Under what conditions should aircrew not taxi on runways or taxiways?

The correct answer focuses on the critical impact snow or ice has on runway and taxiway conditions. When snow or ice is adhering to these surfaces, it significantly reduces traction, thereby creating a higher risk of accidents during taxi operations. Aircraft may have difficulty stopping, turning, or maintaining control due to slippery conditions. This necessitates a cautious approach, meaning that aircrew should avoid taxiing in such circumstances to ensure the safety of the aircraft, crew, and passengers.

While decreased visibility can pose risks during taxiing, there are often operational procedures and tools (like ground radar and communication with ground control) that can facilitate movement even in low visibility. Similarly, winds exceeding 15 knots can create challenges but are typically manageable with trained crews and standard procedures. The presence of other aircraft may require increased awareness and communication, but it does not inherently prevent safe taxiing if conducted with caution. Therefore, the adhering snow or ice stands out as the most critical condition warranting a restriction on taxiing.