ZNY center oceanic controller reported they had less than required separation between two aircraft o...

Narrative:

Sector 81 called to coordinate aircraft X with myself at sector 89. Coordination was probed and accepted without conflict for aircraft X at FL360. [Five minutes later] a red conflict began flashing between aircraft Y at 36;000 feet northbound on the airway and aircraft X. I called sector 81 to re-coordinate aircraft X at a different altitude. When I initially probed the aircraft at 36;000 feet; the probe in the coordination window for aircraft X still showed no conflicts despite the data blocks flashing red conflict and a conflict window. Despite the coordination window showing no conflict; I re-coordinated aircraft X at 37;000 feet.sector 81 called with an altitude revision for aircraft X. The aircraft was requesting 38;000 feet so I opened the coordination window; probed the aircraft at 38;000 feet which probed with no conflict so the aircraft was accepted at 38;000 feet. Sector 81 called for aircraft X requesting direct to either gratx or lfano due to weather. Because the aircraft was approaching the boundary; I assumed the aircraft to probe the change in profiled route. Upon assuming the aircraft; a conflict appeared between aircraft X and aircraft Z. Aircraft Z was flying northbound on the airway at 38;000 feet.the conflict window showed 9 minutes and 23 seconds on the cross with 15 minutes needed for required minimum separation. At that point; I told sector 81 the aircraft needs to descend or climb 1;000 feet. Sector 81 immediately descended the aircraft to 37;000 feet and I advised them that direct to lfano was approved. I completed updating the aircraft's profile and completed tasks and took a break. At some point before my break; I measured the two aircraft using the tool in advanced technologies and oceanic procedures (atop) and it showed 35 miles; however they were separated by 1;000 feet at that point and I don't know the closest point in mileage the aircraft got. A [report] is also being filed and the supervisor was notified.it appears as though there is an issue with atop in recognizing conflicts. This is a serious issue that needs to be remedied immediately. If this isn't a system issue and atop is working as designed; a briefing for all controllers needs to occur to explain what happened and how to avoid this.

Original NASA ASRS Text

Title: ZNY Center Oceanic Controller reported they had less than required separation between two aircraft on crossing courses even though the ATOP tool did not identify a separation problem.

Narrative: Sector 81 called to coordinate Aircraft X with myself at sector 89. Coordination was probed and accepted without conflict for Aircraft X at FL360. [Five minutes later] a red conflict began flashing between Aircraft Y at 36;000 feet northbound on the airway and Aircraft X. I called sector 81 to re-coordinate Aircraft X at a different altitude. When I initially probed the aircraft at 36;000 feet; the probe in the coordination window for Aircraft X still showed no conflicts despite the data blocks flashing red conflict and a conflict window. Despite the coordination window showing no conflict; I re-coordinated Aircraft X at 37;000 feet.Sector 81 called with an altitude revision for Aircraft X. The aircraft was requesting 38;000 feet so I opened the coordination window; probed the aircraft at 38;000 feet which probed with no conflict so the aircraft was accepted at 38;000 feet. Sector 81 called for Aircraft X requesting direct to either GRATX or LFANO due to weather. Because the aircraft was approaching the boundary; I assumed the aircraft to probe the change in profiled route. Upon assuming the aircraft; a conflict appeared between Aircraft X and Aircraft Z. Aircraft Z was flying northbound on the airway at 38;000 feet.The conflict window showed 9 minutes and 23 seconds on the cross with 15 minutes needed for required minimum separation. At that point; I told sector 81 the aircraft needs to descend or climb 1;000 feet. Sector 81 immediately descended the aircraft to 37;000 feet and I advised them that direct to LFANO was approved. I completed updating the aircraft's profile and completed tasks and took a break. At some point before my break; I measured the two aircraft using the tool in Advanced Technologies and Oceanic Procedures (ATOP) and it showed 35 miles; however they were separated by 1;000 feet at that point and I don't know the closest point in mileage the aircraft got. A [report] is also being filed and the supervisor was notified.It appears as though there is an issue with ATOP in recognizing conflicts. This is a serious issue that needs to be remedied immediately. If this isn't a system issue and ATOP is working as designed; a briefing for all controllers needs to occur to explain what happened and how to avoid this.

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.

Attributes
ACN	1476381
Time
Date	201708
Local Time Of Day	1201-1800
Place
Locale Reference	ZNY.ARTCC
State Reference	NY
Environment
Flight Conditions	Marginal
Aircraft 1
Make Model Name	B777 Undifferentiated or Other Model
Operating Under FAR Part	Part 129
Flight Phase	Cruise
Route In Use	Airway L456
Flight Plan	IFR
Aircraft 2
Make Model Name	A321
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Person 1
Function	Enroute Oceanic
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 2.75
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy

ZNY center oceanic controller reported they had less than required separation between two aircraft on crossing courses even though the atop tool did not identify a separation problem.