Cr descends below assigned altitude prior to GS intercept.

Attributes
ACN	178741
Time
Date	199105
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bur
State Reference	CA
Altitude	msl bound lower : 2600 msl bound upper : 3500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bur tower : bur
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent : approach landing : go around
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 225 flight time total : 6000 flight time type : 1500
ASRS Report	178741
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 180 flight time total : 4000
ASRS Report	178753
Events
Anomaly	altitude deviation : overshoot non adherence : published procedure non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : became reoriented other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Approaching thousand oaks from fillmore VOR, approach control cleared us to 3500' until established on approach, maintain 180 KTS. The autoplt was selected. After localizer intercept, ILS was armed. Then, thinking we were on G/south (but actually below G/south in IAS mode), I disarmed the altitude alert. The copilot made a remark at 3000' that we were, 'cleared to 3500' until established.' I replied, 'we are established.' then as we were approaching vny I realized the error and started a correction back up to the G/south. By then we had been switched to tower. In an apparently unrelated development, the tower made us do a missed approach because of traffic on final ahead of us. The approach plate depicts a 3000' mandatory altitude until G/south intercept. We descended to approximately 2600'.

Original NASA ASRS Text

Title: CR DESCENDS BELOW ASSIGNED ALT PRIOR TO GS INTERCEPT.

Narrative: APCHING THOUSAND OAKS FROM FILLMORE VOR, APCH CTL CLRED US TO 3500' UNTIL ESTABLISHED ON APCH, MAINTAIN 180 KTS. THE AUTOPLT WAS SELECTED. AFTER LOC INTERCEPT, ILS WAS ARMED. THEN, THINKING WE WERE ON G/S (BUT ACTUALLY BELOW G/S IN IAS MODE), I DISARMED THE ALT ALERT. THE COPLT MADE A REMARK AT 3000' THAT WE WERE, 'CLRED TO 3500' UNTIL ESTABLISHED.' I REPLIED, 'WE ARE ESTABLISHED.' THEN AS WE WERE APCHING VNY I REALIZED THE ERROR AND STARTED A CORRECTION BACK UP TO THE G/S. BY THEN WE HAD BEEN SWITCHED TO TWR. IN AN APPARENTLY UNRELATED DEVELOPMENT, THE TWR MADE US DO A MISSED APCH BECAUSE OF TFC ON FINAL AHEAD OF US. THE APCH PLATE DEPICTS A 3000' MANDATORY ALT UNTIL G/S INTERCEPT. WE DSNDED TO APPROX 2600'.

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.