Expert: Mark Janus - 9/7/2008

Question
Hi,

  I was on an evening walk tonight near the local airport, with a steady stream of mid-sized 2-engine jets descending overhead.  They looked like 737s from the normal carriers, and would land within a mile of us.

  About 45-60 seconds after a jet would pass, we would hear rippling, rushing sounds from the jetwash.  What kind of sound did we hear, and was it caused by the jet turbines?

  Some of the sounds were loud, almost like a door slamming, while others sounded like "Star Wars" samples.  We notice that the turboprop planes definitely didn't leave this trail of sound!

Thanks in advance for your help.

-Nathan Edwards

Answer
Nathan,

I'm not sure by your description, but you may have heard the jet reversing (after landing).  Also, depending on how far overhead but you may have heard winds associated with the wingtip vortices...that may sound like a rippling or rushing sound (in trees)...  the thing is though that would exist even with a turboprop...  I doubt you would hear the jet exhaust 45-60 seconds after being overhead...  that sounds like a sound that is probably coming from the plane landing (about a mile away as you say)...  Jets do reverse thrust after landing to help slow down...  turboprops don't accomplish this in the same way...  they change the pitch of the prop such that the prop "blows" in the opposite direction....  jets redirect the jet airstream back around toward the front (and rev the engine)....

Hope this explains a bit,
mj