Captain commenced descent prior to intercepting localizer until corrected by first officer.

Attributes
ACN	321330
Time
Date	199511
Day	Thu
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : oma
State Reference	NE
Altitude	msl bound lower : 3000 msl bound upper : 3000
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Controlling Facilities	tracon : oma
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 218 flight time total : 7556 flight time type : 1730
ASRS Report	321330
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 other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were cleared to 'maintain 3000 ft until established' and cleared for the ILS approach. We were on an assigned heading to intercept the localizer. The captain visually acquired the runway prior to intercepting the localizer. (I believe RVR was 6000 ft or greater when starting the approach but deteriorated to approximately 3000 ft while on approach. The skies were basically clear but the field was partially obscured due to ground fog.) the captain then started to turn inbound towards the runway and also started to descend below 3000 ft prior to being established. I immediately told him (the captain) we were to maintain 3000 ft until established, but he said he had it (the runway) visually. While we were very close to joining the localizer, but not on it, I told him we must join the localizer. He then intercepted the localizer and completed the approach without further incident. Proper knowledge of instrument procedures is a must. In addition a descent should never be initiated until both crew members are satisfied it is both safe and legal.

Original NASA ASRS Text

Title: CAPT COMMENCED DSCNT PRIOR TO INTERCEPTING LOC UNTIL CORRECTED BY FO.

Narrative: WE WERE CLRED TO 'MAINTAIN 3000 FT UNTIL ESTABLISHED' AND CLRED FOR THE ILS APCH. WE WERE ON AN ASSIGNED HEADING TO INTERCEPT THE LOC. THE CAPT VISUALLY ACQUIRED THE RWY PRIOR TO INTERCEPTING THE LOC. (I BELIEVE RVR WAS 6000 FT OR GREATER WHEN STARTING THE APCH BUT DETERIORATED TO APPROX 3000 FT WHILE ON APCH. THE SKIES WERE BASICALLY CLR BUT THE FIELD WAS PARTIALLY OBSCURED DUE TO GND FOG.) THE CAPT THEN STARTED TO TURN INBOUND TOWARDS THE RWY AND ALSO STARTED TO DSND BELOW 3000 FT PRIOR TO BEING ESTABLISHED. I IMMEDIATELY TOLD HIM (THE CAPT) WE WERE TO MAINTAIN 3000 FT UNTIL ESTABLISHED, BUT HE SAID HE HAD IT (THE RWY) VISUALLY. WHILE WE WERE VERY CLOSE TO JOINING THE LOC, BUT NOT ON IT, I TOLD HIM WE MUST JOIN THE LOC. HE THEN INTERCEPTED THE LOC AND COMPLETED THE APCH WITHOUT FURTHER INCIDENT. PROPER KNOWLEDGE OF INST PROCS IS A MUST. IN ADDITION A DSCNT SHOULD NEVER BE INITIATED UNTIL BOTH CREW MEMBERS ARE SATISFIED IT IS BOTH SAFE AND LEGAL.

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.