Final answer:
The ESCAT Air Traffic Priority List (EATPL) is a hierarchical system that determines the priority of flights during emergencies, but the exact number of priorities is not public information as it depends on the particular circumstances and security needs.
Step-by-step explanation:
The Emergency Security Control of Air Traffic (ESCAT) is a plan implemented in the United States that entails a hierarchical system of air traffic priority control. The list known as the ESCAT Air Traffic Priority List (EATPL) establishes various levels of priority for different types of flights. However, the exact number of priorities contained within the EATPL is not public information, as it can vary based on national security needs and the specific protocols in effect at the time.
For the purpose of national security and the safety of air travel, the details of the EATPL are generally not disclosed to the public. When the ESCAT plan is activated, authorities prioritize air traffic according to the specific situation and the level of the threat, which could influence the number of priorities defined in the EATPL at that moment.