Communications: directive radio wave systems and devices (e.g. – With particular circuit – Display
Reexamination Certificate
2002-01-11
2004-01-27
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
With particular circuit
Display
C342S029000, C342S030000, C342S042000, C342S046000, C342S175000, C342S176000, C342S195000, C701S200000, C701S300000, C701S301000, C340S945000, C340S961000
Reexamination Certificate
active
06683562
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a traffic display for tracking aircraft; more particularly, but not exclusively, the invention relates to a display device for traffic surveillance and and collision avoidance systems in formation aircraft.
Presently, most aircraft utilize systems that provide pilots information to avoid potential collisions in the air and/or on the ground. There are many varieties of collision avoidance systems (CAS) and conflict detection systems in aircraft that fall into the following general category: (1) passive systems; and (2) active systems. Active collision avoidance systems utilize transmission broadcasts from the aircraft to determine relevant information relating to other aircraft in the area, and/or provide its own relative information to other aircraft in an area. The most prevalent active system used in the U.S. today, is the Traffic Alert and Collision Avoidance System or “TCAS.” (TCAS is internationally known as ACAS or Airborne Collision Avoidance System).
TCAS offers pilots of private, commercial and military aircraft reliable information to track traffic and avoid potential collisions with other aircraft. TCAS is a family of airborne devices that operate independently of the ground-based Air Traffic Control (ATC) systems. Since TCAS inception, three different control levels have evolved: TCAS I is intended for commuter and general aviation aircraft and provides a proximity warning only, assisting the pilot in visually acquiring intruder aircraft; TCAS II is intended for commercial airliners and business aircraft to provide pilots with traffic and resolution advisories in the vertical plane; and TCAS III, which has yet to be approved by the FAA, will purportedly provide resolution advisories in the horizontal as well as vertical plane.
TCAS detects the presence of nearby aircraft equipped with transponders that reply to ATCRBS Mode C or Mode S interrogations. When nearby aircraft are detected, TCAS tracks and continuously evaluates the potential of these aircraft to collide with its own aircraft.
For surveillance, TCAS interrogations are transmitted over an interrogation channel (e.g., 1030 MHz) from the TCAS equipped aircraft to any aircraft within the range of the transmission. The interrogation requests a reply from transponder-equipped aircraft within range of the transmission to provide their pertinent position and/or intent information. Transponder-equipped aircraft within range of the transmitted interrogation, reply over a reply channel (e.g., 1090 MHz) by providing their associated information. This information can include altitude, position, bearing, airspeed, aircraft identification and other information of the in-range aircraft to assist the TCAS in tracking and evaluating the possibilities of collision with the in-range aircraft.
Essentially, TCAS is a surveillance system and a collision avoidance system. For tracking nearby aircraft or “intruders,” a symbol depicting the surrounding aircraft is displayed on traffic displays located in the cockpit. The displayed symbols allow a pilot to maintain awareness of the number, type and position of aircraft within the vicinity of his own aircraft.
For collision avoidance, TCAS predicts the time to an intruder's closet point of approach (CPA) and a separation distance at the CPA, by calculating range, closure rate, vertical speed and altitude. TCAS provides the capability of tracking other aircraft within a certain range, evaluating collision potential, displaying/announcing traffic advisories (TAs), and depending on the type of system used (e.g., TCAS II) recommending evasive action in the vertical plane to avoid potential collisions, otherwise known as a Resolution Advisories (RAs).
It should be noted that in certain circumstances aircraft may not be detected by TCAS, for example, aircraft not equipped with operating transponders cannot reply to interrogations; military aircraft equipped with identification friend or foe (IFF) systems operating in mode 4 do not reply to interrogations; and aircraft that may not hear interrogations for one reason or another (e.g., interference, lowering landing gear when intruder was being tracked by only the bottom antenna or interference limiting).
The Federal Aviation Administrations (FAA) set guidelines for collision, warning and caution areas for implementation of TCAS II. A volume of space defines these areas, and/or a time tau (&tgr;) to penetration of that space, around the TCAS equipped aircraft. Examples of a collision area
110
, warning area
115
and caution area
150
of an aircraft
105
equipped with TCAS II, are illustrated in
FIGS. 1A
(top view) and
1
B (perspective view). If oncoming aircraft
120
actually penetrates caution area
150
it may be designated as an intruder and a traffic advisory may be issued to the pilot or crew of TCAS equipped aircraft
105
. The TA may consist of an audible warning and visual display indicating the distance and relative bearing to intruder
120
. If an intruder
122
penetrates warning area
115
, a resolution advisory may be issued to the crew or pilot of TCAS equipped aircraft
105
. The RA may be corrective or preventive and may consist of instructions to climb or descend at a recommended vertical rate, or caution the pilot not to make changes in the present vertical rate.
The shapes, horizontal and vertical dimensions of the respective areas are a function of the range and closure rate of oncoming aircraft
120
.
The time-space domain for TCAS interrogations is limited in that each interrogation-reply takes a certain period of time. When several different aircraft are interrogating in the same proximity, the amount of transponder replies can saturate the surrounding airspace and cause ATC tracking problems. To overcome this problem TCAS was designed with logic that, when a certain number of TCAS equipped aircraft are within a predetermined vicinity of each other, output power and processor interrogations are reduced. This is known as Interference Limiting. The reduction of output power effectively shortens the TCAS intruder tracking range. Low traffic density areas allow for increased transmission power whereas high traffic density areas (often called Terminal Control Areas “TCAs”) require a reduced transmission power. For example, the TCAS of an aircraft flying over Western Kansas may have a 80 nm (nautical miles) interrogation range or longer, whereas an aircraft flying near Chicago may reduce its interrogation range down to 5 nm with greater link margin. The reduction of transmission power from a low density area to a high density area may be as much as 10 dB. This is done to reduce RF interference between other TCAS equipped aircraft and to reduce RF interference with ATC ground tracking stations.
Certain aircraft, typically military aircraft, frequently fly in multi-aircraft groups known as formations. A problem occurs when all planes in a given formation are actively interrogating with their TCAS. Notably, the TCAS of planes in and outside the formation may detect a seemingly high density of planes in a traffic area due to the formation and thus reduce the transmission power of their respective broadcasts and reduce their receiver sensitivity to compensate for the perceived density. This type of unnecessary range adjustment due to reduced transmission power and reduced receiver sensitivity is referred to as “Interference Limiting” and degrades collision avoidance safety to unacceptable levels (e.g., interrogation range is significantly decreased in areas where aircraft may be flying at high speeds). Even small formations of two or three TCAS enabled aircraft may result in Interference Limiting to non-formation and formation aircraft.
Honeywell (formerly Allied Signal) developed a collision avoidance system designed to specifically address military formation-flying insufficiencies of conventional TCAS; this system is known as Enhanced TCAS or “ETCAS.” ETCAS provided means for military planes to fly in formation by offering a rendezvous-type feature in collision
Stayton Greg T.
Troxel James R.
Ybarra Kathryn W.
Aviation Communications & Surveillance Systems LLC
Bachand William R.
Gregory Bernarr E.
Squire Sanders & Dempsey LLP
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