- No wind
- Light crosswind
- Strong crosswind
Former "FAA Safety Counselor of the Year" Bob Nardiello provides the answer. He also offers tips for avoiding wake turbulence on takeoff.
"Vortices tend to move outward from the aircraft. So if you are behind a departing aircraft, the vortex from the right wing will tend to move to the right. The vortex from the left wing will tend to move to the left in no wind conditions.If we have a crosswind, the wind will tend to influence the movement of the vortices. A crosswind of about 3 knots will hold the upwind vortex pretty much in place at the runway where it was created, while the downwind vortex will rapidly move away from the runway.
Crosswinds greater than approximately 5 knots will tend to break up the vortices. So stronger crosswinds are good things, as far as vortices are concerned. At least the way we look at it, from our perspective; we want the vortices to begin to break up and decay. So light crosswinds require maximum caution, and I'm talking about a light crosswind of maybe 3 knots.
We need to note the point of rotation of the larger aircraft. That point of rotation is where the vortices will be developed. From that point on, there will be vortices off the wings of that departing aircraft. So it’s important that your rotation point occurs prior to the rotation point of the preceding aircraft, because we do not want to be rotating in the vortices of the preceding aircraft. We need to do that prior to reaching the preceding aircraft’s point of rotation.
You want to climb upwind of the departing aircraft for the same reason we talked about relative to the crosswinds’ effect on the vortices. So if the crosswind will move the vortices to the left, our departure path should be to the right to avoid those vortices."
