Narrative:

I was the r-side working sector 30/33 combined. I descended aircraft X to FL330. Aircraft X read back what I thought was fl 330; and then aircraft X asked if that was 'pilot discretion.' I said 'negative'; but did not restate the altitude because I thought the read back was correct. Aircraft X then reported leaving FL350 for FL230. I heard FL330. I put aircraft X on ZLA's frequency. Aircraft X was descended to FL330 for procedures going into ZLA. I was working 11 aircrafts in the sector to the north of this incident. I had a d-side. I did observe aircraft X at FL330 just before crossing the ZLA boundary. It would have showed this for about 600 feet while descending. At the ZLA boundary the conflict alert (ca) activated between aircraft X and aircraft Y; northwest bound at FL320. I made a comment to my d-side questioning if maybe I issued FL310 instead of FL330. My d-side thought that we issued the correct altitude. It appeared that ZLA turned aircraft X to the east; but it was a small turn.my 1st mistake was not hearing the readback. My 2nd mistake was not reissuing FL330 after the pilot asked for 'pilot's discretion.' it did cross my mind. I missed the 2nd read back; also. I should have called in sick. I don't hear as well as I used to and don't deal with distractions as well; either. The new control rooms for display system replacement (dsr) are very noisy compared to the old main display monitor (mdm) control room. I transferred to ZOA just over 2 years ago. The dsr control room in ZOA is designed differently than the dsr control room in ZLC. The 4 most used sectors are all up against the wall. When training; there can be as many as 16 people in that small area. I mentioned this in a previous report. You can hear every clearance and conversation. It is very noisy for an old controller. Also; we have had radio problems with the MVA; specific transmitter site location; transmitter for days. The radios are not very clear. It sounds much clearer when listening to the playback than at the sector. I had 2 breaks early in the shift; but did not eat anything because I thought I would get another break soon. That was a mistake because I was feeling weak and unreadable towards the end of that session. We were on the southeast plan for bay area arrivals and almost every aircraft needed to be re-cleared via a new arrival. We also had some complex traffic situations earlier and I was feeling tired. This is not an excuse. I think it is time to retire.

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Original NASA ASRS Text

Title: ZOA Controller describes a read back hear back issue resulting in an aircraft descending lower than the Controller wanted. Controller complains about the noise level in the control room as a distraction. Descending aircraft was traffic for another aircraft 1000 feet below what controllers thought was the altitude assigned; resulting in a loss of separation.

Narrative: I was the R-side working sector 30/33 combined. I descended Aircraft X to FL330. Aircraft X read back what I thought was FL 330; and then Aircraft X asked if that was 'Pilot discretion.' I said 'Negative'; but did not restate the altitude because I thought the read back was correct. Aircraft X then reported leaving FL350 for FL230. I heard FL330. I put Aircraft X on ZLA's frequency. Aircraft X was descended to FL330 for procedures going into ZLA. I was working 11 aircrafts in the sector to the north of this incident. I had a D-side. I did observe Aircraft X at FL330 just before crossing the ZLA boundary. It would have showed this for about 600 feet while descending. At the ZLA boundary the Conflict Alert (CA) activated between Aircraft X and Aircraft Y; northwest bound at FL320. I made a comment to my D-side questioning if maybe I issued FL310 instead of FL330. My D-side thought that we issued the correct altitude. It appeared that ZLA turned Aircraft X to the east; but it was a small turn.My 1st mistake was not hearing the readback. My 2nd mistake was not reissuing FL330 after the pilot asked for 'Pilot's discretion.' It did cross my mind. I missed the 2nd read back; also. I should have called in sick. I don't hear as well as I used to and don't deal with distractions as well; either. The new control rooms for Display System Replacement (DSR) are very noisy compared to the old Main Display Monitor (MDM) control room. I transferred to ZOA just over 2 years ago. The DSR control room in ZOA is designed differently than the DSR control room in ZLC. The 4 most used sectors are all up against the wall. When training; there can be as many as 16 people in that small area. I mentioned this in a previous report. You can hear every clearance and conversation. It is very noisy for an old controller. Also; we have had radio problems with the MVA; specific transmitter site location; transmitter for days. The radios are not very clear. It sounds much clearer when listening to the playback than at the sector. I had 2 breaks early in the shift; but did not eat anything because I thought I would get another break soon. That was a mistake because I was feeling weak and unreadable towards the end of that session. We were on the southeast plan for bay area arrivals and almost every aircraft needed to be re-cleared via a new arrival. We also had some complex traffic situations earlier and I was feeling tired. This is not an excuse. I think it is time to retire.

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.