Narrative:

Being vectored for the approach to runway 4R at ord we apparently flew into wake of an air carrier B777 6 mi ahead being vectored for the same runway. We experienced a high rate of roll to the left which required most of the available aileron and substantial rudder to stop the roll. This was followed by (2) more encounters of less magnitude. We asked for more spacing and flew approach 1 DOT high on GS to runway. No other problems noted. No injuries to flight crew or passenger. Autoplt was disconnected after 1ST encounter. Callback conversation with reporter revealed the following information: this reporter participated in the structured wake turbulence callback study. Descending and close to the airport, this reporter was flying when his aircraft encountered wake turbulence from a preceding B777. He had a roll left and right of 20 degrees. Maximum flight path displacement was only 50 ft. He did not have full control during the encounter but had partial control. The encounter lasted about 9 seconds. As soon as they were able to fly up and out of the wake, the reporter flew 1 DOT high on the GS to clear any other wake generated by the B777. Remainder of the approach and landing went well. Reporter feels he would like greater spacing behind a heavy aircraft. The other thing he would do is question TRACON where a preceding aircraft started his descent. He would like more information as to the preceding aircraft ground track and vertical track. That information would help him plan to be above or displaced laterally from any wake. Supplemental information from acn 331996: we had a high rate of roll to the left which required most of the available aileron and a substantial amount of rudder to stop, and then correct the roll. This was followed by 2 more roll events of less magnitude. Asked for and was given more spacing behind the traffic and flew 1 DOT high on approach to runway. Callback conversation with reporter of acn 331996 revealed the following information: this reporter participated in the wake turbulence incident callback. The reporter has been involved in other wake turbulence incidents and this was not as severe as others, however, it was longer lasting. His estimate of the duration was 9 seconds. During this time he reported that there was partial control of the aircraft available. His airspeed at the time of the incident was 210 KTS which helped them climb up and out of the wake. Reporter suggestion on how to avoid wake in the future is assign additional separation, descend narrow body aircraft on a track different from wide body aircraft, and give following aircraft an offset ground track to the runway. Reporter did state that since the aileron control was reduced when in the wake, control was established by large input of rudder control. Rudder is most effective in stopping the rolling action of the wake.

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Original NASA ASRS Text

Title: B737 ACFT ENCOUNTERS WAKE TURB BEHIND A B777.

Narrative: BEING VECTORED FOR THE APCH TO RWY 4R AT ORD WE APPARENTLY FLEW INTO WAKE OF AN ACR B777 6 MI AHEAD BEING VECTORED FOR THE SAME RWY. WE EXPERIENCED A HIGH RATE OF ROLL TO THE L WHICH REQUIRED MOST OF THE AVAILABLE AILERON AND SUBSTANTIAL RUDDER TO STOP THE ROLL. THIS WAS FOLLOWED BY (2) MORE ENCOUNTERS OF LESS MAGNITUDE. WE ASKED FOR MORE SPACING AND FLEW APCH 1 DOT HIGH ON GS TO RWY. NO OTHER PROBS NOTED. NO INJURIES TO FLC OR PAX. AUTOPLT WAS DISCONNECTED AFTER 1ST ENCOUNTER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR PARTICIPATED IN THE STRUCTURED WAKE TURB CALLBACK STUDY. DSNDING AND CLOSE TO THE ARPT, THIS RPTR WAS FLYING WHEN HIS ACFT ENCOUNTERED WAKE TURB FROM A PRECEDING B777. HE HAD A ROLL L AND R OF 20 DEGS. MAX FLT PATH DISPLACEMENT WAS ONLY 50 FT. HE DID NOT HAVE FULL CTL DURING THE ENCOUNTER BUT HAD PARTIAL CTL. THE ENCOUNTER LASTED ABOUT 9 SECONDS. AS SOON AS THEY WERE ABLE TO FLY UP AND OUT OF THE WAKE, THE RPTR FLEW 1 DOT HIGH ON THE GS TO CLR ANY OTHER WAKE GENERATED BY THE B777. REMAINDER OF THE APCH AND LNDG WENT WELL. RPTR FEELS HE WOULD LIKE GREATER SPACING BEHIND A HVY ACFT. THE OTHER THING HE WOULD DO IS QUESTION TRACON WHERE A PRECEDING ACFT STARTED HIS DSCNT. HE WOULD LIKE MORE INFO AS TO THE PRECEDING ACFT GND TRACK AND VERT TRACK. THAT INFO WOULD HELP HIM PLAN TO BE ABOVE OR DISPLACED LATERALLY FROM ANY WAKE. SUPPLEMENTAL INFO FROM ACN 331996: WE HAD A HIGH RATE OF ROLL TO THE L WHICH REQUIRED MOST OF THE AVAILABLE AILERON AND A SUBSTANTIAL AMOUNT OF RUDDER TO STOP, AND THEN CORRECT THE ROLL. THIS WAS FOLLOWED BY 2 MORE ROLL EVENTS OF LESS MAGNITUDE. ASKED FOR AND WAS GIVEN MORE SPACING BEHIND THE TFC AND FLEW 1 DOT HIGH ON APCH TO RWY. CALLBACK CONVERSATION WITH RPTR OF ACN 331996 REVEALED THE FOLLOWING INFO: THIS RPTR PARTICIPATED IN THE WAKE TURB INCIDENT CALLBACK. THE RPTR HAS BEEN INVOLVED IN OTHER WAKE TURB INCIDENTS AND THIS WAS NOT AS SEVERE AS OTHERS, HOWEVER, IT WAS LONGER LASTING. HIS ESTIMATE OF THE DURATION WAS 9 SECONDS. DURING THIS TIME HE RPTED THAT THERE WAS PARTIAL CTL OF THE ACFT AVAILABLE. HIS AIRSPD AT THE TIME OF THE INCIDENT WAS 210 KTS WHICH HELPED THEM CLB UP AND OUT OF THE WAKE. RPTR SUGGESTION ON HOW TO AVOID WAKE IN THE FUTURE IS ASSIGN ADDITIONAL SEPARATION, DSND NARROW BODY ACFT ON A TRACK DIFFERENT FROM WIDE BODY ACFT, AND GIVE FOLLOWING ACFT AN OFFSET GND TRACK TO THE RWY. RPTR DID STATE THAT SINCE THE AILERON CTL WAS REDUCED WHEN IN THE WAKE, CTL WAS ESTABLISHED BY LARGE INPUT OF RUDDER CTL. RUDDER IS MOST EFFECTIVE IN STOPPING THE ROLLING ACTION OF THE 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.