Air carrier inadvertently climbed out of assigned altitude.

Attributes
ACN	80231
Time
Date	198801
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : elx
State Reference	MI
Altitude	msl bound lower : 33000 msl bound upper : 37000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau
Operator	common carrier : air carrier
Make Model Name	Heavy Transport, Low Wing, 4 Turbojet Eng
Flight Phase	climbout : intermediate altitude
Route In Use	enroute airway : zau
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 210 flight time total : 14000 flight time type : 6000
ASRS Report	80231
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : atp
Experience	flight time total : 22000
ASRS Report	80230
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were flying heavy transport X from ord and clrd to FL330 expecting clearance to FL370. At approximately FL320 we acknowledged a clearance to FL370. Approaching FL340 chi center asked us what our altitude was. We replied, 'FL340 climbing to FL370.' we were instructed to des to FL330 immediately. At approximately FL335 we were then clrd to FL370. Prior to this, in the early part of the climb, we told the center controller that his transmissions were not clear, like he was talking inside a barrel. Transmissions from other aircraft were clear. The controller tried other mics and transmitters with no improvement. In trying to assess the reason for the altitude clearance misunderstanding, we concluded that we had acknowledged an altitude clearance for another aircraft. Possibly that aircraft acknowledged the clearance at the same time we did, thus blocking center from hearing the mistake. Another factor was that we had just received a route change so both of us were somewhat engrossed in our maps when the altitude clearance was received. Supplemental information from acn 80230: 2 company flts in area with similar call signs were on frequency. We believe both trips read back clearance at same time smearing each other.

Original NASA ASRS Text

Title: ACR INADVERTENTLY CLIMBED OUT OF ASSIGNED ALT.

Narrative: WE WERE FLYING HVT X FROM ORD AND CLRD TO FL330 EXPECTING CLRNC TO FL370. AT APPROX FL320 WE ACKNOWLEDGED A CLRNC TO FL370. APCHING FL340 CHI CENTER ASKED US WHAT OUR ALT WAS. WE REPLIED, 'FL340 CLBING TO FL370.' WE WERE INSTRUCTED TO DES TO FL330 IMMEDIATELY. AT APPROX FL335 WE WERE THEN CLRD TO FL370. PRIOR TO THIS, IN THE EARLY PART OF THE CLB, WE TOLD THE CENTER CTLR THAT HIS TRANSMISSIONS WERE NOT CLEAR, LIKE HE WAS TALKING INSIDE A BARREL. TRANSMISSIONS FROM OTHER ACFT WERE CLEAR. THE CTLR TRIED OTHER MICS AND TRANSMITTERS WITH NO IMPROVEMENT. IN TRYING TO ASSESS THE REASON FOR THE ALT CLRNC MISUNDERSTANDING, WE CONCLUDED THAT WE HAD ACKNOWLEDGED AN ALT CLRNC FOR ANOTHER ACFT. POSSIBLY THAT ACFT ACKNOWLEDGED THE CLRNC AT THE SAME TIME WE DID, THUS BLOCKING CENTER FROM HEARING THE MISTAKE. ANOTHER FACTOR WAS THAT WE HAD JUST RECEIVED A ROUTE CHANGE SO BOTH OF US WERE SOMEWHAT ENGROSSED IN OUR MAPS WHEN THE ALT CLRNC WAS RECEIVED. SUPPLEMENTAL INFORMATION FROM ACN 80230: 2 COMPANY FLTS IN AREA WITH SIMILAR CALL SIGNS WERE ON FREQ. WE BELIEVE BOTH TRIPS READ BACK CLRNC AT SAME TIME SMEARING EACH OTHER.

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.