Published: 12 July 2011
Effective: 12 July 2011

ATA Chapter: 34


Mode S Transponder Maintenance


Mode S Transponder


All operators and maintainers of aircraft fitted with Mode S Transponders.


This Continuing Airworthiness Notice (CAN) is issued to highlight the potential problems associated with Mode S transponders and provide guidance for the testing and inspection of transponders.


The CAA is aware of incidents where complete or intermittent loss of detection has been experienced by Mode S SSR interrogators, and incidents of aircraft operating with an incorrect ICAO 24-bit aircraft address code. A safe navigation environment in transponder mandatory airspace relies on accurate and reliable surveillance information transmitted by Mode S transponders. Incorrect of missing transponder data can result in increased controller and/or flight crew work load which may develop into a hazardous situation.

EASA and Eurocontrol have identified similar incidents with aircraft operating in the European airspace and EASA subsequently issued Safety Information Bulletin (SIB) 2011-15 dated 4 July 2011.


In addition to the requirements in NZCAA rule 91.605 (e)(3) the CAA recommends the checks contained in EASA Safety Information Bulletin (SIB) 2011-15. These checks are in the interest of aviation safety and the SIB provides guidance for the ground testing of Mode S transponders to ensure acceptable transponder performance.

If you become aware, or are notified of a transponder deficiency affecting your aircraft, the CAA recommends that you initiate an unscheduled maintenance action to correct any deficiencies.

A copy of EASA SIB No: 2011-15 can be obtained from: link)