ARTCC controller and small transport pilot misunderstanding about clearance altitude.

Attributes
ACN	130752
Time
Date	198912
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : eat
State Reference	WA
Altitude	msl bound lower : 11000 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : mdw
Operator	common carrier : air taxi
Make Model Name	Small Transport
Flight Phase	climbout : intermediate altitude
Route In Use	enroute airway : v25
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 150 flight time total : 4400
ASRS Report	130752
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	other

Narrative:

I departed eat, flew the IFR departure procedure and contacted ZSE passing 5000'. Upon contacting center I was told to maintain 9000' and leveled at 9000'. I was then assigned 12000', as far as I can remember, but it may have been 11000'. As I was beginning to level at 12000', the center controller requested that I confirm my altitude. I replied that I had been cleared to 12000'. He then replied that I had only been cleared to 11000'. I then responded that I would be level 11000' momentarily, descended to 11000' and continued at that altitude. Nothing else was mentioned about the incident.

Original NASA ASRS Text

Title: ARTCC CTLR AND SMT PLT MISUNDERSTANDING ABOUT CLRNC ALT.

Narrative: I DEPARTED EAT, FLEW THE IFR DEP PROC AND CONTACTED ZSE PASSING 5000'. UPON CONTACTING CENTER I WAS TOLD TO MAINTAIN 9000' AND LEVELED AT 9000'. I WAS THEN ASSIGNED 12000', AS FAR AS I CAN REMEMBER, BUT IT MAY HAVE BEEN 11000'. AS I WAS BEGINNING TO LEVEL AT 12000', THE CENTER CTLR REQUESTED THAT I CONFIRM MY ALT. I REPLIED THAT I HAD BEEN CLRED TO 12000'. HE THEN REPLIED THAT I HAD ONLY BEEN CLRED TO 11000'. I THEN RESPONDED THAT I WOULD BE LEVEL 11000' MOMENTARILY, DSNDED TO 11000' AND CONTINUED AT THAT ALT. NOTHING ELSE WAS MENTIONED ABOUT THE INCIDENT.

Data retrieved from NASA's ASRS site as of August 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.