When should you notify ATC of a speed variation on an IFR flight plan?

Notifying ATC of a speed variation is important for maintaining situational awareness and ensuring safe separation between aircraft. The requirement to report a change in average true airspeed (TAS) of 10 knots or 5 percent is a standard practice because it is significant enough to impact air traffic control’s planning and traffic management.

When a pilot experiences such a change, it indicates a material deviation from the flight plan that ATC is using to maintain separation between aircraft, especially in congested airspace. By reporting this change, the pilot enables ATC to adjust their workload, possibly alter the sequencing of other aircraft, and ensure safe operation within controlled airspace.

Understanding that variations of less than this threshold do not typically require notification helps pilots maintain communication efficiency with ATC and keeps them focused on other critical aspects of their flight. In contrast, options suggesting different thresholds for notification may not adequately reflect the importance of the speed change in relation to air traffic management.