1. — HARMONISATION OF REGULATIONS GOVERNING AIRBORNE SSR EQUIPMENT
1. General
1.1 The purpose of this Circular is to present comprehensive information on the current planning of the EUROCONTROL Member States and other States in the ICAO EUR Region concerning the requirements for the airborne carriage and operation of SSR equipment and more specifically SSR Mode S.
1.2 This Circular supersedes AIC 02/90 and 003/91 which provided initial information on then measures needed to achieve harmonized regulations governing the carriage and operation of SSR equipment. There is now a need to extend the scope of these procedures, taking account of developments within the European Harmonization and Integration Program (EATCHIP) and, in particular, the recommendations pertaining to airborne equipment in the Concept of Operations Mode 5 in Europe (Mode 5 CONOPS) Document, Edition 2.0.
1.3 Various regulations requiring the carriage of SSR transponders in certain designated airspace and by certain user categories have been issued at national level in a number of States. These will be subject to amendment in accordance with the coordinated plan outlined hereunder
1.4 Fuller information regarding this Circular may be obtained from the relevant department within national authorities or from the following source:
Post:
Director General
Eurocontrol Agency
Rue de la Fusee, 96
B -.1130 Brussels
Belgium
2. DEVELOPIVIENT OF SSR SERVICES
2.1 Radar Equipment Development
2.1.1 Air Traffic Services in Europe continue to rely heavily on Secondary Surveillance Radar (SSR) and most States require the carriage and operation of a serviceable transponder capable of operating in Mode A 4096 codes together with Mode C altitude reporting, for aircraft flying in controlled airspace in accordance with Instrument Flight Rules (IFR).In certain areas it has been possible to dispense with the use of primary radar. SSR provides data on the position, iden6ficauion and altitude of the aircraft permitting the tracking of individual flights in three dimensions. Azimuth accuracy is improved by the utilization of monopulse techniques.Problems associated with the Mode A/C system are in the main:
2.1.4 - Garbling i.e. interference due to overlapping replies from two or more aircraft in close proximity in azimuth and distance.
- Fruit i.e. interference at one interrogator caused by the replies from a transponder in response to interrogations from another interrogator.
- Availability of only 4096 codes in Mode A for identification of aircraft.
- Shielding of the antenna caused by the attitude of the aircraft.
To overcome the limitations of Mode A/C, ICAO has published Standards and Recommended Practices (SARPS) for Mode S, a mode selective system which is interoperable with the Mode A/C system and which has been designed to replace it. Mode S offers, inter alia, selective surveillance of individual flights, each aircraft being assigned a unique address from almost 17 million available aircraft addresses. Antenna shielding can be mitigated by antenna diversity, which is incorporated in Mode S (subject to airframe practicability).
2.2 Airborne Equipment
2.2.1 In order to improve the effectiveness of air traffic services in areas where such services are provided on the basis of SSR information, it is essential for aircraft flying in the airspace concerned to be detectable by the carriage and operation of an appropriate transponder.
2.2.2 Furthermore, many aircraft have been and will continue to be equipped with Mode S transponders (at least Level 2 capability) to support airborne collision avoidance systems (ACAS). The operation of these devices depend upon the SSR replies provided by adjacent aircraft, regardless of the SSR coverage available for ATS purposes.
2.3 Interoperability of Ground and Airborne Equipment
2.3.1 It must be ensured that equipment used on the ground and on board aircraft are compatible and remain so during their respective development and full operational life. .Accordingly, it is necessary to define on a common basis the capabilities of the airborne SSR equipment required for the various categories of airspace users.
2.3.2 It is in the general interest of ATS, airspace users and equipment manufacturers to be given maximum advance notice on future intentions. AIC 02/90 and 003/91, in addition to outlining harmonization measures pertaining to the mandatory carriage and operation of Mode A/C transponders, provided advance information concerning the carriage of Mode S equipment.
2.3.3 On the basis of the work carried out under the aegis of EATCHIP, the European Air Navigation Planning Group (EANPG) in 1992 at its 34th meeting, accepted that the provisions concerning IFR flights could constitute an initial step towards implementation of SSR Mode S in the EUR Region. Consequently, the EANPG determined that a proposal for amendment to Doc 7030 be circulated to States and international organizations. A similar conclusion was adopted, in 1993, pertaining to VFR flights.
2.3.4 In the light of updated scheduling for the introduction of Mode S based surveillance services,revised timescales and capability requirements for the carriage and operation of airborne equipment have been formulated. These have been notified to the EANPG so that action can be taken to amend ICAO Doc 7030, accordingly.
3. COORDINATED REGULATION DEVELOPMENT
3.1 The aim of coordinated regulation development has been to achieve the capability of identifying and racking, by means of SSR, all aircraft in airspace so defined for that purpose. This has led to:
a. - Definition on a wide and common basis of the areas where the carriage and operation of transponders is mandatory.
- The mandating of Mode C pressure altitude reporting.
- Planning for the Initial Implementation of Mode S Enhanced Surveillance services.
3.2 For all powered aircraft operating under IFR (or, when permitted, under VFR at night),regulations have been such as to render mandatory the carriage and operation of transponders, at lease Mode A with 4096 codes and Mode C with pressure altitude reporting, within controlled airspace where SSR coverage exists.
3.3 For all powered aircraft operating under VFR by day, regulations have been issued which render mandatory the carriage and operation of transponders, at least Mode A with 4096 codes and Mode C with pressure altitude reporting, in the areas of airspace where the risk of conflict with IFR traffic exists. These areas of airspace are as follows:
- At and above a published level.
Note 1 In mountainous areas above such level the requirement will be waived in the layer of airspace between ground and the minimum en-route flight level.
Note 2 Altitude 5000 ft and levels 100, 120 have been published by certain States However, the aim should be to establish a common level as low as possible - Below this published altitude or flight level: to enter certain portions of designated airspace and in particular to operate in the vicinity of major aerodromes. Outside of these specific areas, the carriage and operation of transponders should be actively encouraged.
3.4 In the airspace subject to the Initial Implementation of Mode S Enhanced Surveillance (IIMSES), regulations should be such as to render mandatory the carriage and operation of Mode S transponders to meet the provisions specified in 3.2, and 3.3, a) and b). Mode S transponders are capable of operating in Mode A and Mode C with automatic pressure altitude reporting and are thus interoperable in the airspace not subject to specific IIMSES airborne equipment regulation.
3.5 Levels of Mode S Transponders
3.5.1 It is stipulated in ICAO Annex 10(1) that Mode S transponders shall conform to one of four Levels capability as follows:
| Level 1 | This is the basic transponder. Level I permits surveillance based on Mode A/C as well as on Mode S. With a Mode S aircraft address it comprises the minimum features for compatible operation with Mode S interrogators. It has no datalink capability and will not be used by international air traffic. |
| Level 2 | Level 2 has the same capabilities as Level I and permits standard length datalink communication from ground to air and air to ground. It includes automatic aircraft identification reporting. This is the minimum level permitted for international fights. |
| Level 3 | Level 3 has the same capabilities as level 2 but permits extended datalink communications from the ground to the aircraft. |
| Level 4 | Level 4 has the same capabilities as level 3 but allows extended datalink communications from the aircraft to the ground. |
(SARPS for an additional level, Level 5, are being processed for inclusion in ICAO Annex 10 in 1996 to provide enhanced datalink capability in an environment of several interrogators.)
4. MODE S AIRBORNE EOUIPMENT REGULATION
4.1 As a result of the EANPG decisions outlined in 2.3.3, requirements for the carriage and operation of Mode S transponders were incorporated in Doc 7030 Regional Supplementary Procedures, EURIRAC Part 1, paragraph 7. This was to afford aircraft operators the seven years notice required at that time in accordance with the provisions of ICAO Annex 10. Consequently, it was not possible to include the onboard extraction and transmission to the ground of aircraft parameters intrinsic to IIMSES, or to take account of any necessary rescheduling of the implementation program.
4.2 Current planning within EATCHIP envisages the progressive introduction of the IIMSES ground infrastructure from the year 2001 with pre-operational system validation beginning some three years earlier. Thus for the purposes of airborne equipment regulation, the IIMSES operational date is set at I January 2001. A contiguous volume of airspace, within which ATS employment of Mode S Enhanced Surveillance is feasible, is expected to be available from the year 2003 onwards.
4.3 As guidance to States, I January 2001 is designated as the earliest date for which the carriage and operation of Mode S airborne equipment is required for IIMSES. Initial carriage requirements can therefore be restricted to new aircraft, registered on and after this date, operating if FR as General Air Traffic (GAT) in the airspace where the carriage and operation of Mode S transponders has been prescribed by the appropriate ATS authority.
4.4 Downlink Aircraft Parameters
4.4.1 Specific requirements for downlink aircraft parameters (DAPs) are classed, separately, as follows;
| a) | Basic Functionality (2)
Automatic reporting of Flight Identity (callsign used in flight)
Transponder Capability Report
Altitude reporting in 25ft intervals (subject to aircraft availability)
Flight Status (airborne/on the ground) |
| b) | Enhanced Surveillance Functionality (3)
Magnetic Heading
Speed (IAS/TAS/Mach No)
Roll Angle
Track Angle Rate
Vertical Rate (barometric rate of climb/descend or, preferably, baro-inertial)
True Track Angle / Ground Speed |
| c) | Intended Future Use Functionality
Additional DAPs, which includes those relating to aircraft intention, is currently under evaluation.Their employment in Mode S Enhanced Surveillance is subject to the resolution of certain technical and institutional issues as explained in Chapter 6 of this Circular. |
4.5 Carriage and Operation of Mode S Airborne Equipment
4.5.1 The carriage and operation of Mode S airborne equipment shall be mandatory as follows:
a. - For IFR/GAT flights, in the airspace designated by the appropriate ATS authority, a Level 2 Mode S transponder as a minimum, with DAP capability (Basic and Enhanced Surveillance Functionality), required by new aircraft with effect from 1 January 2001 and by all aircraft with effect from 1 January 2003.
Note 1 : Annex 10 to the Convention on International Civil Aviation - Aeronautical Telecommunications, Volume IV First Edition, July 1995
Note 2 :These are described as DAPs and/or standard features of Mode S replies as defined in ICAO Annex: 10/Manual on Mode S Specific Services.
Note 3 :These parameters are defined in the ICAO Manual on Mode S specific Services. BDS Registers 5.0 and 6.0. - For VFR flights, conducted in Class B and C airspace as designated by the appropriate ATS authority and in defined portions of Class D, E, F and G airspace where the carriage and operation of SSR transponders has already been prescribed, a Level 2 transponder as a minimum, with DAP capability (Basic Functionality) required by new aircraft with effect from I January 2003 and by all aircraft with effect from I January 2005.
- Mode S equipped aircraft shall report automatically Basic Functionality which includes aircraft identification (callsign used in flight).
- Mode S equipped aircraft with a maximum mass in excess of 5,700 Kg or a maximum cruising true airspeed in excess of 324 Km/h (176 Kt) shall operate with antenna diversity (subject to airframe practicability).
- Specific provisions relating to State aircraft shall be subject to regulations issued by the States concerned.
Note 1 - Automatic reporting of aircraft identification is not provided by the 24 -bit aircraft address.
Note 2 - Level 1 Mode S transponders are not prescribed for use in the European Region.
Note 3 The requirements for IFR flights, originally promulgated in ICAO Doc 7030, refer to Level 3/4 Mode S transponders. However, this level of Mode S data communications capacity is not required for Enhanced Surveillance but could be required in the future. Therefore it may well be in the interests of Aircraft Operators to equip initially to the higher standard. See Paragraph 8.2. Additionally, duo to the technical link between ACAS and Mode S Enhanced Surveillance, it may also be in the interests of Aircraft Operators to install the necessary equipment at an earlier stage. See Paragraph 9.2.2.
Note 4 The requirement for VFR flights is intended to ensure the widespread installation of Mode S transponders with Level 2 capabilities in preference to Mode A C transponders, in order to meet the requirements for air traffic management.
Note 5 Dispensation from these requirements may be granted by the appropriate ATS authority in accordance with the coordinated exemption arrangements set out in Section 5 of this Circular.
5. COORDINATED EXEMPTION ARRANGEMENTS
5.1 Aplication Principles
The granting of exemptions from the requirements for the carriage and operation of Mode S airborne equipment have been coordinated, in accordance with the provisions of ICAO Doc 7030, in the interests of regional harmonization.
Therefore, States should endeavor to comply with the exemption application principles set out below, subject to specific flight safety considerations and any significant penalty, which might otherwise be incurred. Additionally, State authorities should make every effort, within the airspace under their jurisdiction, to accommodate, in that airspace, aircraft which, have been granted an exemption by another State participating in the IIMSES program.
5.1.1 Exemptions may be granted for VFR flights conducted by aircraft: already equipped with non-Mode S transponders having Mode A 4096 code capability and Mode C altitude reporting, or; when the carriage of a transponder is impracticable, or, when an exception to the requirement is authorized for a specific purpose.
5.1.2 Exemptions should be granted to the operators of older aircraft where airframe life remaining is shown to be less than 3 years from I January 2003.
5.1.3 Exemptions should be granted for IFR flights conducted by State (military) aircraft required t occasionally (Note 1) operate as GAT, subject to the availability of a Mode 3/A transponder with 4096 code capability and Mode C altitude reporting. This concession should also apply, in the same circumstances, to State (military) aircraft equipped with a Mode S transponder but without the capability, either technically or operationally, to downlink the full set of prescribed DAPs.Note 1 In this context 'occasionally' is taken to mean an average total flying time of 30 hours annually in the airspace subject to the mandatory carriage and operation of Mode S transponders.
5.1.4 Aircraft operators who are granted exemptions should be advised that it will not be possible to provide the same level of ATM service as that applied to aircraft which comply with the Mode S transponder carriage and operation requirements.
5.1.5 Aircraft operators who are granted exemptions should be advised that the policy pertaining to exemptions will be subject to periodic review and, in the first instance, should be for a period not exceeding 3 years
5.2 Partial CompIiance for Older Aircraft
5.2.1 Operators of older aircraft (civil or state aircraft) which are equipped with Mode S transponders but where the avionics do not permit the extraction and transmission of the full set of prescribed DAPs, should be granted air traffic services to the maximum extent possible without penalty. However, this dispensation should be subject to review as in 5.1.5, above.
5.2.2
6. FUTURE EXPANSION OF MODE S SURVEILLANCE SERVICES
6.1 In anticipation of further expansion of Mode S surveillance services, consideration needs to be given to the downlinking of additional aircraft parameters. Those which indicate aircraft intention (selected parameters) offer the greatest potential benefit to the ATM system and in particular to the safety nets in terms of enhanced tracking and anticipated knowledge of aircraft maneuvers. They would be used to considerable advantage in ground systems with ARTAS or ARTAS-similar surveillance data processing. However, the resolution of certain technical and institutional issues associated with the downlinking of these aircraft parameters is essential before they can be introduced for operational use in IIMSES.
Therefore once these issues have been resolved, the following parameters (5) are recommended for inclusion:
- Selected Flight Level / Altitude.
- Selected Magnetic Heading.
- Selected Course.
- Selected IAS / Mach No.
Other candidate DAPs are also under active consideration for inclusion in the further development of Mode S Enhanced Surveillance. Detailed technical definitions of all the parameters are contained in the ICAO Manual on Mode S Specific Services.
7. FUTURE EXPANSION OF MODE S DATALINK SERVICES
7.1 Purpose and Scone
7.1.1 This section contain additional guidance information that States may wish to include as recommendations in their national regulations for Mode S transponder carriage requirements. It aims to give advance information on potential future Mode S system developments.
7.2 Ground Infrastructure Improvements
7.2.1 It is envisaged within EATCHIP that extension of Mode S datalink services will be progressively introduced following on from the IIMSES program. This includes implementation of the Mode S Subnetwork and integration of Mode S datalink services within the future aeronautical telecommunications network (ATN).
7.3 Future Airborne Datalink Equipment Requirements
7.3.1 It is important that aircraft operators are made aware as early as possible of planned ground infrastructure developments, which could affect future airborne equipment carriage requirements. Mode S Level 2 transponders, as a minimum, have been prescribed because the employment of the full Mode S datalink has not yet been endorsed in the context of an overall European Datalink Strategy. However, work is ongoing to evaluate its suitability for this purpose. Endorsement of the extended use of Mode S datalink would lead to a requirement for Mode S Level 4 transponders, as a minimum.
8. FUTURE AIRBORNE EOUIPMENT CARRIAGE REGULATION
8.1 Aircraft operators should be aware that changes resulting from the factors set out in Chapters 6 and 7, could result in additional requirements for the carriage and operation of airborne equipment as follows:
- Additional DAP capability for the future expansion of Mode S Surveillance (as outlined in Chapter 6).
Mode S Level 4 transponder (as outlined in Chapter 7).
Any such requirement would be promulgated with due regard to an agreed minimum S year notification period.
8.2 Therefore aircraft operators may wish to equip initially to a higher standard than that prescribed for IIMSES in chapter 4 of this Circular.
8.3 (4) ARTAS EUROCONTROL ATC Radar Tracker and Server
8.4 (5) These parameters are included in the ICAO Manual on Mode S Specific Services, BDS Register 4,0.
9. AIRBORNE COLLISION AVOIDANCE SYSTEMS (ACAS)
9.1 Airborne Collision and Avoidance Systems (ACAS) SARPS were adopted by ICAO in 1995.However, since December 1993, the Traffic Alert and Collision Avoidance System (TCAS II), which is currently not compliant with these SARPS. has been mandated for use in US airspace by aircraft of more than 30 passenger seats. Consequently, evaluation of TCAS II operations has been ongoing in European airspace over a number of years. These systems, which imply the use of a Mode S transponder of at least level 2 capability, interrogate the transponders (Mode S and Classical) of other aircraft. They process the information received to provide, where appropriate, collision avoidance advice in the vertical plane of traffic in the vicinity of ACAS equipped†aircraft.European ACAS Policy and implementation Schedule
9.2.1 European ACAS policy is to require the mandatory carriage and operation of an ACAS conforming to ICAO SARPS in the airspace of ECAC member States. An implementation schedule has been adopted, in principle, as follows:
- with effect from I January 2000, ail civil fixed-wing turbine-engine aircraft having a maximum takeoff mass exceeding 15,000 kg or maximum approved passenger seating configuration of more than 30 will be required to be equipped with ACAS II, and,
- with effect from I January 2005, all civil fixed-wing turbine engine aircraft having a maximum takeoff mass exceeding 5,700 kg or maximum approved seating configuration of more than 30 will be required to be equipped with ACAS II
9.2.2 Therefore due to the technical link between ACAS and Mode S. aircraft operators may wish to install the prescribed Mode S equipment for IIMSES at an earlier stage.
10. ADDITIONAL INFORMATION
10.1 This circular is issued for the particular attention of aircraft operators and ATM services.
10.2 This circular supersedes AIC 02/90 and 003/91
