Secondary surveillance radar (SSR)

1.6.2 Secondary Surveillance Radar (SSR)

Burgas (range 370 km (200NM)); Varna (range 370 km (200NM)); Varbica (range 463 km (250NM)); Plovdiv (range 463 km (250NM)); Sofia (range 370 km (200NM)); Cherni vrah (range 463 km (250NM)). Emergency procedures

For identified aircraft in flight emergency the controller shall:

a) monitor the aircraft and plot on the radar display the position (whenever possible) until the aircraft passes out of radar coverage;

b) provide position information for the aircraft to all ATS units, which may be able to give assistance to the aircraft


c) transfer radar control to the adjacent radar sectors when appropriate. If the pilot of an aircraft encountering a state of emergency has previously been instructed to operate the transponder on a specific code, that code will normally be maintained unless, in special circumstances, the pilot has decided or has been advised otherwise. When the ATS unit has not assigned secondary code, the pilot will set the transponder to Mode A, Code 7700. Communication failure and unlawful interference procedures Communication failure

a) transponder-equipped aircraft experiencing communication failure will operate the transponder on Mode A,

Code 7600;

b) when it has been established by the controller, that the aircraft's radio receiver is functioning, continued service of transponder-equipped aircraft where SSR is available can be effected, using code changes or IDENT transmissions to obtain acknowledgement of clearances issued to the aircraft.

c) as soon as it known that the two-way communication has failed the pilot-in-command follow the procedures, given in item 3. on p. ENR 1.6-4. Unlawful interference

In event of an unlawful interference in the crew's activity the pilot-in-command shall set the transponder on Mode A,

Code 7500. SSR Code assignment management system To ensure the safe and efficient use of secondary surveillance radars and transponders, pilots and controllers shall strictly adhere to the fixed operating procedures.

Standard radiotelephony phraseology shall be used and the correct setting of transponder codes shall be ensured. SSR Codes 7500, 7600 and 7700 shall be reserved for use by pilots encountering unlawful interference, communication failure and state of emergency. SSR Codes are to be allocated and assigned in accordance with the following principle:

To aircraft operating into the airspace of the Republic of Bulgaria, codes are allocated in accordance with specific code blocks according ICAO Code allocation. The tolerance value, used to determine that Mode C-derived level information and displayed on the radar screen is accurate, shall be equal to ±60 m (±200 ft). Verification of the accuracy of Mode C-derived level information and displayed on the radar screen shall be effected at least once by each suitably equipped ATS unit on initial contact with the aircraft concerned or, if this is not feasible, as soon as possible thereafter. The verification of the accuracy shall be effected by simultaneous comparison with altimeter derived level information received from the pilot and the level information displayed on the radar screen and if the difference is within the approved tolerance value the controller is not obliged to inform the pilot. 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 controller shall inform the pilot and shall request the pilot to check the pressure setting and to confirm the aircraft's level. When entering the airspace of the Republic of Bulgaria the pilot-in-command of shall:

a) maintain the SSR code assigned by the controller and the ATS units of the adjacent states;

b) switch on the transponder on Mode A, Code 2000 5(five) min before entry into the controlled airspace of the Republic of Bulgaria, if no SSR code has been assigned. When an aircraft experiencing transponder failure after departure is operating or expected to operate in an area where the carriage of a functioning transponder with specified capabilities is mandatory, the ATS unit concerned should endeavour to provide for continuation of the flight to the aerodrome of landing in accordance with the flight plan of the aircraft. In accordance with the traffic situation, continuation of the flight may not be possible, particularly when failure is detected shortly after take-off. In the cases as per item, the aircraft may return to the departure aerodrome or to land at the nearest suitable aerodrome acceptable to the operator concerned and to the ATS unit. In case of a transponder failure which is detected before departure from an aerodrome where it is not practicable to effect a repair, the aircraft concerned should be permitted to proceed, as directly as possible, to the nearest suitable aerodrome where the failure can be eliminated. When granting clearance as per item to such aircraft, ATS unit should take into consideration the existing or anticipated traffic situation and may have to modify the time of departure, flight level or route of the intended flight. Subsequent adjustments may be done and during the course of the flight.