Date: 201606
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Second aircraft: B787 Dreamliner Undifferentiated or Other Model
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Inflight Event / Encounter Wake Vortex Encounter
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert
Contributing factors: Procedure; Environment - Non Weather Related
Primary problem: Ambiguous

Narrative: On arrival into ZZZ; we encountered the wake of a preceding B787 that was reported to be 9 miles ahead. We were descending VIA the arrival in VERY smooth air above the haze layer right at ZZZZZ intersection. Our speed was 220 assigned. The aircraft made 3 uncommanded rolls of approximately 5-10 degrees. The rolls were less than 1 second each and were consecutive (LRL or RLR--not sure). It also felt like yaw and pitch accelerations; but not very much magnitude. After the encounter; the air was still smooth; but we descended into the haze layer shortly afterwards (30 seconds or so) where it was intermittent light turbulence. The autopilot and autothrottles remained on. We all remarked that it was a wake encounter and I called ATC and asked what we were following. He said it was a B787 9 miles in front of us. We had heard him get 210 knots earlier and we were at 220 assigned. At about 4 miles a minute groundspeed; we were about 2 minutes behind him and because of the STAR; should have been at the same altitude/descent profiles at that crossing restriction (ZZZZZ intersection 7000 ft). I am not sure what the winds were but it was very smooth just above the haze layer. ATC offered to let us fly higher on the arrival; but by that time; we were in the haze layer where it was intermittent light turbulence and that should have broken up the wake quicker. We didn't feel that an offset would help; either; once we entered the haze layer. The wind vector there showed a SW crossing headwind and it was bumpy. The encounter was more than light turbulence in roll accelerations; but was smoother in vertical g load. I am not sure if there was much; if any; pitch change due to the wake encounter; but it was very characteristic of wake encounters. We continued the arrival to a visual behind the heavy and kept track of the crosswind on final to mitigate the chance of another encounter. We had a 10 knot crosswind on final (although a slight tailwind component) and felt that the wake would be well east of us. We did monitor that we had almost 5nm on final (TCAS estimate).If I were 'rating' this encounter; I would say it was a 'minor' severity event. These things happen; and the wake had decayed to a point where it was manageable for us; a B757. I wouldn't have wanted to hit that in an RJ or even a short coupled B737 or A319. We were about 172k pounds. That said; a cup of coffee would have spilled; and flight attendants could have been injured (they were not). If a passenger had been up getting things into/out of the overhead; it could have been an injury (it felt a bit like a very tight 'dutch roll').

Callback: Reporter stated the incident would have been more severe for a smaller aircraft.



Synopsis: B757 First Officer reported encountering wake turbulence in 9-mile trail of a B787 on descent.