A center controller reported an aircraft misunderstood their traffic information; possibly due to po...

Narrative:

Aircraft X was climbing. I had to stop the aircraft at 26;000 ft. For traffic at 27;000 ft. When cleared; I climbed aircraft X to 28;000 ft. Because of aircraft Y at 29;000 ft. Passing overhead. A few minutes later; aircraft X reported an RA. I informed pilot that traffic was passing to the west 1;000 ft. Above. Pilot respondent 'roger; leaving FL280 for FL380.' I replied 'negative; maintain FL280. FL280 was your assigned altitude'. At this time; aircraft Y informed me that they were responding to an RA also. I never observed aircraft Y change altitude nor aircraft X above 28;100 ft. The aircraft passed 2 miles abreast. Listening to the tape later; my clearance could have been garbled but the pilot read back FL380.in my opinion; fatigue and frequency issues could be a contributing factor. As far as fatigue; I have worked 28 days of overtime in the last 36 weeks; with 6 scheduled for the next 6 weeks. I am lower in hours than most on the overtime list and we are not even into the high leave part of the year. After 31 years of a 2-2-1 schedule; I can cope with the ups and downs of that; but throw in a random shift on my weekend; never knowing which day or which shift; it make rest hard. With our staffing levels it appears this will continue for the foreseeable future. Add in home life; and now the stress of having to work and not getting paid and my anxiety levels are at a peak. The burn-out factor and negativity is high; and I feel I speak for a lot of controllers here.as far as frequencies; they have been problematic for quite some time. Not as clear as they used to be; static on both the pilots side and ours; over all weak; with no clear plan for a fix. The soc will change telephone company paths and it may clear them up momentarily but it is no true fix. The feeling around the control room is that no feels frequencies are a priority. We can't do our job without them. They are as important as the radar. I can't say any of these thing were truly contributory to this incident; but I also can't say they weren't.need to listen more closely to read backs. Increase staffing. Clean up frequencies. Get the government opened back up.

Original NASA ASRS Text

Title: A Center Controller reported an aircraft misunderstood their traffic information; possibly due to poor radio coverage; and climbed above their assigned altitude into confliction with converging traffic.

Narrative: Aircraft X was climbing. I had to stop the aircraft at 26;000 ft. for traffic at 27;000 ft. When cleared; I climbed Aircraft X to 28;000 ft. because of Aircraft Y at 29;000 ft. passing overhead. A few minutes later; Aircraft X reported an RA. I informed pilot that traffic was passing to the west 1;000 ft. above. Pilot respondent 'ROGER; leaving FL280 for FL380.' I replied 'Negative; maintain FL280. FL280 was your assigned altitude'. At this time; Aircraft Y informed me that they were responding to an RA also. I never observed Aircraft Y change altitude nor Aircraft X above 28;100 ft. The aircraft passed 2 miles abreast. Listening to the tape later; my clearance could have been garbled but the pilot read back FL380.In my opinion; fatigue and frequency issues could be a contributing factor. As far as fatigue; I have worked 28 days of overtime in the last 36 weeks; with 6 scheduled for the next 6 weeks. I am lower in hours than most on the overtime list and we are not even into the high leave part of the year. After 31 years of a 2-2-1 schedule; I can cope with the ups and downs of that; but throw in a random shift on my weekend; never knowing which day or which shift; it make rest hard. With our staffing levels it appears this will continue for the foreseeable future. Add in home life; and now the stress of having to work and not getting paid and my anxiety levels are at a peak. The burn-out factor and negativity is high; and I feel I speak for a lot of controllers here.As far as frequencies; they have been problematic for quite some time. Not as clear as they used to be; static on both the pilots side and ours; over all weak; with no clear plan for a fix. The SOC will change TELCO paths and it may clear them up momentarily but it is no true fix. The feeling around the control room is that no feels frequencies are a priority. We can't do our job without them. They are as important as the RADAR. I can't say any of these thing were truly contributory to this incident; but I also can't say they weren't.Need to listen more closely to read backs. Increase staffing. Clean up frequencies. Get the Government opened back up.

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	1611932
Time
Date	201901
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Gulfstream G650
Operating Under FAR Part	Part 135
Flight Phase	Climb
Route In Use	Direct
Flight Plan	IFR
Aircraft 2
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 26
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance

A center controller reported an aircraft misunderstood their traffic information; possibly due to poor radio coverage; and climbed above their assigned altitude into confliction with converging traffic.