What type of altitudes must aircraft assigned to specific fixes and routes be given?

Aircraft assigned to specific fixes and routes must be given pre-coordinated odd and even altitudes to ensure safe and efficient separation between different aircraft in the airspace. This system of assigning altitudes helps to manage air traffic by organizing flights in a predictable manner, where aircraft traveling in opposite directions are assigned altitudes that alternate between odd and even.

For example, odd altitudes may be assigned to aircraft flying eastbound while even altitudes are given to those flying westbound. This structured approach minimizes the risk of mid-air collisions and facilitates smoother operations within controlled airspace, allowing air traffic controllers to maintain an orderly flow of traffic.

The other choices do not adhere to established air traffic management protocols. Random altitude assignments would undermine the safety and predictability needed in busy airspace. Minimum safe altitudes, while important for terrain clearance, do not specifically address the altitude separation needed for aircraft on specified routes. Flight levels based on urgency would not provide the necessary structured separation observed in standard operational procedures.