Narrative:

During descent to FL200 in smooth air, encountered abrupt 30 degree left roll and moderate turbulence. Aircraft returned to wings level by aileron. Autoplt was engaged and disconnected in roll without pilot action. Queried ATC and was advised 14.5 NM in trail of B757 in descent on same route. Callback conversation with reporter revealed the following information: reporter participated in the wake turbulence study. This wake event was short lived and had less effect on the following aircraft. However, the main significance is the fact it happened 14.5 mi behind the wake producing aircraft. The aircraft rolled 30 degrees but there was no other loss of altitude or heading change. Reporter felt the preceding aircraft type should have been announced to his flight crew, but, realizes it would be difficult to know exactly where to fly to avoid the wake from the B757. This was a chance encounter that could be classified as light wake.

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Original NASA ASRS Text

Title: A S80 ON DSCNT INTO ORD, ENCOUNTERS WAKE TURB FROM A PRECEDING B757. ALL THIS HAPPENS IN ZAU AIRSPACE.

Narrative: DURING DSCNT TO FL200 IN SMOOTH AIR, ENCOUNTERED ABRUPT 30 DEG L ROLL AND MODERATE TURB. ACFT RETURNED TO WINGS LEVEL BY AILERON. AUTOPLT WAS ENGAGED AND DISCONNECTED IN ROLL WITHOUT PLT ACTION. QUERIED ATC AND WAS ADVISED 14.5 NM IN TRAIL OF B757 IN DSCNT ON SAME RTE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB STUDY. THIS WAKE EVENT WAS SHORT LIVED AND HAD LESS EFFECT ON THE FOLLOWING ACFT. HOWEVER, THE MAIN SIGNIFICANCE IS THE FACT IT HAPPENED 14.5 MI BEHIND THE WAKE PRODUCING ACFT. THE ACFT ROLLED 30 DEGS BUT THERE WAS NO OTHER LOSS OF ALT OR HEADING CHANGE. RPTR FELT THE PRECEDING ACFT TYPE SHOULD HAVE BEEN ANNOUNCED TO HIS FLC, BUT, REALIZES IT WOULD BE DIFFICULT TO KNOW EXACTLY WHERE TO FLY TO AVOID THE WAKE FROM THE B757. THIS WAS A CHANCE ENCOUNTER THAT COULD BE CLASSIFIED AS LIGHT WAKE.

Data retrieved from NASA's ASRS site as of July 2007 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.