The crew of an A320 encountered B777 wake turbulence at FL390.

Attributes
ACN	699546
Time
Date	200606
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : ape.vortac
State Reference	PA
Altitude	msl single value : 39000
Environment
Flight Conditions	VMC
Aircraft 1
Controlling Facilities	artcc : zid.artcc
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zid.artcc
Operator	common carrier : air carrier
Make Model Name	B777 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : enroute altitude change
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 190 flight time total : 7100 flight time type : 584
ASRS Report	699546
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	inflight encounter : wake turbulence other anomaly
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : exited adverse environment flight crew : regained aircraft control flight crew : took precautionary avoidance action
Supplementary
Problem Areas	Airspace Structure
Primary Problem	Airspace Structure

Narrative:

B777 air carrier Y reported poor ride at FL400 and descended to FL390 less than 20 mi ahead. We were at FL390 and encountered roll left of 15 degree angle of bank and moderate turbulence accompanied by engine #1 stall advisory. Immediately turned left 10 degrees to exit wake turbulence and recovered attitude then notified ATC with no loss of altitude. All engine indications showed normal with no further advisories. Flight attendant in rear of aircraft strained arm while attempting to maintain balance during wake turbulence encounter. Passenger had previously been seated with fasten seatbelt sign on before incident due to light chop.

Original NASA ASRS Text

Title: THE CREW OF AN A320 ENCOUNTERED B777 WAKE TURB AT FL390.

Narrative: B777 ACR Y RPTED POOR RIDE AT FL400 AND DSNDED TO FL390 LESS THAN 20 MI AHEAD. WE WERE AT FL390 AND ENCOUNTERED ROLL L OF 15 DEG ANGLE OF BANK AND MODERATE TURB ACCOMPANIED BY ENG #1 STALL ADVISORY. IMMEDIATELY TURNED L 10 DEGS TO EXIT WAKE TURB AND RECOVERED ATTITUDE THEN NOTIFIED ATC WITH NO LOSS OF ALT. ALL ENG INDICATIONS SHOWED NORMAL WITH NO FURTHER ADVISORIES. FLT ATTENDANT IN REAR OF ACFT STRAINED ARM WHILE ATTEMPTING TO MAINTAIN BAL DURING WAKE TURB ENCOUNTER. PAX HAD PREVIOUSLY BEEN SEATED WITH FASTEN SEATBELT SIGN ON BEFORE INCIDENT DUE TO LIGHT CHOP.

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.