Altitude deviation. Mode confusion.

Attributes
ACN	318230
Time
Date	199510
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : sfo
State Reference	CA
Altitude	msl bound lower : 5300 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tower : oak tower : iad
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 180 flight time total : 12600 flight time type : 500
ASRS Report	318230
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot non adherence : published procedure 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 descended below 6000 ft (to 5300 ft) on quiet bridge visual to runway 28R, sfo prior to the 18.0 DME fix. So we actually descended below floor of class B airspace. We were cleared for the approach (visual). All points were programmed into the FMC. First officer was flying. I was PNF. In autoplt mode 'flch' flight level change, instead of VNAV, first officer dialed in 1900 ft on altitude window in mode control panel. By operating in flch, aircraft was going for 1900 ft (a constraint at the 6.0 DME fix). Bottom line: mismanagement of the autoplt by the first officer and my failure to catch it soon enough. Result: descended below a mandatory altitude on a charted visual approach, going below floor of class B airspace.

Original NASA ASRS Text

Title: ALTDEV. MODE CONFUSION.

Narrative: WE DSNDED BELOW 6000 FT (TO 5300 FT) ON QUIET BRIDGE VISUAL TO RWY 28R, SFO PRIOR TO THE 18.0 DME FIX. SO WE ACTUALLY DSNDED BELOW FLOOR OF CLASS B AIRSPACE. WE WERE CLRED FOR THE APCH (VISUAL). ALL POINTS WERE PROGRAMMED INTO THE FMC. FO WAS FLYING. I WAS PNF. IN AUTOPLT MODE 'FLCH' FLT LEVEL CHANGE, INSTEAD OF VNAV, FO DIALED IN 1900 FT ON ALT WINDOW IN MODE CTL PANEL. BY OPERATING IN FLCH, ACFT WAS GOING FOR 1900 FT (A CONSTRAINT AT THE 6.0 DME FIX). BOTTOM LINE: MISMANAGEMENT OF THE AUTOPLT BY THE FO AND MY FAILURE TO CATCH IT SOON ENOUGH. RESULT: DSNDED BELOW A MANDATORY ALT ON A CHARTED VISUAL APCH, GOING BELOW FLOOR OF CLASS B AIRSPACE.

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.