Flight crew of an large transport descended below assigned altitude in response to a clearance for a...

Attributes
ACN	360738
Time
Date	199702
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : cos
State Reference	CO
Altitude	msl bound lower : 10000 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise other descent other
Route In Use	enroute airway : zdv
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : private pilot : instrument pilot : flight engineer pilot : commercial pilot : atp
Experience	flight time last 90 days : 300 flight time total : 4000 flight time type : 250
ASRS Report	360738
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
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	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flight was flown from den-cos. ATC issued traffic and an altitude change from 12000 ft to 8000 ft. The traffic and altitude change was read back to ATC. Descent was initiated to 8000 ft. Passing 10200 ft, ATC asked what our assigned altitude was and why we had left 12000 ft without clearance. Aircraft was leveled at 10000 ft. ATC said the original clearance was for a UHF equipped aircraft. An uneventful recovery into cos followed.

Original NASA ASRS Text

Title: FLC OF AN LGT DSNDED BELOW ASSIGNED ALT IN RESPONSE TO A CLRNC FOR ANOTHER ACFT.

Narrative: FLT WAS FLOWN FROM DEN-COS. ATC ISSUED TFC AND AN ALT CHANGE FROM 12000 FT TO 8000 FT. THE TFC AND ALT CHANGE WAS READ BACK TO ATC. DSCNT WAS INITIATED TO 8000 FT. PASSING 10200 FT, ATC ASKED WHAT OUR ASSIGNED ALT WAS AND WHY WE HAD LEFT 12000 FT WITHOUT CLRNC. ACFT WAS LEVELED AT 10000 FT. ATC SAID THE ORIGINAL CLRNC WAS FOR A UHF EQUIPPED ACFT. AN UNEVENTFUL RECOVERY INTO COS FOLLOWED.

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.

Flight crew of an large transport descended below assigned altitude in response to a clearance for another aircraft.