The upper limit of the white arc indicates what?

The upper limit of the white arc on an airspeed indicator represents the maximum speed at which flaps can be safely extended. This speed is crucial for pilots to know because exceeding it could lead to structural damage to the aircraft or affect its controllability when flaps are deployed. The white arc itself indicates the range of airspeeds where the aircraft can operate safely with the flaps extended, and the upper limit ensures that pilots are aware of this critical threshold.

Understanding this limit helps in ensuring safe operations during landing and approach phases when flaps are typically deployed to enhance lift and drag, allowing for a slower approach speed. The other options, while relevant to flight operations, do not specifically define the characteristics associated with the upper limit of the white arc. For example, minimum flap operating speed and stall speed with gear down relate to different aspects of aircraft performance but are not indicated by the white arc's upper limit.