Severe wake turbulence encounter following a B757 at FL320 during descent.

Attributes
ACN	744176
Time
Date	200706
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sfo.airport
State Reference	CA
Altitude	msl single value : 32000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa.artcc
Operator	general aviation : corporate
Make Model Name	Challenger CL604
Operating Under FAR Part	Part 91
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : multi engine
Experience	flight time last 90 days : 100 flight time total : 6500 flight time type : 900
ASRS Report	744176
Events
Anomaly	inflight encounter : wake turbulence
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control
Consequence	faa : investigated
Supplementary
Problem Areas	Airspace Structure Environmental Factor
Primary Problem	Environmental Factor

Narrative:

During descent in to sfo; we encountered severe wake turbulence. Aircraft encountered was a B757.callback conversation with reporter revealed the following information: reporter stated they were descending from FL400 to FL300. The preceding aircraft was a B757; however after checking with ATC after arrival the probability of an encounter with crossing traffic wake was thought to be the more likely cause. ATC reported that no less than ten miles separation was noted. The encounter caused the aircraft to roll; resulting in spontaneous automatic pilot disconnect. Recovery was an uneventful one G maneuver.

Original NASA ASRS Text

Title: SEVERE WAKE TURBULENCE ENCOUNTER FOLLOWING A B757 AT FL320 DURING DESCENT.

Narrative: DURING DESCENT IN TO SFO; WE ENCOUNTERED SEVERE WAKE TURB. ACFT ENCOUNTERED WAS A B757.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THEY WERE DESCENDING FROM FL400 TO FL300. THE PRECEDING ACFT WAS A B757; HOWEVER AFTER CHECKING WITH ATC AFTER ARRIVAL THE PROBABILITY OF AN ENCOUNTER WITH CROSSING TRAFFIC WAKE WAS THOUGHT TO BE THE MORE LIKELY CAUSE. ATC REPORTED THAT NO LESS THAN TEN MILES SEPARATION WAS NOTED. THE ENCOUNTER CAUSED THE ACFT TO ROLL; RESULTING IN SPONTANEOUS AUTO PILOT DISCONNECT. RECOVERY WAS AN UNEVENTFUL ONE G MANEUVER.

Data retrieved from NASA's ASRS site as of January 2009 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.