Cpr pilot deviates from altitude assignment when clearance is misunderstood.

Attributes
ACN	463150
Time
Date	200001
Day	Mon
Local Time Of Day	0601 To 1200
Place
State Reference	MO
Altitude	msl bound lower : 26000 msl bound upper : 27000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zkc.artcc
Operator	general aviation : corporate
Make Model Name	IAI1124/1124A/Westwind
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zkc.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : instrument pilot : atp pilot : commercial
Experience	flight time last 90 days : 108 flight time total : 9000 flight time type : 1610
ASRS Report	463150
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : instrument pilot : multi engine pilot : commercial
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	aircraft equipment : tcas other flight crewa
Resolutory Action	none taken : detected after the fact
Miss Distance	horizontal : 21000 vertical : 600
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I reported off the frequency to call unicom. When I came back on, the PF told me he thought they said descend to FL260, but it was FL270. He had returned to altitude before I was aware of a problem, so I'm not sure what altitude he descended to before climbing back to FL270.

Original NASA ASRS Text

Title: CPR PLT DEVIATES FROM ALT ASSIGNMENT WHEN CLRNC IS MISUNDERSTOOD.

Narrative: I RPTED OFF THE FREQ TO CALL UNICOM. WHEN I CAME BACK ON, THE PF TOLD ME HE THOUGHT THEY SAID DSND TO FL260, BUT IT WAS FL270. HE HAD RETURNED TO ALT BEFORE I WAS AWARE OF A PROB, SO I'M NOT SURE WHAT ALT HE DSNDED TO BEFORE CLBING BACK TO FL270.

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.