EASA SIB 2011-13: WITHDRAWN - RECOMMENDATIONS NOT NEEDED ANYMORE. Topic addressed by EASA SIB 2011-15R3

What to do

Operators and maintenance personnel should promptly address any known or reported Mode S transponder deficiencies by initiating unscheduled maintenance to correct faults at the earliest opportunity. They should follow the ground testing guidance provided in the bulletin to verify transponder performance, including coordination with Air Traffic Control during testing. Since the recommendations are not mandatory, compliance deadlines are not specified, but proactive maintenance is advised to maintain safety.

Summary

WITHDRAWN - RECOMMENDATIONS NOT NEEDED ANYMORE is an EASA Safety Information Bulletin (SIB) 2011-13 addressing issues with Mode S transponders installed on various aircraft types including those certificated under FAR, JAR, and CS Parts 22, 23, 25, 27, 29, 31HB, VLA, or VLR. The bulletin highlights occurrences of complete or intermittent loss of detection by Mode S SSR interrogators due to installation deficiencies, maintenance errors, or equipment failures. It provides guidance for ground testing of transponders and emphasizes that the issue does not currently warrant an Airworthiness Directive.

What changed

This document withdraws previous recommendations related to Mode S transponder detection issues as they are no longer considered necessary. It clarifies that the identified transponder deficiencies do not constitute an unsafe condition requiring mandatory corrective action under current regulations. The bulletin also provides detailed guidance for ground testing procedures to help operators verify transponder functionality.

Why it matters

The bulletin is important for aviation professionals because faulty Mode S transponders can lead to intermittent or complete loss of aircraft detection by Air Traffic Control and other aircraft using collision avoidance systems, potentially compromising traffic separation and safety. Operators and maintenance organizations need to be aware of the risks and ensure proper maintenance and testing to avoid degraded surveillance and collision avoidance capabilities. Understanding the non-mandatory nature of the recommendations helps prioritize maintenance actions appropriately.