Narrative:

While descending through FL290 on the eagul five RNAV arrival into phx; we encountered unexpected wake turbulence that put the aircraft into a 20-degree right bank followed by a 20-degree left bank. There were no reports of turbulence in the area. We noticed another aircraft descending ahead of us approximately 20 miles ahead and 2;000 ft below. We queried ATC told them what happened and asked what kind of aircraft were we following. They told us it was another B737NG. He gave us a 15-degree heading change to the right in order to put more distance between us and the other aircraft. After a few minutes; we were cleared back on course and had no other wake turbulence issues. Once we were sure that the aircraft was under control; the captain called the cabin to check on the flight attendants. They stated that [one] flight attendant had felt a jolt in her neck and felt that she may have twisted wrong during the event. Once on the ground; the captain reported the incident as per the fom and spoke to the [injured] flight attendant at length. She assured us that she was okay and continued the trip. We continued the remainder of the trip with no other incidents. I'm not sure if there was much that could have been done in this event. We just happened to get caught up in wake turbulence. However; we did have a direct headwind on the arrival. That could have been the cause of the wake not dissipating soon enough. I will now be more aware of the potential hazards of encountering wake even though we have 20 miles of separation especially when there is a strong headwind along the flight path.

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Original NASA ASRS Text

Title: B737-800 flight crew reported encountering wake turbulence in trail of another B737NG on descent to PHX.

Narrative: While descending through FL290 on the EAGUL Five RNAV Arrival into PHX; we encountered unexpected wake turbulence that put the aircraft into a 20-degree right bank followed by a 20-degree left bank. There were no reports of turbulence in the area. We noticed another aircraft descending ahead of us approximately 20 miles ahead and 2;000 FT below. We queried ATC told them what happened and asked what kind of aircraft were we following. They told us it was another B737NG. He gave us a 15-degree heading change to the right in order to put more distance between us and the other aircraft. After a few minutes; we were cleared back on course and had no other wake turbulence issues. Once we were sure that the aircraft was under control; the Captain called the cabin to check on the flight attendants. They stated that [one] Flight Attendant had felt a jolt in her neck and felt that she may have twisted wrong during the event. Once on the ground; the Captain reported the incident as per the FOM and spoke to the [injured] Flight Attendant at length. She assured us that she was okay and continued the trip. We continued the remainder of the trip with no other incidents. I'm not sure if there was much that could have been done in this event. We just happened to get caught up in wake turbulence. However; we did have a direct headwind on the arrival. That could have been the cause of the wake not dissipating soon enough. I will now be more aware of the potential hazards of encountering wake even though we have 20 miles of separation especially when there is a strong headwind along the flight path.

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.