Air carrier advised by TRACON that they are below the class B airspace on approach to san.

Attributes
ACN	480420
Time
Date	200007
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : san.airport
State Reference	CA
Altitude	msl bound lower : 4000 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : sct.tracon
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer only : 27 other
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : sct.tracon
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer only : 27
Flight Phase	descent : approach
Route In Use	approach : instrument non precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : atp pilot : commercial pilot : flight engineer pilot : multi engine
Experience	flight time last 90 days : 175 flight time total : 6500 flight time type : 2000
ASRS Report	480420
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	non adherence : published procedure other anomaly
Independent Detector	other controllerb
Resolutory Action	controller : issued advisory none taken : anomaly accepted
Supplementary
Problem Areas	Flight Crew Human Performance Airspace Structure Chart Or Publication
Primary Problem	Environmental Factor

Narrative:

At 6000 ft, 6-10 mi from vydda intersection, ATC cleared us for a visual approach to runway 27 behind an air carrier jet to runway 27 at san. We began a descent to cross vydda at 4000 ft and were advised by ATC we were leaving class B airspace and would re-enter momentarily. The boundary markers should be made from DME the approach is based on, not xradials. One cannot immediately reference xradials when ATC gives you a sudden change.

Original NASA ASRS Text

Title: ACR ADVISED BY TRACON THAT THEY ARE BELOW THE CLASS B AIRSPACE ON APCH TO SAN.

Narrative: AT 6000 FT, 6-10 MI FROM VYDDA INTXN, ATC CLRED US FOR A VISUAL APCH TO RWY 27 BEHIND AN ACR JET TO RWY 27 AT SAN. WE BEGAN A DSCNT TO CROSS VYDDA AT 4000 FT AND WERE ADVISED BY ATC WE WERE LEAVING CLASS B AIRSPACE AND WOULD RE-ENTER MOMENTARILY. THE BOUNDARY MARKERS SHOULD BE MADE FROM DME THE APCH IS BASED ON, NOT XRADIALS. ONE CANNOT IMMEDIATELY REF XRADIALS WHEN ATC GIVES YOU A SUDDEN CHANGE.

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.