Note : This requirement is equivalent to the GPS horizontal protection limit of 0.5 Nm. This is equivalent to a 95 percentile of reports within 0.25 Nm (similar to radar).
e. External interference issues
With Mode S based ADS-B external interference is identical to radar because the same frequency is used. However a radar is able to sometimes restrict the interference to a single azimuth for example when the radar is pointing towards the interference source. On the other hand ADS-B receivers only need a single message to break through any interference for valid data to be received, whereas radar requires coherence from interrogation to interrogation and normally from antenna scan to antenna scan. The impact of interference on the application of separation standards is probably more related to a question of system reliability : ie either radar or ADS-B could fail at any time due to interference.
f. Positional data source – nav system or stand alone position
APPENDIX 2
HAZARD LOG
Hazards
Project ICAO SASPOperational Use of ADS-B in Non Radar Airspace
Hazard No. 1 Failure of ADS-B transponder on the aircraft
Generic Description
Failure of ADS-B transponder on the aircraft cause a loss of ADS-B message to the ground station
Hazard Cause/Initiating Events
Increase in controller workload due to requirement to revert back to procedural control and reassess traffic.
Initial Risk Residual
Risk
Likelihood Remote Remote
Consequence Cat 3 Cat 3
Risk D D
Existing Mitigation
Safety Requirement Details
ADS-B Transponder Ensure ADS-B transponder in the aircraft Reliability Spec has reliability requirement equivalent to existing Mode A/C transponder
ADS-B Fallback Validated and published instructions procedure for reverting back to procedural control
Transition Process for Training and lesson plans to adequately ADS-B Failure cover the transition process and procedures from ADS-B control to procedural control
Project ICAO SASPOperational Use of ADS-B in Non Radar Airspace
Hazard No. 2 Failure of ADS-B ground station Generic Description Failure of ADS-B ground station
Hazard Cause/Initiating Events Loss of ADS-B positional data to the controller. Increase in workload due to transitioning period back to procedural control and reassess traffic.
Initial Risk Residual
Risk
Likelihood Remote Remote
Consequence Cat 3 Cat 3
Risk D D
Existing Mitigation
Safety Requirement Details
ADS-B Ground System Allocate an availability requirement of Availability 0.9995 to the ADS-B ground station sub Specification
Monitoring of ADS-B Monitoring of health status of ADS-B ground Ground Station stations at a remote central position
Transition Process for Training and lesson plans to adequately ADS-B Failure cover the transition process and procedures from ADS-B control to procedural control
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