Which factor can increase stall speeds during turns?

Increasing load factor is a significant factor that can raise stall speeds during turns. When an aircraft enters a turn, the load factor increases due to the combination of the aircraft's weight and the centrifugal force acting on it. This results in a higher effective weight of the aircraft, requiring a greater angle of attack to maintain level flight. As the angle of attack increases, the stall speed rises because stalls occur at higher speeds when the load factor is elevated. This phenomenon is particularly critical during steep turns where the increase in load factor is more pronounced.

In contrast, decreasing the bank angle would lower the load factor and consequently could decrease the stall speed, while reducing engine output might not directly relate to stall speed in a turn as it affects thrust, not load. Similarly, altering the aircraft's altitude does not have a direct impact on stall speeds as it pertains more to the air density and performance characteristics rather than the load factor during a turn.