ATC questioned ATR42 flight crew for leaving assigned altitude after issuing clearance for visual ap...

Attributes
ACN	596611
Time
Date	200310
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 150
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz.tracon
Operator	common carrier : air carrier
Make Model Name	ATR 42
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : commercial
Experience	flight time last 90 days : 240 flight time total : 2800 flight time type : 1200
ASRS Report	596611
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : nmac non adherence : clearance
Independent Detector	aircraft equipment : tcas other flight crewa
Resolutory Action	controller : issued new clearance flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 400
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

While transitioning from the descent phase to approach phase of flight, the approach controller advised us to descend to 3200 ft MSL. While descending we got a TCASII TA, we leveled off but the traffic was climbing. Therefore, we got an RA. After acting immediately we cleared traffic. At this point as we saw the airport and judged our relative ht, we realized we needed to descend rapidly. The PNF called the visual and the controller cleared us. We descended to 1500 ft MSL and requested frequency change to tower. At that point the approach controller advised us that he never cleared us to descend below 3200 ft MSL and we were at 1500 ft MSL at this point. He requested us to call ATC once we landed and we proceeded with tower. It is our understanding that once you have been cleared for the approach, altitude is at pilot's discretion considering ht above obstacle regulations.

Original NASA ASRS Text

Title: ATC QUESTIONED ATR42 FLT CREW FOR LEAVING ASSIGNED ALT AFTER ISSUING CLRNC FOR VISUAL APCH.

Narrative: WHILE TRANSITIONING FROM THE DSCNT PHASE TO APCH PHASE OF FLT, THE APCH CTLR ADVISED US TO DSND TO 3200 FT MSL. WHILE DSNDING WE GOT A TCASII TA, WE LEVELED OFF BUT THE TFC WAS CLBING. THEREFORE, WE GOT AN RA. AFTER ACTING IMMEDIATELY WE CLRED TFC. AT THIS POINT AS WE SAW THE ARPT AND JUDGED OUR RELATIVE HT, WE REALIZED WE NEEDED TO DSND RAPIDLY. THE PNF CALLED THE VISUAL AND THE CTLR CLRED US. WE DSNDED TO 1500 FT MSL AND REQUESTED FREQ CHANGE TO TWR. AT THAT POINT THE APCH CTLR ADVISED US THAT HE NEVER CLRED US TO DSND BELOW 3200 FT MSL AND WE WERE AT 1500 FT MSL AT THIS POINT. HE REQUESTED US TO CALL ATC ONCE WE LANDED AND WE PROCEEDED WITH TWR. IT IS OUR UNDERSTANDING THAT ONCE YOU HAVE BEEN CLRED FOR THE APCH, ALT IS AT PLT'S DISCRETION CONSIDERING HT ABOVE OBSTACLE REGS.

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.

ATC questioned ATR42 flight crew for leaving assigned altitude after issuing clearance for visual approach.