ENR 1.6  ATS Surveillance Services and Procedures


1.1   Transponder requirement

The carriage and operation of Mode S transponders with basic functionality is mandatory in the Brussels FIR/UIR for all aircraft operating:

  • in civil class C airspace;
  • in civil class D airspace;
  • in class G airspace for VFR flights at night.

During missions, police aircraft are exempted for operating the Mode S transponder provided they activate the mode A and C transponder and advise the ATC unit concerned.

The carriage and operation of a serviceable transponder - capable of replying to Mode A and C interrogations - is mandatory in the Brussels FIR/UIR for all aircraft operating in military controlled airspace.

An exemption to these rules may be granted, provided that the request is made before the flight, to the authority having jurisdiction over the airspace concerned.

Note: Pilots are reminded about the importance of having a well-functioning transponder to be switched on in the Belgian part of the Brussels FIR/UIR; ATC is allowed when possible to refuse aircraft without a well-functioning one.

1.2   Operation of an SSR Transponder (SERA.13001)

When an aircraft carries a serviceable SSR transponder, the pilot shall operate the transponder at all times during flight, regardless of whether the aircraft is within or outside airspace where SSR is used for ATS purposes.

Pilots shall not operate the IDENT feature unless requested by ATS.

Except for flight in airspace designated by the competent authority for mandatory operation of transponder, aircraft without sufficient electrical power supply are exempted from the requirement to operate the transponder at all times.

Note 1: Pilots of aircraft engaged in formation join-ups are expected to continue operating the transponder until established in formation. Once established in formation, all except the lead aircraft should be instructed to ‘squawk standby’.

Note 2: Pilots of non-powered aircraft are also encouraged to operate the transponder during flight outside airspace where carriage and operation of SSR transponder is mandatory.

1.3   Standard SSR Operating Procedures
1.3.1   General

Except when encountering a state of emergency, pilots shall operate transponders and select modes and codes in accordance with ATC instructions. In particular, when entering the Brussels FIR, pilots who have already received specific instructions from ATC concerning the setting of the transponder shall maintain that setting until otherwise instructed.

1.3.2   SSR transponder Mode A code setting (SERA.13005)

To indicate that it is in a specific contingency situation, the pilot of an aircraft equipped with SSR shall:

  1. select Code 7700 to indicate a state of emergency unless ATC has previously directed the pilot to operate the transponder on a specified code. In the latter case, a pilot may nevertheless select Code 7700 whenever there is a specific reason to believe that this would be the best course of action;
  2. select Code 7600 to indicate a state of radio-communication failure;
  3. attempt to select Code 7500 to indicate a state of unlawful interference. If circumstances so warrant, Code 7700 should be used instead.

Note 1: If a pilot has selected Mode A Code 7500 and has been requested to confirm this code by ATC, the pilot should, according to circumstances, either confirm this or not reply at all. If the pilot does not reply, ATC will take this as confirmation that the use of Code 7500 is not an inadvertent false code selection.

Except in the cases described above, the pilot shall:

  1. select codes as instructed by the ATS unit; or
  2. in the absence of ATS instructions related to code setting, select code 2000
  3. when not receiving air traffic services, select code 7000 in order to improve the detection of suitably equipped aircraft.

Note 2: When requested by ATC to confirm the code selected, the pilot should verify the Mode A code setting on the transponder; reselect the assigned code if necessary; and confirm to ATC the setting displayed on the controls of the transponder.

1.3.3   Pressure altitude derived information (SERA 13010)

When the aircraft carries serviceable Mode C equipment, the pilot shall continuously operate this mode unless otherwise dictated by ATC.

1.3.4   SSR transponder Mode S aircraft identification setting (SERA.13015)

Aircraft equipped with Mode S having an aircraft identification feature shall transmit the aircraft identification as specified in Item 7 of the ICAO flight plan or, when no flight plan has been filed, the aircraft registration.

In order to be interpreted properly, there must be no spaces between the designator letters and flight number, nor any additional/superfluous zeros preceding the flight number. In case the aircraft identification can be entered manually, entry should be part of the start-up procedures.

Correct setting of aircraft identification is essential for identification and correlation (of radar track with flight plan data). An incorrect setting of the aircraft identification will be reported to the Belgian Civil Aviation Authority.

Note 1: For Mode S transponder ground operation at EBBR, see EBBR AD 2.20, § 1.4.

Note 2: For Mode S transponder ground operation at ELLX, see ELLX AD 2.20, § 1.1.

1.4   SSR transponder failure when the carriage of a functioning transponder is mandatory (SERA.13020)
1.4.1   Transponder failure after departure

In case of a transponder failure after departure, ATC units will attempt to provide for continuation of the flight to the destination aerodrome in accordance with the flight plan. Pilots may, however, be expected to comply with specific restrictions.

Note: 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 ATC units concerned will endeavour to provide for continuation of the flight to the aerodrome of first intended landing in accordance with the flight plan. However, in certain traffic situations, either in terminal areas or en- route, continuation of the flight may not be possible, particularly when failure is detected shortly after take- off. The aircraft may then be required to return to the departure aerodrome or to land at the nearest suitable aerodrome acceptable to the operator concerned and to ATC.

1.4.2   Transponder failure before departure

In the case of a transponder which has failed and cannot be restored before departure, pilots shall:

  1. inform ATS as soon as possible, preferably before submission of a flight plan;
  2. insert in Item 10 of the ICAO flight plan form under SSR the character ‘N’ for complete unserviceability of the transponder or, in case of partial transponder failure, insert the character corresponding to the remaining transponder capability; and
  3. comply with any published procedures for requesting an exemption from the requirements to carry a functioning SSR transponder.

Note: 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 repair can be made. When granting clearance to such aircraft, ATC will 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 become necessary during the course of the flight.

1.5   System of SSR Code Assignment

Codes will be assigned in accordance with the SSR code allocation list for the ICAO EUR Region, which is based on the Originating Region Code Assignment Method (ORCAM).

Codes protected for international transit, transit codes, which are assigned to overflying or inbound flights, will be retained by ATC.

Code 1000 will be assigned or retained to indicate an eligible (flagged by the IFPS) IFR flight, where the downlinked aircraft identification is validated as matching the aircraft identification entered in the flight plan.

1.5.1   In Belgium
Departing International IFR Flights
0101 - 0117departing traffic
7101 - 7167departing traffic
4401 - 4427departing traffic inbound the United Kingdom, the Netherlands, Ireland, Greenland, Iceland, Canada or the United States, and departing traffic re-entering Belgium.
1000eligible (flagged by the IFPS) departing traffic
Domestic Flights
4450 - 4457codes assigned by Brussels ACC/APP
5101 - 5167codes assigned by Brussels APP
6301 - 6313codes assigned by Brussels TWR
6314 - 6327codes assigned by Charleroi TWR/APP
6330 - 6343codes assigned by Liège TWR/APP
6344 - 6361codes assigned by Oostende TWR/APP
6362 - 6367codes assigned by Antwerpen TWR
VFR Flights
0041 - 0057codes assigned by Brussels INFO
1.5.2   In Luxembourg
Departing International IFR Flights
3501 - 3507Departing traffic
5650 - 5657Departing traffic
7170 - 7177Departing traffic
1000Eligible (flagged by the IFPS) departing traffic
Flights remaining in Luxembourg TMA below FL 165
and solely controlled by Luxembourg APP
4460 - 4464Codes assigned by Luxembourg APP
VFR Flights
4465 - 4467Codes assigned by Luxembourg APP/TWR
4470 - 4477Codes assigned by Luxembourg APP/TWR


2.1   General

ATS units and Air Defence Stations use SSR for identification and automatic tracking of aircraft.

The carriage of a serviceable transponder capable of replying to Mode A and C is compulsory for all aircraft operating in all military controlled airspace. An exemption to this rule may be granted, provided that the request is made before the flight to the authority having jurisdiction over the airspace concerned. Aircraft flying OAT within the Brussels FIR/UIR must have a serviceable SSR transponder.

The carriage of a serviceable Mode S (ELS or EHS) SSR transponder is highly recommended but not yet compulsory for State aircraft flying OAT within the Brussels FIR/UIR including low level VFR flights.

State aircraft flying GAT within the Brussels FIR/UIR shall comply with the regulation for the carriage and operation of SSR mode S airborne equipment published in the AIP and/or related AIC.

State aircraft that do not transmit ADS-B out for technical or operational reasons, will be accommodated in the Brussels FIR/UIR through traditional surveillance methods such as Mode A/C/S.

Flights with a wrong Mode S ACID will be instructed by ATC to correct this. Flight limitations may be imposed until the ACID is correct (e.g. not leaving the CTR or TMA).

2.2   SSR Mode

Aircraft flying OAT within the Brussels FIR/UIR shall squawk:

Mode 1as instructed by the appropriate NATO authority
Mode 2always activated unless instructed otherwise
Mode 3/Aas instructed by the controlling agency
Mode Calways activated unless instructed otherwise
Mode SOnly mandatory for declared Mode S capable Belgian military aircraft. Mode S ACID must exactly match the ACID as entered in item 7 of the FPL (See ENR 1.10, §

Note: In a formation flight, only one aircraft shall squawk as mentioned above, the other aircraft shall squawk “stand-by”.

Note: Mode 4 is forbidden.

2.3   SSR Mode 3 Code Allocation

Domestic Flights
1401 - 1477Steenokkerzeel ATCC
2601 - 2627Cross-border to EH/ED
5401 - 5417Koksijde/HELI
5420 - 5427RPAS
5430 - 5477SF260M
6001 - 6077Beauvechain CRC
6401 - 6477Steenokkerzeel ATCC
Local Flights
4201 - 4207Chièvres
4210 - 4227Beauvechain
4230 - 4247Kleine-Brogel
4250 - 4267Florennes
4270 - 4277Koksijde
Special Codes
A1000conspicuity code applicable to civil city pair aircraft, forbidden for OAT fligths.
A7000 + Cuncontrolled flights, which have not received an instruction concerning the setting of their transponder
A7500unlawful interference
A7600radio communication failure
A7700emergency (unless instructed otherwise by the controlling agency)
2.4   Radio Communication Failure
2.4.1   Receiver Failure

The pilot shall transmit reports at the scheduled times or positions, preceded by “transmitting in the blind due to receiver failure”. These reports should include his intentions and the time of his next intended transmission.

2.4.2   Receiver and Transmitter Failure   VFR
  • Squawk A7600, and
  • Maintain VMC, and
  • Land at the nearest suitable aerodrome, and
  • Report his arrival by the most expeditious means to the appropriate ATC unit.   IFR
  • Squawk A7600, and
  • Proceed according to flight plan and hold over the last navaid, and
  • Commence a descent from this navaid as close as possible to the last acknowledged EAT or the flight plan EAT, and
  • Complete the normal instrument approach procedure and land, if possible within 30 MIN of EAT (last acknowledged or flight plan).

If the pilot is established on a published ATS route, he shall maintain the last assigned speed and level for a period of 7 MIN. After this period, he shall adjust to the level in accordance with the flight plan. If the pilot is established on a published ATS route but he was receiving radar vectors or he was proceeding offset, the pilot shall proceed in the most direct manner possible to rejoin the current flight plan route.

If the pilot has been given level clearances for only a part of the route, he shall fly this level to the point specified in the clearance and then the cruising level of the flight plan. Departing aircraft shall fly the level they are cleared to for 3 MIN and then fly the cruising level of their flight plan.

2.4.3   Transmitter (and Receiver) Failure and SSR inoperative

The pilot may or, if transponder is inoperative, shall fly triangles of 1 MIN legs (TAS higher than 300 KT) or 2 MIN legs (TAS equal or less than 300 KT) clockwise if his receiver still works, anti-clockwise if the radio receiver and transmitter are both out of service. He can expect to be intercepted by a shepherd aircraft.