This publication provides recommendations and examples, further to the applicable regulation, certification specifications, and AMCs. They have no legal value and are only advisory.
Should a change to type design installing ADS-B out capability be classified as Minor or Major?
Due to the ‘major’ failure effect associated to ADS-B Integrity and Continuity conditions (due to potential disrupting effects at ATC level) and the novelty of the function and potential extension of the operational capabilities, the changes that use CS-ACNS are expected to be classified as Major.
However, changes using only AMC 20-24 may be classified as Minor if certain conditions are met:
- The transponder is ETSO-2C112b approved and complies with the requirements of ED-102/DO-260 or DO-260A, and
- The GNSS receiver is approved under any of ETSO C-129A, TSO C-129, TSO C-129A, ETSO C-145/C-146, or TSO C-145A/C146A, and
- The interface between the transponder and GNSS received is direct (no routing through other equipment).
Should I choose CS-ACNS, or AMC 20-24 as part of the certification / compliance basis for installation of ADS-B (for a new TC or a change to a TC/STC)?
The intents of CS-ACNS and AMC 20-24 are different. The former provides the means to comply with the rules set forth in the Commission Implementing Regulation (EU) No 1207/2011 (amended by (EU) No 1028/2014) (‘SPI regulation’) and supports applications where the ADS-B could be used to replace Radar (RAD) applications with a 3 Nm separation between aircraft. The latter is intended to support Non-Radar Areas (NRA) applications, with a 5 Nm separation and less stringent integrity and continuity needs.
For certification of ADS-B installations, CS-ACNS applies to aircraft with a maximum certified take-off mass exceeding 5700 kg or having a maximum cruising true airspeed capability greater than 250 knots.
Compliance to CS-ACNS (including book 2) has to be demonstrated for the initial airworthiness and changes to those aircraft. For a new TC, CS-ACNS is expected to be part of the certification basis.
For other aircraft, the applicant may elect to use AMC 20-24 instead of CS-ACNS.
What are the differences between CS-ACNS and AMC 20-24 regarding requirements for ADS-B?
There are several differences in terms of parameters required, continuity of the function, ES version used, as shown in this non-exhaustive list:
The term ‘remote’ corresponds to quantitative probability of 1E-5 / F.H.
The terms ‘major’ and ‘minor’ are Failure Condition classifications corresponding to quantitative probability objectives of respectively 1E-5 and 1E-3 / F.H.
What does the Continuity requirement imply and how is Continuity calculated?
- The assessment should encompass all equipment contributing to the ADS-B function and not just the transponder.
- The reliability of each component contributing to the function (e.g. transponder, control panels, position and velocity source) has to be considered,
- The probability of failure of the power source failure has to be considered,
- Common modes have to be considered.
Our analysis show that the Continuity meets the Implementing Rule / AMC 20-24 requirement, but not the CS-ACNS requirement.
CS-ACNS requires compliance to a qualitative probability of ‘remote’, which corresponds to a quantitative probability of 1E-5 / F.H. This is more challenging to meet than the Implementing Rule Annex II and AMC 20-24 figure (2E-4 / F.H.).
A deviation to this requirement may be accepted on a case-by-case basis and under conditions by the Agency after review of the compliance data. Such a deviation is published by EASA under reference ‘Deviation Request CS-ACNS#1’.
No deviations to the requirements of the Implementing Rule will be granted.
Is a dedicated ADS-B failure annunciator required in the instrument panel?
CS ACNS.D.ADSB.090 requires that a means is provided to indicate the non-operational status or failure of the ADS-B Out system without undue delay.
This can be an indicator dedicated to an ADS-B failure, however a single transponder failure indicator may be acceptable if the crew are able to distinguish between ADS-B device or function failures and other transponder failures using suitable troubleshooting procedures.
AMC 20-24 does not contain an equivalent requirement.
What are the requirements on the GNSS source?
The requirements are described in AMC 20-24 and CS-ACNS.
- Position and velocity information must come from the same source.
- ETSO-C129A is the minimum equipage qualification in Europe.
- For compliance with CS-ACNS, the applicable ETSOs (C129a/196/145/146) alone does not guarantee that the unit is suitable as an ADS-B position source. Further demonstration is required (see in particular AMC1 ACNS.D.ADSB.070 and .080).
- The System Design Assurance (SDA) parameter can be set to 2 without analysis if the GPS and ADS-B unit are both qualified (ETSO’d) and directly connected (i.e. direct wiring from GPS to receiver with no routing through other equipment). Aircraft with other architectures require a system safety analysis to set the SDA.