A C560 flown by single pilot misunderstood descent clearance and descended below assigned altitude.

Attributes
ACN	702989
Time
Date	200607
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zlc.artcc
State Reference	UT
Altitude	msl bound lower : 29000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc.artcc
Operator	general aviation : corporate
Make Model Name	Citation V
Operating Under FAR Part	Part 91
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 75 flight time total : 7500 flight time type : 1500
ASRS Report	702989
Person 2
Affiliation	government : faa
Function	controller : radar
Events
Anomaly	non adherence : clearance non adherence : far
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

Descent out of FL430 to FL370 center assigned continued descent to 'FL330' with my readback of 'FL230' and no correction by ATC. Flying 'single pilot' in the continued descent I was calling ahead to FBO at boi for notice of arrival. Out of FL300 realizing that FL230 is not a normal high altitude assigned; ie; FL240; I verified with ATC of assigned altitude of FL230. ATC advised 'no' FL330 was assigned. ATC then assigned FL290. I leveled the aircraft at FL290. No further action taken. Continued normal descent and landing to boi. Failure to understand and a missed communication with ATC as well as a distraction with calling to FBO for arrival. Working 2 radio frequencys at same time. Being single pilot needs added awareness and caution; ie; don't call and worry about arrival notice to FBO being single pilot. Limit to radio communicating. ATC not correcting an incorrect readback. Added attention to ATC clearance.

Original NASA ASRS Text

Title: A C560 FLOWN BY SINGLE PLT MISUNDERSTOOD DSCNT CLRNC AND DSNDED BELOW ASSIGNED ALT.

Narrative: DSCNT OUT OF FL430 TO FL370 CTR ASSIGNED CONTINUED DSCNT TO 'FL330' WITH MY READBACK OF 'FL230' AND NO CORRECTION BY ATC. FLYING 'SINGLE PLT' IN THE CONTINUED DSCNT I WAS CALLING AHEAD TO FBO AT BOI FOR NOTICE OF ARR. OUT OF FL300 REALIZING THAT FL230 IS NOT A NORMAL HIGH ALT ASSIGNED; IE; FL240; I VERIFIED WITH ATC OF ASSIGNED ALT OF FL230. ATC ADVISED 'NO' FL330 WAS ASSIGNED. ATC THEN ASSIGNED FL290. I LEVELED THE ACFT AT FL290. NO FURTHER ACTION TAKEN. CONTINUED NORMAL DSCNT AND LNDG TO BOI. FAILURE TO UNDERSTAND AND A MISSED COM WITH ATC AS WELL AS A DISTR WITH CALLING TO FBO FOR ARR. WORKING 2 RADIO FREQS AT SAME TIME. BEING SINGLE PLT NEEDS ADDED AWARENESS AND CAUTION; IE; DON'T CALL AND WORRY ABOUT ARR NOTICE TO FBO BEING SINGLE PLT. LIMIT TO RADIO COMMUNICATING. ATC NOT CORRECTING AN INCORRECT READBACK. ADDED ATTN TO ATC CLRNC.

Data retrieved from NASA's ASRS site as of January 2009 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.