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Old Feb 6, 2007 | 5:18 pm
  #4  
nd_eric_77
 
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Originally Posted by jimbo99
The speed of sound falls significantly with temperature. Down to 660mph at cruising altitude according to http://en.wikipedia.org/wiki/Speed_of_sound

"there's more than one way to skin a cat"
The sound barrier is also relative to the air around the airplane. In other words, at cruising altitude, a jet would need a ground-speed of 660mph PLUS the speed of any tailwind. (IOW, 550 MPH speed + 120 MPH tailwind = 670 MPH ground speed, but < the 660 MPH sound barrier at that altitude).
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