What kind of turn should an aircraft perform from the base leg before landing?

The correct response involves an aircraft performing a 90-degree turn from the base leg before landing. This maneuver is standard protocol in aviation to align the aircraft with the runway. As the aircraft approaches the runway, it typically enters the base leg of the traffic pattern, where it is positioned to make a turn toward the final approach.

Executing a 90-degree turn allows the pilot to accurately transition from the base leg to the final approach, ensuring that the aircraft is properly aligned for landing. This turn is essential for maintaining a safe and effective approach trajectory, enabling the pilot to control airspeed and descent rate while preparing for a smooth landing.

Other options represent maneuvers that may be less applicable or less effective in typical landing approaches. For instance, a left turn might apply to specific flight patterns but is not universally standard in the context of runway alignment. An ascending turn would not be appropriate because the aircraft is usually descending for landing, and a gradual slope turn could lead to misalignment and complicate the approach. Therefore, the 90-degree turn is the definitive choice for properly aligning the aircraft during the landing sequence.