Air carrier descended below assigned altitude while making an approach.

Attributes
ACN	107998
Time
Date	198903
Day	Fri
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : dfw
State Reference	TX
Altitude	msl bound lower : 4000 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Dawn
Aircraft 1
Controlling Facilities	tracon : dfw
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 5150 flight time type : 1120
ASRS Report	107988
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance none taken : detected after the fact
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Initially cleared to intercept runway 26L localizer at dfw to maintain 5000'. As we were passing through the G/south I thought we had been cleared for the approach. Then the captain started discussing techniques to descend on the G/south and maintain speed and yet not get high on the approach when configuring. At this point controller said he wanted us over on runway 35R and we could fly 030 degree heading to intercept. As we intercepted runway 35R localizer we were down to 4000'. The captain asked approach if we were cleared for the approach. Controller said no, then asked if we had traffic in sight 6 mi ahead. We did. He then cleared us for the visibility. There was no conflict and no further problem. The confusion was whether or not we were cleared for the approach to runway 36L and then what controller meant when he wanted us over on runway 35R. These types of situations are usually clarified before any misunderstandings occur. I feel it was missed this time due to the crew being tired as a result of the odd trip cycle, plus the timing of the captain starting to discuss techniques for descending on the G/south when we were passing through the G/south and starting to go high on it, then the controller switching runways.

Original NASA ASRS Text

Title: ACR DESCENDED BELOW ASSIGNED ALT WHILE MAKING AN APCH.

Narrative: INITIALLY CLRED TO INTERCEPT RWY 26L LOC AT DFW TO MAINTAIN 5000'. AS WE WERE PASSING THROUGH THE G/S I THOUGHT WE HAD BEEN CLRED FOR THE APCH. THEN THE CAPT STARTED DISCUSSING TECHNIQUES TO DSND ON THE G/S AND MAINTAIN SPD AND YET NOT GET HIGH ON THE APCH WHEN CONFIGURING. AT THIS POINT CTLR SAID HE WANTED US OVER ON RWY 35R AND WE COULD FLY 030 DEG HDG TO INTERCEPT. AS WE INTERCEPTED RWY 35R LOC WE WERE DOWN TO 4000'. THE CAPT ASKED APCH IF WE WERE CLRED FOR THE APCH. CTLR SAID NO, THEN ASKED IF WE HAD TFC IN SIGHT 6 MI AHEAD. WE DID. HE THEN CLRED US FOR THE VIS. THERE WAS NO CONFLICT AND NO FURTHER PROB. THE CONFUSION WAS WHETHER OR NOT WE WERE CLRED FOR THE APCH TO RWY 36L AND THEN WHAT CTLR MEANT WHEN HE WANTED US OVER ON RWY 35R. THESE TYPES OF SITUATIONS ARE USUALLY CLARIFIED BEFORE ANY MISUNDERSTANDINGS OCCUR. I FEEL IT WAS MISSED THIS TIME DUE TO THE CREW BEING TIRED AS A RESULT OF THE ODD TRIP CYCLE, PLUS THE TIMING OF THE CAPT STARTING TO DISCUSS TECHNIQUES FOR DSNDING ON THE G/S WHEN WE WERE PASSING THROUGH THE G/S AND STARTING TO GO HIGH ON IT, THEN THE CTLR SWITCHING RWYS.

Data retrieved from NASA's ASRS site as of August 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.