Narrative:

We had just about leveled at FL330 when we encountered what we suspected was wake turbulence from aircraft at FL340 about 20 NM ahead. Winds at the time were direct tailwinds at about 40 KTS so that might be why the wake persisted in the area for so long. Duration of turbulence was approximately 5-10 second of mod duration. Seat belt sign was off but passenger were not up only flight attendants. We adjusted our course to the right 2 NM; turned on the seat belt sign. By that time the turbulence was over. We called the purser to see if everyone was ok. She said yes at the time; but about an hour later she found out 2 flight attendants were complaining of back pains after falling to the floor. They were ok to continue duties and didn't want medical personnel to meet the flight.

Google
 

Original NASA ASRS Text

Title: TWO FLT ATTENDANTS ABOARD B767-300 RECEIVE SLIGHT INJURIES WHEN THROWN TO THE FLOOR DURING WAKE TURB ENCOUNTER.

Narrative: WE HAD JUST ABOUT LEVELED AT FL330 WHEN WE ENCOUNTERED WHAT WE SUSPECTED WAS WAKE TURBULENCE FROM ACFT AT FL340 ABOUT 20 NM AHEAD. WINDS AT THE TIME WERE DIRECT TAILWINDS AT ABOUT 40 KTS SO THAT MIGHT BE WHY THE WAKE PERSISTED IN THE AREA FOR SO LONG. DURATION OF TURBULENCE WAS APPROX 5-10 SEC OF MOD DURATION. SEAT BELT SIGN WAS OFF BUT PAX WERE NOT UP ONLY FLT ATTENDANTS. WE ADJUSTED OUR COURSE TO THE R 2 NM; TURNED ON THE SEAT BELT SIGN. BY THAT TIME THE TURBULENCE WAS OVER. WE CALLED THE PURSER TO SEE IF EVERYONE WAS OK. SHE SAID YES AT THE TIME; BUT ABOUT AN HOUR LATER SHE FOUND OUT 2 FLT ATTENDANTS WERE COMPLAINING OF BACK PAINS AFTER FALLING TO THE FLOOR. THEY WERE OK TO CONTINUE DUTIES AND DIDN'T WANT MEDICAL PERSONNEL TO MEET THE FLT.

Data retrieved from NASA's ASRS site as of January 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.