Please help me understand this logic because I don't think I have ever heard that figure. If ATC slows you to 240kts and asks you to descend from say 14,000 to 6,000, are you telling me that the aircraft will attempt to do this in 125 seconds. Not likely IMO and doing the opposite going from say 6,000 to 14,000 at an IAS in the window of say 250kts I'm no so sure about that either.
Maybe I'm missing something here,
but I don't get the logic nor have I seen any reference to the 125 sec. Please expand a little so I can get onboard.
Thanks