When should flaps be lowered and the before landing checklist performed?

Lowering the flaps and completing the before landing checklist once established on the downwind leg is considered standard procedure for a safe and effective approach to landing. This timing allows for a controlled and gradual configuration of the aircraft as you prepare to land. By extending the flaps during the downwind, you can gradually slow down the aircraft and create more lift at lower speeds, which is essential for a stable approach and landing.

Performing the checklist on the downwind leg provides enough time to address any items before turning onto the base and final legs, ensuring that the aircraft is adequately prepared before entering the critical phases of landing. Additionally, executing these actions early in the approach allows for any necessary adjustments to be made well before the runway is reached, thereby enhancing safety.

In contrast, other options suggest performing these actions at points that may not leave sufficient time for evaluation or adjustments, potentially leading to rushed or incomplete preparations as the aircraft approaches landing.