Thread: Mach-nr or IAS?
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Old 11th Jan 2019, 09:35
  #4 (permalink)  
ATCO1962
 
Join Date: Jul 2005
Location: Middle East
Posts: 270
I'd stick with Mach number at or above FL280 and IAS below that. It's easier for everyone as ATCOs know the Mach number range for most jets above that level but we certainly couldn't tell you what a good, assured IAS would be above that without a few questions first as to whether you can make the speed or not. I haven't heard IAS used at all above FL280 ; that's after 38 years of controlling, mostly in upper airspace.
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