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Summary

Summary

Circumstances The B737 was operating on airway B580 and had passed waypoint URGUS at 1234 EST maintaining FL350 and was estimating waypoint MULID at 1322. Flight plan estimates indicated that the B737 would cross airway A464 at approximately 1343 and the next waypoint APORA at 1424. The B74F was operating on airway A464 and had passed waypoint RELIK at 1251 maintaining FL350 and was estimating over Lord Howe Island at 1323. Flight plan estimates indicated that the B74F would cross airway B580 at approximately 1331 and the next waypoint UDIKO at 1401. At approximately 1254, Brisbane oceanic control sector 8 (Sect 8) relayed a level change requirement instruction through Sydney Flight Service International (FS INT) for the B737 to descend from FL350 to FL330. The instruction was intended to provide separation assurance between the B737 and the B747F. The level change requirement was notated on the correct flight progress strip, but entered in an incorrect information box relating to waypoint URGUS, the waypoint just passed. The FS INT officer was provided with a temporary relief break at approximately 1310. The level change requirement had still neither been passed to the B737 nor been included in the handover/takeover to the relieving officer. At approximately 1328, the relieving FS INT provided Sect 8 with reports for the B737 passing MULID and the B74F passing Lord Howe Island. Both aircraft were still maintaining FL350. Sector 8 realised that the aircraft level change instruction had not been issued and that lateral separation standards had been infringed. Due to the prevailing poor communications propagation conditions, FS INT was unable to re-establish contact with the B737 until approximately 1336. The B737 then descended to FL330 and crossed airway A464 approximately seven minutes later. Although the prescribed separation standards were not maintained, there was no risk of collision. No new safety deficiencies were identified during this investigation.
 
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