B737-200 flight crew overshot their ATC assigned altitude when the clearance being exercised was for another company aircraft. A matter of clearance interpretation and a hearback problem. Alert second controller catches error and issues a diverging heading for both involved aircraft and a descent for aircraft X. No loss of separation.

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Attributes
ACN	377840
Time
Date	199708
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ekr
State Reference	CO
Altitude	msl bound lower : 28000 msl bound upper : 29500
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 200 flight time total : 7000 flight time type : 280
ASRS Report	377840
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 200 flight time total : 3300 flight time type : 2000
ASRS Report	377841
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Operational Deviation Pilot Deviation

Narrative:

On climb out of den, center controllers gave us a climb to FL310. Before reaching approximately FL260 we were reclred to FL280. Soon after reaching FL280 we were cleared to FL350 and given a handoff to another controller. After having checked in, center acknowledged and asked us our altitude. We informed them FL295 climbing FL350. He gave us a 'descend immediately to FL280 and turn right 30 degrees.' we of course complied. Our TCASII equipment showed traffic no closer than 15 mi with no TCASII alerts. We were then asked our assigned altitude and replied FL350. He soon thereafter cleared us back to FL350. Both pilots confirmed all altitudes at all times. Upon further review we may have responded to a clearance given same company with similar flight numbers. The controller, being busy, didn't catch the readback either. Our other company aircraft probably responded to their clearance also, and we blocked each other's communication.

Original NASA ASRS Text

Title: B737-200 FLC OVERSHOT THEIR ATC ASSIGNED ALT WHEN THE CLRNC BEING EXERCISED WAS FOR ANOTHER COMPANY ACFT. A MATTER OF CLRNC INTERP AND A HEARBACK PROB. ALERT SECOND CTLR CATCHES ERROR AND ISSUES A DIVERGING HDG FOR BOTH INVOLVED ACFT AND A DSCNT FOR ACFT X. NO LOSS OF SEPARATION.

Narrative: ON CLBOUT OF DEN, CTR CTLRS GAVE US A CLB TO FL310. BEFORE REACHING APPROX FL260 WE WERE RECLRED TO FL280. SOON AFTER REACHING FL280 WE WERE CLRED TO FL350 AND GIVEN A HDOF TO ANOTHER CTLR. AFTER HAVING CHKED IN, CTR ACKNOWLEDGED AND ASKED US OUR ALT. WE INFORMED THEM FL295 CLBING FL350. HE GAVE US A 'DSND IMMEDIATELY TO FL280 AND TURN R 30 DEGS.' WE OF COURSE COMPLIED. OUR TCASII EQUIP SHOWED TFC NO CLOSER THAN 15 MI WITH NO TCASII ALERTS. WE WERE THEN ASKED OUR ASSIGNED ALT AND REPLIED FL350. HE SOON THEREAFTER CLRED US BACK TO FL350. BOTH PLTS CONFIRMED ALL ALTS AT ALL TIMES. UPON FURTHER REVIEW WE MAY HAVE RESPONDED TO A CLRNC GIVEN SAME COMPANY WITH SIMILAR FLT NUMBERS. THE CTLR, BEING BUSY, DIDN'T CATCH THE READBACK EITHER. OUR OTHER COMPANY ACFT PROBABLY RESPONDED TO THEIR CLRNC ALSO, AND WE BLOCKED EACH OTHER'S COM.

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.