Narrative:

While being vectored for a visual approach to runway 24R at lax, our aircraft encountered the wake of a B747 which was being vectored for an approach to the south complex (runway 25L/right). Our aircraft abruptly, but smoothly, rolled about 45 degrees to the left. I applied immediate control input to level the aircraft only to experience the same situation about 5-7 seconds later. At this point, I initiated an immediate climb to gain 500 ft altitude to preclude encountering the wake again. At the time of the encounter, the B747 was about 6-7 mi ahead of us on a downwind leg. Since he was vectored for a wider pattern and subsequently a longer downwind, I assume that his altitude was above ours and we entered his descending wake. When the ILS is being flown, it's generally easy to avoid this situation by being on or slightly above the glide path to avoid the descending wake, but while maneuvering for visual approachs there must be more reliance on ATC to avoid crossing a lighter aircraft behind and below a 'heavy' aircraft. This is particularly critical when common arrival rtes are flown (ie, depart smo on heading 070 degrees). In retrospect, although the encounter was random, the probabilities appear to be higher when using the arrival rtes common at lax. If aircraft arriving from the south were to land on the south complex and north arrs were to utilize the north complex, there would be less xover (ie, although we arrived over smo as did the B747, it was necessary for him to cross the final approach course of both runways 24L&right to line up with runway 25L). Additionally, it was necessary for us to be at a lower altitude in order to execute a visual approach to the near complex. Curiously, having considerable experience operating into and out of many 'heavy' hubs -- atl, bos, den, ord, mia, etc, the only wake turbulence encounters I've had were at lax. Callback conversation with reporter revealed the following information: the reporter is an MD83 captain and he said that, as far as he knew, the controller followed the wake separation program. He said that he has had many encounters with wake at lax and he suspects that the cause may be the fact that the same ground track is used by a number of aircraft of differing weights. In this case, he said that the B747 that was going to runway 25L crossed smo at 7000 ft about 7 mi in front of his MD83 and started a descent to 3500 ft. He then crossed smo and was cleared to 2500 ft. Shortly after his leveloff, the MD83 rolled smoothly to the left, reaching at least a 45 degree angle of bank even though he had applied full aileron to the right to counter the roll. Shortly after the aircraft recovered from this, it rolled to the left again and this time it reached 60 degrees of bank with both pilots attempting to counter with the control wheel full to the right. As they recovered from this roll the captain started a climb to avoid further encounters and he advised the approach controller of the rolls and of his climb to escape. After landing, he said that he briefed the passenger about the encounters and as they left the aircraft, a number of passenger spoke to him about the event and all of them were upset. Apparently he said, there had been something on television about windshear and other upset causes and many of the passenger had seen the program. 1 passenger wrote a letter to the company and the captain was one of the several respondents.

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Original NASA ASRS Text

Title: AN ACR MD83 FLC HIT THE WAKE OF A B747 AND ROLLED TO THE L TWICE BEFORE THE FLC COULD ESCAPE BY CLBING. THE FIRST ROLL WAS TO AT LEAST 45 DEGS AND THE SECOND TO 60 DEGS. THE B747 WAS 7 MI AHEAD AND THE PROPER WAKE ADVISORIES HAD BEEN GIVEN BY THE APCH CTLR.

Narrative: WHILE BEING VECTORED FOR A VISUAL APCH TO RWY 24R AT LAX, OUR ACFT ENCOUNTERED THE WAKE OF A B747 WHICH WAS BEING VECTORED FOR AN APCH TO THE S COMPLEX (RWY 25L/R). OUR ACFT ABRUPTLY, BUT SMOOTHLY, ROLLED ABOUT 45 DEGS TO THE L. I APPLIED IMMEDIATE CTL INPUT TO LEVEL THE ACFT ONLY TO EXPERIENCE THE SAME SIT ABOUT 5-7 SECONDS LATER. AT THIS POINT, I INITIATED AN IMMEDIATE CLB TO GAIN 500 FT ALT TO PRECLUDE ENCOUNTERING THE WAKE AGAIN. AT THE TIME OF THE ENCOUNTER, THE B747 WAS ABOUT 6-7 MI AHEAD OF US ON A DOWNWIND LEG. SINCE HE WAS VECTORED FOR A WIDER PATTERN AND SUBSEQUENTLY A LONGER DOWNWIND, I ASSUME THAT HIS ALT WAS ABOVE OURS AND WE ENTERED HIS DSNDING WAKE. WHEN THE ILS IS BEING FLOWN, IT'S GENERALLY EASY TO AVOID THIS SIT BY BEING ON OR SLIGHTLY ABOVE THE GLIDE PATH TO AVOID THE DSNDING WAKE, BUT WHILE MANEUVERING FOR VISUAL APCHS THERE MUST BE MORE RELIANCE ON ATC TO AVOID XING A LIGHTER ACFT BEHIND AND BELOW A 'HVY' ACFT. THIS IS PARTICULARLY CRITICAL WHEN COMMON ARR RTES ARE FLOWN (IE, DEPART SMO ON HDG 070 DEGS). IN RETROSPECT, ALTHOUGH THE ENCOUNTER WAS RANDOM, THE PROBABILITIES APPEAR TO BE HIGHER WHEN USING THE ARR RTES COMMON AT LAX. IF ACFT ARRIVING FROM THE S WERE TO LAND ON THE S COMPLEX AND N ARRS WERE TO UTILIZE THE N COMPLEX, THERE WOULD BE LESS XOVER (IE, ALTHOUGH WE ARRIVED OVER SMO AS DID THE B747, IT WAS NECESSARY FOR HIM TO CROSS THE FINAL APCH COURSE OF BOTH RWYS 24L&R TO LINE UP WITH RWY 25L). ADDITIONALLY, IT WAS NECESSARY FOR US TO BE AT A LOWER ALT IN ORDER TO EXECUTE A VISUAL APCH TO THE NEAR COMPLEX. CURIOUSLY, HAVING CONSIDERABLE EXPERIENCE OPERATING INTO AND OUT OF MANY 'HVY' HUBS -- ATL, BOS, DEN, ORD, MIA, ETC, THE ONLY WAKE TURB ENCOUNTERS I'VE HAD WERE AT LAX. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR IS AN MD83 CAPT AND HE SAID THAT, AS FAR AS HE KNEW, THE CTLR FOLLOWED THE WAKE SEPARATION PROGRAM. HE SAID THAT HE HAS HAD MANY ENCOUNTERS WITH WAKE AT LAX AND HE SUSPECTS THAT THE CAUSE MAY BE THE FACT THAT THE SAME GND TRACK IS USED BY A NUMBER OF ACFT OF DIFFERING WTS. IN THIS CASE, HE SAID THAT THE B747 THAT WAS GOING TO RWY 25L CROSSED SMO AT 7000 FT ABOUT 7 MI IN FRONT OF HIS MD83 AND STARTED A DSCNT TO 3500 FT. HE THEN CROSSED SMO AND WAS CLRED TO 2500 FT. SHORTLY AFTER HIS LEVELOFF, THE MD83 ROLLED SMOOTHLY TO THE L, REACHING AT LEAST A 45 DEG ANGLE OF BANK EVEN THOUGH HE HAD APPLIED FULL AILERON TO THE R TO COUNTER THE ROLL. SHORTLY AFTER THE ACFT RECOVERED FROM THIS, IT ROLLED TO THE L AGAIN AND THIS TIME IT REACHED 60 DEGS OF BANK WITH BOTH PLTS ATTEMPTING TO COUNTER WITH THE CTL WHEEL FULL TO THE R. AS THEY RECOVERED FROM THIS ROLL THE CAPT STARTED A CLB TO AVOID FURTHER ENCOUNTERS AND HE ADVISED THE APCH CTLR OF THE ROLLS AND OF HIS CLB TO ESCAPE. AFTER LNDG, HE SAID THAT HE BRIEFED THE PAX ABOUT THE ENCOUNTERS AND AS THEY LEFT THE ACFT, A NUMBER OF PAX SPOKE TO HIM ABOUT THE EVENT AND ALL OF THEM WERE UPSET. APPARENTLY HE SAID, THERE HAD BEEN SOMETHING ON TELEVISION ABOUT WINDSHEAR AND OTHER UPSET CAUSES AND MANY OF THE PAX HAD SEEN THE PROGRAM. 1 PAX WROTE A LETTER TO THE COMPANY AND THE CAPT WAS ONE OF THE SEVERAL RESPONDENTS.

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.