Narrative:

The flight was in the area of raddy intersection at 16;000. The clearance was to cross raddy at or below 15;000 and aubrn at 12;000. The VNAV was programmed for this descent profile. Just as the VNAV became active the flight encountered moderate wake turbulence. We asked ATC what we were following and were advised it was a 747. We told ATC we were in the wake and requested a turn to avoid any further wake. He responded that the 747 was 10 miles ahead. I indicated that I did not care how far ahead he was; we need a turn to avoid any additional wake. I disconnected the autopilot and descended to remain out of the wake if it were to become more intense. The controller gave us the turn and speed reduction to increase separation. We continued our descent and had no further encounter. The flight did not have any deviation from our clearance; far or aircraft limitation. I also believe the controller to be in compliance. The purpose of this submission is to bring attention to the practice of descending heavy aircraft through the flight path of other aircraft. Although the encounter was unnerving to the flight deck crew; the flight attendants were bothered by it too. They called the flight deck after the encounter to make sure everything was alright.

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Original NASA ASRS Text

Title: A Q400 Captain reported encountering wake turbulence on descent from a preceding B747 and requested a new clearance which ATC provided.

Narrative: The flight was in the area of RADDY Intersection at 16;000. The clearance was to cross RADDY at or below 15;000 and AUBRN at 12;000. The VNAV was programmed for this descent profile. Just as the VNAV became active the flight encountered moderate wake turbulence. We asked ATC what we were following and were advised it was a 747. We told ATC we were in the wake and requested a turn to avoid any further wake. He responded that the 747 was 10 miles ahead. I indicated that I did not care how far ahead he was; we need a turn to avoid any additional wake. I disconnected the autopilot and descended to remain out of the wake if it were to become more intense. The Controller gave us the turn and speed reduction to increase separation. We continued our descent and had no further encounter. The flight did not have any deviation from our clearance; FAR or aircraft limitation. I also believe the Controller to be in compliance. The purpose of this submission is to bring attention to the practice of descending heavy aircraft through the flight path of other aircraft. Although the encounter was unnerving to the flight deck crew; the flight attendants were bothered by it too. They called the flight deck after the encounter to make sure everything was alright.

Data retrieved from NASA's ASRS site as of April 2012 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.