Fine Resolution Errors in Secondary Surveillance Radar Altitude Reporting
ROYAL SIGNALS AND RADAR ESTABLISHMENT MALVERN (UNITED KINGDOM)
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The reliability of aircraft pressure altitude information telemetered via Secondary Surveillance Radar SSR links has come under considerable scrutiny recently following proposals for the implementation of Airborne Collision Avoidance Systems such as TCAS II and similar ground based systems. Certain persistent faults in the SSR pressure altitude replies, known to have deleterious effects on the functioning of TCAS II, have been traced to malfunctions in the three C bits used to encode the fine resolution part of the SSR pressure altitude verification procedures. C bit faults have therefore been investigated for aircraft using UK airspace and transmitting SSR Mode A identification Codes other than the Conspicuity Code 4321 and 4322. Of 132,773 aircraft trajectories investigated, 581 trajectories, involving at least 68 aircraft, were found to exhibit a C bit fault, a frequency of occurrence of 0. 44 Great Britain.
- Military Aircraft Operations
- Active and Passive Radar Detection and Equipment