A B757 flight crew and ZKC have confusion as to what the altitude assignment was.

Attributes
ACN	526480
Time
Date	200110
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : enl.vortac
State Reference	IL
Altitude	msl bound lower : 34000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B757-200
Flight Phase	descent : intermediate altitude descent : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 110 flight time total : 4000 flight time type : 110
ASRS Report	526480
Events
Anomaly	other anomaly other other spatial deviation
Resolutory Action	controller : issued new clearance flight crew : returned to assigned altitude
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Ambiguous

Narrative:

ATC cleared flight from FL370 to 340, captain read back FL370 for FL340. Upon reaching level flight at FL340 ATC instructed us to climb and maintain FL350. First officer read back 'out of FL340 for FL350' and captain flew back to FL350. Captain asked ATC if there was a problem. ATC responded, 'no, I thought I gave you FL350.' captain responded 'I read back out of FL370 for FL340.' ATC indicated no conflict and flight proceeded at FL350. Prior to event first officer stepped out of cockpit to use lavatory and missed call from ATC to descend. Reentered cockpit just prior to leveloff and commented that it was strange to receive an even flight level from ATC.

Original NASA ASRS Text

Title: A B757 FLT CREW AND ZKC HAVE CONFUSION AS TO WHAT THE ALT ASSIGNMENT WAS.

Narrative: ATC CLRED FLT FROM FL370 TO 340, CAPT READ BACK FL370 FOR FL340. UPON REACHING LEVEL FLT AT FL340 ATC INSTRUCTED US TO CLB AND MAINTAIN FL350. FO READ BACK 'OUT OF FL340 FOR FL350' AND CAPT FLEW BACK TO FL350. CAPT ASKED ATC IF THERE WAS A PROB. ATC RESPONDED, 'NO, I THOUGHT I GAVE YOU FL350.' CAPT RESPONDED 'I READ BACK OUT OF FL370 FOR FL340.' ATC INDICATED NO CONFLICT AND FLT PROCEEDED AT FL350. PRIOR TO EVENT FO STEPPED OUT OF COCKPIT TO USE LAVATORY AND MISSED CALL FROM ATC TO DSND. REENTERED COCKPIT JUST PRIOR TO LEVELOFF AND COMMENTED THAT IT WAS STRANGE TO RECEIVE AN EVEN FLT LEVEL FROM ATC.

Data retrieved from NASA's ASRS site as of July 2007 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.