Wake turbulence encounter.

Attributes
ACN	316745
Time
Date	199509
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : lax
State Reference	CA
Altitude	msl bound lower : 8000 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : lax artcc : zse
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 19000 flight time type : 4500
ASRS Report	316745
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	inflight encounter other other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action none taken : unable
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

Coming down ILS on runway 25L and cleared for the approach at about 25 DME the aircraft started to roll to the right. The autoplt recovered initially but an instant later, it started to roll to the right again. This time the roll continued past 15 degree bank and the autoplt seemed to be struggling, so I disconnected the autoplt, increased thrust, and recovered with ailerons. At no time did bank angle exceed 20 degrees. Although we were aware of traffic ahead, we were not advised that it was a B-757 until after the event. Shortly afterward we were advised of B757 8 mi ahead. However, he must have been very slow, because we closed the gap rapidly at only 210 KIAS. Remainder of flight was uneventful as we stayed 1 DOT above GS. Callback conversation with reporter revealed the following information: reporter participated in wake turbulence callback and was quite knowledgeable in wake turbulence recognition, avoidance and recovery techniques. The reporter stated that because of the high volume of traffic, they were in a high state of awareness, but did not realize that the B-757 was above glide path and descending through their flight path.

Original NASA ASRS Text

Title: WAKE TURB ENCOUNTER.

Narrative: COMING DOWN ILS ON RWY 25L AND CLRED FOR THE APCH AT ABOUT 25 DME THE ACFT STARTED TO ROLL TO THE R. THE AUTOPLT RECOVERED INITIALLY BUT AN INSTANT LATER, IT STARTED TO ROLL TO THE R AGAIN. THIS TIME THE ROLL CONTINUED PAST 15 DEG BANK AND THE AUTOPLT SEEMED TO BE STRUGGLING, SO I DISCONNECTED THE AUTOPLT, INCREASED THRUST, AND RECOVERED WITH AILERONS. AT NO TIME DID BANK ANGLE EXCEED 20 DEGS. ALTHOUGH WE WERE AWARE OF TFC AHEAD, WE WERE NOT ADVISED THAT IT WAS A B-757 UNTIL AFTER THE EVENT. SHORTLY AFTERWARD WE WERE ADVISED OF B757 8 MI AHEAD. HOWEVER, HE MUST HAVE BEEN VERY SLOW, BECAUSE WE CLOSED THE GAP RAPIDLY AT ONLY 210 KIAS. REMAINDER OF FLT WAS UNEVENTFUL AS WE STAYED 1 DOT ABOVE GS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN WAKE TURB CALLBACK AND WAS QUITE KNOWLEDGEABLE IN WAKE TURB RECOGNITION, AVOIDANCE AND RECOVERY TECHNIQUES. THE RPTR STATED THAT BECAUSE OF THE HIGH VOLUME OF TFC, THEY WERE IN A HIGH STATE OF AWARENESS, BUT DID NOT REALIZE THAT THE B-757 WAS ABOVE GLIDE PATH AND DSNDING THROUGH THEIR FLT PATH.

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.