Date: 201202
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Government
Reporter function: Supervisor / CIC
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown
Second reporter function: Enroute
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Overshoot; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic
Contributing factors: Procedure; Human Factors
Primary problem: Human Factors

Narrative: We owned FL240-FL350 at X/Y Sector. We handed off a DC10 level at FL340. A B737 appeared on our scope descending out of FL355 when conflict alert went off with the B737 and the DC10. We were not talking to either aircraft nor had we released control on the B737. I learned later that the sector above us had cleared the B737 to cross a point at FL360; and the pilot acknowledged the correct altitude; FL360. When the B737 checked on to the next frequency; however; he stated he was descending to FL340 instead of FL360. The Controller missed that read back. That Controller only recently became a CPC and inexperience may have been a factor. I attempted to call the sector who was talking to the B737 but the call seemed to be more of a distraction than a help so I hung up. The aircraft were about 2-3 miles apart at the same altitude. Vectors were issued to separate the aircraft. A supervisor in the area where the B737 checked on was visually watching the sector; and quickly questioned the Controller about the B737 and his altitude change from FL360; but the Controller did not respond quickly enough to the supervisor's comments to insure separation. Recommendation; no changes are needed to procedures; unless you can make DATA COMM available soon. That would have prevented it by forcing the pilot to input the correct altitude from an ACARS message; and not memory. The B737 pilot reported that he had input FL340 into the FMS because when he responded to the original crossing restriction clearance; he said; 'Cross 50 miles east of ZZZZZ at and maintain FL360; the B737.' Saying the B737 caused the pilot to input FL340; not FL360. DATA COMM would probably prevent an issue just like this. Also; the Controller who heard the check in of the B737 was barely into his CPC status; and he just didn't hear the error. He has not learned to be vigilant at all times; regardless of traffic level. Also; the new Controller needs to be more responsive to other people's questions about what is happening; both the supervisor and the D-Side at the sector; who was also trying to help.


Second narrative: A B737 received a crossing to cross 65 NM east of ZZZZZ Intersection at and maintain FL360. The B737 read the crossing back correctly. The B737 checked in with the next sector 'passing FL360 for FL340.' Moderate level of complexity and volume at the time; and the next sector missed the incorrect check on. A DC10 was southwest bound 3 NM southeast of the B737 at FL340. Conflict Alert was activated and the B737 was asked to confirm level at FL360. The B737 responded negative. The B737 was then issued a right turn to 300 heading. The DC10 checked on FL340 was turned 20 left. Traffic was then issued to both aircraft. Recommendation; always remain diligent. This was a standard crossing to give. Do not expect to hear the correct read back.


Synopsis: Enroute controllers and flight crew describe a conflict event in which an ATC issued crossing restriction was not achieved. The reporters provided multiple perspectives on the circumstances experienced.