Traffic assigned FL350 continued the climb above the assigned altitude conflicting with other traffic. Several versions of the factors involved are provided in this combined ATC/flight crew report.
Synopsis
Traffic assigned FL350 continued the climb above the assigned altitude conflicting with other traffic. Several versions of the factors involved are provided in this combined ATC/flight crew report.
Narrative
I was working Sector 80. A CRJ checked on climbing to FL330. I had traffic at FL360; a B737; that I knew was a factor for the CRJ. At the lateral airspace boundary; per normal procedure; I climbed the CRJ to FL350. The pilot read back the altitude correctly. I was consciously attending to the altitude read back because I knew the traffic was a factor; they were red on URET; and I was kind of busy at the time. When the two were around 25 miles or so apart; I called the traffic. During my normal scan; I saw the CRJ was showing FL352 when they were nearly abeam the B737 and I asked the CRJ pilot their altitude; thinking it might have been a Mode C anomaly or sort box jump. The pilot said they were showing 300 FT high; apologized; and said they were correcting. I turned the CRJ 40 degrees left; told them to expedite. I turned the B737 20 degrees left in an attempt to keep some kind of separation. The Conflict Alert activated. The highest I saw the CRJ was FL355. I saw them go back down to FL350; then back up to FL351. Once I had them pried apart and back on course; I asked the CRJ what had happened. The pilot said that the altitude capture on the autopilot hadn't worked. They implied that it had failed twice.
Second reporter narrative
The event happened north of SSO VOR on climb out. ATC assigned and altitude of FL330 initially. Nearing FL330 ATC assigned a new altitude of FL350 and informed us of opposite direction traffic at FL360. I guess the Captain (flying pilot) heard FL360 but I read back 'climb and maintain FL350. The Captain put 36;000 in the altitude preselect I guess. I looked at the altitude on the primary flight display and verified 35;000; which was the correct assigned altitude. The reason for possible confusion on my part was the sun was hitting the co-pilots primary flight display and was also in the corner of my eye bothering me. It appeared to me that the altitude set was 35;000 not 36;000 in which a six and a five on a sunned out reflecting display looked very similar. After I verified the altitude I put up the sun visor to get the sun out of the corner of my eye. I then begin looking for the traffic outside and then turned my attention to the TCAS. I noticed that the traffic was 25 NM away and 1;000 FT above. I then looked at the altimeter and noticed that we were climbing through FL350. I told the Captain to stop the climb [and that] we were supposed to stop at FL350. It took the Captain a couple of seconds to realize what was going on before he disconnected the autopilot and nosed the aircraft forward. At the same time we got a TCAS advisory and ATC asked us what altitude we were at. We had climbed to 35;400 before arresting the climb. I told ATC the autopilot did not capture because I still thought that 35;000 was set in the altitude preselect. The other aircraft was still 10 NM away and to our right when recovered. I was also tired; not yet fatigued; on my sixth leg and over 11 hours of duty. Suggest verifying the altitude more carefully under those circumstances.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.