A weak mixture is typically used during which phase of flight?

A weak mixture is typically used during the cruising phase of flight due to the operational efficiency it provides. At cruising altitude, the engine operates at a higher, more stable airspeed and the air density is lower, allowing for a leaner fuel-air mixture. This leaner mixture maximizes fuel efficiency without compromising performance, as the engine achieves optimal combustion under these conditions.

During cruising, pilots can afford to reduce the mixture for better fuel economy and to keep the engine temperatures in an acceptable range. In contrast, during takeoff and climbing, a richer mixture is often required to ensure adequate power and prevent engine knocking. Similarly, during engine starting, a richer mixture helps with initial combustion. Thus, the use of a weak mixture is more appropriate for cruising when the engine can function effectively with a leaner fuel mix.