Narrative:

Inbound vkz 198 degree radial, approaching kains intersection, inbound on the heatt 5 arrival. We had just leveled off at 12000 and 250 KTS. Mia approach requested descent to 8000 ft and he noted that heavy B747 was 8 mi ahead of us. Checked the TCASII and noted that the aircraft was ahead of us but below us by 1000 ft and was already descending itself. We had been in trail by 10-12 mi but the distance had narrowed all of a sudden. The first officer asked to delay descent and I concurred. Several seconds later we encountered the first of 2 violent rolling moments. First officer was able to stop the first at about 35 degree bank with full opposite aileron and rudder as he was kicking off the autoplt. The second roll occurred approximately 3-4 seconds later in opposite direction and he had again to use full opposite rudder and aileron to stop roll but we probably exceeded 35 degree bank. He asked to climb and I ordered him to take a 20 degree turn left, away from the B747 and climb to 12500 ft. I immediately tried to contact mia approach by declaring over the radio an emergency and telling them we were taking the turn and climbing to 12500 ft. Mia approach came back and said I want you down to 8000 ft as he was trying to understand the situation. Now that I had his full attention I was able to convey we had taken 2 sharp rolls and we had separated our flight paths/trail. He asked our heading and then assigned 180 degrees and 210 KTS. We followed B747 to runway 9L for uneventful landing. Kept approach high as the B747 kept a high approach. Seat belt sign was on and since I had not made a 'prepare for landing' PA, the flight attendants were still in their seats. No injuries to crew or passenger although several people complained of roll. The #1 galley and lost all of its bottles/glasses that were out and any drinks that customers had in either cabin turned over. No bags were reported to have fallen out of the overhead. Repeat -- no reported injuries. After the aircraft was stable and situation was under control I made a PA to the people explaining what happened. I suspect that the B747 had put out its approach flaps to aid in its descent rate without using spdbrakes. We unfortunately flew into the air that had been disturbed by the confign change. I would like to command the first officer for his good airmanship in getting the aircraft back under control without overctling the situation and aggravating the problem. I saw no need to override his inputs as they were correct and most appropriate for the situation. He kept his head and made smooth corrections without an abrupt pitch moment that could have caused us to depart under the high roll rate. Request this incident and his correct response be recorded in his records. Callback conversation with reporter revealed the following information: the B727 captain wants an advisory issued by any crew that is in the position faced by the B747 crew, extending flaps at an earlier point in time that might affect wake turbulence separation values. ATC had issued a wake turbulence advisory to this crew prior to the descent, which is why they waited a short time to start descent. The first officer was flying the B727 and had just started bringing the power back to start a descent when the B727 hit the first shock. The B727 was 'clean' and at 250 KTS. The aircraft oscillated through pitch, roll and yaw and lost about 50 ft both times during the first and second shock, the second lasting a bit longer than the first. On a scale of 1-5 the shock was a #3. The visibility wasn't the best, marginal VMC with about 3 mi at our altitude, a hazy day.

Related reports:

Google
 

Original NASA ASRS Text

Title: A B727 DSNDING 8 MI BEHIND AND 1000 FT ABOVE A B747 RUNS INTO THE WAKE TURB CREATED BY A B747 WHO HAD UNEXPECTEDLY DEPLOYED WING FLAPS FOR A MORE RAPID DSCNT.

Narrative: INBOUND VKZ 198 DEG RADIAL, APCHING KAINS INTXN, INBOUND ON THE HEATT 5 ARR. WE HAD JUST LEVELED OFF AT 12000 AND 250 KTS. MIA APCH REQUESTED DSCNT TO 8000 FT AND HE NOTED THAT HVY B747 WAS 8 MI AHEAD OF US. CHKED THE TCASII AND NOTED THAT THE ACFT WAS AHEAD OF US BUT BELOW US BY 1000 FT AND WAS ALREADY DSNDING ITSELF. WE HAD BEEN IN TRAIL BY 10-12 MI BUT THE DISTANCE HAD NARROWED ALL OF A SUDDEN. THE FO ASKED TO DELAY DSCNT AND I CONCURRED. SEVERAL SECONDS LATER WE ENCOUNTERED THE FIRST OF 2 VIOLENT ROLLING MOMENTS. FO WAS ABLE TO STOP THE FIRST AT ABOUT 35 DEG BANK WITH FULL OPPOSITE AILERON AND RUDDER AS HE WAS KICKING OFF THE AUTOPLT. THE SECOND ROLL OCCURRED APPROX 3-4 SECONDS LATER IN OPPOSITE DIRECTION AND HE HAD AGAIN TO USE FULL OPPOSITE RUDDER AND AILERON TO STOP ROLL BUT WE PROBABLY EXCEEDED 35 DEG BANK. HE ASKED TO CLB AND I ORDERED HIM TO TAKE A 20 DEG TURN L, AWAY FROM THE B747 AND CLB TO 12500 FT. I IMMEDIATELY TRIED TO CONTACT MIA APCH BY DECLARING OVER THE RADIO AN EMER AND TELLING THEM WE WERE TAKING THE TURN AND CLBING TO 12500 FT. MIA APCH CAME BACK AND SAID I WANT YOU DOWN TO 8000 FT AS HE WAS TRYING TO UNDERSTAND THE SIT. NOW THAT I HAD HIS FULL ATTN I WAS ABLE TO CONVEY WE HAD TAKEN 2 SHARP ROLLS AND WE HAD SEPARATED OUR FLT PATHS/TRAIL. HE ASKED OUR HDG AND THEN ASSIGNED 180 DEGS AND 210 KTS. WE FOLLOWED B747 TO RWY 9L FOR UNEVENTFUL LNDG. KEPT APCH HIGH AS THE B747 KEPT A HIGH APCH. SEAT BELT SIGN WAS ON AND SINCE I HAD NOT MADE A 'PREPARE FOR LNDG' PA, THE FLT ATTENDANTS WERE STILL IN THEIR SEATS. NO INJURIES TO CREW OR PAX ALTHOUGH SEVERAL PEOPLE COMPLAINED OF ROLL. THE #1 GALLEY AND LOST ALL OF ITS BOTTLES/GLASSES THAT WERE OUT AND ANY DRINKS THAT CUSTOMERS HAD IN EITHER CABIN TURNED OVER. NO BAGS WERE RPTED TO HAVE FALLEN OUT OF THE OVERHEAD. REPEAT -- NO RPTED INJURIES. AFTER THE ACFT WAS STABLE AND SIT WAS UNDER CTL I MADE A PA TO THE PEOPLE EXPLAINING WHAT HAPPENED. I SUSPECT THAT THE B747 HAD PUT OUT ITS APCH FLAPS TO AID IN ITS DSCNT RATE WITHOUT USING SPDBRAKES. WE UNFORTUNATELY FLEW INTO THE AIR THAT HAD BEEN DISTURBED BY THE CONFIGN CHANGE. I WOULD LIKE TO COMMAND THE FO FOR HIS GOOD AIRMANSHIP IN GETTING THE ACFT BACK UNDER CTL WITHOUT OVERCTLING THE SIT AND AGGRAVATING THE PROB. I SAW NO NEED TO OVERRIDE HIS INPUTS AS THEY WERE CORRECT AND MOST APPROPRIATE FOR THE SIT. HE KEPT HIS HEAD AND MADE SMOOTH CORRECTIONS WITHOUT AN ABRUPT PITCH MOMENT THAT COULD HAVE CAUSED US TO DEPART UNDER THE HIGH ROLL RATE. REQUEST THIS INCIDENT AND HIS CORRECT RESPONSE BE RECORDED IN HIS RECORDS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE B727 CAPT WANTS AN ADVISORY ISSUED BY ANY CREW THAT IS IN THE POS FACED BY THE B747 CREW, EXTENDING FLAPS AT AN EARLIER POINT IN TIME THAT MIGHT AFFECT WAKE TURB SEPARATION VALUES. ATC HAD ISSUED A WAKE TURB ADVISORY TO THIS CREW PRIOR TO THE DSCNT, WHICH IS WHY THEY WAITED A SHORT TIME TO START DSCNT. THE FO WAS FLYING THE B727 AND HAD JUST STARTED BRINGING THE PWR BACK TO START A DSCNT WHEN THE B727 HIT THE FIRST SHOCK. THE B727 WAS 'CLEAN' AND AT 250 KTS. THE ACFT OSCILLATED THROUGH PITCH, ROLL AND YAW AND LOST ABOUT 50 FT BOTH TIMES DURING THE FIRST AND SECOND SHOCK, THE SECOND LASTING A BIT LONGER THAN THE FIRST. ON A SCALE OF 1-5 THE SHOCK WAS A #3. THE VISIBILITY WASN'T THE BEST, MARGINAL VMC WITH ABOUT 3 MI AT OUR ALT, A HAZY DAY.

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.