Last evening I got a caution wake turbulence callout from ATC for a 747 that departed after me but was on a converging path. Obviously when the alert was issued ATC had no way of knowing exactly how much vertical separation there would be once our paths converged. Realistically there was probably 2000 + feet. My questions for POA, how much vertical separation is needed between a 747 and a small trainer, for there to not be a concern?
I understood 2000’ or 2 minutes was enough to dissipate the wake enough so that a light aircraft would not be too adversely impacted. Would love to hear if others have better wisdom.
I have wondered that as I fly at 3499.44' and the 737s landing at BWI are about 1000' above me... https://www.faa.gov/air_traffic/pub...:text=Air Traffic Wake Turbulence Separations
I would say don't underestimate wakes. In the right conditions, they can remain strong for several minutes. https://flightsafety.org/a380-wake-turbulence-encounter/
I frequently have large aircraft overhead of me in the DC & NY area. If we are crossing paths than I am not overly concerned. I know if I hit their wake that I will be through it quickly. Crossing paths with the larger airplane 1000' overhead and I will usually feel enough to know when I went through their wake. On the other hand if we are flying the same track then I could be in the wake for a much longer time. The winds at the time obviously make a big difference how long the wake lasts and where it goes. I have had ATC put us as close to 500' vertical separation which is really not comfortable for me, not in terms of wake but just it feels too close and makes me nervous. I also get more nervous with wake the closer I am to the ground. In the NY area, I am typically higher up so have more time to deal with anything. In the DC area, I am usually quite low. Inside of Bravo, unless I have a real reason for "Unable" than I pretty much have to fly where they tell me to fly.
This is quite common when I am at the traffic pattern of KHWD. The left downwind of 28L goes directly under the final approach of Oakland international. Every few minutes you will have large jets crossing 1000-1500 feet above you. My CFI said a vertical separation of 1000 feet is typically safe.
I crossed paths with a 747 Heavy climbing outta SFO and advised as such by ATC...He was MILES off by time I crossed his path and I thought I was well above his his climb path but we still got tangled up in the wake turbulence and it was like hitting a brick wall. We were all thrown into the ceiling even buckled in and I was nearly knocked out...wake turbulence is no joke and can linger quite a while. 2000' is safe till it isn't.
There was an arrow going to Oshkosh with a new ppl and a 33,000 hr cfi that broke up near Milwaukee from wake turbulence from an md-80 a decade or so ago. It's no joke. https://www.flyingmag.com/technique-accidents-aftermath-prelude-wake/
Been a number of years ago when headed over to Tennessee I saw up ahead, 10-12 miles away, a stack of C17's coming at me. It appeared they would pass off my left by a few miles at roughly the same altitude, but being the chicken I am I made a turn to the right and gave them plenty of room. It looked something like this:
I can't remember what we were following. I think it was an A-320. We were decending into CDG. Anyway you can largely predict where it goes. Slow and heavy wing loading causes the most severe wake. It descends at a fairly predictable rates. Wind currents etc play a very important part of predicting the wake. I had an RJ roll a B-757 45+ degrees @ Fl300. So absolutely worth being aware of and have a healthy respect for it.
