What action should not be authorized when an arriving aircraft is within the ILS OM?

When an arriving aircraft is within the ILS Outer Marker (OM), the priority is to maintain a safe and clear environment for the landing aircraft. This means that allowing taxiing of ground vehicles can pose a significant risk, as these vehicles could inadvertently enter the runway or conflict with the final approach path of the aircraft. The ILS OM is a critical point during the approach phase, and any ground movement in that vicinity could distract or interfere with the pilots' focus on the landing.

Permitting flying near the runway is typically managed with specific clearances to avoid conflict, while authorizing aircraft to land and clearing for takeoff are standard operations that must be done with caution but are acceptable actions provided that the air traffic control is managing the situation safely. The core reason for not authorizing ground vehicle taxiing is to ensure the highest level of safety and efficiency during a crucial phase of flight operations.