CS ACNS.D.ELS.010 Transponder characteristics

ED Decision 2013/031/R

(See AMC1 ACNS.D.ELS.010)

(a) The transponder(s) is (are) an approved level 2 or greater Mode S transponder(s) with Elementary Surveillance and Surveillance Identifier (SI) capability.

(b) The transponder(s) of aircraft that have ACAS II installed is (are) ACAS compatible

(c) The peak pulse power available at the antenna end of the transmission line of the transponder is more than 125 W (21 dBW) and not more than 500 W (27 dBW) for aircraft that operate at altitudes exceeding 4 570 m (15 000 ft) or with a maximum cruising speed exceeding 90 m/s (175 knots).

(d) The peak pulse power available at the antenna end of the transmission line of the transponder is more than 70 W (18.5 dBW) and not more than 500 W (27 dBW) for aircraft operating at or below 4 570 m (15 000 ft) with a maximum cruising airspeed of 90 m/s (175 knots) or less.

AMC1 ACNS.D.ELS.010 Transponder characteristics

ED Decision 2013/031/R

(a) Transponder capabilities

(1) To be approved, the Mode S transponder should hold an EASA equipment authorisation in accordance with European Technical Standard Order ETSO-C112d, or an equivalent standard that is consistent with ICAO Annex 10 Volume IV and which is acceptable to the responsible certification authority.

 Note: ETSO-C112d requires compliance with EUROCAE ED-73E.

(2) The transponder class can be verified by checking that the transponder DDP declares the transponder level as ‘2’, ‘3’, ‘4’, or ‘5’.

 Note: The definition of a level 2 transponder and associated functions can be found in EUROCAE ED-73E paragraph 1.4.2.1, 3.22 and 3.23.

(3) The SI code capability can be verified by checking that the transponder DDP indicates the letter ‘s’ in the transponder capability declaration.

 Note 1: The DDP indicates those requirements of ED-73E (or later version) with which the transponder is not compliant with.

 Note 2: The transponder SI code capability can be found in EUROCAE ED-73E paragraph 3.18.4.34. SI codes have been allocated to Mode S radars used in Europe and it is, therefore, an important capability to ensure correct detection of the aircraft.

(4) The Elementary Surveillance functionality can be verified by checking that the transponder DDP indicates the letter ‘l’ for ELS or ‘n’ for EHS in the transponder capability declaration.

 Note: Such transponders meet the requirements specified in EUROCAE ED-73E 3.29. According to ED-73E, a transponder with the Enhanced Surveillance capability has also the Elementary Surveillance capability.

(5) ACAS compatibility can be verified by checking that the transponder DDP indicates the letter ‘a’ in the transponder capability declaration.

 Note: Necessary capabilities to be an ACAS-compatible Mode S transponder are described in section 3.27 of EUROCAE ED-73E.

(b) Minimum output power level: The transponder power output capability should be verified as follows, depending on the aircraft capability:

(1) For aircraft that operate at altitudes exceeding 4 570m (15 000ft) or with maximum cruising speed exceeding 90 m/s (175 knots), the class of the transponder declared in the transponder DDP should be Class 1.

(2) For aircraft operating at or below 4570m (15 000ft) with a maximum cruising airspeed of 90 m/s (175 knots) or less, the class of the transponder declared in the transponder DDP should be Class 1 or Class 2.

 Note: Classes of equipment are defined in EUROCAE ED-73E 1.4.2.4. Power characteristic is defined in ICAO Annex 10 Volume IV 3.1.1.7.11.

CS ACNS.D.ELS.015 Data transmission

ED Decision 2013/031/R

(See AMC1 ACNS.D.ELS.015)

(a) The surveillance system provides the following data in the Mode S replies:

(1) The Mode A Code in the range 0000 to 7777 (Octal);

(2) The pressure altitude corresponding to within plus or minus 38 m (125 ft), on a 95 per cent probability basis, with the pressure-altitude information (referenced to the standard pressure setting of 1013.25 hectopascals), used on board the aircraft to adhere to the assigned flight profile. The pressure altitude ranges from minus 300 m (1 000 ft) to the maximum certificated altitude of aircraft plus 1 500 m (5 000 ft);

(3) On-the-ground status information;

(4) The Aircraft Identification as specified in Item 7 of the ICAO flight plan or the aircraft registration;

(5) Special Position Indication (SPI);

(6) Emergency status (Emergency, Radio communication failure, Unlawful interference);

(7) The data link capability report;

(8) The common usage GICB capability report;

(9) The ICAO 24-bit aircraft address; and

(10) Aircraft that have ACAS II installed provide the ACAS active resolution advisory report.

(b) All other data transmitted is verified.

(1) If the system transmits one or more additional downlink airborne parameters in addition to those listed in paragraph (a), then the relevant sub specifications of CS ACNS.D.EHS.015 are also complied with.

(2) If the system transmits additional parameters on the extended squitter and if their full compliance with CS ACNS.D.ADSB has not been verified, as a minimum the aircraft identification, pressure altitude, ICAO 24-bit aircraft address is identical to those transmitted in the Mode S replies. Additionally the position and velocity quality indicators reports the lowest quality.

AMC1 ACNS.D.ELS.015 Data transmission

ED Decision 2022/008/R

Data transmission verifications

(a) Table 1 below provides the parameters that should be verified for Mode S elementary surveillance.

Table 1 — List of parameters to be verified on an ELS installation

Note 1: Information about how Mode S ELS data is used by Mode S ground systems can be found in Subpart D, Appendix B.

Note 2: Downlink formats (DFs) are defined in ICAO Annex 10, Volume IV and EUROCAE ED-73E. A summary can also be found in Subpart D, Appendix B.

Note 3: It is not recommended to have 2 transponders installed without a common control panel.

(b) Pressure Altitude

(1) The consistency of the altitude reported in Mode C replies and Mode S replies should be checked.

Note: An incorrect installation of altimeters using Gillham encoding may result in altitude transmitted in Mode C replies and no altitude transmitted in Mode S replies.

(2) For aircraft transmitting parameters via the Extended Squitter, for which compliance with Subpart D section 4 is not required, the pressure altitude data should be checked in the Extended Squitter register for airborne position (register 05₁₆).

(c) Pressure altitude resolution transmission

(1) The resolution of the transmitted pressure altitude should be 7.62 m (25 ft) for aircraft equipped with a pressure altitude source having a resolution better than 7.62 m (25 ft) for all altitudes except those above 15 298 m (50 187.5 ft).

(2) Aircraft equipped with altimeters that have a resolution greater than 7.62 m (25 ft) (e.g. 30.48 m (100 ft)) should report their altitude in 30.48 m (100 ft) encoding.

(3) Verify that the encoding of the altitude is appropriate to the altimeter resolution as defined in paragraphs 1 and 2 above.

(4) For aircraft transmitting parameters via the Extended Squitter, for which compliance with Subpart D section 4 is not required, the pressure altitude resolution data should be checked in the Extended Squitter register for airborne position (register 05₁₆).

(d) Aircraft Identification

(1) For aircraft transmitting parameters via the Extended Squitter, for which compliance with Subpart D section 4 is not required, the Aircraft Identification received via the Extended Squitter should be checked to ensure that it is identical to the information transmitted in register 20₁₆.

(e) Special Position Indication (SPI)

The FS field should report FS = 4 or 5 for 18 seconds (+/-1 second) in replies DF4, DF5, DF20 or DF21 after the SPI (IDENT) has been manually activated.

Note: Flight Status values can be found in ICAO Annex 10, Vol IV, paragraph 3.1.2.6.5.1.

(f) ACAS active Resolution Advisory report

For aircraft that have ACAS II installed, no undue RA report should be announced (DR field never set to 2, 3, 6 or 7) within (5 minutes).

(g) Common usage GICB capability report: BDS 17₁₆ = 0 is an acceptable means of compliance for transponders that are strictly ELS (not transmitting other parameters).

(h) Transmission of other parameters

When one or more other airborne data items are transmitted, they should be verified as proposed in AMC1 ACNS.D.EHS.015.

Note 1: The minimum data transmission verification of transponder also having ADS-B ES capabilities has been defined above. Transponders that are transmitting parameters other than the minimum tested above, are encouraged to demonstrate compliance with Subpart D section 4.

Note 2: The implementation of registers E316, E416, E516 and E616 is recommended.

[Issue: CS-ACNS/4]

CS ACNS.D.ELS.020 On-the-ground status determination

ED Decision 2013/031/R

(See AMC1 ACNS.D.ELS.020)

(a) The on-the-ground status is not set by a manual action.

(b) If automatic determination of the On-the-ground status is not available, the On-the-ground status is set to airborne.

AMC1 ACNS.D.ELS.020 On-the-ground status determination

ED Decision 2013/031/R

The automatic determination of the on-the-ground status should be obtained from:

(a) Weight On Wheel (WOW) sensor: When the aircraft is equipped with an automatic sensor to determine if the aircraft is on the ground (i.e. Weight On Wheel sensor), this sensor should be used as the on-the-ground status source of the transponder. For Aircraft with transponders that have access to at least one of the following parameters (ground speed, radio altitude, airspeed) the following validation check should be performed when detected ‘on the ground’ and the air/ground status should be overridden and changed to ‘airborne’ if [Ground speed > 50 m/s (100 knots) OR airspeed > 50 m/s (100 knots) OR radio altitude> 15 m (50 feet)].

Note: Care should be taken to ensure the wiring of the WOW to the correct transponder pins.

(b) automatic algorithm : If ground speed, radio altitude, or airspeed parameters are being used in the algorithm and the ‘on-the-ground’ condition is being reported or if the on-the-ground status has been commanded via the TCS subfield, the on-the-ground status is to be overridden and changed to ‘airborne’ if :

Ground Speed OR Airspeed > X or Radio height > 15 m (50 ft).

Note 1: Care should be taken to ensure that the chosen threshold values of X are such that the aircraft can never report ‘on ground’ status when in the air, and should be based on the aircraft nominal performance.

Note 2: Systems that support Enhanced Surveillance and ADS-B might use available airborne parameters in their automatic algorithm to determine if they are on the ground. More information can be found in Subpart D section 4.

CS ACNS.D.ELS.025 Altitude source

ED Decision 2022/008/R

(See AMC1 ACNS.D.ELS.025)

(a) The reported pressure altitude is obtained from an approved source.

(b) The altitude resolution is less than or equal to 30.48 m (100 ft).

(c) The altitude source connected to the active transponder is consistent with the source being used to fly the aircraft.

[Issue: CS-ACNS/4]

AMC1 ACNS.D.ELS.025 Altitude source

ED Decision 2022/008/R

(a) Compliance with JAA TGL No 6 is an approved acceptable means of compliance for an altimeter as an altitude source.

(b) A pressure altitude resolution of less than or equal to 7.62 m (25 ft) is an approved acceptable means of compliance for an altimeter.

Note: An altitude source resolution of less than or equal to 7.62 m (25 ft) is required for aeroplanes intended to be used for international air transport, as defined in ICAO Annex 6, Part 1, Section 6.19.

(c) A pressure altitude resolution of less than or equal to 30 m (100 ft) and greater than 7.62 m (25 ft) is an approved acceptable means of compliance for an aircraft altimeter, provided that the following conditions are met:

(1) There is no conversion of the Gillham-encoded data to another format before it is input to the transponder unless failure detection can be provided, and the resolution (quantisation) is set in the transmitted data to indicate 30 m (100 ft).

 Note 1: It is not recommended to install altimeters with a Gillham altitude encoder interface, as it supports a resolution of only 30 m (100 ft).

 Note 2: Losses or errors of pressure altitude have an impact on the provision of separation by the air traffic control (ATC). It is, therefore, important to design the altitude pressure source to minimise the loss of this data or the provision of erroneous data.

 Note 3: Further guidance on altitude measurement and coding systems can be found in EUROCAE Document ED-26.

(2) Altitude source comparison:

 For aircraft equipped with ACAS II, where the available source of pressure altitude information is only in Gillham-encoded format, the requirement for detection of an altitude source or encoder failure can be satisfied by means of dual independent altitude corrected sensors, together with an altitude data comparator (which may be incorporated and enabled in the transponder). Similar provisions are also acceptable for alternative altitude information sources that do not signal erroneous data.

The flight deck interface should provide a means to inhibit the transmission of pressure altitude information for aircraft equipped with a Gillham-encoded altitude interface.

(d) If it is impractical to connect the transponder to the altitude source used to fly the aircraft, consistency may be achieved by:

(1) connecting the pressure altitude source directly (e.g. via a T-junction) to the same pitot/static-pressure line(s) as the altitude source being used to fly the aircraft; and

(2) ensuring that the pressure altitude source has built-in test equipment (BITE) that permanently or frequently runs an automatic system self-test and triggers a ‘FAIL’ annunciator/indicator (e.g. an amber light) in the pilot’s normal field of view upon detection of a failure; and

 (3) ensuring that the altitude source meets design and performance standards that achieve an adequate level of integrity of its output, to mitigate the risk of a possible inconsistency between the output of the altitude source and the altimeters used by the flight crew to fly the aircraft.

The altitude source may be integrated into the transponder if the above-mentioned requirements are met.

(e) The provision of manual or automatic selection of the altitude source is an acceptable means of compliance.

[Issue: CS-ACNS/4]

CS ACNS.D.ELS.030 Flight deck interface

ED Decision 2013/031/R

(See AMC1 ACNS.D.ELS.030 )

(a) A means is provided :

(1) to select Mode A Code, including emergency indicators;

(2) to initiate the IDENT (SPI) feature;

(3) for an aircraft identification to be inserted by the flight crew if the aircraft uses variable aircraft identification;.

(4) to notify the flight crew when the transmission of pressure altitude information has been inhibited, if a means to inhibit the transmission of pressure altitude is provided;

(5) to select the transponder to the ‘standby’ or ‘OFF’ condition;

(6) to indicate the non-operational status or failure of the transponder system without undue delay and without the need for flight crew action;

(7) to display the selected Mode A code to the flight crew;

(8) to display the aircraft identification to the flight crew; and

(b) Input which is not intended to be operated in flight, is not readily accessible to the flight crew.

AMC1 ACNS.D.ELS.030 Flight deck interface

ED Decision 2013/031/R

Modes of operation should be identified. Attention should be closely paid to line select keys, touch screens or cursor controlled trackballs as these can be susceptible to unintended mode selection resulting from their location in the flight deck.