CS 09/10 - Airworthiness Directives Relating to Transponder Anomalies
This project is now closed.
11 Jan 2011
This project is now closed.
Refer to Project closure notes for full details.
22 Dec 2010
This NFRM is now available.
16 Mar 2010
Comments to this NPRM closed on 25 May 2010.
Project title change.
4 Aug 2009
Project closure notes
Amended Airworthiness Directive has been issued and is available in the Airworthiness Directives section of the website.
With the introduction and continuing rollout of Mode S Secondary Surveillance radars, aircraft fitted with TDR94/94D transponders have been detected not responding to interrogations, incorrectly responding to interrogation on ground, or broadcasting erroneous and potentially misleading data.
In addition there have been a significant number of reports from Airservices Australia (AsA) Air Traffic Control (ATC), that, with the introduction and continuing rollout of the new Mode S Secondary Surveillance Radars (SSR), aircraft fitted with some models of transponders have been detected transmitting spontaneously varying Mode A codes.
This situation, if not corrected could lead to one or more of the following situations:
- Aircraft does not respond to interrogations used by the Mode S ground radar stations causing the aircraft to not appear on controller screens. The transponder is not operating in accord with the standards and there is a clear adverse safety impact when used in environments using Mode S radar. Australia is currently developing Mode S radars, which are expected to become operational in September 2009. This situation is urgent and will become critical in September 2009 when the Australian AMSTAR radars become operational. This issue is primarily due to a transponder software error.
- Aircraft are required to respond to Mode S interrogations whilst on the ground. This allows the proper operation of Advanced Surface Movement Guidance and Control Systems which provide safety improvements at major Australian airports. However, some transponders inappropriately reply to Mode A/C interrogations causing garbling, incorrect position reporting and incorrect activation of ATC flight plans. This situation is already critical and is causing disruption to ATC today. This issue is primarily due to a wiring error on the transponder backplane.
- Invalid selected altitude data can be transmitted to the Mode S ground station creating disruptions in the ATC processes. It is planned that selected altitude will be used as an additional safety net to detect altitude busts before they occur. This issue will not become critical for two years but will be resolved with the software upgrade that addresses the first anomaly described.
- An aircraft transmitting an apparently spontaneously varying Mode A code would appear on the ATC console as multiple aircraft, thus triggering a short term conflict alert (STCA). As these Mode A codes are assigned by ATC for the purposes of aircraft identification in a control zone, during periods of high workload there is a safety risk that the controller may be distracted from other real potential conflicts.
These anomalies have significant safety implications that will continue to escalate as the new Mode S radars are commissioned and the older Mode A/C radars are phased out.
EASA has issued Airworthiness Directives applicable to TDR94/94D.
To issue appropriate Airworthiness Directives that will address the safety issues identified with transponders.
This project was approved by Peter Boyd, Executive Manager, Standards Development and Future Technology Division on 27 July 2009
Project Leader: Charles Lenarcic, Principal Engineer, Avionics, Initial Airworthiness Branch, Standards Development and Future Technology Division
Project Sponsor: Peter Boyd, Executive Manager Standards Development and Future Technology Division
Standards Development Program Manager: Nick Ward