Mdt encounters wake turbulence even though proper 3 mi spacing existed.

Attributes
ACN	195104
Time
Date	199111
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 7000 msl bound upper : 7000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Medium Transport
Navigation In Use	Other Other
Flight Phase	descent : approach descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 10000
ASRS Report	195104
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp pilot : instrument
Events
Anomaly	other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

After deere intersection cleared ord VOR at 7000 encountered wake from preceding large transport at same altitude approximately visually appeared to be the required 3 mi separation by ATC. Aircraft started roll to the left and started buffeting. Autoplt, yaw damper and adu failed, negative G's were felt and cockpit and cabin items were dislodged and a very rough shaking was experienced. Flight attendant was hurt, minor injuries. Aircraft was inspected for damage. The only damage I'm aware of was inside the aircraft from the flight attendant being tossed around and bent curtain rod. The conditions of flight were smooth air and the legal separation does not appear to be adequate under some atmospheric conditions such as smooth air. At this point in time I understand this is classified as an incident and the NTSB is investigating it.

Original NASA ASRS Text

Title: MDT ENCOUNTERS WAKE TURB EVEN THOUGH PROPER 3 MI SPACING EXISTED.

Narrative: AFTER DEERE INTXN CLRED ORD VOR AT 7000 ENCOUNTERED WAKE FROM PRECEDING LGT AT SAME ALT APPROX VISUALLY APPEARED TO BE THE REQUIRED 3 MI SEPARATION BY ATC. ACFT STARTED ROLL TO THE L AND STARTED BUFFETING. AUTOPLT, YAW DAMPER AND ADU FAILED, NEGATIVE G'S WERE FELT AND COCKPIT AND CABIN ITEMS WERE DISLODGED AND A VERY ROUGH SHAKING WAS EXPERIENCED. FLT ATTENDANT WAS HURT, MINOR INJURIES. ACFT WAS INSPECTED FOR DAMAGE. THE ONLY DAMAGE I'M AWARE OF WAS INSIDE THE ACFT FROM THE FLT ATTENDANT BEING TOSSED AROUND AND BENT CURTAIN ROD. THE CONDITIONS OF FLT WERE SMOOTH AIR AND THE LEGAL SEPARATION DOES NOT APPEAR TO BE ADEQUATE UNDER SOME ATMOSPHERIC CONDITIONS SUCH AS SMOOTH AIR. AT THIS POINT IN TIME I UNDERSTAND THIS IS CLASSIFIED AS AN INCIDENT AND THE NTSB IS INVESTIGATING IT.

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.