Flap handle in position 1 will extend flaps and slats (1+F) when the:

The flap handle in position 1, which corresponds to the configuration known as 1+F, indicates that both the flaps and slats will extend for takeoff. This configuration is specifically designed for takeoff and is essential for enhancing the lift characteristics of the aircraft at lower speeds, thereby ensuring safe and optimal performance during this critical phase.

When the flap lever is set to position 1, the aircraft is typically at a speed where extending the flaps and slats significantly improves lift and control, making it suitable for the demands of takeoff. This position is used as part of the pre-takeoff checklist and is crucial for achieving the correct aerodynamic profile during takeoff.

In contrast, moving the flap lever from 0 to 1 in flight would not be reflective of typical procedures since flap settings are usually configured prior to takeoff. Similarly, while flying at very slow airspeeds may be a factor in extension scenarios, it doesn't specifically activate position 1 as it's primarily intended for the takeoff phase. Speed brakes being extended does not relate to the flap settings, since speed brakes are used to increase drag and reduce speed rather than assisting with takeoff lift.