What indicates the need to reduce flaps from 20 to 8?

The correct answer refers to the operational procedures during a climb phase in aviation, particularly regarding flap retraction. Reducing the flaps from 20 to 8 usually occurs when the aircraft is in a safe and stable climb, and the parameters of speed provide assurance that the aircraft can fly without the additional lift created by the extended flaps.

Specifically, above V2+10 to 15 knots is the ideal range for initiating this reduction. V2 is the takeoff safety speed, a critical speed that ensures the aircraft can climb adequately in the event of an engine failure. Once the aircraft exceeds this speed, it signifies that there is sufficient lift and control authority available. Therefore, allowing a slight buffer (10 to 15 knots above V2) ensures that the aircraft is fully capable of handling the change without risking a stall or loss of control, even with the reduction in lift that comes from retracting the flaps.

In contrast, the other options suggest either a speed that is too low or not tailored to the aircraft's performance capabilities following takeoff. Reducing the flaps at those speeds could compromise safety and aircraft handling capacity during a critical phase of flight.