What information is included on an en route strip regarding altitude?

The information included on an en route strip regarding altitude is the requested altitude. This detail is crucial for air traffic controllers for several reasons. It allows controllers to understand what altitude the pilot intends to fly at, which aids in ensuring that the aircraft stays on a safe flight path and avoids conflicts with other air traffic.

The requested altitude helps in managing altitude assignments, making it possible for controllers to efficiently provide clearances and instructions to maintain safe separation between aircraft. It serves as a reference point for any altitude changes that may need to be communicated later in the flight.

In contrast, while aspects such as the center estimated time over fix, actual departure time, and flight level requested may be relevant to flight operations, they do not specifically pertain to the altitude selection made by the pilot in the same direct manner as the requested altitude does.