Wake Turbulence

Frequently in central Washington we share the air with some pretty large aircraft. Military jets, Boeing out for a “test drive”, sailplanes, ultra-lights and so on. Of particular interest to me is the occasional “Heavy”. Boeing often test out variants of the 747 and in recent years The Boeing Dreamliner (787). On my last flight I had a 787 cross my course line and I was faced with trying to remember what a safe separation is for wake turbulence. (Been a very long time since I looked at my “From the Ground Up” training manual.

I found the following interesting training manual from the FAA:

http://www.faa.gov/training_testing/training/media/wake/04SEC2.PDF

In it I found the following:

“2.4.4 Vertical Motion of the Wake
The wake of an aircraft has behavioral characteristics which can help the pilot visualize the
wake location and thereby take avoidance
precautions.  The initial descent rate of the
wake is adequately described by classical
theory; the descent rate is determined by the
weight, flight speed and wingspan of the generating aircraft.  Generally, vortices descend
at the initial rate of about 300 to 500 feet per
minute for about 30 seconds.  The descent rate
decreases and eventually approaches zero at
between 500 and 900 feet below the flightpath.
Flying at or above the flightpath provides the
best method for avoidance.  Maintaining a
vertical separation of at least 1000 feet  when
crossing below the preceding aircraft may be
considered safe.”

Not a bad idea to glance through this article if you share the air with the big boys….