Система предотвращения столкновений воздушных судов (TCAS)

Aircraft collision avoidance system
A traffic alert and collision avoidance system (TCAS, pronounced /t//i://k//æ//s/; TEE kas), is an aircraft collision avoidance system designed to reduce the incidence of mid air collision (MAC) between aircraft. It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder equipped aircraft which may present a threat of MAC. It is a type of airborne collision avoidance system mandated by the International Civil Aviation Organization to be fitted to all aircraft with a maximum take off mass (MTOM) of over or authorized to carry more than 19 passengers. CFR 14, Ch I, part 135 requires that TCAS I be installed for aircraft with 10 30 passengers and TCAS II for aircraft with more than 30 passengers. ACAS/TCAS is based on secondary surveillance radar (SSR) transponder signals, but operates independently of ground based equipment to provide advice to the pilot on potentially conflicting aircraft. In modern glass cockpit aircraft, the TCAS display may be integrated in the Navigation Display (ND) or Electronic Horizontal Situation Indicator (EHSI). In older glass cockpit aircraft and those with mechanical instrumentation, an integrated TCAS display including an instantaneous vertical speed indicator (IVSI) may replace the mechanical IVSI, which only indicates the rate at which the aircraft is descending or climbing.

TCAS involves communication between all aircraft equipped with an appropriate transponder (provided the transponder is enabled and set up properly). Each TCAS equipped aircraft interrogates all other aircraft in a determined range about their position (via the 1030 MHz radio frequency), and all other aircraft reply to other interrogations (via 1090 MHz). This interrogation and response cycle may occur several times per second.

Type Text Meaning Required action TA Traffic; traffic. Intruder near both horizontally and vertically. Attempt visual contact, and be prepared to manoeuvre if an RA occurs. RA Climb; climb. Intruder will pass below Begin climbing at RA Descend. Descend. Intruder will pass above. Begin descending at RA Increase climb. Intruder will pass just below Climb at RA Increase descend. Intruder will pass just above. Descend at RA Reduce climb. Intruder is probably well below. Climb at a slower rate. RA Reduce descent. Intruder is probably well above. Descend at a slower rate. RA Climb; climb now. Intruder that was passing above, will now pass below. Change from a descent to a climb. RA Descend; descend now. Intruder that was passing below, will now pass above. Change from a climb to a descent. RA Maintain vertical speed; maintain. Intruder will be avoided if vertical rate is maintained. Maintain current vertical rate. RA Level off, level off. Intruder considerably away, or weakening of initial RA. Begin to level off. RA Monitor vertical speed. Intruder ahead in level flight, above or below. Remain in level flight. RA Crossing. Passing through the intruder's level. Usually added to any other RA. Proceed according to the associated RA. CC Clear of conflict. Intruder is no longer a threat. Return promptly to previous ATC clearance.

TCAS I is a cheaper but less capable system than the modern TCAS II system introduced for general aviation use after the FAA mandate for TCAS II in air transport aircraft. TCAS I systems are able to monitor the traffic situation around a plane (to a range of about 40 miles) and offer information on the approximate bearing and altitude of other aircraft. It can also generate collision warnings in the form of a "Traffic Advisory" (TA). The TA warns the pilot that another aircraft is in near vicinity, announcing "Traffic, traffic", but does not offer any suggested remedy; it is up to the pilot to decide what to do, usually with the assistance of Air Traffic Control. When a threat has passed, the system announces "Clear of conflict".

TCAS II is the first system that was introduced in 1989 and is the current generation of instrument warning TCAS, used in the majority of commercial aviation aircraft (see table below). A US Airways 737 was the first aircraft certified with the AlliedBendix (now Honeywell) TCAS II system. It offers all the benefits of TCAS I, but will also offer the pilot direct, vocalized instructions to avoid danger, known as a "Resolution Advisory" (RA). The suggestive action may be "corrective", suggesting the pilot change vertical speed by announcing, "Descend, descend", "Climb, climb" or "Level off, level off" (meaning reduce vertical speed). By contrast a "preventive" RA may be issued which simply warns the pilots not to deviate from their present vertical speed, announcing, "Monitor vertical speed" or "Maintain vertical speed, Maintain". TCAS II systems coordinate their resolution advisories before issuing commands to the pilots, so that if one aircraft is instructed to descend, the other will typically be told to climb – maximising the separation between the two aircraft. was Version 7.0 of TCAS II, produced by three avionics manufacturers: Rockwell Collins, Honeywell, and ACSS (Aviation Communication & Surveillance Systems; an L3 Technologies and Thales Avionics joint venture company). After the 2002 Überlingen mid air collision (July 1, 2002), studies have been made to improve TCAS II capabilities. Following extensive Eurocontrol input and pressure, a revised TCAS II Minimum Operational Performance Standards (MOPS) document has been jointly developed by RTCA (Special Committee SC 147) and EUROCAE. As a result, by 2008 the standards for Version 7.1 of TCAS II have been issued and published as RTCA DO 185B Other changes in this version are the replacement of the ambiguous "Adjust Vertical Speed, Adjust" RA with the "Level off, Level off" RA, to prevent improper response by the pilots (Change proposal CP115). ; and the improved handling of corrective/preventive annunciation and removal of green arc display when a positive RA weakens solely due to an extreme low or high altitude condition (1000 feet AGL or below, or near the aircraft top ceiling) to prevent incorrect and possibly dangerous guidance to the pilot (Change proposal CP116). Studies conducted for Eurocontrol, using recently recorded operational data, indicate that currently the probability of a mid air collision for each flight hour in European airspace is 2.7 x 10−8 which equates to one in every 3 years. When TCAS II Version 7.1 is implemented, that probability will be reduced by a factor of 4.

Originally designated TCAS II Enhanced, TCAS III was envisioned as an expansion of the TCAS II concept to include horizontal resolution advisory capability. TCAS III was the "next generation" of collision avoidance technology which underwent development by aviation companies such as Honeywell. TCAS III incorporated technical upgrades to the TCAS II system, and had the capability to offer traffic advisories and resolve traffic conflicts using horizontal as well as vertical manouevring directives to pilots. For instance, in a head on situation, one aircraft might be directed, "turn right, climb" while the other would be directed "turn right, descend." This would act to further increase the total separation between aircraft, in both horizontal and vertical aspects. Horizontal directives would be useful in a conflict between two aircraft close to the ground where there may be little if any vertical maneuvering space. TCAS III attempted to use the TCAS directional antenna to assign a bearing to other aircraft, and thus be able to generate a horizontal maneuver (e. g. turn left or right). However, it was judged by the industry to be unfeasible due to limitations in the accuracy of the TCAS directional antennas. The directional antennas were judged not to be accurate enough to generate an accurate horizontal plane position, and thus an accurate horizontal resolution. By 1995, years of testing and analysis determined that the concept was unworkable using available surveillance technology (due to the inadequacy of horizontal position information), and that horizontal RAs were unlikely to be invoked in most encounter geometries. Hence, all work on TCAS III was suspended and there are no plans for its implementation. The concept has later evolved and been replaced by TCAS IV.

TCAS IV uses additional information encoded by the target aircraft in the Mode S transponder reply (i. e. target encodes its own position into the transponder signal) to generate a horizontal resolution to an RA. In addition, some reliable source of position (such as Inertial Navigation System or GPS) is needed on the target aircraft in order for it to be encoded. TCAS IV had replaced the TCAS III concept by the mid 1990s. One of the results of TCAS III experience was that the directional antenna used by the TCAS processor to assign a bearing to a received transponder reply was not accurate enough to generate an accurate horizontal position, and thus a safe horizontal resolution. TCAS IV used additional position information encoded on an air to air data link to generate the bearing information, so that the accuracy of the directional antenna would not be a factor. TCAS IV development continued for some years, but the appearance of new trends in data link such as Automatic Dependent Surveillance – Broadcast (ADS B) have pointed out a need to re evaluate whether a data link system dedicated to collision avoidance such as TCAS IV should be incorporated into a more generic system of air to air data link for additional applications. As a result of these issues, the TCAS IV concept was abandoned as ADS B development started.

Although the system occasionally suffers from false alarms, pilots are now under strict instructions to regard all TCAS messages as genuine alerts demanding an immediate, high priority response. Only Windshear Detection and GPWS alerts and warnings have higher priority than the TCAS. The FAA, EASA and most other countries' authorities' rules state that in the case of a conflict between TCAS RA and air traffic control (ATC) instructions, the TCAS RA always takes precedence. This is mainly because of the TCAS RA inherently possessing a more current and comprehensive picture of the situation than air traffic controllers, whose radar/transponder updates usually happen at a much slower rate than the TCAS interrogations. This accident could have been prevented if TCAS was able to reverse the original RA for one of the aircraft when it detects that the crew of the other one is not following their original TCAS RA, but conflicting ATC instructions instead. This is one of the features that would later be implemented within Version 7.1 of TCAS II. Implementation of TCAS II Version 7.1 has been originally planned to start between 2009 and 2011 by retrofitting and forward fitting all the TCAS II equipped aircraft, with the goal that by 2014 the version 7.0 will be completely phased out and replaced by version 7.1. The FAA and EASA have already published the TCAS II Version 7.1 Technical Standard Order (TSO C119c and ETSO C119c, respectively) effective since 2009, based on the RTCA DO 185B providing guidance for obtaining airworthiness approval for TCAS II systems, including the new version 7.1. On 5 October 2009, the Association of European Airlines (AEA) published a Position Paper showing the need to mandate TCAS II Version 7.1 on all aircraft as a matter of priority. On 25 March 2010, the European Aviation Safety Agency (EASA) published Notice of Proposed Amendment (NPA) No. 2010 03 pertaining to the introduction of ACAS II software version 7.1. On 14 September 2010, EASA published the Comment Response Document (CRD) to the above mentioned NPA. Separately, a proposal has been made to amend the ICAO standard to require TCAS II Version 7.1 for compliance with ACAS II SARPs. ICAO has circulated an amendment for formal member state agreement which recommends TCAS II Change 7.1 adoption by 1 January 2014 for forward fit and 1 January 2017 for retrofit. Following the feedback and comments from airline operators, EASA has proposed the following dates for the TCAS II Version 7.1 mandate in European airspace: forward fit (for new aircraft) 1 March 2012, retrofit (for existing aircraft) 1 December 2015. These dates are proposed dates, subject to further regulatory processes, and are not final until the Implementing Rule has been published. certified Change 7.1 for their TCAS 2000 and Legacy TCAS II systems, and is currently offering Change 7.1 upgrade for their customers. By June 2010 Honeywell published a white paper with their proposed solutions for TCAS II Version 7.1. Rockwell Collins currently announces that their TCAS 94, TCAS 4000 and TSS 4100 TCAS II compliant systems are software upgradeable to Change 7.1 when available.

Jurisdiction (Agency)Classification of aircraftTCAS modeDate of mandateIndia (DGCA)Aeroplane having a maximum certified passenger seating configuration of more than 30 seats or a maximum payload capacity of more than 3 tonsTCAS II31 December 1998USA (FAA)All commercial turbine powered transport aircraft with more than 30 passenger seats (or MTOM above )TCAS II1 January 1994Europe (EASA)All civil turbine powered transport aircraft with more than 30 passenger seats (or MTOM above 15,000 kg)TCAS II1 January 2000Europe (EASA)All civil turbine powered transport aircraft with more than 19 passenger seats (or MTOM above 5,700 kg)TCAS II1 January 2000Hong Kong (Civil Aviation Department)All aircraft in Hong Kong with more than 9 passenger seats (or MTOM greater than 5,700 kg)TCAS II Version 7.01 January 2000Brazil (National Civil Aviation Agency)All transport category aircraft with more than 30 passenger seatsTCAS II Version 7.01 January 2008Peru (Dirección General de Aeronáutica Civil)All civil turbine powered transport aircraft with more than 19 passenger seats (or MTOM above 5,700 kg)ACAS II (Effectively TCAS II Version 7.0)1 January 2005Argentina (ANAC)All civil turbine powered transport aircraft with more than 19 passenger seats (or MTOM above 5,700 kg)ACAS II (Effectively TCAS II Version 7.0)1 December 2014