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.

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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.