Loss of separation — two Saab 340s, Rex network

Summary

Two Rex Saab 340s operating on intersecting airways near Broken Hill lost radar separation when both descended to assigned altitudes simultaneously without ATC awareness. TCAS Resolution Advisories were triggered in both aircraft; both crews followed TCAS guidance and separation was restored. Minimum separation was estimated at 900 ft vertically and 3 nm laterally.

Investigation Findings (4)

1. 01An ATC computer system anomaly delayed the correlation of the two flight plans, resulting in simultaneous clearances to conflicting altitudes.
2. 02Both crews followed TCAS RAs correctly.
3. 03Airservices Australia modified the clearance-issuance logic to require a conflict alert check before altitude clearances on intersecting routes.
4. 04ATSB published a safety message on TCAS RA compliance.