ZSE center controller reported missing an initial call where the pilot reported descending to an alt...

Attributes
ACN	1470494
Time
Date	201708
Local Time Of Day	0001-0600
Place
Locale Reference	ZSE.ARTCC
State Reference	WA
Aircraft 1
Make Model Name	A321
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Aircraft 2
Make Model Name	Medium Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 3
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

Narrative:

I was working R31 and it started to get busy. Fellow controllers noticed I was getting busy and told a certified professional controller who was working D32 to go get D31; because the supervisor was not around. Aircraft X had FL280 descending to FL250 in his data block when I took the handoff from R07 because he was above aircraft Y who was level at FL240. When the aircraft X checked on; I did not hear him say that he was profile descent (pd) to FL240. I noticed when aircraft X was at FL247 two miles in front of aircraft Y and I told him to maintain FL250. He said he would climb back up and the data block showed he was at FL243 before he climbed back to FL250. Upon listening to the tapes; I realized he did in fact say he was pd to FL240. When I listened to the R07 controller; he had issued a pd descent to FL250 and the pilot read back FL240. Hearback/readback error should have been caught both times. Should have had a d-side earlier so I didn't get behind. Because I was trying to catch up and quickly move from one task to another I missed the incorrect altitude on initial check on.

Original NASA ASRS Text

Title: ZSE Center Controller reported missing an initial call where the pilot reported descending to an altitude which caused a loss of separation with another aircraft.

Narrative: I was working R31 and it started to get busy. Fellow controllers noticed I was getting busy and told a Certified Professional Controller who was working D32 to go get D31; because the Supervisor was not around. Aircraft X had FL280 descending to FL250 in his data block when I took the handoff from R07 because he was above Aircraft Y who was level at FL240. When the Aircraft X checked on; I did not hear him say that he was Profile Descent (PD) to FL240. I noticed when Aircraft X was at FL247 two miles in front of Aircraft Y and I told him to maintain FL250. He said he would climb back up and the data block showed he was at FL243 before he climbed back to FL250. Upon listening to the tapes; I realized he did in fact say he was PD to FL240. When I listened to the R07 controller; he had issued a PD descent to FL250 and the pilot read back FL240. Hearback/Readback error should have been caught both times. Should have had a D-side earlier so I didn't get behind. Because I was trying to catch up and quickly move from one task to another I missed the incorrect altitude on initial check on.

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.

ZSE center controller reported missing an initial call where the pilot reported descending to an altitude which caused a loss of separation with another aircraft.