Clearance reply to wrong call sign. Began unclred descent out of assigned altitude.

Attributes
ACN	195814
Time
Date	199112
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dag
State Reference	CA
Altitude	msl bound lower : 22600 msl bound upper : 23000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla artcc : zny
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 4700 flight time type : 1000
ASRS Report	195814
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time total : 20000
ASRS Report	195684
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

This flight crew received a clearance that we understood to be to cross whigg at 10000 ft. At this time the aircraft was approaching the point at which a normal idle descent would enable crossing whigg at 12000 ft. Crew was expecting further descent clearance to cross whigg at 12000 ft as per the creso STAR, therefore the clearance was read back concisely to ATC, including aircraft call sign. With no immediate reply from ATC that there might be any error in the readback, 10000 ft was set into the MCP altitude alert window and a descent was commenced. Approximately 400 ft below FL230 ATC called and said the 10000 clearance was for another aircraft and for us to maintain 230 for conflicting traffic. An immediate pull up was initiated and the aircraft returned promptly to FL230. There was a TCASII TA after the ATC call. No TCASII RA. Contributing factors/perceptions: heavy radio traffic. Multiple altitude clrncs to multiple aircraft. Conflicting traffic in the normal descent path of the STAR. Possible call sign confusion. Possible controller overload. Possible to probable radio transmitter cross blocking/jamming.

Original NASA ASRS Text

Title: CLRNC REPLY TO WRONG CALL SIGN. BEGAN UNCLRED DSCNT OUT OF ASSIGNED ALT.

Narrative: THIS FLC RECEIVED A CLRNC THAT WE UNDERSTOOD TO BE TO CROSS WHIGG AT 10000 FT. AT THIS TIME THE ACFT WAS APCHING THE POINT AT WHICH A NORMAL IDLE DSCNT WOULD ENABLE XING WHIGG AT 12000 FT. CREW WAS EXPECTING FURTHER DSCNT CLRNC TO CROSS WHIGG AT 12000 FT AS PER THE CRESO STAR, THEREFORE THE CLRNC WAS READ BACK CONCISELY TO ATC, INCLUDING ACFT CALL SIGN. WITH NO IMMEDIATE REPLY FROM ATC THAT THERE MIGHT BE ANY ERROR IN THE READBACK, 10000 FT WAS SET INTO THE MCP ALT ALERT WINDOW AND A DSCNT WAS COMMENCED. APPROX 400 FT BELOW FL230 ATC CALLED AND SAID THE 10000 CLRNC WAS FOR ANOTHER ACFT AND FOR US TO MAINTAIN 230 FOR CONFLICTING TFC. AN IMMEDIATE PULL UP WAS INITIATED AND THE ACFT RETURNED PROMPTLY TO FL230. THERE WAS A TCASII TA AFTER THE ATC CALL. NO TCASII RA. CONTRIBUTING FACTORS/PERCEPTIONS: HVY RADIO TFC. MULTIPLE ALT CLRNCS TO MULTIPLE ACFT. CONFLICTING TFC IN THE NORMAL DSCNT PATH OF THE STAR. POSSIBLE CALL SIGN CONFUSION. POSSIBLE CTLR OVERLOAD. POSSIBLE TO PROBABLE RADIO XMITTER CROSS BLOCKING/JAMMING.

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.