pb 9/11 flight log picture thing maybe explained
United Airlines (Pre-Loaded Data): In 2001, United's dispatch software automatically attached the specific aircraft's tail number (like N612UA) to the public Department of Transportation data stream before the plane ever pushed back from the gate.
Because that data packet was generated and transmitted early in the morning, the tail numbers were already hardcoded into the system when the planes took off.
American Airlines (Post-Arrival Sync): American Airlines used a different system architecture. Their data stream sent the scheduled flight number ahead of time, but it was designed to dynamically pull and append the actual physical tail number from internal logs only after the flight landed and finalized its flight logs.
Because Flights 11 and 77 never reached Los Angeles to trigger this post-arrival sync, the system never populated the field, leaving the database software to display its default placeholder: "UNKNOWN."