What measure indicates an aircraft is performing a standard rate turn?

A standard rate turn is defined as a turn in which an aircraft changes its heading at a rate of three degrees per second. This rate is considered a universal standard for flight operations, especially in instrument flying, as it provides consistent, predictable performance for the pilot. In practice, this means that in a complete turn of 360 degrees, the maneuver would take approximately two minutes to execute.

Understanding this rate is essential for maintaining control and coordination during flight, particularly in instrument meteorological conditions where visual references are limited. Operators use this standard to ensure that turns can be accomplished safely and efficiently, without losing altitude or risking excessive bank angles.

The other options present different rates that do not align with the standard, which could lead to misunderstandings in the execution of turns under various flying conditions. Therefore, three degrees per second is clearly established as the correct answer for identifying a standard rate turn in aviation.