Air carrier flight crew descended below chart authority/authorized altitude.

Attributes
ACN	436200
Time
Date	199909
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : dfw.ils
Altitude	msl bound lower : 3000 msl bound upper : 4000
Environment
Weather Elements	other
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : d10.tracon tower : fll.tower
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 35r other
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : multi engine
ASRS Report	436200
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 : published procedure non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to original clearance
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Location: 16 DME from runway 35R on the localizer frequency 111.75. Cleared for the ILS runway 35R to dfw, maintain 4000 ft till established, we were on the localizer tracking inbound and started to descend to 3000 ft after passing galop which is 16.4 DME. After looking at the approach chart more carefully, I noticed that we weren't supposed to descend until frizz which is 13.2 DME. I immediately informed the captain and he corrected back to 4000 ft and maintained that until reaching frizz. We had descended about 300-400 ft before returning to 4000 ft.

Original NASA ASRS Text

Title: ACR FLC DSNDED BELOW CHART AUTH ALT.

Narrative: LOCATION: 16 DME FROM RWY 35R ON THE LOC FREQ 111.75. CLRED FOR THE ILS RWY 35R TO DFW, MAINTAIN 4000 FT TILL ESTABLISHED, WE WERE ON THE LOC TRACKING INBOUND AND STARTED TO DSND TO 3000 FT AFTER PASSING GALOP WHICH IS 16.4 DME. AFTER LOOKING AT THE APCH CHART MORE CAREFULLY, I NOTICED THAT WE WEREN'T SUPPOSED TO DSND UNTIL FRIZZ WHICH IS 13.2 DME. I IMMEDIATELY INFORMED THE CAPT AND HE CORRECTED BACK TO 4000 FT AND MAINTAINED THAT UNTIL REACHING FRIZZ. WE HAD DSNDED ABOUT 300-400 FT BEFORE RETURNING TO 4000 FT.

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.