Wake turbulence encounter.

Attributes
ACN	316323
Time
Date	199509
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 4000 msl bound upper : 7000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	B767-300 and 300 ER
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	MD-11
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 120 flight time total : 9900 flight time type : 2200
ASRS Report	316323
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	inflight encounter other other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

At ord on right downwind for runway 4R abeam midfield autoplt engaged. When we checked in with our final approach controller he advised we were following a MD11 caution wake turbulence. We were cleared to descend from 7000 ft to 4000 ft. As I started down it became obvious that we were entering the wake of the MD11. The ride was similar to light turbulence. Just as I began to shallow the descent in order to remain above the wake our aircraft rolled at a rapid rate to the left. I disengaged the autoplt at approximately 30 degrees of bank and applied full right aileron to stop the roll. The aircraft was slow in responding and exceeded 40 degrees of bank before starting to roll back to level. The captain requested greater separation from the MD11 and ATC responded by giving us 5 mi in trail. The remainder of the flight was uneventful. Callback conversation with reporter revealed the following information: reporter participated in the wake turbulence structured callback program. During callback the reporter felt the beginning of the wake encounter describing it as light turbulence. Then the sharp jolt occurred and rolled the aircraft into a 40 degree bank. There was not much flight path displacement but the roll was accompanied with an increase in 'G' forces and some yaw. The aircraft was taken off of autoplt and manual control forces were used for the recovery. Reporter felt that full control deflection could not stop the roll. The autoplt was left on as the bank increased to 30 degrees, then disconnected, manual input could not stop the roll from increasing to 40 degrees of bank. Reporter felt that the unusual attitude training offered by his air carrier was most helpful in the recovery process. What he would do differently during recovery next time, is add more rudder into the direction of the desired roll. Encounter was a big surprise to all of the flight crew. Reporter would ask controller for more spacing the next time he is following a heavy jet.

Original NASA ASRS Text

Title: WAKE TURB ENCOUNTER.

Narrative: AT ORD ON R DOWNWIND FOR RWY 4R ABEAM MIDFIELD AUTOPLT ENGAGED. WHEN WE CHKED IN WITH OUR FINAL APCH CTLR HE ADVISED WE WERE FOLLOWING A MD11 CAUTION WAKE TURB. WE WERE CLRED TO DSND FROM 7000 FT TO 4000 FT. AS I STARTED DOWN IT BECAME OBVIOUS THAT WE WERE ENTERING THE WAKE OF THE MD11. THE RIDE WAS SIMILAR TO LIGHT TURB. JUST AS I BEGAN TO SHALLOW THE DSCNT IN ORDER TO REMAIN ABOVE THE WAKE OUR ACFT ROLLED AT A RAPID RATE TO THE L. I DISENGAGED THE AUTOPLT AT APPROX 30 DEGS OF BANK AND APPLIED FULL R AILERON TO STOP THE ROLL. THE ACFT WAS SLOW IN RESPONDING AND EXCEEDED 40 DEGS OF BANK BEFORE STARTING TO ROLL BACK TO LEVEL. THE CAPT REQUESTED GREATER SEPARATION FROM THE MD11 AND ATC RESPONDED BY GIVING US 5 MI IN TRAIL. THE REMAINDER OF THE FLT WAS UNEVENTFUL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB STRUCTURED CALLBACK PROGRAM. DURING CALLBACK THE RPTR FELT THE BEGINNING OF THE WAKE ENCOUNTER DESCRIBING IT AS LIGHT TURB. THEN THE SHARP JOLT OCCURRED AND ROLLED THE ACFT INTO A 40 DEG BANK. THERE WAS NOT MUCH FLT PATH DISPLACEMENT BUT THE ROLL WAS ACCOMPANIED WITH AN INCREASE IN 'G' FORCES AND SOME YAW. THE ACFT WAS TAKEN OFF OF AUTOPLT AND MANUAL CTL FORCES WERE USED FOR THE RECOVERY. RPTR FELT THAT FULL CTL DEFLECTION COULD NOT STOP THE ROLL. THE AUTOPLT WAS LEFT ON AS THE BANK INCREASED TO 30 DEGS, THEN DISCONNECTED, MANUAL INPUT COULD NOT STOP THE ROLL FROM INCREASING TO 40 DEGS OF BANK. RPTR FELT THAT THE UNUSUAL ATTITUDE TRAINING OFFERED BY HIS ACR WAS MOST HELPFUL IN THE RECOVERY PROCESS. WHAT HE WOULD DO DIFFERENTLY DURING RECOVERY NEXT TIME, IS ADD MORE RUDDER INTO THE DIRECTION OF THE DESIRED ROLL. ENCOUNTER WAS A BIG SURPRISE TO ALL OF THE FLC. RPTR WOULD ASK CTLR FOR MORE SPACING THE NEXT TIME HE IS FOLLOWING A HVY JET.

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.