B737-900
Flight Crew Air Transport Pilot (ATP)
Inflight Event / Encounter Wake Vortex Encounter
General None Reported / Taken
Environment - Non Weather Related; Procedure
We were cleared for takeoff on runway 31L full length. Shortly after liftoff; we experienced wake turbulence that rolled the aircraft into an approximately 15 degree left roll before I could stop the roll with a right aileron input. This stopped the roll; then a few seconds later the aircraft rolled to wings level. Prior to our departure; a B757 departed. When we were cleared to takeoff; the B757 was 500-1000 AGL on the upwind. As you may be aware; the FAA changed the criteria for wake turbulence separation for aircraft following B757 aircraft in December 2015. Prior to the change; the B737 was required to have a two minute or 4-5 mile radar separation behind a B757 before being cleared to takeoff. Under the new rules; there are no time or distance requirements for large aircraft; such as the B737; to depart behind a B757. Since the B757 has a higher thrust to weight ratio than the B737; it is often impossible for the B737 to rotate after the point of rotation of a B757. Therefore; wake turbulence encounters are sure to increase under the new rules for B737's departing after B757's. In the future; I will request a two minute delay from the tower prior to accepting a takeoff clearance behind a B757; unless I am light enough to be sure I can rotate and climb above their path.
Reporter expressed additional concern about recent FAA changes to in-trail procedures.
B737-900 Captain reported encountering wake turbulence departing JFK in trail of a B757.