Narrative:

While approaching atlanta from the southwest, we were given a descent to 4000 ft. The autoplt was engaged and we were indicating 245 KTS. Out of the corner of my eye I caught sight of an L1011 crossing right to left. Approximately 30 seconds later, we hit his wake at a 90 degree angle. The encounter was very brief but extreme. The autoplt disconnected itself and the captain and I both lightly placed our hands on the controls to gain control of the aircraft. Shortly after that, we once again engaged the autoplt and the remaining turns were done in smooth air with the autoplt engaged. After lining up on final, I disengaged the autoplt and proceeded to hand fly the aircraft. The L1011 landed on runway 27R. We were initially given this runway but runway 27L became available so we chose it. The landing approach was uneventful. The aircraft would trim (pitch) just fine but I did notice something odd with the pitch forces with the yoke. I couldn't put my finger on it at the time. On landing rollout we got a level 3 llas alert (emergency). First thought was engine fire. As it turns out it was a pitch disconnect. As best as we can figure the wake encounter had disconnected the clutch in-flight but not far enough to set off the sensor. Aerodynamic forces kept the control surfaces together in-flight (smooth conditions). We were never warned of possible wake. Maintenance reconnected the clutch and we finished our trip. Callback conversation with reporter revealed the following information: reporter participated in structured wake turbulence callback program. Feels that educational facts and experience should be shared and reviewed by other pilots. Lack of ATC advisories and crew complacency led to this event.

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Original NASA ASRS Text

Title: INFLT WAKE TURB ENCOUNTER CAUSES AUTOPLT PITCH TRIM DISCONNECT.

Narrative: WHILE APCHING ATLANTA FROM THE SW, WE WERE GIVEN A DSCNT TO 4000 FT. THE AUTOPLT WAS ENGAGED AND WE WERE INDICATING 245 KTS. OUT OF THE CORNER OF MY EYE I CAUGHT SIGHT OF AN L1011 XING R TO L. APPROX 30 SECONDS LATER, WE HIT HIS WAKE AT A 90 DEG ANGLE. THE ENCOUNTER WAS VERY BRIEF BUT EXTREME. THE AUTOPLT DISCONNECTED ITSELF AND THE CAPT AND I BOTH LIGHTLY PLACED OUR HANDS ON THE CTLS TO GAIN CTL OF THE ACFT. SHORTLY AFTER THAT, WE ONCE AGAIN ENGAGED THE AUTOPLT AND THE REMAINING TURNS WERE DONE IN SMOOTH AIR WITH THE AUTOPLT ENGAGED. AFTER LINING UP ON FINAL, I DISENGAGED THE AUTOPLT AND PROCEEDED TO HAND FLY THE ACFT. THE L1011 LANDED ON RWY 27R. WE WERE INITIALLY GIVEN THIS RWY BUT RWY 27L BECAME AVAILABLE SO WE CHOSE IT. THE LNDG APCH WAS UNEVENTFUL. THE ACFT WOULD TRIM (PITCH) JUST FINE BUT I DID NOTICE SOMETHING ODD WITH THE PITCH FORCES WITH THE YOKE. I COULDN'T PUT MY FINGER ON IT AT THE TIME. ON LNDG ROLLOUT WE GOT A LEVEL 3 LLAS ALERT (EMER). FIRST THOUGHT WAS ENG FIRE. AS IT TURNS OUT IT WAS A PITCH DISCONNECT. AS BEST AS WE CAN FIGURE THE WAKE ENCOUNTER HAD DISCONNECTED THE CLUTCH INFLT BUT NOT FAR ENOUGH TO SET OFF THE SENSOR. AERODYNAMIC FORCES KEPT THE CTL SURFACES TOGETHER INFLT (SMOOTH CONDITIONS). WE WERE NEVER WARNED OF POSSIBLE WAKE. MAINT RECONNECTED THE CLUTCH AND WE FINISHED OUR TRIP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN STRUCTURED WAKE TURB CALLBACK PROGRAM. FEELS THAT EDUCATIONAL FACTS AND EXPERIENCE SHOULD BE SHARED AND REVIEWED BY OTHER PLTS. LACK OF ATC ADVISORIES AND CREW COMPLACENCY LED TO THIS EVENT.

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.