Approximately FL220 descending, the reporter in a 737 encountered B747 wake turbulence.

Attributes
ACN	298251
Time
Date	199410
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : eca
State Reference	CA
Altitude	msl bound lower : 22000 msl bound upper : 22000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zoa tower : pit
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B747 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 9000 flight time type : 3000
ASRS Report	298251
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	inflight encounter other
Independent Detector	other flight crewa
Resolutory Action	flight crew : exited adverse environment
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

ZOA controling, descending on madwin 3 arrival to oak to cross locke at 250 KTS at 11000 ft. Airspeed 280 KTS at approximately 2000 FPM descent. No TA's from ZOA. Aircraft entered a slight burble then suddenly rolled left about 10 degrees more burble, then aircraft rolled further left 20-25 degrees. Disconnected autoplt immediately countered roll and at same time pulled up, stopped roll at 30 degrees with aggressive control input with both aileron and rudder. First officer and I suspected wake turbulence but center had given no advisories. Only after handoff to approach did we hear the other aircraft and were told traffic to follow was air carrier XXX heavy, 15 mi in front. Air carrier XXX was a 747 cargo. Seems we were on separate center frequencys until oak approach. We had heard center talking to air carrier but only center portion of conversation. We were unaware that we were in-trail and I suppose center has no obligation to advise beyond normal separation. I'd be happy to discuss this further. It is still very vivid in my mind to say the least! Flight attendants came forward to inquire and later some of the passenger mentioned the incident upon deplaning. Apparently conditions were stable enough to allow the vortices to remain intact until we hit the right wing turbulence. Callback conversation with reporter revealed the following information: the reporter stated he had the seat belt sign on because he always turns the seat belt sign on at top of descent. The autoplt was on and his feet were flat on the floor and not on the rudder pedals. At first he caught a light burble which he now recognizes as the signature of an impending wake encounter. He then encountered an uncommanded 10 degree bank followed by another burble and an additional 20-25 degree bank which put him in about a 35 degree bank. During this bank he disconnected the autoplt, shallowed the descent, and exited the wake using aggressive aileron and elevator. The fact the wake turbulence was an industry issue prompted the reporter to submit his report. Hence, the 5 month delay in submitting the report.

Original NASA ASRS Text

Title: APPROX FL220 DSNDING, THE RPTR IN A 737 ENCOUNTERED B747 WAKE TURB.

Narrative: ZOA CTLING, DSNDING ON MADWIN 3 ARR TO OAK TO CROSS LOCKE AT 250 KTS AT 11000 FT. AIRSPD 280 KTS AT APPROX 2000 FPM DSCNT. NO TA'S FROM ZOA. ACFT ENTERED A SLIGHT BURBLE THEN SUDDENLY ROLLED L ABOUT 10 DEGS MORE BURBLE, THEN ACFT ROLLED FURTHER L 20-25 DEGS. DISCONNECTED AUTOPLT IMMEDIATELY COUNTERED ROLL AND AT SAME TIME PULLED UP, STOPPED ROLL AT 30 DEGS WITH AGGRESSIVE CTL INPUT WITH BOTH AILERON AND RUDDER. FO AND I SUSPECTED WAKE TURB BUT CTR HAD GIVEN NO ADVISORIES. ONLY AFTER HDOF TO APCH DID WE HEAR THE OTHER ACFT AND WERE TOLD TFC TO FOLLOW WAS ACR XXX HVY, 15 MI IN FRONT. ACR XXX WAS A 747 CARGO. SEEMS WE WERE ON SEPARATE CTR FREQS UNTIL OAK APCH. WE HAD HEARD CTR TALKING TO ACR BUT ONLY CTR PORTION OF CONVERSATION. WE WERE UNAWARE THAT WE WERE IN-TRAIL AND I SUPPOSE CTR HAS NO OBLIGATION TO ADVISE BEYOND NORMAL SEPARATION. I'D BE HAPPY TO DISCUSS THIS FURTHER. IT IS STILL VERY VIVID IN MY MIND TO SAY THE LEAST! FLT ATTENDANTS CAME FORWARD TO INQUIRE AND LATER SOME OF THE PAX MENTIONED THE INCIDENT UPON DEPLANING. APPARENTLY CONDITIONS WERE STABLE ENOUGH TO ALLOW THE VORTICES TO REMAIN INTACT UNTIL WE HIT THE R WING TURB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE HAD THE SEAT BELT SIGN ON BECAUSE HE ALWAYS TURNS THE SEAT BELT SIGN ON AT TOP OF DSCNT. THE AUTOPLT WAS ON AND HIS FEET WERE FLAT ON THE FLOOR AND NOT ON THE RUDDER PEDALS. AT FIRST HE CAUGHT A LIGHT BURBLE WHICH HE NOW RECOGNIZES AS THE SIGNATURE OF AN IMPENDING WAKE ENCOUNTER. HE THEN ENCOUNTERED AN UNCOMMANDED 10 DEG BANK FOLLOWED BY ANOTHER BURBLE AND AN ADDITIONAL 20-25 DEG BANK WHICH PUT HIM IN ABOUT A 35 DEG BANK. DURING THIS BANK HE DISCONNECTED THE AUTOPLT, SHALLOWED THE DSCNT, AND EXITED THE WAKE USING AGGRESSIVE AILERON AND ELEVATOR. THE FACT THE WAKE TURB WAS AN INDUSTRY ISSUE PROMPTED THE RPTR TO SUBMIT HIS RPT. HENCE, THE 5 MONTH DELAY IN SUBMITTING THE RPT.

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.