Clearance reply to wrong call sign results in potential conflict and possible loss of separation.

Attributes
ACN	158350
Time
Date	199009
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : den
State Reference	CO
Altitude	msl bound lower : 30700 msl bound upper : 31000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv tower : pty
Operator	common carrier : air carrier
Make Model Name	Heavy Transport
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 100 flight time total : 16000 flight time type : 85
ASRS Report	158350
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance non adherence : required legal separation other anomaly other
Independent Detector	other controllera other other : unspecified
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 18000 vertical : 1700
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation Operational Deviation

Narrative:

We were at cruise at FL310 and in contact with den center. We received and acknowledged ATC clearance to 'descend to FL290, pilot's discretion to fl 240.' we read back this clearance and it was acknowledged. We began our descent and at 30700' we were advised to maintain FL310, traffic below us by ATC. We stopped our descent and returned to FL310. On the ground, and asked for the tapes to be held for review. In questioning all other crew members on board they reported hearing exactly the same thing as I did and presumed ATC had made a mistake with the identification and/or flight number. The ATC supervisor said we had acknowledged another flight's clearance. Supplemental information from acn 158078. We received a traffic advisory of maintain FL310, traffic below at FL290. We then stopped descent and climbed to FL310. When frequency was clear we questioned ATC and he apologized for the misunderstanding. During this time I was not actively involved with the pilots because of my inrange duties getting ATIS calling company etc. I feel congestion of arriving aircraft and similar call signs led to a potential near miss! Supplemental information from acn 158573. Center advised descent from cruise altitude. Before we could answer the clearance it was read back by another aircraft. We then advised center that aircraft other ours responded. We then read back ATC clearance to descend.

Original NASA ASRS Text

Title: CLRNC REPLY TO WRONG CALL SIGN RESULTS IN POTENTIAL CONFLICT AND POSSIBLE LOSS OF SEPARATION.

Narrative: WE WERE AT CRUISE AT FL310 AND IN CONTACT WITH DEN CTR. WE RECEIVED AND ACKNOWLEDGED ATC CLRNC TO 'DSND TO FL290, PLT'S DISCRETION TO FL 240.' WE READ BACK THIS CLRNC AND IT WAS ACKNOWLEDGED. WE BEGAN OUR DSNT AND AT 30700' WE WERE ADVISED TO MAINTAIN FL310, TFC BELOW US BY ATC. WE STOPPED OUR DSNT AND RETURNED TO FL310. ON THE GND, AND ASKED FOR THE TAPES TO BE HELD FOR REVIEW. IN QUESTIONING ALL OTHER CREW MEMBERS ON BOARD THEY RPTED HEARING EXACTLY THE SAME THING AS I DID AND PRESUMED ATC HAD MADE A MISTAKE WITH THE ID AND/OR FLT NUMBER. THE ATC SUPVR SAID WE HAD ACKNOWLEDGED ANOTHER FLT'S CLRNC. SUPPLEMENTAL INFO FROM ACN 158078. WE RECEIVED A TFC ADVISORY OF MAINTAIN FL310, TFC BELOW AT FL290. WE THEN STOPPED DSNT AND CLBED TO FL310. WHEN FREQ WAS CLR WE QUESTIONED ATC AND HE APOLOGIZED FOR THE MISUNDERSTANDING. DURING THIS TIME I WAS NOT ACTIVELY INVOLVED WITH THE PLTS BECAUSE OF MY INRANGE DUTIES GETTING ATIS CALLING COMPANY ETC. I FEEL CONGESTION OF ARRIVING ACFT AND SIMILAR CALL SIGNS LED TO A POTENTIAL NEAR MISS! SUPPLEMENTAL INFO FROM ACN 158573. CTR ADVISED DSNT FROM CRUISE ALT. BEFORE WE COULD ANSWER THE CLRNC IT WAS READ BACK BY ANOTHER ACFT. WE THEN ADVISED CTR THAT ACFT OTHER OURS RESPONDED. WE THEN READ BACK ATC CLRNC TO DSND.

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.