A B757 at FL340 encountered a B747's strong wake vortex after it passed opposite direction at FL350.

Attributes
ACN	798852
Time
Date	200808
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 34000
Environment
Flight Conditions	VMC
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B747 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 180 flight time total : 20000 flight time type : 4500
ASRS Report	798852
Events
Anomaly	conflict : airborne less severe inflight encounter : wake turbulence other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control
Supplementary
Problem Areas	Environmental Factor
Primary Problem	Environmental Factor

Narrative:

While smooth at FL340 near ZZZ; a B747 passed opposite direction at FL350 and just upwind of us. Shortly thereafter we were hit by its wake. It lasted for just over a second; but was fairly strong. This was my first encounter with wake under rvsm. The seat belt sign was off and passenger were up. The purser initially told us everyone was ok; but he needed to talk to the aft flight attendant and a female passenger in a lav. He called us back shortly thereafter and said no one was hurt.

Original NASA ASRS Text

Title: A B757 AT FL340 ENCOUNTERED A B747'S STRONG WAKE VORTEX AFTER IT PASSED OPPOSITE DIRECTION AT FL350.

Narrative: WHILE SMOOTH AT FL340 NEAR ZZZ; A B747 PASSED OPPOSITE DIRECTION AT FL350 AND JUST UPWIND OF US. SHORTLY THEREAFTER WE WERE HIT BY ITS WAKE. IT LASTED FOR JUST OVER A SECOND; BUT WAS FAIRLY STRONG. THIS WAS MY FIRST ENCOUNTER WITH WAKE UNDER RVSM. THE SEAT BELT SIGN WAS OFF AND PAX WERE UP. THE PURSER INITIALLY TOLD US EVERYONE WAS OK; BUT HE NEEDED TO TALK TO THE AFT FLT ATTENDANT AND A FEMALE PAX IN A LAV. HE CALLED US BACK SHORTLY THEREAFTER AND SAID NO ONE WAS HURT.

Data retrieved from NASA's ASRS site as of May 2009 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.