Narrative:

Aircraft X was in level flight and lost cabin pressure and started a descent out of 24;000 feet without clearance. Aircraft Y was leaving 15;000 feet when aircraft X began his descent. I was the radar assistant during this event. The radar controller stopped aircraft Y at 18;000 feet and then issued aircraft X 19;000 feet. I coordinated with [the adjacent center] and sector and informed them we were turning aircraft Y to the right to accommodate aircraft X who needed a lower altitude. The radar controller turned aircraft Y to a heading of 240 degrees and the pilot turned to a heading of 140 degrees. We later learned that aircraft Y misheard the clearance when he turned to a 140 heading. At this time I coordinated with TRACON and requested 10;000 feet and informed them of the situation. While on the line; aircraft X was just nearing 19;000 feet and requested 10;000 feet again. The radar controller issued 10;000 feet. At this time we noticed aircraft Y had made a left turn (he heard heading 140 instead of 240) and the radar controller issued aircraft Y the descending traffic and instructed him to turn to a 220 degree heading for the traffic. Aircraft Y said he's making the turn now as aircraft X said he has the traffic in sight.when aircraft X requested lower than 19;000 feet we should have issued the traffic. In my opinion this would not have prevented the event because aircraft X needed to continue descending; but the aircraft would not have been as close especially considering aircraft Y turned to an incorrect heading.

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Original NASA ASRS Text

Title: An aircraft was making an emergency descent. ATC issued a heading to opposite direction climbing traffic to avoid the descending traffic. The climbing traffic turned to the wrong heading causing a conflict with the emergency descending traffic.

Narrative: Aircraft X was in level flight and lost cabin pressure and started a descent out of 24;000 feet without clearance. Aircraft Y was leaving 15;000 feet when Aircraft X began his descent. I was the Radar Assistant during this event. The Radar Controller stopped aircraft Y at 18;000 feet and then issued aircraft X 19;000 feet. I coordinated with [the adjacent Center] and sector and informed them we were turning aircraft Y to the right to accommodate aircraft X who needed a lower altitude. The Radar Controller turned aircraft Y to a heading of 240 degrees and the pilot turned to a heading of 140 degrees. We later learned that aircraft Y misheard the clearance when he turned to a 140 heading. At this time I coordinated with TRACON and requested 10;000 feet and informed them of the situation. While on the line; aircraft X was just nearing 19;000 feet and requested 10;000 feet again. The Radar Controller issued 10;000 feet. At this time we noticed aircraft Y had made a left turn (he heard heading 140 instead of 240) and the Radar Controller issued aircraft Y the descending traffic and instructed him to turn to a 220 degree heading for the traffic. Aircraft Y said he's making the turn now as aircraft X said he has the traffic in sight.When aircraft X requested lower than 19;000 feet we should have issued the traffic. In my opinion this would not have prevented the event because aircraft X needed to continue descending; but the aircraft would not have been as close especially considering aircraft Y turned to an incorrect heading.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.