An air carrier mdt may have responded to a similar callsign and descended without clearance.

Attributes
ACN	246471
Time
Date	199307
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : cvg
State Reference	OH
Altitude	msl bound lower : 8000 msl bound upper : 10000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : cvg tower : bru
Operator	common carrier : air carrier
Make Model Name	Medium Transport, Low Wing, 2 Turboprop Eng
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 150 flight time total : 4600 flight time type : 600
ASRS Report	246471
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : cfi
Experience	flight time last 90 days : 200 flight time total : 3300 flight time type : 250
ASRS Report	246470
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

After the handoff to cvg approach from ZID, we found the frequency to be congested. Similar sounding callsigns were also on the frequency. I was PF, the first officer was handling the radios. On several occasions, the first officer took calls for another aircraft, all but the one in question were caught. We believed we were instructed to descend out of 10000 to 7000 ft. The controller caught us at 8000 ft at which time we were told to maintain 8000 ft and given a new heading. A contributing factor may have been the first officer's strong spanish accent, which may have influenced callback -- readback error, as all instructions were read back.

Original NASA ASRS Text

Title: AN ACR MDT MAY HAVE RESPONDED TO A SIMILAR CALLSIGN AND DSNDED WITHOUT CLRNC.

Narrative: AFTER THE HDOF TO CVG APCH FROM ZID, WE FOUND THE FREQ TO BE CONGESTED. SIMILAR SOUNDING CALLSIGNS WERE ALSO ON THE FREQ. I WAS PF, THE FO WAS HANDLING THE RADIOS. ON SEVERAL OCCASIONS, THE FO TOOK CALLS FOR ANOTHER ACFT, ALL BUT THE ONE IN QUESTION WERE CAUGHT. WE BELIEVED WE WERE INSTRUCTED TO DSND OUT OF 10000 TO 7000 FT. THE CTLR CAUGHT US AT 8000 FT AT WHICH TIME WE WERE TOLD TO MAINTAIN 8000 FT AND GIVEN A NEW HDG. A CONTRIBUTING FACTOR MAY HAVE BEEN THE FO'S STRONG SPANISH ACCENT, WHICH MAY HAVE INFLUENCED CALLBACK -- READBACK ERROR, AS ALL INSTRUCTIONS WERE READ BACK.

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.