Skyhawk 172/Cutlass 172
Flight Crew Student
Flight Crew Last 90 Days 16; Flight Crew Type 47
Situational Awareness
Inflight Event / Encounter Wake Vortex Encounter
Flight Crew Executed Go Around / Missed Approach
Human Factors; Environment - Non Weather Related
I was cleared to land behind a Boeing 787. I was warned about wake turbulence and substantially extended my downwind leg for what felt at the time like a sufficient distance in order to avoid the wake turbulence. When I was approximately 20 ft AGL my plane made an uncommanded 30-45 degree roll to the right. I was able to recover using the go around procedure.At the time I thought that the high level of turbulence I was experiencing at traffic pattern altitude had been to blame but on further reflection the air near the surface was otherwise very calm. I believe that what I experienced was wake turbulence from the landing 787. I knew that I needed to give the 787 ~8 miles of separation but a review of my GPS data indicates that at best I had ~6 miles of separation. My lack of awareness about exactly how far I was from the landing AC made me rely on estimates that turned out to be incorrect. It would be helpful if ATC could give advisories about how far or long I needed to circle or extend to avoid the wake turbulence.
C172SP pilot reported encountering wake turbulence at 20 ft AGL in trail of a B787.