A S80 on descent into ord, encounters wake turbulence from a preceding B757. All this happens in ZAU...

Attributes
ACN	366935
Time
Date	199704
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : pmm
State Reference	MI
Altitude	msl bound lower : 21000 msl bound upper : 21000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau artcc : zid
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	descent other
Route In Use	arrival star : star
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 14000 flight time type : 2100
ASRS Report	366935
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	inflight encounter other other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : regained aircraft control
Consequence	Other
Supplementary
Air Traffic Incident	other

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.

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.

A S80 on descent into ord, encounters wake turbulence from a preceding B757. All this happens in ZAU airspace.