Operational Use of ADS-B In Non Radar Airspace Generic Design Safety Case
figure also does not include the SSR transponder in the aircraft. In this safety case, an operational availability requirement similar to the Monopulse SSR radar will be specified for the ADS-B based surveillance system. An operational availability of 0.9995 will be required for the ADS-B ground station. A comparative end to end operational availability requirement prediction for the ADS-B system will be conducted as part of the safety analysis. The UK NATS Risk Model will be used for classifying the likelihood, consequences and risk class associated with the hazards identified.
Conventional SSR (RSR) Monopulse SSR radar ADS-B based surveillance
radar using a 5NM separation system
standard
Position measurement by radar Position measurement by radar Position measurement by avionics
Reporting rate of once every 12 Reporting rate of once every Broadcast rate of every sec with
seconds (rotation rate of 5 rpm) 3.64 seconds (rotation rate of controller update rate of once per
16.4 rpm) 5 seconds
Controller update rate of once
per 5 seconds is used
Accuracy performance of + or – Non manoeuvre accuracy Accuracy performance equal to or
0.77 NM at 3 sigma @ 160NM performance of + or – 0.65 NM better than 0.46 NM at 3 sigma
range at 3 sigma at 250 NM range for NUC level 5 and above. TSO
equipment will flag loss of
accuracy or integrity
Azimuth resolution performance Azimuth resolution Azimuth resolution problem does
: 2 aircraft separated by 12.6 performance : 2 aircraft not exist. Aircraft at same location
NM @ 160 NM range can’t be separated by 4 NM @ 250 NM can be resolved.
resolved range can’t be resolved
Reliability and Availability Reliability and Availability Reliability and Availability
performance for radar and performance for radar and performance based on modern
transponder based on 1960’s transponder based on 1990’s electronics components with no
technology with mechanical and technology with mechanical mechanical and rotating
rotating components. and rotating components. components.
TABLE 1 – Comparison of ADS-B and SSR Radar used by one State
Operational Use of ADS-B In Non Radar Airspace Generic Design Safety Case
A detailed comparison is provided in the working paper in Appendix 1. This working paper is subject to change as more information is obtained, catalogued and assessed.
5.2 Hazard Identification
Hazard The safety requirements associated with the operational use of ADS-B Identification based surveillance system for non-radar airspace were derived from the
hazard identification processes undertaken by some States already implementing ADS-B systems. These processes included Functional Hazard Assessment (FHA) based on a structured brain storming exercise by a group of experienced senior operational controllers and system engineers. The hazards and the associated safety requirements detailed at Appendix 2 are included for ongoing review by SASP as part of their work in developing safety assessments for introduction of ADS-B separation minima. The hazard identification process will continue through the panels development work and is intended to permit the capture of additional hazards identified by SASP.
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