B737 Undifferentiated or Other Model
Flight Crew Last 90 Days 240; Flight Crew Total 11000; Flight Crew Type 3000
Human-Machine Interface; Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach
Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft; Human Factors; Procedure
We were flying the Tip Toe visual to Runway 28L; San Francisco. About the time we were intercepting the localizer; ATC asked us to slow to final approach speed. I think we were at Flaps 5 and about 210 knots. The Captain asked for gear down and additional flaps as we slowed. After selecting Flaps 30 and slowing to extend Flaps 40 (our briefed final configuration); the Captain noticed that the flaps were still at 25; but the handle was at 30. I'm not sure if they just got stuck at 25 or if they blew back up to 25 from 30...I had fixated on the airspeed indicator and hadn't checked the flap indicator for the selected movement. We concluded that the most likely cause was a blow back due to an overspeed because we were extending flaps right as we slowed past the limit speeds. I asked the Captain if I could reselect the flaps...he agreed; so I moved the flap lever to 25 and back to 30. I've since learned that the flaps will re-extend below 171 knots; but I was unaware of that at the time. They initially didn't move and we began to discuss going around (we were both keenly aware of what a hot training topic this is of late)...but then the flaps started moving and we thought we would meet stabilized criteria. As we approached 1;000 feet the flaps were not yet to 40; but there was a 747 on take-off roll from our same Runway 28L. In my mind it looked like there was the potential for a midair conflict if we went missed as it was lifting off; so I didn't call for a go-around. At the time it seemed like a tough call; but now as I write this it seems pretty clear that we should have gone around at 1;000 feet and turned away from the traffic as per the approach plate go-around instructions...and SOP.
Visual approach to 28L at SFO. ATC left us high over MENLO intersection for traffic landing on 28R. Put gear down around 4;500 feet so I could descend faster to get back on path and then I could start configuring flaps. Passing 3;500; ATC requested to slow to final approach speed so they could launch an aircraft. We told ATC it is not easy to slow down and go down. They said do the best you can. They cleared a B747 for takeoff. We continued to slow. I called for Flaps 25...30 ...and at 162 knots I called for Flaps 40. At that instant; the speed increased about 5 knots to 167. I tried to get the speed back below 162. I looked at the flap indicator and they were at 25. Continued to slow passing 1;000 feet was able to get flaps to 30; then somewhere around 500 feet we got the flaps to 40. The B747 was just starting to lift off and we both agreed to continue the landing. It seemed safer to land instead of going around behind the 747. Taxied to the gate and wrote in the maintenance log possible flap overspeed from flaps 30 to 25.
B737 flight crew experiences a flap overspeed and blow up from 30 to 25 during approach. Flaps 25 are selected then 30 (successfully); then 40 but not until 500 feet on the approach. A normal landing ensues behind a departing B747.