What weather phenomenon poses danger during approach but is not particularly hazardous to en route aircraft?

Low-level wind shear is a specific weather phenomenon that presents significant hazards during the approach phase of flight. It occurs when there are sudden changes in wind speed and direction at lower altitudes, particularly during takeoff and landing. These rapid changes can lead to loss of control or difficulty in maintaining the correct flight path as the aircraft transitions to the ground environment. Pilots must be particularly cautious during these moments as the aircraft can experience severe unexpected changes in performance.

In contrast, phenomena such as clear air turbulence, thunderstorms, and fog can present risks during en route flight or at any phase, but they are not tied as closely to a specific flight phase as low-level wind shear is. For example, while clear air turbulence can be a concern at cruising altitudes, it does not typically affect aircraft during the critical phases of approach like low-level wind shear does. Thunderstorms can be hazardous in various phases of flight due to severe weather, but their impact is also felt en route. Fog, on the other hand, primarily impacts visibility during takeoff and landing but does not have the same abrupt wind changes associated with low-level wind shear, which can catch pilots off guard during approach.