 
responded correctly to the instructions. If the wrong aircraft (or 
multiple aircraft) comply with the instructions and several aircraft are 
on the controller's screen, it may be difficult for the controller to 
recognize the error and safety can easily be compromised. Another common 
communication problem a controller may encounter is receiving an initial 
call from an aircraft and having difficulty identifying the corresponding 
aircraft on his radar screen. This is prevalent with the current system 
since all aircraft operating under Visual Flight Rules ("VFR") emit the 
same transponder code (1200). While standard codes emitted by a 
transponder are understood to communicate specific information, such as 
transponder code "7600" indicates radio failure, and code "7700" indicates 
an emergency, such transponder (radar) communication provides very limited 
communication of information (limited types of messages and only one 
message/communication at a time) and only operates in a radar environment. 
Alternative ATC systems have been proposed that would use the global 
positioning satellites (GPS). Such a proposed alternative is discussed in 
chapter 12 of Logsdon, The Navstar Global Positioning System, Von 
Neistrand Reinhold (1992). In The Navstar Global Positioning System, 
Logsdon discusses the proposed use of GPS receivers on board aircraft, 
wherein the aircraft transmits its GPS aircraft vector to air traffic 
controllers for display on the air traffic controllers' screen. However, 
Logsdon's discussion fails to provide any details of such a system or how 
it could be implemented. Furthermore, Logsdon's proposal does not address 
ground or surface detection of aircraft. Also, the Logsdon proposal fails 
to address the need for improved communication of information between 
aircraft and air traffic controllers, and the need for a technique to 
identify the aircraft that is communicating with the air traffic 
controller. 
Furthermore, present aircraft navigation and precision landing systems have 
a number of disadvantages. In the 48 contiguous United States, most 
instrument navigating is done with the aid of a VHF Omnidirectional Range 
(VOR) receiver for using the VHF radio signals emitted by the ground based 
VOR transmitters. Virtually all enroute navigation and many instrument 
approaches use these signals, which are broadcast in the frequency range 
108.0 to 119.0 Mhz. The VOR signal is a blinking omnidirectional pulse, 
and has two parts: a reference phase signal and the variable phase signal. 
It its transmitted in such a way that the phase between these two signals 
is the same as the number of degrees the receiving aircraft is from the 
VOR station. The VOR receiver and equipment uses the signals to determine 
its magnetic direction, or course, from the VOR. 
An additional navigation aide is known as Direction Measurement Equipment 
(DME). DME uses two-way (interrogation and reply) active spherical ranging 
to measure the slant range between the aircraft and the DME transmitting 
station. Many pilots and navigators vector airplanes from waypoint to 
waypoint using the signals from VOR/DME, rather than traveling in a 
straight line. As a result, aircraft are not traveling the shortest 
distance, causing increased fuel usage and increased travel time. Also, 
routes along the VOR/DME stations become heavily traveled resulting in 
increased probability of mid-air collisions. 
In addition, many aircraft employ so-called Instrument Landing Systems 
(ILS) for performing precision landings. ILS includes several VHF 
localizer transmitters that emit focused VHF signals upwardly from the 
airport to provide horizontal guidance to the aircraft and its autopilot 
systems. ILS also includes a UHF glideslope transmitter that radiates a 
focused UHF signal that angles downwardly across the runway to provide 
vertical guidance. While ILS provides an effective technique for precision 
landings, such ILS precision landings are not possible where the airport 
does not include such localizer and glideslope transmitters. 
The foregoing demonstrates a need for an improved air and ground traffic 
control systems for aircraft. There is also a need for improved 
communication and exchange of information between aircraft and air traffic 
controllers, and a need for a system that allows controllers to verify the 
communicating aircraft. There is also a need for an effective navigation 
system that does not rely on VOR/DME stations, and for an aircraft landing 
system that does not rely on localizer and glideslope transmitters. 
SUMMARY OF THE INVENTION 
The traffic control system of the invention meets these needs and overcomes 
the disadvantages and drawbacks of the prior art by providing an aircraft 
unit on board an aircraft and an air traffic control (ATC) facility that 
communicate via data link. The aircraft unit includes an ATC Aircraft 
Reporting and Tracking System (AARTS) processor for controlling operations 
of the aircraft unit, GPS receivers for determining the aircraft' 
position, trace altitude, and speed, a GPS data comparator for comparing 
the GPS data, a two-way radio, and a transmitter and receiver for 
transmitting and receiving (communicating) data and other information over 
a data link. Data that are communicated may include GPS data (altitude, 
position, heading and speed) and aircraft identification data 
(registration number, flight number, etc.), while other information 
communicated may include aircraft status information, requests, questions, 
responses, fight instructions, landing instructions, flight path 
information, information concerning conflicting aircraft, etc. 
The ATC facility includes a transmitter and receiver for transmitting and 
receiving an information transmission (comprising data and other 
information) over the data link, a data decoder/detector for detecting 
data and communications in a received information transmission, a two way 
radio, an ATC computer for controlling operations at the ATC facility and 
identifying received data and communications, and a display for displaying 
the location and status of aircraft. Aircraft periodically transmit 
identification information, their GPS position, track, speed, and 
altitude, their status, and other information to the ATC facility. Based 
on this received information, the ATC facility continuously monitors and 
tracks aircraft. Because each aircraft transmits a different and 
predetermined identification, the ATC facility knows the identity of each 
target on the ATC controller's display. This system provides the 
additional advantage of allowing the ATC to accurately track aircraft 
without using radar, thereby avoiding the problems and disadvantages of 
radar, such as ghosts, limited range due to curvature of the earth and 
line-of-sight problems, etc. Furthermore, the tracking system of the 
invention may operate even in areas where no radar coverage is available. 
Also, the communication of requests, responses, information and data over 
a data link between aircraft and the ATC facility provides more accurate 
and complete communications than two-way radio, and avoids any 
miscommunications or misinterpretation of speech that commonly occur with 
two-way radio. 
In addition, the aircraft unit also includes a transmit detector for 
detecting when the aircraft's two-way radio is transmitting. The ATC 
facility receives the transmit detect code along with the aircraft's 
identification via data link, thereby indicating when the aircraft's 
two-way radio is transmitting. This code may be displayed on the 
controller's display and allows the controller to identify or confirm 
exactly which aircraft on his screen/display he is communicating verbally 
over the two-way radio. 
The system of the invention may be used to track aircraft in the air or on 
the ground. The ATC facility may include a pseudo-satellite, or a GPS 
receiver that acts as a base station to allow aircraft GPS receivers to 
operate in differential mode. In differential mode, the ATC facility 
determines the GPS pseudo-range correction by subtracting the geometric 
range (based on the facility's known location) from the pseudo-range 
(calculated using GPS signals). This correction may be used by the 
aircraft or the base station to obtain much more accurate aircraft 
positioning. 
Each aircraft may include a flight control system for automating the flight 
and navigation of the aircraft. The flight control system includes a 
flight control computer for controlling the operation of the flight 
control system, GPS receivers, and a control panel. The flight control 
computer is connected to various aircraft interfacing systems, aircraft 
instrumentation, aircraft sensors, external navigation aids, and autopilot 
servos and servo drives. In an autopilot mode, the flight control computer 
automatically controls the aircraft to fly on a predetermined flight path. 
The flight control computer uses GPS data, and may use signals from 
external navigation aids and aircraft sensors to navigate the aircraft on 
the predetermined flight path. The aircraft may perform a precision 
(automatic) landing in the autoland mode using only GPS data, and 
preferably differential GPS data, rather than relying on the localizer and 
glideslope at the airport. The systems and methods of the invention may 
also be used on other vehicles, such as ships, boats, automobiles, and 
railroads.

DETAILED DESCRIPTION 
Air Traffic Control System 
Referring to the drawings in detail, wherein like numerals indicate like 
elements, FIGS. 1-2 show the overall structure of a satellite based air 
traffic control (ATC) system according to the principles of the invention. 
FIG. 1 illustrates an aircraft unit 18 of the ATC system. FIG. 2 
illustrates an ATC facility 48 of the satellite based ATC system according 
to the principles of the invention. 
Referring to FIG. 1, aircraft unit 18, which is fixed to a conventional 
aircraft platform, includes dual global positioning system ("GPS") 
receivers 20 and 22 for determining the aircraft's position (longitude, 
latitude), speed, altitude, and tracking. Other types of satellite 
receivers, such as receivers for receiving signals from the Soviet Glonass 
satellites, may be used. As well understood by those skilled in the art, 
each GPS satellite transmits binary pulse trains, copies of which are 
created in the GPS receiver electronics. The GPS receiver antenna detects 
the signals (binary pulse trains) transmitted from GPS satellites, 
amplifies the received signals, and inputs them into two tracking loops 
that lock onto the carrier waves. The GPS pulse train is adjusted in the 
tracking loop until it is brought into correspondence with the satellite 
pulse train. When correspondence is achieved, the GPS receiver resident 
processor can determine time signal travel time based on the pulse 
adjustment. The GPS receiver resident processor then may determine the 
pseudo-range (distance from the GPS receiver to each satellite) based on 
the signal travel time (plus or minus clock bias error) multiplied times 
signal travel time; (pseudo-range=C.times.delta T). The GPS receiver may 
then determine its location using four pseudo-ranges, solving four 
simultaneous equations having four unknowns (clock bias error drops out), 
as well known to those skilled in the art. The GPS receiver resident 
microprocessor automatically determines the user's current position 
(longitude, latitude), altitude, tracking and speed (navigation solution). 
Each GPS receiver should be a multi-channel receiver for receiving 
positioning signals from a plurality of GPS satellites. A number of GPS 
receivers are commercially available from such companies as Sony 
Corporation, Motorola, Rockwell International (the Naveore V GPS 
receiver), and others. One such commercially available GPS receiver is the 
Nay 1000 GPS receiver manufactured by Magellan Systems Corporation. The 
data output by GPS receivers 20 and 22 are output to GPS data comparator 
24. 
In a large commercial aircraft, GPS receivers 20 and 22 should be placed at 
opposite ends of the aircraft, for example, 100 feet apart. In large or 
small aircraft, the GPS receivers may alternatively be placed 
side-by-side. GPS data comparator 24 compares the data (location, 
altitude, speed, tracking) from both GPS receivers. 
GPS receiver switch 26 is connected to comparator 24 and allows the 
selection of comparator 24 into one of three modes: 1) normal mode, 2) 
GPS1, and 3) GPS2. In the normal mode, comparator 24 compares the GPS data 
from the two GPS receivers 20, 22, to ensure that the data from these two 
receivers are reasonable compared to each other based on the distance 
separating the two receivers 20 and 22. In the normal mode, for example, 
GPS data comparator 24 may compare the data between the first and second 
GPS receivers 20 and 22 to determine whether the data from the first GPS 
receiver 20 is within a predetermined range of the data of the second GPS 
receiver 22. This GPS data from both GPS receivers is then output to the 
ATC Aircraft Reporting and Tracking System (AARTS) processor 28. The AARTS 
processor 28 controls the overall operation of the aircraft unit 18 of the 
ATC system and is discussed in greater detail hereinbelow. The GPS 
integrity line 25 from comparator 24 indicates whether the GPS data output 
by comparator 24 is correct or reasonable based on the comparison between 
the GPS data of the two GPS receivers 20, 22, or comparison between the 
GPS data and additional aircraft navigation equipment, such as the 
aircraft inertial reference system. In other words, GPS integrity line 
provides an indication as to the integrity of the operation of the GPS 
receivers 20 and 22 and whether such GPS may be relied upon. A logic 
output of "1" on line 25 may indicate that the data of GPS receivers 20 
and 22 are within a predetermined range (i.e., 3%) of one another. A logic 
output of "0" on line 25 may indicate that the data from the two GPS 
receivers are not within the predetermined range, and therefore should not 
be relied upon. Alternatively, comparator 24 may average the data from the 
first GPS receiver with that of the second GPS receiver, and output this 
averaged data to AARTS processor 28, or AARTS processor 28 may average the 
data from the two GPS receivers. While comparator 24 may be a comparator 
circuit, comparator 24 may include a controller, a microprocessor, or a 
computer programmed to perform such comparison and output steps. 
Alternatively, the functions of comparator 24 may be performed by AARTS 
processor 28. 
Referring to the second and third modes of switch 26, by switching switch 
26 to "GPS1" or "GPS2", one of the two GPS receivers 20 and 22 may be 
selected. In these modes, uncompared GPS data from the designated GPS 
receiver is output from comparator 24 to AARTS processor 28. 
Alternatively, the selection of switch 26 to "GPS1" or "GPS2" may 
designate the selected receiver as a primary GPS receiver, and the 
remaining receiver is the secondary GPS receiver. In this mode of 
operation, the data from the primary GPS receiver is output by comparator 
24, and GPS integrity line 25 indicates whether the data of the primary 
GPS receiver is within a predetermined range (i.e., 3%) of the data of the 
secondary GPS receiver. 
Switch 26 may be operated manually, or automatically under control of AARTS 
processor 28. In addition, switch 26 may be manually or automatically 
switched to select an appropriate GPS receiver based on results from the 
built-in-test (or built-in self-test) of the GPS receivers, which may be 
monitored by the AARTS processor 28, or another processor. In the event of 
GPS failure or malfunction, the AARTS processor 28 selects and uses single 
uncompared GPS data from the operational GPS receiver, or may use other 
navigational aids, such as inertial reference system. In the event of 
power failure on the aircraft, power from the aircraft's emergency AC/DC 
electrical busses is used to power at least one of the GPS receivers 20, 
22. It should be understood that the functions of switch 26 and comparator 
24 may be performed in software by AARTS processor 28 or another 
processor. Instead of being separate GPS receivers, first and second GPS 
receivers 20 and 22 may comprise a single GPS receiver having, for 
example, six or more channels, allowing for the selection and/or 
comparison of multiple channels from the same GPS receiver. 
It should be understood that more than two GPS receivers may be used. For 
example, it is advantageous to use three (or more) GPS receivers. In the 
event that one of the GPS receivers fails or malfunctions, comparator 24 
and/or AARTS processor 28 would be able to detect the failed GPS receiver 
by comparison of data between the three receivers. For example, if data 
from two of the three receivers are within a predetermined range of one 
another (say, 3%), but the data from the third is not within this range, 
such a result indicates the likely failure or malfunction of the third GPS 
receiver. The AARTS receiver 28 or even comparator 24 would then be able 
to appropriately select GPS data only from the two correctly operating GPS 
receivers, and disregard the data from the third (malfunctioning) GPS 
receiver. 
Aircraft unit 18 may also include or use a number of external navigation 
aids, such as altimeters, VOR receiver, DME receiver, Instrument Landing 
System (ILS) equipment (localizer and glideslope receivers), Inertial 
Reference System (IRS) 27, or the like. IRS 27 may include standard ring 
laser gyroscopes and accelerometers for determining the position of the 
aircraft. The IRS 27 is presently used by aircraft in conjunction with 
other navigation aids, such as VOR and DME, to determine the location of 
the aircraft. The IRS 27 may be used primarily for two purposes. First, 
aircraft location data from the IRS 27 may be input to comparator 24 or 
AARTS processor 28 to confirm the integrity of the GPS receivers. For 
example, the position, heading, etc., of the aircraft as determined by the 
IRS 27 may be compared to data from one or all GPS receivers to confirm 
that the GPS receivers are operating within a prescribed range or 
tolerance. Second, IRS 27 may be used by the aircraft as an auxiliary 
positioning system. In the event that it is determined that the GPS 
receivers have malfunctioned or failed, AARTS processor 28 may then select 
IRS 27 as the primary positioning system of the aircraft, rather than the 
GPS receivers. 
AARTS processor 28 receives data (status, position, speed, tracking, 
altitude) from comparator 24. AARTS processor 28 controls the function and 
operation of aircraft unit 18. In a preferred embodiment, GPS receivers 20 
and 22 and AARTS processor 28 are contained within a single box, with the 
GPS receivers 20 and 22 receiving and demodulating the received GPS 
positioning signals, and the AARTS processor calculating location, track, 
altitude and speed based on the received positioning signals, and with the 
AARTS processor 28 also controlling or managing the operation of the many 
additional functions of aircraft unit 18. In this manner, smaller size, 
lighter weight, decreased power consumption and cost savings result from 
combining the processor resident in the GPS receiver (not shown) and the 
AARTS processor 28 into a single processor (AARTS processor 28). Also, 
AARTS processor 28 preferably performs the functions of comparator 24 and 
switch 26. 
AARTS processor 28 is connected to a computer memory 30, which stores data 
and information. A data input device 38 may be used to input data, 
information, commands, communications into AARTS processor 28 for storage, 
processing or communication. Data input device 38 may include a code 
generator for generating specific codes that are input to AARTS processor 
28 and which may be communicated via data link to the ATC facility 48. 
Alternatively, AARTS processor 28 receives information from input device 
38 and generates codes to be communicated to the ATC facility 48. Data 
input device 38 is used by a pilot prior to or during each flight to enter 
information or special codes (i.e., emergency code, hi-jacker on-board 
code) identifying the aircraft into AARTS processor 28. For example, the 
identification code will be the aircraft's identification, tail or "N" 
number, airline flight number, or other code or number for identifying the 
aircraft. The type of aircraft will be indicated by the appropriate 
aircraft designator, such as B727 (Boeing 727), or C310 (Cessna 310). In 
addition, a special flight plan code for the type of flight plan and/or 
operation (VFR or IFR) and the type of aircraft is input. An "I" or a "V" 
is input to identify that the aircraft is operating under Instrument 
Flight Rules or Visual Flight Rules, respectively. The aircraft designator 
or identification code or other permanent information may be permanently 
stored in memory 40 to simplify or minimize the information that is input 
at the beginning of each flight into AARTS processor 28 using the data 
input device 38. In such case, a copy of the stored information is 
automatically copied from memory 40 into AARTS processor 28 (or RAM) at 
the beginning of each flight. In addition, speech recognition equipment 
may be connected to AARTS processor 28 to convert the pilot's verbal 
instructions into coded data that is input into AARTS processor 28, rather 
than having the pilot enter or type in the data using data input device 
38. Display 39 is connected to AARTS processor 28 to provide visual 
information to the pilot and to allow the pilot to confirm the data or 
information that has been input using data input device 38. 
Aircraft status sensors 42 are connected to AARTS processor 28 and may 
comprise switches, sensors or other devices for detecting a number of 
different aircraft status. For example, sensors 42 may comprise an 
emergency switch for detecting the presence or occurrence of an emergency 
condition or request for assistance, a sensor for detecting low fuel, a 
sensor or switch for detecting the lowering of the aircraft landing gear, 
a sensor for detecting a fault or failure in the navigation sensors, 
radio, equipment or electronics, etc., or a sensor or switch for detecting 
a request to close the aircraft's flight plan. Sensors 42 may include a 
sensor or switch for detecting when an aircraft has crashed or has been 
unintentionally downed. Sensors 42 may include a sensor or switch for 
detecting the lowering of the aircraft's landing gear. Sensors 42 may 
comprise sensors or switches that may be actuated automatically or 
manually. AARTS processor 28 may monitor sensors 42 using a number of 
different well known techniques. For example, AARTS processor 28 may 
monitor sensors 42 through the detection of interrupts generated by the 
sensors 42 to processor 28, or by periodically polling the sensors 42. 
AARTS processor 28 may record the actuation of the detected sensor or 
switch in memory 30. As discussed in greater detail hereinbelow, AARTS 
processor 28 communicates via data link the aircraft GPS data (position, 
speed, altitude, track), information of the various aircraft status 
sensors 42 identifying the different status of the aircraft, and 
information identifying the aircraft (aircraft identification data), 
flight number, flight plan code, etc., and other information to the ATC 
facility 48. AARTS processor 28 may also receive information from the ATC 
facility 48 via data link prior to take-off, or during flight. Prior to 
take-off, the ATC facility 48 may transmit the aircraft's flight plan 
(which was provided to the ATC facility 48) and other information to the 
AARTS processor 28, where it is stored in memory 30. ATC facility 48 may 
also communicate with processor 28 via data link to communicate data, 
information, or verify the flight plan or other information with the 
aircraft. 
A standard VHF two-way radio 44 is used by the pilot or co-pilot to 
communicate with ATC facility 48. As understood by those skilled in the 
art, other types of radios may be used. A transmit detector 46 detects 
when radio 44 is transmitting. The detection of transmission from radio 44 
may be performed in a number of different ways. For example, transmit 
detector 46 may be connected to the microphone of the radio and detects 
whenever the microphone is keyed or actuated. Voice detection circuitry 
may be connected to an intercom box, or electronic circuitry may be 
connected directly to transmission circuitry of radio 44 to detect when 
radio 44 is transmitting. In response to detecting the transmission of 
information by radio 44, transmit detector 46 notifies AARTS processor 28 
of the transmission from radio 44. Detector 46 may notify AARTS processor 
28 of the detected transmission in a number of different ways. For 
example, detector 46 may generate an interrupt that is detected by AARTS 
processor 28, or detector 46 may change the logic value on its output line 
from a "0" to a "1" to indicate a transmission from radio 44. This output 
line may be monitored by AARTS processor 28, or the detector 46 may be 
frequently polled by AARTS processor 28 to determine when the radio is 
transmitting. As discussed below, the AARTS processor 28 communicates via 
data link to inform the ATC facility 48 of a detection of a transmission 
from radio 44 during the period that radio 44 is transmitting. In response 
to detecting a transmission from radio 44, either a code generator or 
AARTS processor 28 generates a predetermined code or symbol to be 
transmitted to the ATC facility 48 via data link during the period which 
radio 44 is transmitting. Preferably, this communication from AARTS 
processor 28 informs the ATC facility 48 of the transmission from radio 44 
and causes equipment (i.e., a display) at the ATC facility 48 to generate 
the predetermined symbol. 
Although a number of different symbols, codes, or other indications of 
transmission may be used, a T or (T) is preferably used to indicate that 
radio 44 is transmitting. The transmission of a radio transmit detect code 
or symbol from the aircraft to the ATC facility 48 during the transmission 
of radio 44 allows the air traffic controller at the ATC facility 48 to 
identify (and confirm) the aircraft associated with the voice he is 
hearing over his/her radio. The use of the radio transmit detect code and 
the transmission of an aircraft identification code or symbol identifies 
or tags each aircraft to allow the ATC facility 48 to keep track of each 
aircraft. 
If the aircraft is equipped with a Satellite Tracking Alert Resolution 
System (STARS) (see STARS processor 29) or another an anti-collision 
system that provides anti-collision evasive commands, a signal will be 
output from the STARS processor 29 or other evasive command control unit 
to immediately notify AARTS processor 28 of the aircraft unit 18 of the 
directed evasive command. An evasive command code generator may generate 
an evasive command code to notify AARTS processor 28, or the AARTS 
processor may be interrupted or otherwise informed of the evasive command. 
The aircraft may then automatically control its flight or course to 
implement the evasive command. The AARTS processor 28 communicates via 
data link to the air traffic controller to transmit the evasive command 
code to the ATC facility 48, or otherwise inform the air traffic 
controller of the evasive command that has been issued to the pilot, and 
whether the evasive command is being followed. The evasive command code 
may be received at ATC facility 48 and visually observed as a flashing 
annunciator, fight or other indicator to inform the air traffic controller 
of the aircraft's intent to climb, descend, turn right, turn left, etc. 
Aircraft unit 18 also includes a transmitter 32 and a receiver 33 for 
transmitting and receiving information and data over data link. Receiver 
33 is a standard type receiver and its structure is well known to those 
skilled in the art. Receiver 33 may include a demodulator for demodulating 
an information transmission, and a data decoder/detector 37 for detecting 
information and data on the received information transmission. Data 
decoder/detector may be a digital detector for detecting digital data and 
information. AARTS processor 28 may control decoder/detector 37 to detect 
specific data and information. 
Transmitter 32 is a standard transmitter and includes a data encoder 34 for 
encoding data and information received from AARTS processor 28. 
Transmitter 32 also includes modulator 36 for modulating the encoded data 
prior to transmission. Transmitter 32 may comprise a number of different 
types of transmitters, and the various components and operation of 
transmitter 32 are well known to those skilled in the art. Transmitter 32 
receives information, data, codes and instructions from AARTS processor 
28, and, under control of AARTS processor 28, transmits this information, 
data codes, etc. to ATC facility 48, or others, including other aircraft, 
via data link. Transmitter 32 preferably transmits information and data to 
a communications satellite (uplink). The information is then relayed from 
the communications satellite to the ATC facility 48 (downlink), or another 
receiver. The use of satellites to transmit the information from the 
aircraft to the ATC facility 48 has the advantage of having total coverage 
at all altitudes, and all locations, and avoiding the problems associated 
with VHF/UHF radio, such as line of sight problems, very limited range, 
and congestion on each frequency due to a high number of transmitting RF 
signals. However, a number of other communication or transmission 
techniques may be used, such as very high frequency radio (VHF), 
ultra-high frequency radio (UHF), optical communications, cellular 
telephone, etc., or a combination of these techniques. The term "data 
link" herein indicates one or more of the many available communications 
techniques (satellite, HF, UHF, or VHF radio, optical, cellular, etc.) 
Data encoder 34 uses well known techniques to encode data and information 
received from AARTS processor 28 into a digital format (i.e., data is 
converted to a series of bits). One such encoding technique is pulse code 
modulation (PCM), however, others may be used. Alternatively, analog 
encoding techniques may be used (amplitude, frequency or phase 
modulation), or a combination of digital and analog techniques. Modulator 
36 then modulates the encoded data onto a carrier wave prior to 
transmission. In addition, transmitter 32 may include a dedicated 
processor (not shown) for interpreting instructions and information and 
controlling operation of transmitter 32. Preferably, these transmitter 
control functions are performed by AARTS processor 28. 
Referring to FIG. 2, the ATC facility 48 is illustrated and may be located 
on the grounds of an airport, or at a remote location, and may keep track 
of aircraft including their location, heading, speed, status, etc. The ATC 
facility 48 may also be located in the air or space, such as a satellite 
based ATC facility or an aircraft based ATC facility. Alternatively, a 
portion or all of the apparatus of ATC facility 48 may be located in the 
air or in space, such as on a satellite or aircraft, with information 
gathered by one or more such airborne ATC facilities transmitted down to a 
ground based master ATC facility for nationwide coordination. 
ATC facility 48 includes a conventional two way radio 52 for communicating 
with aircraft. A pseudo-satellite 54 is provided to enhance accuracy of 
the GPS data, and is discussed in greater detail hereinbelow. An ATC 
facility receiver 60 receives signals transmitted via satellite 
communications on a satellite dish 56, and/or may receive signals 
transmitted via VHF or UHF radio on antenna 58, or may receive signals 
transmitted using other well known communication techniques, such as 
cellular telephone, optical communications link, etc. ATC facility 
receiver 60 includes a demodulator for demodulating the received signal. 
Receiver 60 also includes a data decoder/detector 64 for decoding or 
detecting the data or information received in the information 
transmission. Data decoder/detector 64 may be a digital detector for 
detecting digital data in information transmissions. ATC computer 66 may 
control decoder/detector 64 to detect specific data or information. The 
received and detected data or information is input to ATC computer 66, 
where the data and information are identified. ATC facility transmitter 61 
similarly includes a data encoder 63 and modulator 65, and transmits data 
and information via satellite or using other communications technique. 
An ATC computer 66 receives information and data from ATC receiver 60, and 
outputs data and information to ATC transmitter 61. ATC computer 66 
includes one or more processors (not shown) and a computer memory (not 
shown) for storing information and data received and other information. 
ATC computer 66 controls the overall function and operation of the ATC 
facility 48. GPS receiver 67 (or multiple GPS receivers) provide GPS data 
of the ATC facility 48 to ATC computer 66. ATC video processor 68 
generates the symbols or graphics to allow the display of aircraft, 
aircraft location, altitude, speed, status, etc. based on information 
received from the ATC computer 66 and information received via data link. 
ATC display 70 selectively displays certain aircraft and selected 
information about each aircraft under control of video processor 68 and/or 
ATC computer 66. 
In operation, ATC computer 66 stores data and information about the 
different aircraft, such as aircraft identification codes (i.e., B727), 
registration or "N" numbers, flight plan identification codes (I or V), 
airline flight numbers (i.e. AA 235), aircraft flight plans for the 
different aircraft, characteristics about each aircraft (max. airspeed, 
altitude, turning characteristics, etc.). The aircraft flight plan may 
additionally include the route of the aircraft's flight, aircraft type, 
equipment code, true airspeed, departure airport, proposed departure time 
(Zulu), required flight level/altitude, destination airport, estimated 
time enroute, fuel on board (hours, minutes), pilot in command, number of 
passengers on board, color of aircraft, and remarks. 
In addition, ATC computer 66 preferably stores and performs traffic 
separation alert functions. ATC computer 66 is programmed with the minimum 
horizontal and vertical separation requirements between aircraft ("traffic 
separation standards"). For example, current basic standards are typically 
a horizontal separation of 3 miles if the aircraft is within 40 miles of 
the radar antenna, and 5 miles if beyond. Typical vertical separation 
standards include 1,000 feet for altitudes up to 18,000 feet, 2,000 feet 
for altitudes of 18,000-29,000 feet, and 4000 feet for altitudes above 
29,000 feet. The present invention may allow a decrease in such required 
separation due to improved accuracy of aircraft tracking over radar. 
In accordance with the traffic separation alert functions, ATC computer 66 
tracks each aircraft, monitors the location, tracking, speed altitude, 
status, and the relative location, altitude and tracking of each aircraft 
with respect to other aircraft. Based on GPS data for each aircraft, the 
received flight plan for each aircraft, and information on each type of 
aircraft regarding the aircraft's maximum and average speed, altitude, and 
flight characteristics, ATC computer 66 models the projected path and 
predicts possible (and even probable) separation standards violations, in 
addition to identifying existing separation standards violations. ATC 
computer 66 monitors the distance separating aircraft, identifies any 
possible conflicts or separation standards violations, and alerts or 
notifies the air traffic controller of these possible violations or 
conflicts so flights may be redirected. 
ATC computer 66 may alternatively automatically redirect an aircraft's 
course, heading, altitude, etc., by the computer 66 determining the 
appropriate new course and transmitting via data link (i.e., transmitter 
61) information to the aircraft informing it of the mandatory (or, 
alternatively, suggested) new route, altitude, heading, etc. Computer 66 
may calculate an aircraft's new course, altitude speed, etc. based upon 
predicted routes of aircraft, aircraft location, altitude, tracking and 
speed, destinations of the aircraft, preferred routes of the aircraft, the 
shortest distance between each aircraft and its destination, each 
aircraft's flight plan, flight characteristics of each aircraft (maximum 
speed, altitude,...), aircraft status, separation standards, etc. 
ATC computer 66 has preprogrammed flight plans for all aircraft. If ATC 
computer instructs an aircraft to change routes, directions, altitude, 
speed, etc. (whether temporarily to avoid another plane or permanently), 
the ATC computer 66 must update its stored flight plan in real-time to 
maintain accurate information on each aircraft. ATC computer 66 may 
instruct an aircraft to temporarily change direction or altitude to avoid 
another aircraft because, for example, computer 66 has estimated, based on 
the present flight paths of two aircraft and based on other information 
that there is likely to be a separation standards violation. Accordingly, 
ATC computer 66 may provide additional instructions to the aircraft to 
alter its course and altitude, etc. to place the aircraft back on its 
original flight path, altitude, speed, etc. ATC computer 66 may constantly 
update the stored flight paths and other information on aircraft to allow 
ATC computer 66 to accurately track, guide and control all aircraft. 
Computer 66 may calculate the aircraft's new course, heading, speed, 
altitude, etc. based upon various information (such as listed hereinabove) 
and using well known mathematical approximations, calculations or 
techniques. For example, the calculation of the new aircraft heading, 
altitude, speed etc. may be performed by redirecting the aircraft to a 
heading that removes the aircraft from the predicted path of the 
conflicting aircraft by a predetermined distance or time. Or, the new 
heading may require the aircraft to make a 20 degree (for example) 
adjustment in heading so as to avoid the predicted path of the conflicting 
aircraft. Or, the aircraft heading and altitude may both be adjusted so as 
not to come within, say, 2 miles of the predicted path of the conflicting 
aircraft, or not to come within 2 miles of the conflicting aircraft itself 
based on the predicted path of the aircraft and of the conflicting 
aircraft. 
The air traffic controller may be notified of the computer calculated new 
route or heading, altitude, speed, etc., for an aircraft and asked to 
acknowledge that such new course is acceptable prior to transmission from 
the ATC facility 48 to the aircraft. Alternatively, the air traffic 
controller may simply be notified of the aircraft's new course after it 
has been communicated to the aircraft. ATC computer 66 may communicate via 
transmitter 61 information such as the aircraft's location, altitude, 
heading or tracking, speed, aircraft status, closest aircraft, to the 
aircraft to allow the aircraft to verify that the ATC facility 48 has 
correct information. Also, ATC computer 66 may also transmit such 
information to other aircraft in the area to allow such aircraft to be 
aware of other aircraft that are nearby. To direct the information 
transmission from the ATC facility 48 to the correct aircraft, each 
information transmission may include a header segment that identifies the 
aircraft (by registration number, flight number, etc.), and an information 
segment that includes information, messages, or instructions. The 
transmissions from the aircraft should also follow this same format. The 
information transmitted between the ATC facility 48 and aircraft, and 
between aircraft, may include a wide variety of types of data and 
information, such as aircraft location, speed, altitude, tracking, 
aircraft status, inquiries to the aircraft pilot, responses to inquiries, 
instructions or commands to the aircraft from the ATC facility 48, 
information regarding the aircraft that are nearby, and other types of 
information discussed herein. This information is received by an aircraft 
and may be displayed on the aircraft's display 39 (FIG. 1) as text, 
graphic symbols, or other indicia. Alternatively the information may be in 
the form of synthesized voice or digitized speech generated at ATC 
facility 48, communicated to the aircraft via data link, and output to the 
pilot headset or a speaker. The information may be transmitted from the 
ATC facility in coded form and output as synthesized voice or speech on 
the aircraft. The pilot may respond to such inquiries or input new 
information to be transmitted to the ATC facility 48 or another aircraft 
via data input device 38 or by speaking into a microphone. Well known 
speech recognition equipment and software may interpret voice signals at 
both the ATC facility 48 and the aircraft and convert such voice signals 
into text or information prior to transmission. 
ATC video processor 68 generates the graphics and text to illustrate the 
location of each aircraft on ATC display 70. ATC display 70 displays to 
the air traffic controller a pictorial or graphic representation of 
specified aircraft, their locations, status, headings, and other 
information in text or graphics based on information on the aircraft 
stored at and received by the ATC computer 66. Alternatively, the function 
of ATC video processor 68 may be performed by computer 66. Each air 
traffic controller should have his/her own display 70. Each ATC display 70 
may have a separate video processor 68. ATC computer 66 may include a 
single computer, or may comprise a plurality of computers, where incoming 
information transmission and data therein are identified and forwarded to 
the appropriate computer. Aircraft display 39 (FIG. 1) may also include a 
video processor and a display for generating and displaying similar types 
of information to the pilot. 
ATC computer 66 processes the incoming data for display. Computer 66 
preferably identifies each received data. Each data may include, for 
example, an aircraft registration number, GPS position, GPS altitude, GPS 
speed, aircraft status information, messages of communications to and from 
aircraft, etc. There are a plurality of data in an information 
transmission, each information transmission including a header segment and 
an information segment. After detecting and/or identifying the data in the 
information transmission, ATC computer 66 processes the data. Such 
processing may include a number of different tasks, such as notifying the 
air traffic controller of the received data (by audible or visual display 
or annunciator) and identifying the associated aircraft, and making 
information about each aircraft available to the air traffic controller. 
ATC computer 66 selects and displays targets (aircraft) on a controller's 
display 70 based on the controller's assigned sector and altitude (i.e., 
north sector, 10,000-23,000 ft. alt.). Inhibit functions may be programmed 
into computer 66 such that the aircraft are displayed on the (each) 
display 70 for the appropriate controller. Some overlap may occur to 
ensure proper tracking of aircraft passing from one sector to another. The 
ATC computer 66 models the path of all detected incoming aircraft and 
displays (via display 70) these aircraft along with selected information 
on each aircraft. ATC computer 66 also displays any untagged aircraft 
(aircraft that transmit only "1200" (VFR) on a transponder code, and/or 
transmit no identification code via other communications or data link). 
Display 70 may be a conventional radar scope, a dedicated CRT display, or 
other display. Selected information on each aircraft on the radar screen 
are displayed in the flight data box 71. Information displayed in the 
flight data box 71 may include: 
1) Aircraft Identification (i.e., UAL195 or 5043J(V)); 
2) Aircraft Type (i.e., B757, C150); 
3) Aircraft Operation (VFR V! or IFR I!); 
4) Aircraft Heading (Tracking): (i.e., arrow pointing in the direction of 
travel); 
5) Aircraft Speed in Knots (i.e., number above the arrow 300 knots!); 
6) Aircraft Altitude (reference to sea level; reference to pressure; 
altitude above 18,000 ft.) (i.e., 50=5000 ft., 180=18,000 ft.); 
7) Aircraft Location 
8) Destination of Aircraft; 
9) Notification of when an aircraft is transmitting - T, (T) or (circle T); 
10) Whether the aircraft is planning to land at this airport, and if so, a 
designation of the runway to be used, and an indication when the runway is 
dear for landing; 
11) Aircraft Status and other: Low fuel, emergency condition, aircraft 
equipment malfunction, aircraft electronics failure or malfunction, power 
failure, landing gear down, notification that aircraft is off flight plan, 
notification that two aircraft are too close (possible violation of 
separation standards), indication of evasive maneuvers being conducted by 
an aircraft in response to anti-collision equipment (i.e., a blinking 
arrow up or down), receipt of aircraft's request to dose flight plan, 
receipt of information typed in by pilot into data input device, 
notification that two aircraft are likely to come too close (separation 
standards violations) based on projected paths or flight plans. 
While all this information may be displayed in each flight box 71 on 
display 70, it is advantageous to display only selected information (such 
as the information shown displayed in FIG. 2) in each flight box 71, while 
allowing the air traffic controller to "click" or select on an aircraft 
using a mouse, trackball or other pointing device to cause the remaining 
information on the selected aircraft to be displayed in text or graphical 
form on another screen, window, or another display. For example, 
information such as the aircraft's heading, identification or flight 
number, aircraft type, altitude and/or location, and an indication that 
the aircraft's radio is transmitting (T) may be displayed in flight box 
71, with the remaining information on the selected aircraft available on 
the second screen or display. By displaying only selected information on 
display 70, the air traffic controller is allowed to quickly view many 
different aircraft on display 70 while still having access to more 
detailed or additional information by selecting an aircraft using a 
pointing device. 
Referring to FIGS. 1-2, the satellite based ATC system illustrated in FIGS. 
1-2 provides an air traffic control system that may effectively replace 
radar or at least supplement radar. The ATC system of FIGS. 1-2 allows air 
traffic controllers to track and control aircraft even in areas outside 
the range of conventional radar. The system of FIGS. 1-2 also provides 
improved accuracy over radar, and provides improved communication between 
aircraft and air traffic controllers as compared to conventional radio 
communications. 
Prior to a flight, the pilot registers the aircraft and its flight plan 
with the ATC facility 48. Computer 66 stores information on the 
identification of the aircraft, the aircraft flight plan, and other 
information. Prior to take-off, the flight plan and other information for 
each aircraft may be transmitted via data link (satellite, VHF/UHF, 
cellular telephone, etc.) from the ATC facility 48 to the aircraft unit 
18. AARTS processor 28 receives the information and downloads (stores) 
this received information in memory 30. Also, various communications may 
occur between aircraft and the ATC facility 48 prior to aircraft take-off, 
such as to confirm the flight plan, etc. The flight data box 71 of display 
70 displays a variety of information to the air traffic controller 
regarding each aircraft in his/her assigned sector and altitude range. As 
discussed above, the information displayed to the controller on the 
display 70 may include aircraft identification, speed, heading, altitude, 
and notification as to the status of the aircraft. The GPS data is input 
into AARTS processor 28 from comparator 24 and is continuously updated. 
While in flight, the aircraft may communicate with ATC facility 48 via 
two-way radio 44. In addition to using two-way radios, the aircraft and 
the ATC facility 48 may communicate with each other over an additional 
communications link (i.e., a data link) using transmitter 61 and receiver 
60 of the ATC facility and transmitter 32 and receiver 33 of the aircraft. 
In particular, AARTS processor 28 periodically communicates via 
transmitter 32 and receiver 60 over a data link (preferably satellite 
communications) to transmit the GPS data of the aircraft, aircraft 
identification, status of the aircraft, and other information to the ATC 
facility 48. Upon receipt of the transmitted data at ATC facility 48, 
computer 66 processes the data and then displays the data on the display 
70. The data displayed on display 70 allows the air traffic controller to 
keep track of and control aircraft in his/her assigned sector and altitude 
range. 
When a pilot on an aircraft transmits information using his two-way radio 
44, transmit detector 46 detects the transmission of information from 
radio 44. AARTS processor 28 is informed of the transmission from radio 44 
and controls transmitter 32 to transmit additional data notifying the ATC 
facility 48 that the aircraft is transmitting over its two-way radio. 
AARTS processor 28 preferably generates a code (a radio transmit detect 
code) that indicates a radio transmission from aircraft radio 44. This 
transmit detect code is preferably a T or (T), although a wide variety of 
symbols could be used. The transmit detect code, or information 
representing this transmit code, is then encoded as a series of bits, 
modulated and transmitted to ATC facility 48. The receiver 60 of ATC 
facility 48 receives, demodulates, and decodes this transmit detect code. 
ATC computer 66 recognizes this transmit detect code and instructs symbol 
generator to generate the (T) symbol and output this (T) symbol to display 
70 adjacent the other information in the flight box 71 for this aircraft. 
The aircraft identification information (transmitted with the transmit 
detect code) identifies the specific aircraft to which the (T) symbol 
corresponds. The (T) symbol indicates that the identified aircraft is 
presently transmitting via two-way radio. This (T) symbol makes it very 
easy for the controller to determine what aircraft with which he is 
communicating via 2-way radio, and allows the controller to more easily 
confirm that the correct aircraft is responding to his/her instructions. 
When the transmission from radio 44 is complete, transmit detector 46 
detects that radio 44 is no longer transmitting, and notifies AARTS 
processor 28 that the transmission has terminated. AARTS processor 28 then 
instructs transmitter 32 to cease transmitting the transmit detect code 
(T). ATC computer 66 then fails to receive the (T) code from receiver 60 
and in response, instructs symbol generator 68 to cease generating the (T) 
code for display. The result is that only when the pilot is speaking on 
his two-way radio 44, a (T) symbol is displayed on the controller's 
display 70. 
Surface Movement and Detection System For Aircraft 
During low visibility conditions or under any conditions, it is 
advantageous for controllers at the ATC facility 48 to know the exact 
location and status of all aircraft on the ground at an airport. In 
addition to an air traffic control system, the system of FIGS. 1-2 may 
also be used to provide a non-radar surface movement and detection system 
for aircraft located on the ground. 
For aircraft located on the ground at the airport, including aircraft in 
storage or in hangars, aircraft loading passengers, aircraft preparing to 
take-off, aircraft that have just landed, etc., each aircraft should 
preferably include on board thereon an aircraft unit 18. The ATC facility 
48 and aircraft units 18 on board each aircraft located on the ground of 
the airport allows the ATC facility 48 to track the location and status of 
each aircraft on the ground, and allows for the communication of data and 
other information (in addition to verbal communications over two-way 
radio) between the aircraft and the ATC facility 48 via data link. While 
use of a communications satellite as a data link is advantageous during 
flight, the communications satellite may also be used as the data link 
while aircraft are on the ground. Alternatively, other communication 
techniques may be used for aircraft on the ground, such as cellular 
telephone, HF/VHF/UHF radio, etc., to communicate data and information 
between aircraft and ATC facility 48. 
ATC facility 48 tracks aircraft on the ground in the same manner that 
aircraft are tracked while in flight. As discussed above, each aircraft, 
its registration number or flight number, and other information is 
registered with the ATC facility 48. Aircraft, while on the ground (or in 
the air) may periodically transmit an information transmission comprising 
coded signals or data. As with other information transmissions from 
aircraft during flight to the ATC facility 48, the information 
transmission transmitted while on the ground may comprise a header segment 
and an information segment. The header segment includes aircraft 
identification information (i.e., registration number, flight number), 
while the information segment may include other information such as GPS 
data (position, altitude, track, speed), aircraft status information, and 
other information. 
The ATC facility 48 receives the information transmission from each 
aircraft, and ATC computer 66 identifies each aircraft, and displays the 
aircraft or a symbol representing the aircraft, its location on a display 
at the ATC facility 48. ATC computer 66 identifies the aircraft using the 
received identification information. Because each aircraft transmits its 
location and a different predetermined identification code (known by ATC 
computer 66), each aircraft is effectively "tagged," allowing the identity 
and location of each aircraft to be ascertained by computer 66. The 
surface movement and detection system also includes a mapping system 
(i.e., software) resident in ATC computer 66 that maps the different 
airport structures, including airport ramps, taxi ways, runways, hangars, 
buildings, etc., and is programmed with the GPS coordinates of the 
location of each of these airport structures, so the relative location of 
each aircraft on the ground may be determined by ATC computer 66. ATC 
computer 66 may display all structures on the airport (runways, taxi ways, 
buildings, etc.), or just selected ones at the request of the air traffic 
controller. The surface movement and detection system may use the same 
display (70) as used for the tracking of aircraft while in the air, or may 
use a separate display. ATC computer 66 keeps track of all aircraft on the 
ground, including their locations and status. 
Tracking and coordination of aircraft on the ground is enhanced by each 
aircraft transmitting a transmit detect code to the ATC facility 48 when 
the pilot on the aircraft is communicating (transmitting) using his 
two-way radio 44, as discussed hereinabove. The transmit detect code is 
accompanied by the aircraft's identification information. This information 
is received by the ATC facility, and a predetermined symbol, such as a T 
or a (T) is displayed at display 70 (or other display) to indicate 
reception of the transmit detect code. The display of the predetermined 
symbol (T) indicates to the air traffic controller that the pilot is 
transmitting on his two-way radio 44. This transmit detect code and 
aircraft identification information allows the controller to determine 
which aircraft on his display he is communicating with over his two-way 
radio. This information also allows the controller to verify that when he 
communicates an instruction to a designated aircraft (i.e., you are clear 
to take off), only that designated aircraft responds to that instruction. 
Through the automatic communication of information and data via data link 
between aircraft and the ATC facility 48 (and even other airports), and 
real-time processing of the received information and data by ATC computer 
66, ATC computer 66 keeps track of (and may control) the aircraft flying 
in the area, aircraft on the ground and their locations, the anticipated 
landings and take-offs for aircraft, the scheduled runways to be used, and 
the timing/scheduling of all events. The air traffic controller located at 
the ATC facility 48 would typically use ATC computer 66 to coordinate the 
movement of aircraft. 
Alternatively, ATC computer 66 may automatically coordinate and control the 
occurrence of all events at the airport, and communicate with aircraft on 
the ground and in the air to ensure that all aircraft movement on the 
ground and in the air, including landings, take-offs, etc. occurs in an 
orderly and efficient manner while maintaining a safe predetermined 
distance or time separating each aircraft/event, so as to avoid separation 
standards violations and collisions. ATC computer 66 is programmed to 
receive aircraft location, status and other information from aircraft, 
aircraft flight plans, requests from aircraft (to land, take-off, 
emergency condition, etc.), and to provide the appropriate responses, 
information and instructions to each aircraft in order to coordinate and 
control the movement of aircraft in the air and on the ground. In this 
manner, the systems of the invention provide an intelligent and automated 
airport. 
The accuracy of aircraft positioning used by the ATC facility 48 for the 
surface movement and detection system (determination of the locations of 
aircraft located on the ground) may be improved through the use of: 1) 
differential navigation and/or 2) pseudo-satellites. GPS receivers 20, 22 
and 67 may operate in either absolute navigation mode, or differential 
navigation mode. In the absolute navigation mode, the GPS receivers 
determine their position absolutely with respect to a specific set of map 
coordinates, such as longitude and latitude. Although GPS receivers are 
one of the most accurate ways to determine location, heading, etc., a 
number of errors are inherently introduced that affect GPS accuracy, such 
as, satellite ephemeris and clock bias error, ionospheric and tropospheric 
delays, and line of sight ranging errors. As a result, a GPS receiver 
operating in absolute navigation mode may include average errors of over 
100 feet. 
In differential navigation, two GPS receivers continuously exchange 
navigation information with one another in real time. One of the GPS 
receivers (67) acts as a base station; The other GPS receiver (20 or 22) 
navigates relative to the base station's location. The base station (ATC 
facility 48) determines its real-time pseudo-range solution based upon the 
received binary pulse trains (pseudo-range=C.times.delta T). Because the 
base station also knows its exact location, it also determines a real-time 
geometrical solution (geometrical range=satellite position-base station 
position). The base station then calculates a pseudo-range correction by 
subtracting the geometrical range from the pseudo-range. This pseudo-range 
correction is periodically calculated and transmitted to all GPS receivers 
(20 and 22). GPS receivers located on aircraft (on ground and in air) may 
subtract this correction from their calculated pseudo-ranges to obtain GPS 
position, altitude, speed, and track that are much more accurate. The GPS 
resident processor of GPS receivers 20 and 22, and/or AARTS processor 28, 
and ATC computer 66 are programmed with software, using well known 
techniques, for performing the appropriate calculations and communications 
of pseudo-range corrections and other data. While the pseudo-range errors 
may be transmitted from the base station (ATC facility 48) to all 
aircraft, it is preferable that ATC computer 66 receives the uncorrected 
GPS data from each aircraft, and then performs this subtraction or 
adjustment of the received aircraft GPS data using the pseudo-range 
correction prior to displaying aircraft and their position on the ATC 
display at the ATC facility 48. Thus, using differential navigation, the 
GPS position calculated by each aircraft is transmitted to the ATC 
facility 48, and the ATC computer 66 subtracts the pseudo-range correction 
to obtain the corrected position of each aircraft. 
An improvement in the accuracy of aircraft positioning at ATC facility 48 
using differential navigation is possible due to substantially common 
errors between the ATC GPS receiver 67 and aircraft GPS receivers 20 and 
22. Satellite and ephemeris and clock bias error tend to be common to GPS 
receivers, and commonality also exists between the ionospheric and 
tropospheric delays, which are introduced as the L-band signals (binary 
pulse trains) travel toward the ground. Any remaining line of sight 
ranging errors tend to be minimal. Therefore, the use of differential 
navigation may be advantageously used to remove many errors and improve 
the accuracy of GPS receivers. The use of differential navigation is 
particularly effective on a surface movement and detection system where 
the aircraft are positioned on the ground relatively near to the base 
station (ATC facility 48). However, differential navigation may also be 
used for an ATC system for the tracking of aircraft in flight. In an ATC 
system, the ATC facility 48 may be used as the base station, or other base 
stations may be located at various positions on the ground throughout the 
U.S. and the world. These base stations may be interconnected via data 
link (optical fiber cable, VHF/UHF, satellite, etc.) to provide a network 
of base stations. In addition, satellites, whose positions are known, may 
be used as base stations. 
The second way aircraft positioning (accuracy of position) may be improved 
is through the use of so-called pseudo-satellites. Pseudo-satellites are 
"false" satellites that are usually located on the ground at fixed 
locations and transmit navigation signals similar to the ones transmitted 
by the GPS satellites. The GPS receivers must include software to receive 
and process and lock onto these signals transmitted by pseudo-satellites. 
While the use of a ground based pseudo-satellite may be limited by line of 
sight problems, the pseudo-satellite provides an additional source of GPS 
type positioning signals. To avoid jamming the reception of signals of 
real GPS satellites, it is desirable for pseudo-satellites to transmit 
their positioning signals only part of the time, such as by using a 
time-division multiple access technique. Pseudo-satellites may also 
transmit differential corrections. The use of pseudo-satellites may 
improve the accuracy of the positioning of aircraft in a surface movement 
and detection system. 
Aircraft, while on the ground, may communicate with ATC facility 48 via 
data link to transmit and receive a variety of different types of 
information. For example, aircraft instrumentation, switches and 
electronics may be connected to AARTS processor 28. During pre-flight 
testing, information may be transmitted from the aircraft unit 18 to ATC 
facility 48 to inform ATC facility 48 that the aircraft has passed its 
pre-flight test, or to inform ATC facility 48 of those systems that 
malfunctioned or failed pre-flight test, to allow repairs to be performed 
immediately. 
Also, information regarding other status of the aircraft may be 
communicated to ATC facility 48 prior to take-off. The flight plan or 
other information may be communicated from the ATC facility 48 to the 
aircraft unit 18 and stored in memory 30 of aircraft unit 18. Aircraft 
unit 18 may communicate via data link to ATC facility 48 to verify or 
confirm specific information, such as the flight plan, flight 
instructions, departure runway, etc. Display 39 may display, in graphical, 
text or other form, the planned flight plan, or the planned and 
approved/proposed flight route and other information for review and 
confirmation by the pilot. The pilot or crew may input information into 
AARTS processor 28 using data input device 38, which may include a 
keyboard, keypad, a series of buttons or switches, a microphone, etc. This 
information input by the pilot may be communicated to ATC facility 48 via 
data link (satellite, cellular, VHF/UHF, etc.), either automatically after 
being input, in response to actuation of a switch, or in response to 
another event. The ATC facility 48 may transmit questions or responses 
which are displayed to the pilot on display 39 in the form of text or 
graphic symbols. The aircraft unit 18 may also transmit questions and 
responses to ATC facility for display. 
Prior to take-off, aircraft unit 18 may transmit information via data link 
to the ATC facility that it is ready for take-off, and the ATC facility 
may respond with appropriate instructions (i.e., that the aircraft is 
clear to take off and designation of the runway to be used). While such 
communication normally occurs verbally between aircraft and the air 
traffic controller using two-way radios 44 and 52, the invention allows 
such verbal communications process to be replaced or at least supplemented 
by the transmission of coded signals and/or data that are transmitted via 
data link (satellite, HF, VHF, UHF, cellular, etc.) and displayed to 
improve the communications process and the accuracy of information 
communicated. Aircraft that have just landed may receive via data link 
instructions of where to taxi, and whether the terminal is accessible, or 
open, etc. After landing, the aircraft unit 18 may communicate a request 
via data link to close the aircraft's flight plan to ATC facility 48. The 
request may be made manually by the pilot actuating a switch or by 
inputting a predetermined instruction or code using input device 38, or 
the request may be generated automatically in response to the landing of 
the aircraft, the lowering of the landing gear, in response to 
interrogation from the ATC facility 48, or in response to some other 
event. 
The Flight Control System 
FIG. 2 illustrates a flight control system 72 located on an aircraft for 
automatically controlling the flight of the aircraft. A flight control 
computer 74 controls all operations and functions of the flight control 
system 72. Flight control computer 74 receives GPS data from GPS receivers 
20 and 22 through GPS data comparator 24. The flight control computer 
interfaces to a number of aircraft systems 78, such as electrical power, 
fight management system, inertial reference system (IRS), air data system, 
radio altimeter, instrument landing system (ILS), central warning system, 
etc. An input device 76 may be used to input data and information into 
computer 74, and a screen or display may display information and data. The 
display may provide annunciators for indicating to the pilots the 
activation/selection of the various flight modes and systems (autopilot, 
heading select, VOR, etc.). A flight control panel 80 provides the primary 
interface between the fight crew and the other components of the flight 
control system. The control panel 80 includes a number of pushbuttons that 
provide momentary discrete inputs to the flight control system. The 
pushbuttons provide four categories of control: 1) combined control 
(autoland, ILS, Turb, VNAV), 2) pitch control (vert. speed, altitude 
hold), 3) Roll control (VOR Location, Heading hold, heading select, Nay), 
and 4) Autothrottle control (speed select, mach select). The panel also 
includes an autopilot engage switch for engaging the autopilot, and a 
switch for selecting autoland. Next to the autoland switch is a switch for 
selecting the autoland to be performed based on ILS or based upon GPS 
data. A number of control knobs and displays are also on the control panel 
80, including altimeter knob (for dialing in a desired altitude), heading 
knob (for dialing in a desired heading, etc. A number of digital display 
readouts are also provided on the control panel 80, including displays 
for: airspeed (knots), heading (magnetic heading displayed in degrees), 
altitude, pitch (vertical airspeed, mach value, pitch attitude). 
Flight control computer 74 also connects to the various aircraft sensors 84 
(i.e., aileron position sensor, rudder position sensor, flap position 
sensors, spoiler position sensors) and navigational aids (IRS, VOR/DME, 
Tacan, etc.) Computer 74 also connects to standard or conventional 
aircraft instrumentation 82 (gyroscopes (IRS), pressure instruments, 
altimeter, vertical speed indicator, airspeed indicator, magnetic compass, 
engine and power instruments, ammeter, etc.), as well as to aircraft and 
autopilot servos 88 for actuating different aircraft systems or units, 
such as the servos for actuating and controlling the aircraft aileron, 
rudder, engine, flaps, spoiler, etc. Warning indicators 90 provide 
warnings of various conditions to the crew. Flight control computer 74 
also connects and communicates with AARTS processor 28 and STARS processor 
29 for coordinating the operation of all systems. AARTS processor 28, 
STARS processor 29 and flight control computer 74 may be a single computer 
or microprocessor. 
Flight control system 72 may be operated in manual mode or autopilot mode. 
In manual mode, the pilot is in control of the flight of the aircraft, 
including its heading, speed, altitude, etc. The pilot may dial in a 
desired speed, altitude, or air speed, etc. to partially automate flying 
the aircraft. In the manual mode, computer 74 may use information from GPS 
receivers 20, 22 as well as from a number of external navigation aids and 
other equipment, such as sensors and instruments. 
In autopilot mode, the aircraft is controlled by computer 74 to fly a 
predetermined flight path. When flight control system is operated in the 
autopilot mode (i.e., by switching the autopilot switch on panel 80), the 
pilot causes the autopilot to control the aircraft based on information 
input to computer 74. In autopilot mode, flight control computer 
automatically provides control of the roll, pitch, yaw, and operationally 
controls the aircraft attitude, heading, altitude, airspeed, etc. In 
autopilot mode, computer 74 also provides automatic throttle control 
(control of speed, mach and thrust), detects engine failures, monitors 
engine parameters, monitors fuel level, monitors the operation of all 
systems (in autopilot or manual mode). Computer 74 may operate in 
autopilot mode during take off, flight, and landing. In autopilot mode, 
computer 74 provides command signals to the autopilot servo drives for 
servos 88 (which may include aileron, elevator and rudder, etc.). These 
command signals provide proper movement of the aileron, elevator and 
rudder. Computer 74 also controls the thrust and speed by controlling the 
engine throttle, and controls operation of a number of other aircraft 
systems. 
In autopilot mode, the computer 74 controls the servo drives, throttle and 
other systems to control the flight of the aircraft on a predetermined 
flight path that is input in computer 74 or previously stored in computer 
74. The predetermined flight path may include headings, altitudes, speed, 
destinations., locations and other information. This predetermined path 
may include instructions to navigate the aircraft based on signals 
received by computer 74 from GPS receiver(s), or based on a number of 
different external navigation aids, such as ILS, VOR/DME, IRS, or the 
like. The aircraft may periodically receive instructions or information to 
update or change its flight path from the pilot or crew, or from ATC 
facility 48. Computer 74 may even update or alter its flight path based on 
communications from other aircraft. For example, the aircraft may alter 
its flight path to avoid a collision with another aircraft based on 
information it receives from its anti-collision system, such as the STARS 
processor 29. Or, ATC facility 48 may communicate via data link to 
instruct the aircraft to alter its flight path to avoid a separation 
standards violation, or to accommodate hazardous weather conditions. 
In autopilot mode, computer 74 may rely primarily on GPS receivers 20, 22 
for the aircraft's position, altitude, speed, and tracking (heading). The 
input of a flight path may also include a selection as between reliance on 
GPS or other navigation aids. Use of one or more pseudo-satellites, and 
particularly the use of differential navigation may improve navigation of 
the aircraft in the manual or autopilot mode. While in autopilot, the 
aircraft may be placed in the autoland mode, which instructs the aircraft 
to automatically land itself. 
During autoland mode, the aircraft's localizer and glideslope receivers may 
receive the localizer and glideslope signals emitted near the runway. The 
computer 74 may control the aircraft to land based upon the localizer and 
glideslope radio signals, which provide horizontal and vertical control to 
the computer 74 during the ILS precision landing. 
Computer 74, however, preferably uses the differential GPS data, including 
pseudo-range corrections from facility 48, to land the aircraft. The 
computer 74 stores in memory, or receives via data link from ATC facility 
48, information on the location of the airport, locations and dimensions 
of all structures at the airport, including runways, taxiways, buildings, 
terminals, and the direction from which the aircraft should approach each 
runway for landing. Based on this information describing the layout and 
structure of the airport, the computer 74 may display on a screen or 
display a picture or graphical image of the layout of the airport with 
designation as to the route or path to use for landing, the runway to use, 
the location of aircraft on the ground. 
Computer 74 controls the aircraft to automatically land the aircraft based 
on the known positions of the airport and runways, the recommended path 
for landing, the recommended altitude, location and speed for all points 
along the aircraft's flight path during and before the landing. The 
computer 74 may store, or receive via data link from the ATC facility 48, 
such information on the recommended locations, speed, altitude for points 
along the flight path. 
ATC facility 48 may also communicate to the aircraft via data link 
instructions on which runway to use, the aircraft that are on the ground 
and their locations, other approaching aircraft and their location, and 
instructions on what to do after landing (i.e., taxi to terminal 4d). 
Computer 66 automatically receives information (including aircraft GPS 
data, aircraft status information, etc.) in real-time describing the 
landing(s) in progress of the (and all) aircraft via communications from 
each aircraft. The ATC computer 66 also stores information on the layout, 
locations and structures of all runways, landing points, buildings, etc. 
Based on this airport map and the information received from each aircraft 
regarding its GPS data and status, the ATC facility monitors the 
aircraft's speed, positioning, altitude, etc., compares this received 
information to the ideal or suggested position, speed, heading, etc. of 
the ideal or suggested landing (stored in computer 66), and communicates 
via data link instructions or information to the aircraft flight control 
computer 74 to adjust its speed, altitude, positioning; etc. to improve 
the landing, or to avoid an aircraft on the ground, etc. Therefore, ATC 
facility 48 may communicate with aircraft during landings to monitor the 
landings and provide instructions to aircraft to assist the aircraft in 
the landings. 
While the above ATC, surface movement and detection, and flight control 
systems of the invention have been described hereinabove to track, guide, 
control and communicate with aircraft in the air and on the ground, the 
same systems may be employed to track, guide, control and communicate with 
other vehicles such as ships, automobiles, railroads, submarines, etc. 
When the systems of the invention are used on ships, each ship includes 
unit 18, illustrated in FIG. 1. A central facility 48, located at a 
harbor, dock, or a port, on a ship at sea, or other location, includes the 
system shown in FIG. 2. The ship systems (FIGS. 1-3) generally may operate 
like those described for aircraft, but are adapted for use with ships or 
sea vessels. Each ship obtains its position, track, speed from GPS 
receivers 20 and 22, and its status, and periodically communicates this 
information via data link (HF, VHF, UHF, satellite, etc.) to the central 
facility 48, along with ship identification data. The central facility 
(48) keeps track of the location of all ships at sea, for example, within 
a predetermined and limited region. The central facility 48 may also keep 
track of many other objects (including their locations), such as bridges, 
rocks, icebergs, docks, etc. Computer 66 of central facility 48 
anticipates possible ship conflicts or collisions based on the paths of 
the ships and information received from the ships regarding their path and 
destination. Central facility 48 may provide instructions via data link to 
ships to alter their path, or to warn of dangerous objects or other ships 
in their path. Central facility 48 may communicate with ships entering a 
channel or port and provide instructions to guide the ship down the 
channel, river, etc. The ship's transmit detector 46 may detect the 
transmission from ship radio 44 and transmit this transmit detect signal 
(T) along with ship identification information to the central facility 48. 
Ships may provide the status of their ship (i.e., emergency, low fuel, 
send help) to the central facility, along with their GPS data. Each ship 
may also include a system similar to that illustrate in FIG. 3, but for 
the automatic control and guidance of ships.