A Monroe ATCT nonradar departure may not be cleared above 6,000 feet until which condition is fulfilled?

The correct answer emphasizes that a Monroe ATCT nonradar departure may only be cleared above 6,000 feet once the aircraft is established on the ARTCC-assigned route. This requirement is in place to ensure safe and efficient integration of the departing aircraft into the en route air traffic system.

When an aircraft departs from a nonradar facility like Monroe ATCT, air traffic controllers must ensure that it is safely established on a flight path that has been predetermined and communicated by the ARTCC. This procedure is crucial because it allows the ARTCC to manage airspace more effectively, as they can anticipate the aircraft's position and trajectory according to the assigned route plan, thereby minimizing the risk of conflicts with other aircraft.

To contrast this with the other options, being in the zone of the controlling ARTCC or within three minutes of takeoff does not inherently guarantee that the aircraft is on a safe or clear path into the en route air traffic system. Radar contact is also not a prerequisite for altitude assignments, but instead provides a means for continuous tracking and communication with air traffic control. Thus, establishing the aircraft on the ARTCC-assigned route is the key condition to safely allow the climb above 6,000 feet.