B737 flight crew reported a wake turbulence encounter at FL360 in 8-mile trail of another B737 that ...

Attributes
ACN	1357807
Time
Date	201605
Local Time Of Day	1201-1800
Place
Locale Reference	ZID.ARTCC
State Reference	IN
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Aircraft 2
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 229 Flight Crew Type 14000
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 215 Flight Crew Type 7000
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Inflight Event / Encounter Wake Vortex Encounter

Narrative:

We were in cruise at FL360 when the aircraft entered the wake of another 737; later reported as 8 miles ahead. The aircraft initially rolled strongly to the left at a rate the autopilot could not counter. I disconnected the autopilot; and rolled back to the right to level flight. There was a large amount of buffeting; and then we had lost 200 to 300 ft in the initial roll. I began to pitch up to return to FL360; as we entered an equally strong roll to the right. I abandoned the effort to climb back to altitude; and tried to get us back to level flight. We lost an additional 200 to 300 ft of altitude in the second roll. Center called us to verify our assigned altitude; and the first officer reported the wake turbulence encounter; requesting a lower altitude to escape it. Center immediately gave us clearance to FL350; and a vector off course to escape the wake. This was one of the strongest wakes I have ever encountered. We were perfectly aligned behind the preceding 737; with the wind also perfectly aligned with our flight path. Once we entered the wake; we were going to stay in it until we changed course. In the future I will pay more attention to the direction of the winds aloft when considering the effect of wake turbulence.

Original NASA ASRS Text

Title: B737 flight crew reported a wake turbulence encounter at FL360 in 8-mile trail of another B737 that resulted in loss of 500-600 feet of altitude.

Narrative: We were in cruise at FL360 when the aircraft entered the wake of another 737; later reported as 8 miles ahead. The aircraft initially rolled strongly to the left at a rate the autopilot could not counter. I disconnected the autopilot; and rolled back to the right to level flight. There was a large amount of buffeting; and then we had lost 200 to 300 ft in the initial roll. I began to pitch up to return to FL360; as we entered an equally strong roll to the right. I abandoned the effort to climb back to altitude; and tried to get us back to level flight. We lost an additional 200 to 300 ft of altitude in the second roll. Center called us to verify our assigned altitude; and the FO reported the wake turbulence encounter; requesting a lower altitude to escape it. Center immediately gave us clearance to FL350; and a vector off course to escape the wake. This was one of the strongest wakes I have ever encountered. We were perfectly aligned behind the preceding 737; with the wind also perfectly aligned with our flight path. Once we entered the wake; we were going to stay in it until we changed course. In the future I will pay more attention to the direction of the winds aloft when considering the effect of wake turbulence.

Data retrieved from NASA's ASRS site 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.