Narrative:

Cleared for visual approach to dfw runway 17L, having arrived over buj corner-post, then vectored to a 10 NM final. GS was OTS. At 8 mi, I visually acquired my interval aircraft, which was 3-4 mi ahead (via TCASII), in a steep, descending, l- hand turn to final, 500-1000 ft above my altitude. It had apparently arrived over the scy corner-post. When it stabilized on final approach course, lacking GS guidance, I observed it. Another dc-9-82 type, to be flying a significantly steeper approach than I was. WX was clear visibility 10 NM in haze, calm winds at all altitudes below 10000 ft. Aircraft ahead stabilized 2 1/2 - 3 NM ahead of my aircraft, 1/2 - 1 degree above my approach slope. At OM crossing we switched to dfw tower. Almost immediately, the aircraft which had been stable and trimmed up at 170 KTS, flaps 15 degrees, gear up, rolled approximately 30 degrees to the right, then 'snapped' to the left, I applied progressively larger right aileron and right rudder inputs, however, these seemed to have no effect upon the aircraft's roll rate. The aircraft stopped its roll approximately 70-80 degrees left wing down, then gradually righted itself becoming again responsive to the flight controls. The nose lost perhaps 5-10 degrees of pitch, but we lost little additional altitude. I simultaneously added power to correct for the descent and fly a higher approach path, completed the 'dirty up' on schedule and made a brief PA to the 80 passenger about the cause of the roll and to not be concerned excessively. Contributing factors: a) calm winds, B) lack of GS information, C) previous aircraft's steep approach, D) close separation typical of a dfw arrival complex, east) lack of my crew's appreciation for the amount of wake vortex a similar dc-9 aircraft can produce, and its effect on other turbojet aircraft. Callback conversation with reporter revealed the following information: reporter participated in the wake turbulence structured callback program. Reporter wrote an exacting report and added the following to the report. An encounter could have been anticipated as there were calm winds, no knowledge of the GS of the preceding aircraft, preceding aircraft steep approach meant he would go through the wake somewhere, 2 1/2 mi separation, and realization that any jet can cause severe turbulence. His ideas for what to do next time are: fly above other aircraft's GS, carry an extra 10 KTS of speed, be ready for a go around at any sign of wake turbulence. This reporter had no roll control as the encounter progressed. He applied 45 degrees of aileron and heavy rudder, but response to control inputs was slow to take effect. He was positive the bank angle reached at least 70 degrees if not more and the event lasted at least 6 seconds.

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Original NASA ASRS Text

Title: WAKE TURB ENCOUNTER AT DFW.

Narrative: CLRED FOR VISUAL APCH TO DFW RWY 17L, HAVING ARRIVED OVER BUJ CORNER-POST, THEN VECTORED TO A 10 NM FINAL. GS WAS OTS. AT 8 MI, I VISUALLY ACQUIRED MY INTERVAL ACFT, WHICH WAS 3-4 MI AHEAD (VIA TCASII), IN A STEEP, DSNDING, L- HAND TURN TO FINAL, 500-1000 FT ABOVE MY ALT. IT HAD APPARENTLY ARRIVED OVER THE SCY CORNER-POST. WHEN IT STABILIZED ON FINAL APCH COURSE, LACKING GS GUIDANCE, I OBSERVED IT. ANOTHER DC-9-82 TYPE, TO BE FLYING A SIGNIFICANTLY STEEPER APCH THAN I WAS. WX WAS CLR VISIBILITY 10 NM IN HAZE, CALM WINDS AT ALL ALTS BELOW 10000 FT. ACFT AHEAD STABILIZED 2 1/2 - 3 NM AHEAD OF MY ACFT, 1/2 - 1 DEG ABOVE MY APCH SLOPE. AT OM XING WE SWITCHED TO DFW TWR. ALMOST IMMEDIATELY, THE ACFT WHICH HAD BEEN STABLE AND TRIMMED UP AT 170 KTS, FLAPS 15 DEGS, GEAR UP, ROLLED APPROX 30 DEGS TO THE R, THEN 'SNAPPED' TO THE L, I APPLIED PROGRESSIVELY LARGER R AILERON AND R RUDDER INPUTS, HOWEVER, THESE SEEMED TO HAVE NO EFFECT UPON THE ACFT'S ROLL RATE. THE ACFT STOPPED ITS ROLL APPROX 70-80 DEGS L WING DOWN, THEN GRADUALLY RIGHTED ITSELF BECOMING AGAIN RESPONSIVE TO THE FLT CTLS. THE NOSE LOST PERHAPS 5-10 DEGS OF PITCH, BUT WE LOST LITTLE ADDITIONAL ALT. I SIMULTANEOUSLY ADDED PWR TO CORRECT FOR THE DSCNT AND FLY A HIGHER APCH PATH, COMPLETED THE 'DIRTY UP' ON SCHEDULE AND MADE A BRIEF PA TO THE 80 PAX ABOUT THE CAUSE OF THE ROLL AND TO NOT BE CONCERNED EXCESSIVELY. CONTRIBUTING FACTORS: A) CALM WINDS, B) LACK OF GS INFO, C) PREVIOUS ACFT'S STEEP APCH, D) CLOSE SEPARATION TYPICAL OF A DFW ARR COMPLEX, E) LACK OF MY CREW'S APPRECIATION FOR THE AMOUNT OF WAKE VORTEX A SIMILAR DC-9 ACFT CAN PRODUCE, AND ITS EFFECT ON OTHER TURBOJET ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB STRUCTURED CALLBACK PROGRAM. RPTR WROTE AN EXACTING RPT AND ADDED THE FOLLOWING TO THE RPT. AN ENCOUNTER COULD HAVE BEEN ANTICIPATED AS THERE WERE CALM WINDS, NO KNOWLEDGE OF THE GS OF THE PRECEDING ACFT, PRECEDING ACFT STEEP APCH MEANT HE WOULD GO THROUGH THE WAKE SOMEWHERE, 2 1/2 MI SEPARATION, AND REALIZATION THAT ANY JET CAN CAUSE SEVERE TURB. HIS IDEAS FOR WHAT TO DO NEXT TIME ARE: FLY ABOVE OTHER ACFT'S GS, CARRY AN EXTRA 10 KTS OF SPD, BE READY FOR A GAR AT ANY SIGN OF WAKE TURB. THIS RPTR HAD NO ROLL CTL AS THE ENCOUNTER PROGRESSED. HE APPLIED 45 DEGS OF AILERON AND HVY RUDDER, BUT RESPONSE TO CTL INPUTS WAS SLOW TO TAKE EFFECT. HE WAS POSITIVE THE BANK ANGLE REACHED AT LEAST 70 DEGS IF NOT MORE AND THE EVENT LASTED AT LEAST 6 SECONDS.

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.