Narrative:

I was the pilot flying (left seat) in a falcon 900B. [Right seat pilot] was the PIC/pilot not flying. Approaching manassas; while descending from 6;000 to 4;000 ft; ATC instructed us to turn to the left to a heading that was approximately 90 degrees from the current heading. The autopilot was engaged and as the turn was being initiated the aircraft encountered severe wake turbulence. As the aircraft was banking left; without any prior warning; we hit the wake turbulence causing the aircraft to roll instantaneously to a bank angle of at least 90 degrees at which time the autopilot disconnected and I then leveled the wings and stabilized the aircraft. The pilot not flying queried ATC as to what was in front of us and she replied that a B757 was 5-7 miles ahead and asked why? The pilot not flying informed ATC that we were almost inverted. We continued on and landed at hef without incident. Subsequently; I have been informed that there was approximately 6 miles separation between us and the B757. In addition; we crossed the same point in space in about 15 seconds after the B757. I believe that this happened due to our proximity to the other aircraft and that ATC vectored us to the left for spacing. Because we were already banking in the turn when we encountered the wake turbulence; it induced a severe rolling moment that caused the upset. What could be done to prevent this from happening in the future would be to maintain adequate spacing and if it is necessary to vector traffic--do not direct said traffic through the wake of the preceding aircraft.

Related reports:

Google
 

Original NASA ASRS Text

Title: Falcon 900B pilot reported wake vortex encounter in trail of B757 on descent into HEF that resulted in a roll to a 90 degree bank.

Narrative: I was the pilot flying (left seat) in a Falcon 900B. [Right seat pilot] was the PIC/pilot not flying. Approaching Manassas; while descending from 6;000 to 4;000 FT; ATC instructed us to turn to the left to a heading that was approximately 90 degrees from the current heading. The autopilot was engaged and as the turn was being initiated the aircraft encountered severe wake turbulence. As the aircraft was banking left; without any prior warning; we hit the wake turbulence causing the aircraft to roll instantaneously to a bank angle of at least 90 degrees at which time the autopilot disconnected and I then leveled the wings and stabilized the aircraft. The pilot not flying queried ATC as to what was in front of us and she replied that a B757 was 5-7 miles ahead and asked why? The pilot not flying informed ATC that we were almost inverted. We continued on and landed at HEF without incident. Subsequently; I have been informed that there was approximately 6 miles separation between us and the B757. In addition; we crossed the same point in space in about 15 seconds after the B757. I believe that this happened due to our proximity to the other aircraft and that ATC vectored us to the left for spacing. Because we were already banking in the turn when we encountered the wake turbulence; it induced a severe rolling moment that caused the upset. What could be done to prevent this from happening in the future would be to maintain adequate spacing and if it is necessary to vector traffic--do not direct said traffic through the wake of the preceding aircraft.

Data retrieved from NASA's ASRS site 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.