Pilot accepted descent clearance from ZDV without confirming the altitude cleared to.

Attributes
ACN	517427
Time
Date	200107
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : lar.airport
State Reference	WY
Altitude	msl bound lower : 12000 msl bound upper : 15000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv.artcc artcc : zla.artcc
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise : enroute altitude change
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : commercial pilot : instrument
Experience	flight time last 90 days : 25 flight time total : 5700 flight time type : 2000
ASRS Report	517427
Person 2
Affiliation	government : faa
Function	controller : radar
Events
Anomaly	altitude deviation : overshoot non adherence : clearance non adherence : published procedure non adherence : far other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued alert flight crew : returned to assigned altitude none taken : detected after the fact
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were west of laramie, wy, at FL210 and asked ZDV for lower. We heard ZDV say descend at pilot's discretion with no altitude limit. We did not question him on the incomplete clearance. ZDV called us at 12000 ft saying he gave us 15000 ft. We did not hear 15000 ft, but should have questioned the clearance. We immediately climbed.

Original NASA ASRS Text

Title: PLT ACCEPTED DSCNT CLRNC FROM ZDV WITHOUT CONFIRMING THE ALT CLRED TO.

Narrative: WE WERE W OF LARAMIE, WY, AT FL210 AND ASKED ZDV FOR LOWER. WE HEARD ZDV SAY DSND AT PLT'S DISCRETION WITH NO ALT LIMIT. WE DID NOT QUESTION HIM ON THE INCOMPLETE CLRNC. ZDV CALLED US AT 12000 FT SAYING HE GAVE US 15000 FT. WE DID NOT HEAR 15000 FT, BUT SHOULD HAVE QUESTIONED THE CLRNC. WE IMMEDIATELY CLBED.

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.