A321 flight crew reported encountering wake turbulence from a preceding A321 at FL340 that resulted in a minor injury to a Flight Attendant.
Synopsis
A321 flight crew reported encountering wake turbulence from a preceding A321 at FL340 that resulted in a minor injury to a Flight Attendant.
Narrative
We leveled off in cruise flight at FL340 and had a smooth ride for several minutes; prompting my CA (Captain) to turn off the fasten seatbelts sign. We had been following Aircraft Y at the same flight level and on the same route; not within visual range; but close enough to display on our AGD (ADS-B Guidance Display). Between KEMPR and YLEEEE the aircraft abruptly rolled to the right to 25 - 30 degrees of bank and remained there for approximately 5 seconds as the autopilot countered the roll and was then able to recover to a wings level attitude. No altitude was gained or lost; and very little chop accompanied the rolling movement. Once recovered; we evaluated the position of all traffic we could identify within visual range and on the traffic displays around us; and concluded that the only plausible source of wake turbulence capable of influencing our flight path was Aircraft Y directly ahead of us. There was very little other traffic above; below; or at our altitude within 40 miles of our location. I advised ATC that we encountered wake turbulence and requested more separation between us and the preceding aircraft. The controller acknowledged and turned us off course to the right for some time to widen the spacing between our aircraft. I told my CA that the event felt significant enough to me that checking on the passengers and flight attendants would be advisable. He spoke to the flight attendants who said that one fell down and may have bruised her elbow; but felt she could continue her duties and was otherwise okay. They advised that the passengers were also fine. We continued to our destination with no other anomalies.It seems very likely that the cause of our wake turbulence encounter was caused by the preceding A321 at our altitude. The spacing between our aircraft should have been adequate; but we were unable to identify any other aircraft close enough to influence our flight with wake turbulence.It seems to me that this was a somewhat unusual occurrence as aircraft spacing was adequate and wake vortices tend to descend fast enough to make aircraft at the same flight level not a wake turbulence threat to each other in the cruise phase of flight; but I suppose certain conditions may be able to cause exceptions to that rule. I'm not sure this could have been avoided using standard procedures by ourselves or ATC; as our situation didn't seem to warrant more than standard spacing; at least before the event occurred.
Second reporter narrative
On Aircraft X PHL - ZZZ; we encountered unexpected wake turbulence at FL340. One Flight Attendant fell and injured her wrist and elbow. She continued the trip. Dispatch was notified. [The cause was] wake turbulence from preceding aircraft at FL340.
NASA callback
The reporter stated that the roll was quite abrupt and was a concern at their altitude.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.