B757 flight crew encounter jetblast from taxiing B747 when landing at sfo.

Attributes
ACN	430130
Time
Date	199902
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sfo.airport
State Reference	CA
Altitude	agl single value : 20
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : sfo.tower
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach landing other
Route In Use	approach : visual approach other
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tower : sfo.tower
Operator	common carrier : air carrier
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Flight Phase	ground : takeoff roll
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	observation : company check pilot
Qualification	pilot : atp
Experience	flight time last 90 days : 131 flight time total : 21000 flight time type : 3300
ASRS Report	430130
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	ground encounters other other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : insufficient time
Consequence	other Other
Supplementary
Problem Areas	Flight Crew Human Performance Environmental Factor ATC Human Performance
Primary Problem	Environmental Factor

Narrative:

On an FMC approach to sfo runway 28R with a new captain flying, tower requested that we sidestep to runway 28L. After sidestepping to runway 28L, the tower cleared a B747-400 to taxi across the approach end of runway 28L for departure on runway 28R. At this time, we were on about a 2 1/2 - 3 mi final (wind 290 degrees at 12 KTS). By using a higher reference speed and staying high on the PAPI (3 white/1 red), we thought that we would be above and land beyond any blast or wake, as the B747 had not commenced takeoff roll. The approach was normal until about 20 ft on the radar altimeter when the aircraft encountered apparent jetblast and lost airspeed in the area of 12-15 KTS. The aircraft sustained a harder than normal landing. The tower was immediately advised, and they acknowledged the incident. The aircraft was inspected for a hard landing, with no apparent damage. I feel that with the close proximity of the runways (approximately 600 ft), wind direction, and aircraft size, all were contributing.

Original NASA ASRS Text

Title: B757 FLC ENCOUNTER JETBLAST FROM TAXIING B747 WHEN LNDG AT SFO.

Narrative: ON AN FMC APCH TO SFO RWY 28R WITH A NEW CAPT FLYING, TWR REQUESTED THAT WE SIDESTEP TO RWY 28L. AFTER SIDESTEPPING TO RWY 28L, THE TWR CLRED A B747-400 TO TAXI ACROSS THE APCH END OF RWY 28L FOR DEP ON RWY 28R. AT THIS TIME, WE WERE ON ABOUT A 2 1/2 - 3 MI FINAL (WIND 290 DEGS AT 12 KTS). BY USING A HIGHER REF SPD AND STAYING HIGH ON THE PAPI (3 WHITE/1 RED), WE THOUGHT THAT WE WOULD BE ABOVE AND LAND BEYOND ANY BLAST OR WAKE, AS THE B747 HAD NOT COMMENCED TKOF ROLL. THE APCH WAS NORMAL UNTIL ABOUT 20 FT ON THE RADAR ALTIMETER WHEN THE ACFT ENCOUNTERED APPARENT JETBLAST AND LOST AIRSPD IN THE AREA OF 12-15 KTS. THE ACFT SUSTAINED A HARDER THAN NORMAL LNDG. THE TWR WAS IMMEDIATELY ADVISED, AND THEY ACKNOWLEDGED THE INCIDENT. THE ACFT WAS INSPECTED FOR A HARD LNDG, WITH NO APPARENT DAMAGE. I FEEL THAT WITH THE CLOSE PROX OF THE RWYS (APPROX 600 FT), WIND DIRECTION, AND ACFT SIZE, ALL WERE CONTRIBUTING.

Data retrieved from NASA's ASRS site as of July 2007 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.