Of what practical use would the controller make of IAS anyway ?
To make sure those pesky pilots are flying the speeds we tell them to fly!!
"We're 220kts" - No you're not. You're reducing through 310kts
"We're 180kts" - No you're not. You're back at 160kts and about to have matey boy behind you up your chuff
"160kts to 4 DME" - Why are you slowing down at 7DME then?
I could go on...
