Final answer:
In Controlled Airspace, a pilot must report changes in speed exceeding 5% TAS or 0.01 MACH to Air Traffic Control, while in Uncontrolled Airspace, such reports are usually not required.
Step-by-step explanation:
When a pilot experiences a change in True Airspeed (TAS) by more than 5% or a change in MACH number by more than 0.01, it is a significant alteration that can affect the traffic flow and safety in the airspace. In Controlled Airspace, the pilot must immediately contact Air Traffic Control (ATC) to report the speed change, as it may require an adjustment in the aircraft's separation or positioning relative to other traffic. In Uncontrolled Airspace, there is usually no requirement to report such changes as there is no ATC service available; however, good airmanship dictates that the pilot should maintain awareness of surrounding traffic and adjust as necessary to maintain safe separation.