Narrative:

While working sectors xx/yy/zz/ww combined; an A330 was at FL320 and requested a climb to FL340. He was cruising at M0.81 and had an aircraft 8 minutes ahead of him at FL330 cruising at M0.79. I advised the A330 that I was unable higher due to traffic; however; I advised the A330 that higher would be available with a climb at M0.76 to resume M0.81 upon reaching FL340. An A330 acknowledged that advisory but did not request the advised climb. Six minutes later; the A330 then requested to know when to expect a higher altitude. I advised the A330 that he had traffic one thousand feet above him that is M0.03 slower than him and at M0.76 he could climb to FL340 now; otherwise I could offer a reroute. The A330 acknowledged the advisory. And immediately after acknowledging the advisory sent a transmission that he was climbing to FL340. I demanded his ads; his altitude indicated that he was in a climb for FL340; and a trail probe went off with the aircraft in front of him at FL330. He sent a transmission indicating he was leveling at FL340; and I advised him that I had not sent a clearance to him and cleared him to maintain FL340. I believe the situation could have been avoided had I not used the words 'you can climb now' when answering his question as to when he can expect a higher altitude. I believe the language barrier had something to do with it. Also; the A330 should have verified if I had sent him a clearance or not; and waited until I sent an actual clearance to FL340. I would recommend being more clear and concise when dealing with foreign language speaking pilots.

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Original NASA ASRS Text

Title: Enroute Controller working non-RADAR oceanic traffic described an unauthorized climb through occupied airspace; the reporter acknowledging using less than clear and concise phraseology with this international flight crew.

Narrative: While working Sectors XX/YY/ZZ/WW combined; an A330 was at FL320 and requested a climb to FL340. He was cruising at M0.81 and had an aircraft 8 minutes ahead of him at FL330 cruising at M0.79. I advised the A330 that I was unable higher due to traffic; however; I advised the A330 that higher would be available with a climb at M0.76 to resume M0.81 upon reaching FL340. An A330 acknowledged that advisory but did not request the advised climb. Six minutes later; the A330 then requested to know when to expect a higher altitude. I advised the A330 that he had traffic one thousand feet above him that is M0.03 slower than him and at M0.76 he could climb to FL340 now; otherwise I could offer a reroute. The A330 acknowledged the advisory. And immediately after acknowledging the advisory sent a transmission that he was climbing to FL340. I demanded his ADS; his altitude indicated that he was in a climb for FL340; and a trail probe went off with the aircraft in front of him at FL330. He sent a transmission indicating he was leveling at FL340; and I advised him that I had not sent a clearance to him and cleared him to maintain FL340. I believe the situation could have been avoided had I not used the words 'you can climb now' when answering his question as to when he can expect a higher altitude. I believe the language barrier had something to do with it. Also; the A330 should have verified if I had sent him a clearance or not; and waited until I sent an actual clearance to FL340. I would recommend being more clear and concise when dealing with foreign language speaking pilots.

Data retrieved from NASA's ASRS site as of July 2013 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.