TMZ has been conducting a 6-month investigation into United Flight 23, which is scheduled to depart JFK at 9 a.m. and bound for Los Angeles. We interviewed 3 flight attendants, the pilot, the United dispatcher, a member of the 9/11 Commission, and others about a variety of suspicious activity on the plane… suspicious enough for the FBI to get involved.

Four passengers in first class aroused suspicion shortly after boarding. Flight attendants say one of the passengers was a man dressed as a woman. The purser [first class flight attendant] tells us that these passengers did not eat meat and there were only 2 fruit plates in the galley. She wanted to get more fruit plates for the passengers to eat, and it sparked a heated argument … with one of the passengers insisting, “We don’t want to eat anything. We don’t need food. We want to take off. .. We just want to go.”

There were other reasons why the flight attendants were suspicious of the 4 passengers in first and two others in business class.

The plane taxied to the runway and was about to take off when the World Trade Center was hit and the airport closed. United 23 went back to the gate and was evacuated – the plane was empty and locked. Twenty minutes later, people on the ground saw two uniformed people run into United 23’s passenger cabin. Authorities arrived a short time later, opened the door and found that the hatch – leading from the belly of the plane to the cabin – was open.

The pilot believes these 2 people may have been there to remove weapons or other incriminating evidence. We don’t know what was removed from Flight 23, but we do know that someone placed box cutters in the first class seat pockets of the plane that was parked next to United 23… a plane that was not scheduled to take off at the time. The United 23 pilot thinks these boxcutters should be on his flight, but someone mixed up the two planes.

Later that day, the FBI questioned the flight attendants and even took them to a port authority list to see if they could identify the 4 passengers.