LGT ENTERS ACTIVE RWY WITHOUT CLRNC CAUSING ANOTHER ACFT TO GAR.

Narrative

DURING VFR CLR CONDITIONS IN DSCNT AND APCH TO SFO ARPT RWY 28R; RADIO XMISSIONS WERE VERY HVY WITH SOME VECTORING AND SEVERAL SPD REDUCTIONS. VECTORS S OF SFO 095 RADIAL WAS NECESSARY TO OBTAIN MORE INTERVAL ON PRECEDING ACFT AND SEVERAL REQUESTS BY APCH CTRL TO RPT SIGHTING OF ACFT AT 9:30 POS. APPROX 3000 FT AGL; ACFT ON L SIGHTED AND APCH CTRL INSTRUCTED SWITCH TO TWR. SHORTLY THEREAFTER; CAPT WAS HAND FLYING AT 160 KTS WHEN ACFT EXPERIENCED UNCTLED RAPID L WING DROP APPROX 30-40 DEG; AS TWR ADVISED PRECEDING ACFT WAS HVY 767 'CAUTION DUE TO MINIMUM SPACING.' ADDITIONALLY; TWR ADVISED RWY 19L AND R OR TXWY E AVAILABLE FOR TURNOFF. THIS KEYED CAPT TO SENSE ANOTHER ACFT WAS CLOSE BEHIND ESPECIALLY SINCE AN S-TURN TO R WAS BEING CONDUCTED TO OBTAIN MORE INTERVAL PRECEDING HVY 767. DURING LNDG APCH FULLY EXPECTING MORE WAKE TURB FLT WAS STABLE. AFTER LNDG WHILE ACFT WAS DECELERATING IN REVERSE THRUST; THE TWR INSTRUCTED TURN- OFF ON EITHER 19L OR R AVAILABLE. CAPT ELECTED TO TURN L ONTO 19R AS IT APPEARED A 747 ACFT WAS SITTING ON TXWY E AND SPD PERMITTED A 90 DEG L TURN. HOWEVER; BY THE TIME CAPT SLOWED ACT AND ADJUSTED LNDG TAXI LIGHTS; THE NOSE OF THE ACFT WAS OVER THE 28L RWY AND AN ACFT WAS CLOSE IN ON APCH TO 28L. THEREFORE; PWR WAS ADDED TO CLR RWY QUICKLY. SIMULTANEOUSLY; THE TWR TOLD ACFT ON APCH TO GAR AND THEN ADVISED THAT WE WERE TO HAVE HELD SHORT. CAPT AND CREW WOULD HAVE BEEN MORE AWARE OF THE VERY SHORT DISTANCE HAD TWR MENTIONED IT OR ADVISED TURN ON 19 AND STOP VICE 'HOLD SHORT' WHICH IS NORMAL AND THIS IS NOT A NORMAL DISTANCE AFTER CLRING A RWY NOR NORMAL LIGHTING ENVIRONMENT. I.E.; ALL LIGHTS WHITE FOR ALL 3 RWYS AROUND THE ACFT AT THE TIME. CAPT TALKED TO TWR SUPVR BY PHONE AND WAS ADVISED; 'WE ARE AWARE OF SHORT DISTANCE AND WE WATCH CLOSELY TO SEE WHAT ACFT DO WHEN THEY TURN OFF ON THE 19'S.' IF THEY ARE AWARE THEN WHY NOT MAKE EFFORT TO ADVISE COCKPIT CREW OF THIS UNUSUAL SIT ESPECIALLY WHEN ENCOURAGING THE TURNOFF ONTO THE 19 RWYS. SUPPLEMENTAL INFO FROM ACN 267871: CAPT AND CREW WOULD HAVE BEEN MORE AWARE OF EXTREMELY SHORT DISTANCE BTWN RWYS HAD TWR MENTIONED IT OR ADVISED TURN ON 19R OR 19L AND STOP VICE `HOLD SHORT.'