A B737NG crew reported descending below the sfo class B floor flying the serfr RNAV STAR. Norcal ale...

Attributes
ACN	1330674
Time
Date	201602
Local Time Of Day	1201-1800
Place
Locale Reference	SFO.Airport
State Reference	CA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR SERFR 2
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 167 Flight Crew Type 20000
Person 2
Function	First Officer
Experience	Flight Crew Last 90 Days 82 Flight Crew Type 8000
Events
Anomaly	ATC Issue All Types Airspace Violation All Types Deviation - Procedural Clearance Deviation - Procedural FAR

Narrative:

During descent on the sefer 2 RNAV arrival between epick and eddyy; norcal approach told us we were outside of class B airspace and then a few seconds later notified us we were back in. It appeared that when the aircraft was fully coupled in LNAV and VNAV; the FMC continued the descent to 6;000 feet descending below 8;000 feet; 21 miles south of the sfo VOR; which placed us below the class B for about a mile at 250 knots. The arrival was fully briefed and loaded properly. This appears to be an anomaly in the arrival and FMC software limitations that allows the descent below class B to happen.reworking the FMC software or going out of VNAV until the class B restriction is made or slowing on the arrival to 200KTS on the arrival prior to going out of class B.

Original NASA ASRS Text

Title: A B737NG crew reported descending below the SFO Class B floor flying the SERFR RNAV STAR. NORCAL alerted about the deviation but the crew had been unaware of the Class B boundary which was not depicted in either the FMS or on the SERFR chart.

Narrative: During descent on the SEFER 2 RNAV Arrival between EPICK and EDDYY; NorCal Approach told us we were outside of Class B airspace and then a few seconds later notified us we were back in. It appeared that when the aircraft was fully coupled in LNAV and VNAV; the FMC continued the descent to 6;000 feet descending below 8;000 feet; 21 miles south of the SFO VOR; which placed us below the Class B for about a mile at 250 knots. The Arrival was fully briefed and loaded properly. This appears to be an anomaly in the arrival and FMC software limitations that allows the descent below Class B to happen.Reworking the FMC software or going out of VNAV until the Class B restriction is made or slowing on the arrival to 200KTS on the arrival prior to going out of class B.

Data retrieved from NASA's ASRS site 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.

A B737NG crew reported descending below the sfo class B floor flying the serfr RNAV STAR. Norcal alerted about the deviation but the crew had been unaware of the class B boundary which was not depicted in either the FMS or on the serfr chart.