An A320 Flight Crew reported a probable wake turbulence encounter at FL370 that resulted in significant uncommanded roll in both directions. The crew reported what appeared to be spiral-shaped wing tip votices at their flight level.
Synopsis
An A320 Flight Crew reported a probable wake turbulence encounter at FL370 that resulted in significant uncommanded roll in both directions. The crew reported what appeared to be spiral-shaped wing tip votices at their flight level.
Narrative
We were at FL370 (approx); autopilot was on; weather was clear; visibility unlimited; smooth air. Suddenly; for no apparent reason; the aircraft banked approx 25-30 degrees right; then went about 20 degrees left. The autopilot did not disengage; but I disengaged it manually and maintained level flight with aileron input only. After both pilots confirmed that all flight computers were functioning normally; I re-engaged the autopilot. All flight phases were uneventful after I re-engaged the autopilot. Everything was functioning normally. It was at this time that the First Officer (pilot not flying) noticed a spiraling shaped vortex at our flight level. To me; it looked like wing tip vortices. It was there momentarily; and; after a brief discussion; we determined the vortex to possibly be some wake turbulence (like one would see on final approach or while observing landing aircraft) from another aircraft. I then made an announcement to the passengers about our circumstance; and then I talked with the Chief Purser on their experiences in the passenger compartment. Though everyone was startled; all Flight Attendants were OK as well as all of the passengers. There were no reports of any injuries; though I was told one woman in the back was crying. As turbulence is a 'part of the job' and because no passenger or Flight Attendant was injured; both pilots decided that a report was unnecessary for this incident. In retrospect; I believe I should have informed ATC and asked if there were any large/heavy aircraft near our plane that may have caused our temporary problem with their wake; but we did not elect to do this. Finally; I made it a point to go out in the cabin during deplaning to address any passenger concerns or questions. I received no negative comments about our flight; only praise.
Second reporter narrative
At cruise we encountered an uncommanded roll to the left and then a roll to the right of approximately 30 degrees of bank. It was the Captain's leg so he grabbed the side-stick and disconnected the autopilot. The airplane corrected back to level attitude. At this time I noticed the remnants of a contrail just above our altitude. It was parallel to our flight path. We did have traffic pass over us in opposite direction minutes before the incident. I also noted a direct tailwind of 50 KTS. The roll was abrupt enough to cause a coffee pot to fall of a serving cart in the back. No injuries were reported. We figured it must have been wake turbulence but could not be certain.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.