Air carrier cleared for visual approach but maintain 5000'. Flight crew descends below assigned.

Attributes
ACN	155135
Time
Date	199008
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : dfw
State Reference	TX
Altitude	msl bound lower : 3500 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Dawn
Aircraft 1
Controlling Facilities	tracon : dfw
Operator	common carrier : air carrier
Make Model Name	Medium Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 4000 flight time type : 2000
ASRS Report	155135
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 3000 flight time type : 220
ASRS Report	154805
Events
Anomaly	altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Operational Deviation Pilot Deviation

Narrative:

During approach into dfw the flight was cleared for a visibility approach except maintain 5000'. The first officer was busy running checklists. As we got closer to the airport, 5-7 mi, I felt, or needed, to descend. As I was cleared for the visibility approach I started down, momentarily forgetting about the altitude restriction. I caught the mistake as I descended through 3500' and promptly reported it to the approach controller. By luck I did not violate anyone else's airspace. I believe if I had not been 'cleared for the visibility' that this incident might have been avoided. If instructions were to proceed visly to the airport instead of cleared for the visibility runway 18L except maintain 5000' then there might not have been the confusion about the altitude and would have prompted a query of ATC.

Original NASA ASRS Text

Title: ACR CLEARED FOR VISUAL APCH BUT MAINTAIN 5000'. FLT CREW DESCENDS BELOW ASSIGNED.

Narrative: DURING APCH INTO DFW THE FLT WAS CLRED FOR A VIS APCH EXCEPT MAINTAIN 5000'. THE F/O WAS BUSY RUNNING CHKLISTS. AS WE GOT CLOSER TO THE ARPT, 5-7 MI, I FELT, OR NEEDED, TO DSND. AS I WAS CLRED FOR THE VIS APCH I STARTED DOWN, MOMENTARILY FORGETTING ABOUT THE ALT RESTRICTION. I CAUGHT THE MISTAKE AS I DSNDED THROUGH 3500' AND PROMPTLY RPTED IT TO THE APCH CTLR. BY LUCK I DID NOT VIOLATE ANYONE ELSE'S AIRSPACE. I BELIEVE IF I HAD NOT BEEN 'CLRED FOR THE VIS' THAT THIS INCIDENT MIGHT HAVE BEEN AVOIDED. IF INSTRUCTIONS WERE TO PROCEED VISLY TO THE ARPT INSTEAD OF CLRED FOR THE VIS RWY 18L EXCEPT MAINTAIN 5000' THEN THERE MIGHT NOT HAVE BEEN THE CONFUSION ABOUT THE ALT AND WOULD HAVE PROMPTED A QUERY OF ATC.

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.