Undetected Simultaneous Transmissions

Undetected Simultaneous Transmissions


Several cases of AIRPROX have been reported by an ANSP due to pilots reading back a clearance not intended for them at the same time as the pilot for whom the clearance was intended. The ATCO did not detect the error because the transmission was hidden (technical systems transmitting best signal only). Other agencies have reported similar occurrences.

The following Safety Recommendations are made to reduce the risk of (Undetected) Simultaneous Transmissions:

  • ANSPs, Regulators, Aircraft Operators and the EUROCONTROL Agency should continue the work on reducing the risk associated with similar callsigns;
  • ANSPs should provide their controllers with detailed information on RTF cross-coupling and Best Signal Selection functionality if used, including the process itself, how it should be used and the problems inherent in the system;
  • When multiple RTF channels are coupled, priority should be given to duplex coupling (allowing audible simultaneous transmission) rather than simplex coupling;
  • ANSPs, Aircraft Operators and Regulators should continue to promote strict RTF discipline, including rigorous read-back - hear backprocess;
  • Third parties on a communication channel should be encouraged to call out “blocked” if they detect simultaneous transmission;
  • ANSPs and Regulators should monitor the incidence of (Undetected) Simultaneous Transmissions Events;
  • The originator ANSP, and the EUROCONTROL Agency will investigate further the operational and technical aspects of these occurrences;
  • ANSPs, Regulators, Equipment Manufacturers and the EUROCONTROL Agency will investigate the possibility of a technological solution.


© European Organisation for Safety of Air Navigation (EUROCONTROL) December 2003. This alert is published by EUROCONTROL for information purposes. It may be copied in whole or in part, provided that EUROCONTROL is mentioned as the source and to the extent justified by the non-commercial use (not for sale). The information in this document may not be modified without prior written permission from EUROCONTROL. The use of the document is at the user’s sole risk and responsibility. EUROCONTROL expressly disclaim any and all warranties with respect to any content within the alert, express or implied.


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