EASA SIB 2016-05R2: Mode S Enhanced Surveillance - Incorrect Downlinked Barometric Pressure Setting (BPS)

What to do

Flight crews should manually select a barometric pressure setting of 1013 hPa when climbing through the transition altitude before pulling the control marked 'STD' on the altimeter or Flight Control Unit, especially when notified by ATC of incorrect BPS data. Operators should consult updated Airbus Flight Crew Operating Manuals and coordinate with STC holders for any specific instructions. No mandatory compliance deadline or Airworthiness Directive action is currently required.

Summary

EASA Safety Information Bulletin 2016-05R2 is an airworthiness bulletin addressing an incorrect downlinked barometric pressure setting (BPS) issue affecting Airbus A300, A300-600, A300-600ST, A310, A318, A319, A320, A321, A330, and A340 aircraft equipped with certain Mode S Enhanced Surveillance transponders from ACSS, Collins, and Honeywell. The bulletin highlights a design error causing the transponder to downlink the previous BPS instead of the standard 1013 hPa setting when climbing through the transition altitude. This affects ground-based safety net systems relying on accurate BPS data but does not impact the altitude broadcast to other aircraft.

What changed

This revision extends the applicability of the original SIB 2016-05R1 to include aeroplanes with affected transponders installed via Supplementary Type Certificates (STCs) and adds recommendations for flight crews to manually select 1013 hPa BPS before engaging the standard pressure setting. It also clarifies which transponder modifications are not affected by the issue and updates Airbus Flight Crew Operating Manuals accordingly.

Why it matters

Accurate downlinked barometric pressure settings are critical for air traffic control safety net systems to detect potential altitude deviations early. Operators and flight crews need to be aware of this design deficiency to ensure correct BPS transmission during climb, thereby maintaining situational awareness and avoiding false alerts or misinterpretations by ATC. Maintenance and compliance teams must track affected transponder installations and STCs to manage operational risks effectively.