S1, C6 - ATC Surveillance Systems

Question 1

Surveillance services comprise:

Answer 1

1) Separation of arriving, departing and en route traffic
2) vectoring
3) position information to assist in the navigation of aircraft
4) monitoring traffic to provide information to the procedural controller
5) assistance to aircraft crossing CAS

Question 2

Before a controller provides any surveillance services, he shall either:

Answer 2

1) identify the aircraft, using a method appropriate to the surveillance system in use

Or

2) have had the identity of the aircraft transferred from another controller.

The act of identifying an aircraft does not imply that a service is being given

Question 3

Surveillance systems may also be used to provide the following, whether or not the aircraft has been identified:

Answer 3

1) information on the position of aircraft likely to constitute a hazard
2) avoiding action
3) information about observed weather for pilots and other controllers

And

4) assistance to aircraft in emergency

Question 4

Surveillance services shall be provided to the…

Answer 4

…maximum extent practicable to cover the operational requirement subject only to workload, communications or equipment capability

Question 5

Regardless of the type of airspace, or the ATS being provided…

Answer 5

…nothing shall prevent a controller from taking action he considers appropriate if he believes a risk of collision exists

Question 6

The airspace within which the aircraft is flying determines the type of surveillance service available:

Answer 6

CAS - radar control service

OCAS - DS or TS

Question 7

Pilots must be advised if a service commences, terminates or changes when:

Answer 7

1) OCAS
2) entering CAS (except when entering CAS in connection with in IFR flight holding in Class E)
3) changing from IFR to VFR or VFR to IFR within Class E
4) VFR flights entering/leaving Class B-D from/to Class E
5) Leaving CAS

A) unless pilots are provided with advance notice
Or
B) except when leaving CAS in connection with in IFR flight holding in Class E

Question 8

For flights leaving CAS controllers should provide pilots with advance notice of:

Answer 8

1) the lateral or vertical point at which the aircraft will leave CAS. Such notice should be provided between 5-10nm or 3000-6000ft prior to the boundary of CAS
2) the type of ATS that will subsequently be provided, unless the aircraft is coordinated and transferred to another ATSU before crossing the boundary of CAS

Question 9

A radar control service may be provided to aircraft operating:

Answer 9

1) IFR

2) SVFR
and
3) VFR in Class B-D

Question 10

When providing a RCS controllers issue instructions to which:

Answer 10

1) Pilots of IFR are required to comply

And

2) pilots of SVFR or VFR will comply unless they advise the controller otherwise

Question 11

Before an aircraft enter CAS the controller must establish…

Answer 11

…which flight rules the pilot will be operating under

Question 12

Before a RCS to IFR flights is terminated…

Answer 12

…procedural separation must be applied, except at ACCs when an aircraft will be entering an adjacent sector and:

1) a radar handover has been given

Or

2) the conditions of any standing agreement have been met

Question 13

Participating VFR flights in Class E shall not be provided with…

Answer 13

…an Air Traffic Control service, but one of the following UKFIS:

1) BS

OR

2) TS

Question 14

Surveillance services provided within Class G…

Answer 14

…DS and TS are detailed in S1, Ch12 UKFIS

Question 15

One of the following methods is to be employed when using PSR to identify aircraft:

Answer 15

Direction finding equipment should be used to assist the ID provided it has been approved for such use.

• Turn method
• Departing aircraft method
• Position report method

Question 16

Turn Method:

Answer 16

An aircraft may be ID’d by ascertaining its heading and, following a period of track observation, correlating the observed movement of a particular position indication with:

1) the acknowledged execution of an instruction to alter heading by at least 30deg
2) one or more changes of heading by at least 30deg, as instructed by another controller
3) one or more changes of heading by at least 30deg, reported by the pilot

A turn for identification does not constitute the provision of a surveillance service. However, controllers should take into consideration terrain, other surveillance returns, RoA, PSR coverage before instructing an aircraft to alter heading.

In using the turn method a controller shall:

1) Verify that the movements of not more than 1 position indication correspond with those of the aircraft
2) exercise caution particularly when employing this method in areas where changes of heading are commonly made as part of a navigational routine

Question 17

Departing Aircraft Method:

Answer 17

By observing and correlating the position indication of a departing aircraft to a known airborne time.

ID is to be achieved within 1nm of the end of the runway unless otherwise authorised by the CAA.

Particular care should be taken to avoid confusion with aircraft overflying the aerodrome, making a missed approach, departing from an adjacent runway or holding overhead the aerodrome.

Question 18

Position Report Method:

Answer 18

By correlating a position indication with a report from the pilot that an aircraft is:

1) overhead an ERP which is displayed on the situation display
Or
2) at a particular distance not exceeding 30nm on a particular radial from a co-located VOR/DME or TACAN/DME. The source facility must be displayed on the situation display
Or
3) overhead a notified VRP or prominent geographical feature, in either case approved for the purpose and displayed on the situation display, provided that the flight is operating with visual reference to the surface and at a height of 3000ft or less above the surface.

The ID must follow a period of track observation sufficient to enable the controller to compare the movement of the position indication with the pilots reported route.

The reported position and level must indicate that the aircraft is within know PSR cover.

This method must be reinforced by an alternative method if there is any doubt about the ID because of:

1) the close proximity of other returns
Or
2) inaccurate reporting from an aircraft at high level or some distance from nav facilities.

Question 19

When using Mode A to identify aircraft, one of the following methods is to be employed:

Answer 19

1) observing the pilots compliance with the instruction to select a discrete 4 digit code
2) recognising a validated 4 digit code previously assigned to an aircraft call sign. When code call sign conversion procedures are in use and the code call sign pairing can be confirmed, the call sign displayed in the data block may be used to establish identity.
3) observing an ident feature when it has been requested

Caution must be exercised when employing this method because simultaneous requests for SPI transmissions within the same area may result in misidentification.

Aircraft displaying 7000 are not to be identified using this method

Question 20

When providing a surveillance service to an aircraft, controllers at SSR equipped units…

Answer 20

…should allocate that flight with a discrete code iaw the code assignment plan.

Unless otherwise directed by an ATC unit, Mode C will be selected in conjunction with Mode A.

Controllers must, therefore, verify the accuracy of the Mode C readout when assigning discrete codes to aircraft.

Question 21

A controller assigning any Mode A code must…

Answer 21

…validate the code by checking ASAP, either by direct reference to his display or with the assistance of another ATC agency, that the data displayed corresponds with the code which has been assigned.

At units where code call sign conversion equipment is in use, procedures to ensure the correct correlation of the callsign with the assigned code are to be applied.

Question 22

The Mode A code must be checked by one of the following methods:

Answer 22

1) instructing the aircraft to squawk the assigned code and observing that the correct numbers appear on the situation display
2) instructing the aircraft to ‘squawk ident’ and simultaneously checking the code numbers associated with the SSR response
3) matching an already identified position indication with the assigned code for that flight

Question 23

If the Mode A code readout does not correspond to that assigned…

Answer 23

…the pilot is to be instructed to reset the assigned code.

Where this fails to achieve display of the assigned code, the pilot is to be instructed to select code 0000. If a corrupt code still exists the pilot should normally be instructed to switch off the transponder.

However, the corrupt code may be maintained to assist identification and tracking provided the Mode C has been verified.

Associated ATCUs are to be informed of the retention of corrupt data.

Question 24

Controllers may deem Mode A codes to be validated when…

Answer 24

…it can be ascertained from the code assignment plan that an observed Mode A code has been assigned by a unit capable of validating the code, unless:

1) the code is promulgated as being invalidated
Or
2) the controller has been notified that the code is corrupt

Question 25

The Mode A and associated Mode C of special purpose codes must be…

Answer 25

…considered unvalidated and unverified.

Controllers should be aware of the following special purpose codes:

1) emergency codes 7500, 7600, 7700
2) Code 1000 - aircraft conducting IFR as GAT, where the downlinked aircraft ID is validated as matching the aircraft ID entered in the flight plan
3) Code 2000 - aircraft entering U.K. Airspace from an adjacent FIR where the use of transponders is not required
4) Code 7007 - aircraft engaged on airborne observation flights under terms of open skies treaty. Flight Priority Cat B applies, details will be published by NOTAM

Question 26

The Mode A and associated Mode C of conspicuity codes must be…

Answer 26

…considered unvalidated and unverified.

Pilots are required to squawk 7000 when operating at and above FL100 and are advised to do so when below FL100 unless:

1) they have been assigned a discrete code
2) they are transponding on one of the special purpose codes or one of the other specific conspicuity codes assigned iaw the code assignment plan

3) they are flying below 3000ft in the aerodrome traffic circuit and have been instructed to squawk 7010
Or
4) on grounds of safety the aircraft has been instructed to squawk standby.

In view of the associated reduction in protection from ACAS, such circumstances are to be regarded as exceptional. ATSUs shall log the circumstances and duration of any such occurrences.details are to be made available to the CAA on request.

Question 27

Direct recognition of the aircraft ID feature on the situation display may be used to establish surveillance ID, subject to either:

Answer 27

1) correlation of the aircraft ID with the aircraft ID entered in the flight plan and displayed to controllers on FPS
Or
2) correlation of the aircraft ID feature with the aircraft call sign used in a directed RTF transmission to the controller.

However, controllers shall exercise particular caution when there are aircraft with similar call signs on frequency, and they shall utilise an alternative method if they have any doubt about the surveillance ID

Question 28

Whenever it is observed that a downlinked aircraft ID feature is different from that expected from the aircraft…

Answer 28

…the pilot shall be requested to confirm and, if necessary, re-enter the aircraft ID.

If the discrepancy continues to exist following confirmation by the pilot that the correct call sign has been set in the aircraft ID feature, the controller shall take the following minimum actions:

1) inform the pilot of the persistent discrepancy
2) assign a discrete Mode A code
3) notify the erroneous aircraft ID feature transmitted by the aircraft to the next ATSU/position

Question 29

Selected levels display…

Answer 29

…intent based information only and shall not be used for the purposes of separation.

Question 30

Units equipped with enhanced Mode S surveillance systems that enable DAPs should…

Answer 30

…display selected levels on the situation display as a means of mitigating the risk of level busts.

The checking of selected levels shall not be used as a substitute for RT readback of level clearances.

Question 31

Where selected level is seen to be at variance with an ATC clearance…

Answer 31

…controllers shall not state on RT the incorrect level as observed on the situation display.

However, controllers may query the discrepancy using the following phraseology:

“Callsign, check selected level, cleared level is xxxx”

Question 32

If only PSR is available, a controller may transfer the identity of an aircraft to mother controller by any of the following methods:

Answer 32

1) Direct Designation (pointing) of the position indication where 2 situation displays are adjacent or a conference type display is used.

If the information on 2 displays is derived from separate radar heads, the transferring controller must ensure that the blips on both displays correlate before using this method. If parallax is likely to cause an error, an alternative method is to be used.

2) designation of the position indication in terms of a direction and distance from a common reference point (geographical position or nav facility) accurately indicated on both displays.

The position indication as seen by the accepting controller must be within 3nm of the position stated.

The distance between the aircraft and the reference point must not exceed:

A) 30 miles if the aircraft is flying along a published ATS route, or direction is given as a bearing in degrees

B) 15 miles in other circumstances

3) designation of the position indication by positioning an electronic marker or symbol so that only one position indication is thereby indicated and there is no possible doubt of correct identification

Question 33

When must you inform a pilot that identification has been lost?

Answer 33

Except as described below, a pilot shall be advised whenever identification is lost.

When using SSR, controllers may be temporarily unable to read the data blocks associated with aircraft due to overlapping or garbling e.g. In holding areas.

Although this constitutes a loss of identification, the pilot need not be advised that identification has been lost if the controller anticipates that identification will be re-established immediately the overlapping or garbling ceases

Question 34

When providing surveillance services OCAS, when must a pilot be informed that they have been identified?

Answer 34

When providing surveillance services OCAS, a pilot is to be informed as soon as his aircraft has been identified.

Question 35

When providing surveillance services inside CAS, when must a pilot be informed that they have been identified?

Answer 35

When operating inside CAS the pilot of an aircraft need only be so informed if the identification is achieved by using the turn method

Question 36

Pilots should be informed of their position in the following circumstances:

Answer 36

1) following identification using the turn method
2) when the pilot requests the information
3) when the aircraft is flying off the correct track
4) when an aircraft estimate differs significantly from the controllers estimate based on ATS surveillance information
5) when the pilot is instructed to resume own navigation following vectoring, if considered necessary by the controller

Additionally, controllers may pass position information to aircraft whenever they consider it necessary

See table

Question 37

Position information shall be passed in one of the following forms:

Answer 37

1) a well known geographical position; bearing (using points of a compass) and distance from a known position
2) magnetic track and distance to a location displayed on the situation display that is a reporting point, en route nav aid or approach aid
3) Lat & Long (when authorised in MATS 2)
4) distance from touchdown if the aircraft is on final approach

Question 38

When SSR is used to asses vertical separation…

Answer 38

…the Mode C responses are to be continually monitored to ensure the vertical distance is never less than the prescribed minimum

Question 39

Vertical separation using Mode C is not applied against…

Answer 39

…aircraft transponding A0000

Question 40

Minimum vertical separation may be applied between…

Answer 40

…verified Mode C transponding aircraft provided the intentions of both aircraft are known to a controller because either:

1) they are under his control

2) they have been coordinated
Or
3) they are operating iaw established agreements

Question 41

For aircraft receiving a RCS, if the intentions of Mode C transponding aircraft are not known:

Answer 41

1) the minimum separation for IFR flights in Class A-D, and VFR in Class B/C, must be increased to 5000ft
And
2) unverified Mode C data may be used for separation purposes provided a minimum vertical separation of 5000ft in Class A-D is maintained. Radar returns, however presented, are not allowed to merge

3) in Class E, radar returns, however presented, are not allowed to merge unless the pilot in receipt of TI advises that he intends to avoid the other aircraft without ATC assistance

Question 42

For aircraft receiving a DS, if the intentions of Mode C transponding aircraft are not known:

Answer 42

The vertical deconfliction minima must be increased to 3000ft, and unless the SSR Mode A indicates that the Mode C data has been verified, the surveillance returns, however presented, should not merge

Question 43

Controllers are to verify the accuracy of Mode C data…

Answer 43

…once the aircraft has been identified and the Mode A validated, by checking that the readout indicates 200ft or less from the level reported by the pilot. If the aircraft is climbing or descending, the pilot is to be instructed to give a precise report as the aircraft passes through a level.

Verification may be achieved with the assistance of an ATSU with which the aircraft is in contact.

Question 44

A Mode C readout can be assumed to have been verified if…

Answer 44

…it is associated with a deemed validated Mode A code.

Question 45

There is no requirement to monitor level readouts when…

Answer 45

…Mode C is not being used to provide vertical separation.

However, if a controller observes a discrepancy the pilot is to be asked to confirm his altimeter setting and level.

If the discrepancy remains, the pilot is to be instructed to switch off Mode C.

If independent switching of Mode C is not possible, the pilot is to be instructed to select A0000

Question 46

The following criteria apply when assessing the vertical position of a Mode C transponding aircraft:

Answer 46

1) an aircraft may be considered to be st an assigned level provided that the Mode C readout indicates 200ft or less from that level
2) an aircraft which is know to have been instructed to climb or descend may be considered to have left a level when the Mode C readout indicates a change of 400ft or more from that level and is continuing in the anticipated direction
3) an aircraft climbing or descending may be considered to have passed through a level when the Mode C readout indicates that the level has been passed by 400ft or more and continuing in the required direction
4) an aircraft may be considered to have reached an assigned level when 3 successive Mode C readouts indicated 200ft or less from that level

Question 47

Radar Handover - The transfer of responsibility for an aircraft from one controller to another may be effected provided that:

Answer 47

1) satisfactory 2-way speech comms is available between them

2) the ID has been transferred to the accepting controller, or has been established by him
And
3) the accepting controller is informed of any level or vectoring instructions applicable to the aircraft at the stage of transfer

If the route of the aircraft is not known, the offering controller is to pass the observed track or reported aircraft heading to the accepting controller

Question 48

Radar Release - control of arriving aircraft may be transferred to Approach Radar Control, when other aircraft would otherwise delay the released aircraft’s progress, iaw the following conditions:

Answer 48

1) the transfer of control message is prefixed ‘radar release’
2) details of all conflicting aircraft are passed to the Approach radar controller
3) conflicting aircraft are either transferred to Approach Radar Control or ID’d according to the accepting controller’s decision
4) neither the track nor the level of the conflicting traffic is altered without coordination

Question 49

A controller may instruct an aircraft to turn…

Answer 49

…in any direction as dictated by circumstances, but when avoiding unknown aircraft the RoA should be observed if practicable

Question 50

Aircraft flying outside CAS and aircraft flying VFR in Class E are not…

Answer 50

…obliged to following ATC instructions, but where the pilot of an aircraft accepts a TS or DS, the controller can expect that his instructions will be followed

Question 51

Unless an aircraft has planned to leave CAS, it is not to be vectored outside the horizontal or vertical limits, except:

Answer 51

1) when an emergency situation arises requiring the aircraft to be vectored OCAS
2) when avoiding severe weather; the circumstances must be explained to the pilot before the aircraft leaves CAS
3) when specifically requested by the pilot

Question 52

Although IFR flights within Class A-D and VFR flights within Class B/C are deemed to be separated from unknown aircraft flying in adjoining uncontrolled airspace…

Answer 52

…controllers should aim to keep the aircraft under their control at least 2nm within the boundary.

Controllers should monitor the operation of aircraft in uncontrolled adjacent airspace, particularly if circumstances have made it necessary to vector an aircraft to be less than 2nm from the boundary.

In such circumstances, consideration should be given to co-ordinating with the appropriate controlling agency if applicable.

However, regardless of airspace divisions and classifications, controllers should take appropriate action with respect to the safety of aircraft if unknown aircraft appear to present a risk of collision.

Question 53

When vectoring is complete, pilots will be instructed…

Answer 53

…to resume their own navigation.

Where a direct route is required, the controller shall specify this in the instruction.

Question 54

When an aircraft inbound to a VOR/DME holding pattern is vectored away from a standard VOR radial…

Answer 54

…the controller must either provide magnetic track and distance information on instructing the aircraft to resume own navigation, or issue vectoing instructions to intercept the appropriate radial to the holding or routing fix

Question 55

Controllers are to ensure that levels assigned to IFR flights in receipt of RCS provide…

Answer 55

…adequate terrain clearance for the phase of flight as shown in the table:

Within defined final approach area - achieved if levels are assigned iaw an approved procedure

Within the SMAA - levels allocated must be iaw the information published on the SMAC

Within 30nm of the radar antenna - 1000ft above any fixed obstacle within

1)5nm of the aircraft
And
2)15nm ahead and 20deg either side of track

When the aircraft is within 15nm of the antenna, provided SMAC/approved procedure is notified, 5nm/15nm can be reduced to 3nm/10nm

Outside the above phases - 1000ft above any fixed obstacle

1)Which lies within 15nm of the centreline of any airway
Or
2)Within 30nm of the aircraft

Question 56

Within Class F/G, regardless of the service being provided…

Answer 56

…pilots are ultimately responsible for terrain clearance.

However, terrain requirements pertaining to level allocations and the provision of vectors are specified within the conditions of the UK FIS.

Question 57

A position symbol which cannot be associated with an aircraft known by the controller to be operating within the airspace concerned…

Answer 57

…shall be considered to represent an unknown aircraft

Question 58

The action to be taken by controllers when they observe an unknown aircraft, which they consider to be in unsafe proximity to traffic under their control, in various types of airspace is as follows:

Answer 58

If radar derived, or other information, indicates that an aircraft is making an unauthorised penetration of the airspace, is lost, or has experienced radio failure:

Class A - IFR flights shall be given traffic avoidance advice and TI shall be passed

SVFR flights shall be given TI and, if requested, traffic avoidance advice

Class C - IFR flights shall be given traffic avoidance advice and TI shall be passed

SVFR or VFR flights shall be given TI and, if requested, traffic avoidance advice

Class D - IFR flights shall be given traffic avoidance advice and TI shall be passed

VFR and SVFR flights shall be given TI and, if requested, traffic avoidance advice

Class E - pass TI unless the controller’s primary function of sequencing and separating IFR flights is likely to be compromised.

IFR flights shall be given traffic avoidance advice whenever requested by the pilot or if radar derived, or other information, indicates that an aircraft is lost or has experienced a radio failure.

Participating VFR flights shall:

1) under a TS be given TI
2) under a BS be given TI as far as practicable

Class F - Participating IFR flights shall be given TI and traffic avoidance advice if requested

Participating VFR flights shall be given TI as far as practicable

Class G - under a DS, pass TI followed by traffic avoidance advice

Under a TS, pass TI.

Question 59

When passing traffic avoiding advice, controllers shall remind VFR/SVFR pilots…

Answer 59

…of their responsibility to remain clear of cloud with the surface in sight

Question 60

When traffic avoidance advice is issued to an IFR aircraft under a RCS, controllers must…

Answer 60

…seek to achieve the required minima and pilots must comply with the instructions given.

However, when avoiding action is issued to an IFR aircraft under a RCS in Class D or E, and the pilot reports that he has the unknown aircraft in sight and has positively stated that he will maintain his own separation from it, further controller action may be limited to passing TI.

It is recognised that it may not always be possible for controllers to achieve the required separation minima against unknown traffic infringing CAS due to the potential for their sudden appearance and/or unpredictable manoeuvres; however, controllers shall apply all reasonable endeavours

Question 61

When traffic avoidance advice is issued on request to VFR/SVFR aircraft under RCS, controllers are…

Answer 61

…not required to achieve separation minima.

Such avoiding action instructions shall be aimed at ensuring that the risk of collision is reduced as far as possible subject to aircraft proximity and aircraft constraints.

Pilot compliance is subject to prevailing met conditions.

Question 62

Controllers observing an aircraft using an assigned SSR code that is, or is about to, make an unauthorised infringement of their airspace should…

Answer 62

…attempt to contact the relevant agency to identify the aircraft and agree a course of action.

Question 63

For aircraft talking to London/Scottish FIS and about to infringe CAS…

Answer 63

…contact the appropriate FISO who will assist with ID. E.g. Relaying instructions to squawk ident and for the aircraft to be transferred to the controllers frequency.

When the subject aircraft is on frequency, the controller must then ensure that ID of the aircraft is achieved.

Controllers should note that simple transfers of comms form part of a FISO’s SOPs. However, FISOs are not permitted to issue any control instructions to aircraft.

Controllers must not request FISOs to relay any instructions, other than for the aircraft to transfer directly to their frequency so that the controller can resolve the situation.

Question 64

TI shall include the following:

Answer 64

1) bearing from the aircraft in terms of the 12h clock (when the aircraft is turning, direction of the unknown aircraft by compass points)
2) distance from the aircraft in miles
3) direction in which the unknown aircraft is proceeding e.g. Traffic is opposite direction/crossing left to right
4) height information when available, this may include the unverified Mode C of unknown aircraft

Question 65

Under some circumstances, controllers may consider it prudent to inform a pilot of other traffic which is separated from his aircraft.

In such cases, to prevent any possible confusion…

Answer 65

…no reference should be made to the actual level of the other aircraft.

If necessary, the pilot should be informed that the other aircraft is x thousand feet above/below

Question 66

When weather is observed on the situation display, or is known to be present…

Answer 66

…pilots should be advised of the weathers location and, if known, intensity and direction of movement

Question 67

When a pilot requests an alternative heading or route for weather avoidance, controllers shall…

Answer 67

…accommodate such requests, taking into account the prevailing traffic situation.

When a pilots request cannot be accommodated, controllers shall offer an alternative weather avoidance clearance or explain to the pilot why his request cannot be met

Question 68

When weather avoidance will take an aircraft outside CAS…

Answer 68

…the pilot must be informed of this and offered an appropriate service, pilots routing OCAS for weather avoidance should be issued with a clearance to rejoin as required

Question 69

If a pilot is cleared to follow his own navigation, or accepts a heading, in order to avoid weather…

Answer 69

…he should be requested to report when able to accept vectors back on track.

Question 70

There are many potential causes of spurious primary returns (clutter) including:

Answer 70

Weather
Anomalous propagation
Ground/sea returns
Birds
Wind turbine effects
Radar countermeasures such as chaff

Whilst it may be possible for some forms of clutter to be distinguishable from aircraft surveillance returns, this may not always be possible, especially where processed systems are employed.

Question 71

Clutter on the situation display has the potential to impact on ATS provision in the following ways:

Answer 71

1) increased risk of the controller not detecting conflicting traffic
2) aircraft position symbols, track histories, data blocks may be hidden or obscured
3) spurious tracks may be generated, which my indistinguishable from genuine aircraft returns
4) there may be a delay in aircraft being identified and placed under an ATS
5) increased controller workload

These impacts are likely to affect the degree, accuracy and timeliness of the instructions, advice and information that controllers are able to provide to pilots, with consequent impacts on safety and expedition.

Additionally, the existence of clutter may necessitate aircraft being rerouted, or ATS reduced below the level requested by the pilot.

In addition to observable clutter, wind turbines have the potential to generate a variety of other negative affects on ATS systems and these should be considered when participating in planning applications.

Where clutter of a long term or permanent nature is generated in a particular area, in addition to the procedures, the potential impacts and mitigations should be assessed locally and procedures documented in MATS2.

Question 72

Outside CAS:

In the event of clutter being present on the situation display controllers should consider the nature and extent of the clutter and if necessary take the following actions:

Answer 72

1) for aircraft on a DS or TS, controllers should inform the pilot of the extent of the clutter and where practicable offer a reroute.

However, this may not be possible due to traffic density, airspace availability and/or the requirement to follow specific arrival or departure tracks.

The extent of such a rerouted should where possible aim to achieve the planned lateral deconfliction minima from the observed clutter.

However, it may still be necessary to reduce TI, and if applicable deconfliction advice, from the direction of the clutter

2) for aircraft on a TS, and those on a DS that are not rerouted as above, controllers shall inform pilots of a reduction in TI/deconfliction advice. If the controller cannot maintain aircraft ID, the service shall be terminated
3) for all surveillance services, in order to maintain track identity of aircraft being vectored to final approach, if re-routing around the clutter is not practicable for the reasons specified above, an alternative type of approach may need to be conducted.

Question 73

Inside CAS:

In the event of clutter being present on the situation display, RCS shall not be terminated, not the ATS terminated.

Controllers should consider the extent of the clutter and if necessary take the following actions:

Answer 73

1) the controller may vector the aircraft around the clutter; however, this might not be practicable due to traffic density, airspace availability and/or the requirement to follow specific arrival or departure tracks.
2) if the intensity of the clutter is such that the controller is not able to clearly see the aircraft’s PSR or SSR symbol, radar separation shall not be used to separate it and other controlled aircraft.
3) the controller may provide IFR traffic in Class E with reduced TI

In the event of clutter being present of the situation display, VFR flights receiving a TS in Class E shall be managed iaw clutter OCAS.

Question 74

When clutter is displayed, the controller remains responsible for…

Answer 74

…providing advice and information on aircraft that are considered to be infringing CAS.

Therefore, the controller should consider the nature and consistency of the clutter including any observed movement, relative speed and track, and take appropriate action if it is considered to be an unknown aircraft.

Question 75

In addition to clutter procedures ICAS and OCAS, in all classes of airspace for aircraft intending to make a radar approach, the controller shall assess the nature and extent of the clutter and decide whether:

Answer 75

1) a radar approach is not possible owing to clutter, in which case the controller shall inform the aircraft

Or

2) a radar approach could be carried out, but there may be a possibility of radar contact being lost. In this case the controller shall inform the aircraft as early as possible that clutter is affecting his display and that missed approach instructions will be passed in good time if it becomes necessary to abandon the approach.

Question 76

In the event of surveillance system failure, the controller shall…

Answer 76

…inform all aircraft under his control of the failure and apply local contingency procedures.

Reduced vertical separation of half the applicable vertical separation (e.g. 500ft where a controller would normally apply 1000ft) may be employed temporarily if standard separation cannot be provided immediately.

When reduced vertical separation is employed, pilots shall be informed and essential traffic information passed as necessary.

Question 77

When a previously failed surveillance system is notified as being SVC, before any ATS surveillance service is provided, the controller shall…

Answer 77

…re-identify all aircraft by an approved method iaw MATS1

Question 78

In the event that an STCA alert is generated in respect of controlled flights, the controller shall…

Answer 78

…without delay assess the situation and, if necessary, take action to ensure that the applicable separation minimum will not be infringed.