Which of the following is NOT a phase of flight monitored by Air Traffic Controllers?

Refueling is not considered a standard phase of flight that is directly monitored by Air Traffic Controllers. The primary phases of flight include takeoff, ascent, cruising, descent, and landing, as well as the holding phase, where aircraft may be instructed to circle in a designated pattern due to air traffic or other operational considerations.

These phases are crucial for ATC to ensure safe separation between aircraft, manage traffic flow, and facilitate efficient takeoff and landing sequences. During these stages, controllers are actively engaged in controlling the aircraft's movements, providing instructions and maintaining situational awareness.

In contrast, refueling is typically conducted in specific controlled environments such as military operations or at designated facilities and does not generally involve ATC in the same way as the other phases mentioned. This phase may be operationally important, but it falls outside the standard purview of routine air traffic control activities.