Air carrier answered for another company flight and accepted his clearance.

Attributes
ACN	117439
Time
Date	198907
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : hou
State Reference	TX
Altitude	msl bound lower : 15000 msl bound upper : 15500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zhu
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude cruise other cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 200
ASRS Report	117439
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation other

Narrative:

Climbing out of houston hobby en route to abq on vectors to join J-15. Leveling at 15,000, departure control handed us off to ZHU. We reported on frequency and level at 15,000'. 'Company xxy, climb and maintain FL230.' I started the climb as the first officer repeated back the clearance. The controller responded with 'that was for company xyy.' I stopped the climb at 15,500' and told the first officer to confirm our climb clearance. The controller told us to maintain 15,000'. We returned to 15,000'. The controller was very busy and was working more than one frequency. We could hear him talking to our company flight xyy but we could not hear their responses. About 1 minute after being told to return to 15,000', the controller cleared us to FL230. I feel confident that we were cleared to FL230 the first time, but that the controller temporarily lost control of the situation. He sounded somewhat flustered and overwhelmed that day.

Original NASA ASRS Text

Title: ACR ANSWERED FOR ANOTHER COMPANY FLT AND ACCEPTED HIS CLRNC.

Narrative: CLIMBING OUT OF HOUSTON HOBBY ENRTE TO ABQ ON VECTORS TO JOIN J-15. LEVELING AT 15,000, DEP CTL HANDED US OFF TO ZHU. WE REPORTED ON FREQ AND LEVEL AT 15,000'. 'COMPANY XXY, CLIMB AND MAINTAIN FL230.' I STARTED THE CLIMB AS THE F/O REPEATED BACK THE CLRNC. THE CTLR RESPONDED WITH 'THAT WAS FOR COMPANY XYY.' I STOPPED THE CLIMB AT 15,500' AND TOLD THE F/O TO CONFIRM OUR CLIMB CLRNC. THE CTLR TOLD US TO MAINTAIN 15,000'. WE RETURNED TO 15,000'. THE CTLR WAS VERY BUSY AND WAS WORKING MORE THAN ONE FREQ. WE COULD HEAR HIM TALKING TO OUR COMPANY FLT XYY BUT WE COULD NOT HEAR THEIR RESPONSES. ABOUT 1 MINUTE AFTER BEING TOLD TO RETURN TO 15,000', THE CTLR CLRED US TO FL230. I FEEL CONFIDENT THAT WE WERE CLRED TO FL230 THE FIRST TIME, BUT THAT THE CTLR TEMPORARILY LOST CONTROL OF THE SITUATION. HE SOUNDED SOMEWHAT FLUSTERED AND OVERWHELMED THAT DAY.

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.