Light transport encounters extreme roll action on intercepting GS behind 757.

Attributes
ACN	274962
Time
Date	199406
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : lga
State Reference	NY
Altitude	msl bound lower : 3000 msl bound upper : 3000
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : n90
Operator	common carrier : air carrier
Make Model Name	Beech 1900
Operating Under FAR Part	Part 135
Flight Phase	descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp pilot : instrument
Experience	flight time last 90 days : 200 flight time total : 4500 flight time type : 2500
ASRS Report	274962
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	inflight encounter other other anomaly other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted other
Consequence	faa : reviewed incident with flight crew
Supplementary
Air Traffic Incident	other

Narrative:

Vectored to approach ILS 4 at 3000 ft. We intercepted localizer outside grene. We had not intercepted the GS yet, it was above us still. As the aircraft intercepted the slope, the aircraft rolled violently to a 40 degree angle of bank, uncommanded. (Right turn). We were told we had 4 mi separation behind a 757. Apparently, the 757 was following the GS down and we intercepted from underneath. Since we already went through it, we could avoid further by staying above glide path slightly. We declined to be taken off the approach. My solution to this problem is to vector 757's to intercept at lower altitudes than other aircraft. By flying the GS 1 DOT high, we can avoid wake turbulence. Callback conversation with reporter revealed the following information: reporter states they were flying a be 1900 commuter. The commuters are vectored for the normal pattern but the jets usually come straight in from the southwest. The jets are intercepting the glide path about 5 mi prior to the commuter aircraft and from a higher altitude. Reporter would like to see a change so that everyone is brought into the GS at the same altitude. Knowing traffic ahead, the aircraft can remain slightly above the GS.

Original NASA ASRS Text

Title: LTT ENCOUNTERS EXTREME ROLL ACTION ON INTERCEPTING GS BEHIND 757.

Narrative: VECTORED TO APCH ILS 4 AT 3000 FT. WE INTERCEPTED LOC OUTSIDE GRENE. WE HAD NOT INTERCEPTED THE GS YET, IT WAS ABOVE US STILL. AS THE ACFT INTERCEPTED THE SLOPE, THE ACFT ROLLED VIOLENTLY TO A 40 DEG ANGLE OF BANK, UNCOMMANDED. (R TURN). WE WERE TOLD WE HAD 4 MI SEPARATION BEHIND A 757. APPARENTLY, THE 757 WAS FOLLOWING THE GS DOWN AND WE INTERCEPTED FROM UNDERNEATH. SINCE WE ALREADY WENT THROUGH IT, WE COULD AVOID FURTHER BY STAYING ABOVE GLIDE PATH SLIGHTLY. WE DECLINED TO BE TAKEN OFF THE APCH. MY SOLUTION TO THIS PROB IS TO VECTOR 757'S TO INTERCEPT AT LOWER ALTS THAN OTHER ACFT. BY FLYING THE GS 1 DOT HIGH, WE CAN AVOID WAKE TURB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THEY WERE FLYING A BE 1900 COMMUTER. THE COMMUTERS ARE VECTORED FOR THE NORMAL PATTERN BUT THE JETS USUALLY COME STRAIGHT IN FROM THE SW. THE JETS ARE INTERCEPTING THE GLIDE PATH ABOUT 5 MI PRIOR TO THE COMMUTER ACFT AND FROM A HIGHER ALT. RPTR WOULD LIKE TO SEE A CHANGE SO THAT EVERYONE IS BROUGHT INTO THE GS AT THE SAME ALT. KNOWING TFC AHEAD, THE ACFT CAN REMAIN SLIGHTLY ABOVE THE GS.

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.