Under what condition are pilots not authorized to land an aircraft from an instrument approach?

The correct condition under which pilots are not authorized to land an aircraft from an instrument approach is when flight visibility and ceiling are below the required minimums. Pilots must adhere to the minimum visibility and ceiling requirements for the specific approach being conducted to ensure safe landings. If the actual flight visibility falls below these prescribed levels, it indicates that the pilot may not be able to visually acquire the runway environment in a timely manner, compromising safety.

It's crucial for pilots to maintain situational awareness that includes ensuring that they are above the minimum requirements established for the approach type. This ensures that they can see and identify necessary visual references to execute a safe landing.

While other options may also present unsafe conditions, the specifics of minimum visibility and ceiling requirements are paramount for a successful instrument approach.