CL60 on vectors to atl begins descent for visual approach before clearance was issued.

Attributes
ACN	606168
Time
Date	200401
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : atl.airport
State Reference	GA
Altitude	msl single value : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : a80.tracon
Operator	general aviation : corporate
Make Model Name	Challenger CL601
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	approach : visual arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 80 flight time total : 7000 flight time type : 1500
ASRS Report	606168
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance controller : issued advisory
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were at 3000 ft minimum vectoring altitude. We heard controller say cleared for visual approach. I began a descent to traffic pattern altitude of 2500 ft MSL. Controller called back and asked why we were at 2500 ft instead of 3000 ft. We said that we understood cleared for the visual approach. The controller disagreed. I believe that it was possible that he may have said, 'expect a visual approach,' but my copilot and I heard, 'cleared for the approach.' maybe a change in terminology would help or discontinue the use of 'expect.'

Original NASA ASRS Text

Title: CL60 ON VECTORS TO ATL BEGINS DSCNT FOR VISUAL APCH BEFORE CLRNC WAS ISSUED.

Narrative: WE WERE AT 3000 FT MINIMUM VECTORING ALT. WE HEARD CTLR SAY CLRED FOR VISUAL APCH. I BEGAN A DSCNT TO TFC PATTERN ALT OF 2500 FT MSL. CTLR CALLED BACK AND ASKED WHY WE WERE AT 2500 FT INSTEAD OF 3000 FT. WE SAID THAT WE UNDERSTOOD CLRED FOR THE VISUAL APCH. THE CTLR DISAGREED. I BELIEVE THAT IT WAS POSSIBLE THAT HE MAY HAVE SAID, 'EXPECT A VISUAL APCH,' BUT MY COPLT AND I HEARD, 'CLRED FOR THE APCH.' MAYBE A CHANGE IN TERMINOLOGY WOULD HELP OR DISCONTINUE THE USE OF 'EXPECT.'

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.