ATS.TR.155 ATS surveillance services

USE OF INFORMATION DERIVED FROM ATS SURVEILLANCE SYSTEMS FOR AIR TRAFFIC CONTROL SERVICE PURPOSES Information derived from ATS surveillance systems, including safety-related alerts and warnings such as conflict alert and minimum safe altitude warning, should be used to the extent possible in the air traffic control service provision in order to improve capacity and efficiency as well as to enhance safety.

FUNCTIONS OF THE ATS SURVEILLANCE SYSTEMS IN AIR TRAFFIC SERVICES PROVISION

(a)Functions in the area control service and approach control service The information provided by ATS surveillance systems and presented on a situation display may be used to perform one or more of the following functions in the provision of area control service or approach control service:

(1)provide ATS surveillance services as necessary in order to improve airspace utilisation, reduce delays, provide for direct routings and more optimum flight profiles, as well as to enhance safety;

(2)provide vectoring to departing aircraft for the purpose of facilitating an expeditious and efficient departure flow and expediting climb to cruising level;

(3)provide vectoring to aircraft for the purpose of resolving potential conflicts;

(4)provide vectoring to arriving aircraft for the purpose of establishing an expeditious and efficient approach sequence;

(5)provide vectoring to assist pilots in their navigation, e.g. to or from a radio navigation aid, away from or around areas of adverse weather;

(6)provide separation and maintain normal traffic flow when an aircraft experiences communication failure within the area of coverage;

(7)maintain flight path monitoring of air traffic;

(8)when applicable, maintain a watch on the progress of air traffic, in order to provide a procedural air traffic controller with:

(i)improved position information regarding aircraft under control;

(ii)supplementary information regarding other traffic; and

(iii)information regarding any significant deviations by aircraft from the terms of their respective ATC clearances, including their cleared routes as well as levels, when appropriate.

(b)Additional functions in the approach control service In addition to the functions listed in point (a), the position indications presented on a situation display may be used to perform one or more of the following functions in the provision of approach control service:

(1)provide vectoring of arriving traffic on to pilot-interpreted final approach aids;

(2)provide flight path monitoring of parallel ILS approaches and instruct aircraft to take appropriate action in the event of possible or actual penetrations of the no transgression zone (NTZ);

(3)provide vectoring of arriving traffic to a point from which a visual approach can be completed;

(4)provide vectoring of arriving traffic to a point from which a surveillance radar approach can be made;

(5)provide flight path monitoring of other pilot-interpreted instrument approach procedure;

(6)in accordance with prescribed procedures, conduct surveillance radar approaches; and

(7)provide separation between:

(i)succeeding departing aircraft;

(ii)succeeding arriving aircraft; and

(iii)a departing aircraft and a succeeding arriving aircraft.

(c)Functions in the aerodrome control service

(1)When authorised and subject to procedures and conditions prescribed by the air traffic services provider, ATS surveillance systems may be used in the provision of aerodrome control service to perform the following functions:

(i)flight path monitoring of aircraft on final approach;

(ii)flight path monitoring of other aircraft in the vicinity of the aerodrome;

(iii)establishing an appropriate longitudinal and/or distance-based separation based on ATS surveillance systems in between succeeding departing aircraft;

(iv)maintaining separation between succeeding aircraft on the same final approach; and

(v)providing navigation assistance to VFR flights

(2)In prescribing conditions and procedures for the use of ATS surveillance systems in the provision of aerodrome control service, the air traffic services provider should ensure that the availability and use of an ATS surveillance system will not be detrimental to visual observation of aerodrome traffic.

(d)Functions in the flight information service The information presented on a situation display may be used to provide identified aircraft with information:

(1)regarding any aircraft observed to be on a conflicting path with the identified aircraft and suggestions or advice regarding avoiding action;

(2)on the position of significant weather and, as practicable, advice to the aircraft on how best to circumnavigate any such areas of adverse weather. When doing so, attention is to be paid to the fact that under certain circumstances the most active area of adverse weather may not be displayed; and

(3)to assist the aircraft in its navigation.

ATS SURVEILLANCE SERVICES PROVISION IN PRESENCE OF CONTROLLED BUT UNIDENTIFIED AIRCRAFT In the event that the air traffic controller has been notified of a controlled flight entering or about to enter the airspace within which a separation minimum based on ATS surveillance systems is applied, but has not identified the aircraft, the air traffic controller may, if so prescribed by the air traffic services provider, continue to provide ATS surveillance services to identified aircraft, provided that:

(a)reasonable assurance exists that the unidentified controlled flight will be identified using SSR and/or ADS-B and/or MLAT or the flight is being operated by an aircraft of a type which may be expected to give an adequate return on primary radar in the airspace within which the separation is applied; and

(b)the separation is maintained between identified flights and any other observed ATS surveillance system position indications until either the unidentified controlled flight has been identified or procedural separation has been established.

ATS SURVEILLANCE SYSTEM — PERFORMANCE CHECKS

(a)The air traffic controller, FIS officer, and AFIS officer that utilise ATS surveillance systems should adjust the situation display(s) and carry out adequate checks on the accuracy thereof, in accordance with the technical instructions prescribed by the air traffic services provider.

(b)The air traffic controller, FIS officer, and AFIS officer that utilise ATS surveillance systems should be satisfied that the available functional capabilities of the ATS surveillance system as well as the information presented on the situation display(s) are adequate for the functions to be performed.

ATS SURVEILLANCE SYSTEM — PERFORMANCE REQUIREMENTS Performance requirements for ATS surveillance systems and their constituents are specified in the detailed specifications for ATM/ANS equipment subject to certification or declaration in accordance with Commission Delegated Regulation (EU) 2023/1768 — DS-GE.CER/DEC — Issue 1 (or later).

FACTORS DETERMINING THE NUMBER OF AIRCRAFT SIMULTANEOUSLY PROVIDED WITH AIR TRAFFIC CONTROL SERVICE USING ATS SURVEILLANCE SYSTEMS When determining the number of aircraft simultaneously provided with ATS surveillance services, the air traffic services provider should take into account, as a minimum:

(a)the structural complexity of the control area or sector concerned;

(b)the functions to be performed within the control area or sector concerned;

(c)assessments of air traffic controller workloads, taking into account different aircraft capabilities, and sector capacity; and

(d)the degree of technical reliability and availability of the primary and backup communications, navigation and surveillance systems, both in the aircraft and on the ground.

METHODS OF IDENTIFICATION Identification of aircraft should be established by at least one of the following methods:

(a)ADS-B identification procedures Where ADS-B is used for identification, aircraft may be identified by one or more of the following procedures:

(1)direct recognition of the aircraft identification in an ADS-B label;

(2)transfer of ADS-B identification; and

(3)observation of compliance with an instruction to ‘TRANSMIT ADS-B IDENT’.

(b)SSR and/or MLAT identification procedures

(1)Where SSR and/or MLAT is used for identification, aircraft may be identified by one or more of the following procedures:

(i)recognition of the aircraft identification in an SSR and/or MLAT label, in accordance with point (b) of ATS.OR.446;

(ii)recognition of an assigned discrete code, the setting of which has been verified, in an SSR and/or MLAT label, in accordance with point (b) of ATS.OR.446, and in particular with points (e) to (i) of Appendix 1 to Part-ATS;

(iii)direct recognition of the aircraft identification of a Mode S-equipped aircraft in an SSR and/or MLAT label, in accordance with point (b) of ATS.OR.446, and in particular points with (a) to (d) of Appendix 1 to Part-ATS, unless otherwise prescribed by the competent authority for the use of this method for the identification of local flights;

(iv)by transfer of identification;

(v)observation of compliance with an instruction to set a specific code; and

(vi)observation of compliance with an instruction to squawk ‘IDENT’.

(2)When a discrete code has been assigned to an aircraft, a check should be made at the earliest opportunity to ensure that the code set by the pilot is identical to that assigned for the flight. Only after this check has been made, the discrete code should be used as a basis for identification.

(c)PSR identification procedures

(1)Where PSR is used for identification, aircraft may be identified by one or more of the following procedures:

(i)by correlating a particular radar position indication with an aircraft reporting its position over, or as bearing and distance from, a point shown on the situation display, and by ascertaining that the track of the particular radar position is consistent with the aircraft path or reported heading;

(ii)by correlating an observed radar position indication with an aircraft which is known to have just departed, provided that the identification is established within 2 km (1 NM) from the end of the runway used. Particular care should be taken to avoid confusion with aircraft holding over or overflying the aerodrome, or with aircraft departing from or making a missed approach over adjacent runways;

(iii)by transfer of identification;

(iv)when air traffic control service is provided, by ascertaining the aircraft heading, if circumstances require, and following a period of track observation:

(A)instructing the pilot to execute one or more changes of heading of 30 degrees or more and correlating the movements of one particular radar position indication with the aircraft’s acknowledged execution of the instructions given; or

(B)correlating the movements of a particular radar position indication with manoeuvres currently executed by an aircraft having so reported.

(2)When using these methods, the air traffic controller/FIS officer/AFIS officer, as appropriate, should:

(i)verify that the movements of not more than one radar position indication correspond with those of the aircraft; and

(ii)ensure that the manoeuvre(s) will not carry the aircraft outside the coverage of the radar or the situation display.

(d)Additional identification method When two or more position indications are observed in close proximity, or are observed to be making similar movements at the same time, or when doubt exists as to the identity of a position indication for any other reason, the identification procedure in point (c)(1)(iv) should be used (only in case of air traffic control service provision), or additional methods of identification should be employed, until all risk of error in identification is eliminated.

METHODS OF IDENTIFICATION — USE OF ATS SURVEILLANCE SYSTEMS IN SURFACE MOVEMENT CONTROL OR MANAGEMENT Where an ATS surveillance system is used in surface movement control or management, the air traffic controller/AFIS officer may identify aircraft by one or more of the following procedures:

(a)correlating a particular position indication with an:

(1)aircraft position visually observed by the air traffic controller/AFIS officer; or

(2)aircraft position reported by the pilot; or

(3)identified position indication displayed on a situation display;

(b)transfer of identification when authorised by the competent authority; and

(c)automated identification procedures when authorised by the competent authority.

METHODS OF IDENTIFICATION — TRANSFER OF IDENTIFICATION

(a)Transfer of identification from one air traffic controller/FIS officer/AFIS officer to another should only be attempted when it is considered that the aircraft is within the accepting air traffic controller’s/FIS officer’s/AFIS officer’s surveillance coverage.

(b)Transfer of identification should be effected by one of the following methods:

(1)designation of the position indication by automated means, provided that only one position indication is thereby indicated and there is no possible doubt of correct identification;

(2)notification of the aircraft’s discrete SSR code;

(3)notification of the automated or system-to-system aircraft address;

(4)notification that the aircraft is SSR Mode S-equipped with an aircraft identification feature when SSR Mode S coverage is available;

(5)notification that the aircraft is ADS-B-equipped with an aircraft identification feature when compatible ADS-B coverage is available;

(6)direct designation (pointing with the finger) of the position indication if the two situation displays are adjacent or if a common ‘conference’ type of situation display is used;

(7)designation of the position indication by reference to, or in terms of bearing and distance from, a geographical position or navigational facility accurately indicated on both situation displays, together with the track of the observed position indication if the route of the aircraft is not known to both air traffic controllers/FIS officers/AFIS officers;

(8)where applicable, issuance of an instruction to the aircraft by the transferring air traffic controller/FIS officer/AFIS officer to change SSR code and the observation of the change by the accepting air traffic controller/FIS officer/AFIS officer; or

(9)issuance of an instruction to the aircraft by the transferring air traffic controller/FIS officer/AFIS officer to squawk/transmit IDENT and observation of this response by the accepting air traffic controller/FIS officer/AFIS officer.

METHODS OF IDENTIFICATION — SSR AND/OR MLAT IDENTIFICATION PROCEDURES When applying this method of identification, the air traffic controller/FIS officer/AFIS officer should consider that some aircraft equipped with first generation ADS-B avionics do not have the capability of squawking IDENT while the emergency and/or urgency mode is selected.

METHODS OF IDENTIFICATION — PSR IDENTIFICATION PROCEDURE

(a)Caution is to be exercised when employing this method since a position reported in relation to a point may not coincide precisely with the radar position indication of the aircraft on the situation display. The air traffic services provider may, therefore, prescribe additional conditions for the application of this method, e.g.

(1)a level or levels above which this method may not be applied in respect of specified navigation aids; or

(2)a distance from the radar site beyond which this method may not be applied.

(b)The term ‘a point’ refers to a geographical point suitable for the purposes of identification. It is normally a reporting point defined by reference to a radio navigation aid or aids.

POSITION INFORMATION

(a)An aircraft provided with ATS surveillance services should be informed of its position in the following circumstances:

(1)upon identification, except when the identification is established:

(i)based on the pilot’s report of the aircraft position or within one nautical mile of the runway upon departure and the observed position on the situation display is consistent with the aircraft’s time of departure; or

(ii)by use of ADS-B aircraft identification, Mode S aircraft identification or assigned discrete SSR codes and the location of the observed position indication is consistent with the current flight plan of the aircraft; or

(iii)by transfer of identification;

(2)when the pilot requests this information;

(3)when a pilot’s estimate differs significantly from the air traffic controller’s estimate based on the observed position;

(4)unless otherwise prescribed by the competent authority, when the pilot is instructed by the air traffic controller to resume own navigation after vectoring if the current instructions had diverted the aircraft from a previously assigned route; and

(5)when air traffic control service is provided, immediately before termination of ATS surveillance services if the aircraft is observed to deviate from its intended route.

(b)Position information should be passed on to aircraft in one of the following forms:

(1)as a well-known geographical position;

(2)magnetic track and distance to a significant point, an en-route navigation aid, or an approach aid;

(3)direction (using points of the compass) and distance from a known position;

(4)distance to touchdown if the aircraft is on final approach; or

(5)distance and direction from the centre line of an ATS route.

(c)Whenever practicable, position information should relate to positions or routes pertinent to the navigation of the aircraft concerned and shown on the situation display map.

VECTORING INSTRUCTIONS IN AIR TRAFFIC CONTROL SERVICE PROVISION — GENERAL

(a)When vectoring an aircraft, an air traffic controller should comply with the following:

(1)when an aircraft is given its initial vector diverting it from a previously assigned route, the pilot should be informed what the vector is to accomplish, and, the limit of the vector should be specified when the assigned heading is such that a loss of communications may result in a safety risk (e.g. to ... position, for ... approach);

(2)except when transfer of control is to be effected, aircraft should not be vectored closer than 4.6 km (2.5 NM) or, where the minimum permissible separation is greater than 9.3 km (5 NM), a distance equivalent to one-half of the prescribed separation minimum, from the limit of the airspace for which the air traffic controller is responsible, unless local arrangements have been made to ensure that separation will exist with aircraft operating in adjoining areas;

(3)controlled flights should not be vectored into uncontrolled airspace except in the case of emergency or in order to circumnavigate adverse meteorological conditions (in which case the pilot should be so informed), or at the specific request of the pilot; and

(4)when an aircraft has reported unreliable directional instruments, the pilot should be requested, prior to the issuance of manoeuvring instructions, to make all turns at an agreed rate and to carry out the instructions immediately upon receipt.

(b)Special VFR flights should not be vectored unless special circumstances, such as emergencies, dictate otherwise.

(c)In terminating vectoring of an aircraft, the air traffic controller should instruct the pilot to resume own navigation, giving the pilot the aircraft’s position and appropriate instructions, as necessary, in the form prescribed in point (b)(2) of AMC1 ATS.TR.155(c)(2), if the current instructions had diverted the aircraft from a previously assigned route.

VECTORING FOR APPROACH CONTROL

(a)Prior to, or upon commencement of, vectoring for approach, the air traffic controller should advise the pilot of the type of approach as well as the runway to be used.

(b)The air traffic controller should advise the pilot of an aircraft being vectored for an instrument approach of its position at least once prior to commencement of final approach.

(c)When giving distance information, the air traffic controller should specify the point or navigation aid to which the information refers.

(d)Aircraft vectored for final approach should be given a heading or a series of headings calculated to close with the final approach track. The final vector should enable the aircraft to be established on the final approach track prior to intercepting the specified or nominal glide path of the approach procedure from below, and should provide an intercept angle with the final approach track of 45 degrees or less.

(e)Whenever an aircraft is assigned a vector which will take it through the final approach track, it should be advised accordingly, stating the reason for the vector.

(f)When an aircraft is vectored to a pilot-interpreted final approach aid:

(1)the aircraft should be instructed to report when established on the final approach track;

(2)the transfer of communications to the aerodrome air traffic controller should be effected at such a point or time that clearance to land or alternative instructions can be issued to the aircraft in a timely manner.

(g)When an aircraft is vectored for visual approach:

(1)the reported ceiling is to be above the minimum altitude applicable to vectoring and meteorological conditions such that, with reasonable assurance, a visual approach and landing can be completed; and

(2)clearance for visual approach is to be issued after the pilot has reported the aerodrome or the preceding aircraft in sight, at which time vectoring would normally be terminated.

VECTORING — DEFINITION OF INITIAL AND INTERMEDIATE APPROACH PHASES The initial and intermediate approach phases of an approach executed under the direction of an air traffic controller comprise those parts of the approach from the time vectoring is initiated for the purpose of positioning the aircraft for a final approach until the aircraft is on final approach and:

(a)established on the final approach path of a pilot-interpreted aid; or

(b)reports that it is able to complete a visual approach; or

(c)ready to commence a surveillance radar approach.

NAVIGATION ASSISTANCE An identified aircraft observed to deviate significantly from its intended route or designated holding pattern should be advised accordingly. Appropriate action should also be taken if, in the opinion of the air traffic controller such deviation is likely to affect the service being provided.

INFORMATION REGARDING ADVERSE WEATHER

(a)Information that an aircraft appears likely to penetrate an area of adverse weather should be issued in sufficient time to permit the pilot to decide on an appropriate course of action, including that of requesting advice on how best to circumnavigate the adverse weather area, if so desired.

(b)Depending on the capabilities of the ATS surveillance system, areas of adverse weather may not be presented on the situation display. An aircraft’s weather radar will normally provide better detection and definition of adverse weather than radar sensors in use by air traffic services.

(c)In vectoring an aircraft for circumnavigating any area of adverse weather, the air traffic controller should ascertain that the aircraft can be returned to its intended or assigned flight path within the coverage of the ATS surveillance system and, if this does not appear possible, inform the pilot of the circumstances.

ATS SURVEILLANCE SERVICES — PROCEDURES FOR TRANSFER OF CONTROL

(a)Where ATS surveillance services are being provided, transfer of control should be effected, whenever practicable, so as to enable the uninterrupted provision of ATS surveillance services.

(b)Where SSR and/or ADS-B and/or MLAT is (are) used and the display of position indications with associated labels is provided for, transfer of control of aircraft between adjacent control positions or between adjacent air traffic control units may be effected without prior coordination, provided that:

(1)updated flight plan information on the aircraft about to be transferred, including the discrete assigned SSR code or, with respect to Mode S and ADS-B, the aircraft identification, is provided to the accepting air traffic controller prior to transfer;

(2)the ATS surveillance system coverage provided to the accepting air traffic controller is such that the aircraft concerned is presented on the situation display before the transfer is effected and is identified on, but preferably before, receipt of the initial call;

(3)when the air traffic controllers are not physically adjacent, two-way direct-speech facilities, which permit communications to be established instantaneously, are available between them at all times;

(4)the transfer point or points and all other conditions of application, such as direction of flight, specified levels, transfer of communication points, and especially an agreed minimum separation between aircraft, including that applicable to succeeding aircraft on the same route, about to be transferred as observed on the situation display, have been made the subject of specific instructions (for intra-unit transfer) or of a specific letter of agreement between two adjacent air traffic control units;

(5)the instructions or letter of agreement specify explicitly that the application of this type of transfer of control may be terminated at any time by the accepting air traffic controller, normally with an agreed advance notice; and

(6)the accepting air traffic controller is informed of any level, speed or vectoring instructions given to the aircraft prior to its transfer and which modify its anticipated flight progress at the point of transfer.

(c)The minimum agreed separation between aircraft about to be transferred (see point (b)(4)) and the advance notice (see point (b)(5)) should be determined taking into account all relevant technical, operational and other circumstances. If circumstances arise in which these agreed conditions can no longer be satisfied, air traffic controllers should revert to the procedure in point (d) until the situation is resolved.

(d)Where primary radar is being used, and where another type of ATS surveillance system is employed but the provisions in point (b) are not applied, the transfer of control of aircraft between adjacent control positions or between two adjacent air traffic services units may be effected, provided that:

(1)identification has been transferred to or has been established directly by the accepting air traffic controller;

(2)when the air traffic controllers are not physically adjacent, two-way direct-speech facilities which permit communications to be established instantaneously between them are available at all times;

(3)separation from other controlled flights conforms to the minima authorised for use during transfer of control between the sectors or units concerned;

(4)the accepting air traffic controller is informed of any level, speed or vectoring instructions applicable to the aircraft at the point of transfer; and

(5)radio communication with the aircraft is retained by the transferring air traffic controller until the accepting air traffic controller has agreed to assume responsibility for providing the ATS surveillance services to the aircraft. Thereafter, the aircraft should be instructed to change over to the appropriate channel, and from that point the responsibility is that of the accepting air traffic controller.

PROCEDURES FOR TRANSFER OF CONTROL IN ATS SURVEILLANCE SERVICES Guidance on procedures for transfer of control in the ATS surveillance services provision may be found in the EUROCONTROL document titled ‘Guidelines for the Application of European Coordination and Transfer Procedures’ Edition 1.0 of 25 October 2012, which is available at: https://www.eurocontrol.int/publication/guidelines-application-european-coordination-and-transfer-procedures

PROCEDURES FOR AIR TRAFFIC CONTROL SERVICE IN CASE OF ATS SURVEILLANCE SYSTEM FAILURE In the event of complete failure of the ATS surveillance system, where air-ground communications remain, the air traffic controllers should plot the positions of all aircraft already identified, take the necessary action to establish procedural separation between the aircraft and, if necessary, limit the number of aircraft permitted to enter the area.

SEPARATION APPLICATION IN CASE OF ATS SURVEILLANCE SYSTEM FAILURE As an emergency measure, in the event of complete failure of the ATS surveillance system, where air-ground communications remain, the use of flight levels spaced by half the applicable vertical separation minimum may be resorted to temporarily if standard procedural separation cannot be provided immediately.

ATS SURVEILLANCE SYSTEM FAILURE — DATA DEGRADATION In order to reduce the impact of a degradation of aircraft position source data (for example, a receiver autonomous integrity monitoring (RAIM) outage for GNSS), the air traffic services provider should establish contingency procedures to be followed by air traffic services units in the event of data degradation.

DISPLAY OF ATS SURVEILLANCE-BASED SAFETY-RELATED ALERTS AND WARNINGS ATS surveillance systems should provide for the display of safety-related alerts and warnings, including conflict alert, conflict prediction, minimum safe altitude warning and unintentionally duplicated SSR codes and aircraft identification.

SHORT-TERM CONFLICT ALERT (STCA) PROCEDURES The generation of STCAs is a function based on surveillance data, integrated into an air traffic control system. The objective of the STCA function is to assist the air traffic controller in preventing collision between aircraft by generating, in a timely manner, an alert of a potential or actual infringement of separation minima. Procedures and related instructions concerning the use of the STCA function should specify, inter alia:

(a)the types of flight which are eligible for generation of alerts;

(b)the sectors or areas of airspace within which the STCA function is implemented;

(c)the method of displaying the STCA to the air traffic controller;

(d)in general terms, the parameters for generation of alerts as well as alert warning time;

(e)the volumes of airspace within which STCA can be selectively inhibited and the conditions under which this will be permitted;

(f)conditions under which specific alerts may be inhibited for individual flights; and

(g)procedures applicable in respect of volume of airspace or flights for which STCA or specific alerts have been inhibited.

MINIMUM SAFE ALTITUDE WARNING (MSAW) PROCEDURES The generation of MSAWs is a function of an ATS surveillance data-processing system. The objective of the MSAW function is to assist in the prevention of controlled flight into terrain accidents by generating, in a timely manner, a warning of the possible infringement of a minimum safe altitude. Procedures and related instructions concerning the use of the MSAW function should specify, inter alia:

(a)the types of flight which are eligible for generation of MSAW;

(b)the sectors or areas of airspace for which MSAW minimum safe altitudes have been defined and within which the MSAW function is implemented;

(c)the values of the defined MSAW minimum safe altitudes;

(d)the method of displaying the MSAW to the air traffic controller;

(e)the parameters for generation of a MSAW as well as warning time; and

(f)conditions under which the MSAW function may be inhibited for individual aircraft tracks as well as procedures applicable in respect of flights for which MSAW has been inhibited.

INTERRUPTION OR TERMINATION OF ATS SURVEILLANCE SERVICES An aircraft which has previously been informed that it is provided with an ATS surveillance service should immediately be informed when, for any reason, the service is interrupted or terminated.

INFORMATION REGARDING TRAFFIC ON A CONFLICTING PATH

(a)Information regarding traffic on a conflicting path should be given, whenever practicable, in the following form:

(1)relative bearing of the conflicting traffic in terms of the 12-hour clock;

(2)distance from the conflicting traffic in kilometres or nautical miles;

(3)direction in which the conflicting traffic appears to be proceeding; and

(4)level and type of aircraft or, if unknown, relative speed of the conflicting traffic, e.g. slow or fast.

(b)Pressure-altitude-derived level information, even when unverified, should be used in the provision of collision hazard information because such information, particularly if available from an otherwise unknown aircraft (e.g. a VFR flight) and given to the pilot of a known aircraft, could facilitate the location of a collision hazard.

(c)If the level information has not been verified, the accuracy of the information should be considered uncertain and the pilot should be informed accordingly.

TOLERANCE VALUE FOR PRESSURE-ALTITUDE-DERIVED LEVEL INFORMATION The tolerance value used to determine that the pressure-altitude-derived level information displayed to the air traffic controller is accurate should be ±60 m (±200 ft) in RVSM airspace. In other airspace, it should be ±90 m (±300 ft), except that the competent authority may specify a smaller criterion, but not less than ±60 m (±200 ft), if this is found to be more practical.

VERIFICATION OF PRESSURE-ALTITUDE-DERIVED LEVEL INFORMATION The verification should be effected by simultaneous comparison with altimeter-derived level information received from the same aircraft by radiotelephony. Geometric height information should not be used to determine if altitude differences exist.

ERRONEOUS LEVEL INFORMATION IN AIR TRAFFIC CONTROL SERVICE PROVISION

(a)If the displayed level information is not within the approved tolerance value or when a discrepancy in excess of the approved tolerance value is detected subsequent to verification, the pilot should be advised accordingly and requested to check the pressure setting and confirm the aircraft’s level.

(b)If, following confirmation of the correct pressure setting, the discrepancy continues to exist, the following actions should be taken by the air traffic controller according to circumstances:

(1)request the pilot to stop Mode C or ADS-B altitude data transmission, provided this does not cause the loss of position and identity information, and notify the next control positions or air traffic control unit concerned with the aircraft of the action taken; or

(2)inform the pilot of the discrepancy and request that the relevant operation continue in order to prevent loss of position and identity information of the aircraft and, when so prescribed by the local instructions, override the label-displayed level information with the reported level. In addition, the air traffic control unit should notify the next control position or air traffic control unit concerned with the aircraft of the action taken.

(c)It should be highlighted that the airborne collision avoidance system (ACAS) will accept Mode C replies that are erroneous, and it is possible to issue a resolution advisory (RA) based on these inputs. When the measures described in point (b)(1) cannot be implemented, the air traffic controller should take into account the likelihood of generating ACAS RA in the air traffic services provision.

ERRONEOUS LEVEL INFORMATION IN FLIGHT INFORMATION SERVICE PROVISION The procedures for the verification of pressure-altitude-derived displayed information in the provision of flight information service should be established taking into consideration GM1 ATS.TR.155(f), and approved by the competent authority.

VERIFICATION OF LEVEL OCCUPANCY

(a)In accordance with AMC1 ATS.TR.155(f), the criterion which should be used to determine that a specific level is occupied by an aircraft should be ±60 m (±200 ft) in RVSM airspace. In other airspace, this criterion should be ±90 m (±300 ft), except that the competent authority may specify a smaller criterion, but not less than ±60 m (±200 ft), if this is found to be more practical.

(b)Aircraft maintaining a level An aircraft should be considered to be maintaining its assigned level as long as the pressure-altitude-derived level information indicates that it is within the appropriate tolerances of the assigned level, as specified in point (a).

(c)Aircraft vacating a level An aircraft cleared to leave a level should be considered to have commenced its manoeuvre and vacated the previously occupied level when the pressure-altitude-derived level information indicates a change of more than 90 m (300 ft) in the anticipated direction from its previously assigned level.

(d)Aircraft passing a level in climb or descent An aircraft in climb or descent should be considered to have crossed a level when the pressure-altitude-derived level information indicates that it has passed this level in the required direction by more than 90 m (300 ft).

(e)Aircraft reaching a level An aircraft should be considered to have reached the level to which it has been cleared when the elapsed time of three display updates, three sensor updates or 15 seconds, whichever is the greater, has passed since the pressure-altitude-derived level information has indicated that it is within the appropriate tolerances of the assigned level, as specified in point (a).