A B737-800 flight crew received a low altitude alert from sfo tower when they improperly used VNAV g...

Attributes
ACN	997626
Time
Date	201202
Local Time Of Day	0601-1200
Place
Locale Reference	SFO.Airport
State Reference	CA
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	STAR FMS Bridge Visual
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Altitude Crossing Restriction Not Met Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Flight Deck / Cabin / Aircraft Event Other / Unknown Inflight Event / Encounter CFTT / CFIT

Narrative:

On the FMS bridge visual 28R approach; on dogleg to final; between samul and F101D; I was flying the approach manually; using the HUD; with LNAV and VNAV engaged. I followed the HUD commands closely and as I realized we were lower than normal; the tower notified us that they were getting an altitude alert. I recall being above 500 ft. At that time; I was turning to line up with the runway. I leveled off and continued the approach to intercept the PAPI glide path; and landed the airplane. I do not have access to the FMC as I write this; but I do recall that there was a published glide path on this approach. I thought that this would allow the use of VNAV. I am not certain why the HUD commanded a greater than normal descent; but in the future this could be avoided by either engaging the ILS approach mode after samul; or maintaining visual contact with the PAPI after samul.

Original NASA ASRS Text

Title: A B737-800 flight crew received a low altitude alert from SFO Tower when they improperly used VNAV guidance during a FMS Bridge Visual to Runway 28R.

Narrative: On the FMS bridge visual 28R approach; on dogleg to final; between SAMUL and F101D; I was flying the approach manually; using the HUD; with LNAV and VNAV engaged. I followed the HUD commands closely and as I realized we were lower than normal; the Tower notified us that they were getting an altitude alert. I recall being above 500 FT. At that time; I was turning to line up with the runway. I leveled off and continued the approach to intercept the PAPI glide path; and landed the airplane. I do not have access to the FMC as I write this; but I do recall that there was a published glide path on this approach. I thought that this would allow the use of VNAV. I am not certain why the HUD commanded a greater than normal descent; but in the future this could be avoided by either engaging the ILS approach mode after SAMUL; or maintaining visual contact with the PAPI after SAMUL.

Data retrieved from NASA's ASRS site as of July 2013 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 B737-800 flight crew received a low altitude alert from sfo tower when they improperly used VNAV guidance during a FMS bridge visual to runway 28R.