What type of wind conditions may indicate a shear zone during approach or landing?

Calm winds but likely to change is indicative of shear zones during approach or landing because these conditions can often precede sudden shifts in wind direction and speed. Shear zones occur when there are abrupt changes in wind velocity or direction, typically at different altitudes. When pilots experience calm winds before a landing, it may suggest that the atmospheric conditions could shift rapidly, particularly due to nearby weather systems or terrain influences, leading to potential turbulence or wind shear.

This makes it especially important for pilots to remain vigilant for any unexpected changes in wind that could affect their approach or landing. The presence of calm winds followed by sudden changes can pose risks, as they could result in loss of control or miscalculations in descent rate and approach speed.

Other options involve wind conditions that do not typically signal a shear zone. Strong headwinds at high elevations and strong tailwinds during landing are generally more predictable conditions that don't exhibit the abrupt changes characteristic of shear zones. Calm winds with clear skies imply stability and a lack of significant weather activity, which is contrary to the conditions that suggest a shear zone might be developing.