The Evolution of Annex 10: From Prescriptive to Performance-Based 

For decades, the professional world of an ATSEP was measured in microseconds and milliwatts. ICAO Annex 10 served as a technical “cookbook,” prescribing exactly how a pulse should look and how fast an antenna should turn. In this legacy environment, Secondary Surveillance Radar (SSR) standards in Volume IV were hardware-centric, focusing on physical signal characteristics. This approach could have been useful at a moment the technology was developing, to ensure interoperability, but in time it has created a regulatory ceiling unable to accommodate the rapid pace of digital innovation.

The Catalyst for Change

The shift toward Performance-Based Standards (PBS) was born of necessity. As outlined in the ICAO Global Air Navigation Plan (Doc 9750), the focus has moved toward Aviation System Block Upgrades (ASBUs), which prioritize operational outcomes over specific equipment lists. By transitioning to PBS, ICAO moved from “design-based” mandates to a framework where the focus is not on what the machine is, but on how the data performs. This allows Air Navigation Service Providers (ANSPs) to adopt innovative solutions—provided they meet the rigorous safety targets of their specific airspace.

SSR vs. ADS-B: A New Yardstick

The contrast is most visible in Annex 10, Volume IV. Where legacy SSR standards dictate precise timings for Mode A/C pulses, modern ADS-B and Multilateration (MLAT) are defined by performance metrics. As detailed in the ICAO Aeronautical Surveillance Manual (Doc 9924), Required Surveillance Performance (RSP) is now the primary yardstick. Instead of merely maintaining a motor, the ATSEP must ensure the end-to-end data chain delivers position reports with specific levels of accuracy, integrity, and latency. Whether a target is detected by a rotating antenna or a ground station network, the controller receives a signal that is fundamentally trustworthy.

The Impact on the Modern ATSEP

For the frontline ATSEP, this marks a transition from “fixing hardware” to “managing systems.” The framework for this change is anchored in ICAO Doc 9869 (PBCS Manual), which defines the parameters for monitoring the data chain. Maintenance is no longer just about responding to hardware failures; it is about the continuous oversight of data quality. This shift is reflected in the Manual on ATSEP Training and Assessment (Doc 10057), which emphasizes competencies in network architecture and data analytics.

Safety oversight now involves “auditing the invisible”—verifying that statistical performance remains within safety margins over time.

Conclusion: The Data Guardian

Ultimately, PBS future-proofs global infrastructure. By focusing on outcomes, ICAO ensures the surveillance chain remains interoperable, regardless of technological shifts. For the ATSEP, this evolution elevates their role to that of a “Data Guardian,” a critical analyst responsible for the health of the entire CNS ecosystem. Under this approach, safety remains the constant variable in an ever-changing technical landscape.

What are you opinions on this? Has this shift affected you and the work you do? We would love to hear from you!