ZOA developmental controller experienced operational error at FL340 with a descending and climbing aircraft caused by a missed incorrect readback error.

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Attributes
ACN	680864
Time
Date	200511
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zoa.artcc
State Reference	CA
Altitude	msl bound lower : 33800 msl bound upper : 34000
Aircraft 1
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	Regional Jet CL65 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	arrival star : modz
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	Cessna Citation Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar instruction : trainee
Qualification	controller : developmental
Experience	controller radar : 4
ASRS Report	680864
Person 2
Function	controller : radar instruction : instructor
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	atc equipment : conflict alert other controllera
Resolutory Action	controller : issued new clearance controller : issued alert flight crew : took evasive action
Consequence	other
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

During a training session; I had an operational error. I had an air carrier X inbound to sfo on the MOD2 arrival from the east level at FL380. A citation departed rno sbound; I think it was air carrier Y climbing to FL330. I issued a descent to air carrier X to maintain FL340. I heard the pilot read back FL340; but the tapes indicate otherwise. The beginning of the pilot readback was sort of clipped; but he really read back descending to FL240. The air carrier X and air carrier Y aircraft were converging; so I issued merging target procedures to both aircraft and both pilots acknowledged. After that; conflict alert activated and I observed air carrier X altitude at FL338; when I assumed he was stopping at FL340. Meanwhile; air carrier Y was level at FL330 with a j-ring around the target. My trainer took action to turn air carrier X; however; separation was lost. I am unsure of exact details because I never saw an official report with exact information; which is why this report is vague.

Original NASA ASRS Text

Title: ZOA DEVELOPMENTAL CTLR EXPERIENCED OPERROR AT FL340 WITH A DSNDING AND CLBING ACFT CAUSED BY A MISSED INCORRECT READBACK ERROR.

Narrative: DURING A TRAINING SESSION; I HAD AN OPERROR. I HAD AN ACR X INBOUND TO SFO ON THE MOD2 ARR FROM THE E LEVEL AT FL380. A CITATION DEPARTED RNO SBOUND; I THINK IT WAS ACR Y CLBING TO FL330. I ISSUED A DSCNT TO ACR X TO MAINTAIN FL340. I HEARD THE PLT READ BACK FL340; BUT THE TAPES INDICATE OTHERWISE. THE BEGINNING OF THE PLT READBACK WAS SORT OF CLIPPED; BUT HE REALLY READ BACK DSNDING TO FL240. THE ACR X AND ACR Y ACFT WERE CONVERGING; SO I ISSUED MERGING TARGET PROCS TO BOTH ACFT AND BOTH PLTS ACKNOWLEDGED. AFTER THAT; CONFLICT ALERT ACTIVATED AND I OBSERVED ACR X ALT AT FL338; WHEN I ASSUMED HE WAS STOPPING AT FL340. MEANWHILE; ACR Y WAS LEVEL AT FL330 WITH A J-RING AROUND THE TARGET. MY TRAINER TOOK ACTION TO TURN ACR X; HOWEVER; SEPARATION WAS LOST. I AM UNSURE OF EXACT DETAILS BECAUSE I NEVER SAW AN OFFICIAL RPT WITH EXACT INFO; WHICH IS WHY THIS RPT IS VAGUE.

Data retrieved from NASA's ASRS site as of January 2009 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.