Six mysteries of 9/11’s ‘fifth plane’ United Flight 23

A new documentary has raised perplexing questions about the so-called ‘fifth plane’ of 9/11 amid demands for the FBI to reveal what it knows.

The pilot and three crew members of United Flight 23 said TMZ INVESTIGATES: 9/11: THE FIFTH PLANE they believe their jet was meant to be used in the attacks.

They raise questions about why a burka-clad man was sitting in first class with a group of three other Arabs. There was no one else in the exclusive compartment.

One of these passengers became enraged when takeoff was delayed and demanded that the plane take off while he was at the gate.

United 23 was heading to the JFK tarmac before its flight to Los Angeles at 9 a.m. when all flights at New York airport were grounded when the second plane crashed into the World Trade Center on September 11, 2001.

After the plane was evacuated, the FBI came on board to investigate. They found four open hatches in the floor of the main cabin, despite the fact that the crew left them closed and the plane was locked.

Later, a pair of box cutters were discovered on the adjacent aircraft, which had a tail number identical to United 23 with a one-digit slash.

The FBI declined to disclose to the pilot, crew or filmmakers if any of the passengers had been tracked after they left the plane.

United 23 did not appear in the official 9/11 Commission report, and there were never any confirmed arrests of the people on board. Officials have declined to comment on years of speculation about the flight as a possible fifth attack aircraft.

Here DailyMail.com looks at six of United 23’s biggest unsolved mysteries…

WHY WAS THERE A MAN IN A BURQA AND ANOTHER PASSENGER SWEATING PROUDLY?

Flight attendants Sandy Thorngren and Barbara Brockie Smaldino attested to seeing a burka-clad man along with three other Arabs sitting in first class. There was no one in first apart from the four people.

Accompanying the burka-clad man was someone who appeared to be a bodyguard.

A tall, well-built gentleman in a suit was sitting with a boy of about six or seven years old.

Thorgren said the person in the burqa impressed her because “it was so tight and I could barely see his eyes.”

“I explained to our purser (the main flight attendant) that I thought it was not a woman, I thought it was a man. He was a man and you could tell by the size of his hands. He had hair on his hands. There was definitely a man under that burqa,” Thorgren told the filmmakers.

Smaldino corroborated her claims, adding: “I was absolutely convinced that it was a man, absolutely. There was no doubt in my mind.

In business class, Thorgren saw another man who he found suspicious because he was “sweating profusely” in a T-shirt.

‘It was strange because it was eight in the morning and the planes are cold anyway. But it was a cool morning. He wasn’t nervous or anything, but I could see his face sweating, his body, his shirt was wet under his arms,” he said.

WHY DID A PASSENGER INSIST ON SEEING THE CABIN?

Flight attendant Smaldino recounted how she overheard the Arab in a suit talking to the flight attendant, identified only as Deborah, asking if the boy with him could be shown the cabin.

“He asked the flight attendant to show his young son the cabin and the passengers were no longer allowed to enter the cabin,” Smaldino said.

But despite this, Thorngren said that when he returned to first class he saw the boy and the man looking into the cabin.

WHY DID THE PASSENGERS DEMAND TO TAKE OFF?

Before takeoff, Deborah was trying to organize fruit plates to take back to the plane because all the other meals consisted of meat that Arabs couldn’t eat.

Thorngren said: ‘The people in first class, they didn’t want to eat. Our flight attendant was determined to get food because it was going to be a long flight.

However, the passengers were frustrated by this and told him they didn’t need food, they just wanted to go.

They were arguing with her that they didn’t want to eat. They wanted to take off. “We don’t need food, we want to take off, we don’t need food, we just want to go,” Thorngren recounted.

WHO OPENED HATCHES AFTER THE PLANE WAS EVACUATED?

Shortly after the second plane crashed into the World Trade Center, flights at JFK were grounded and the airport was evacuated.

United 23 returned to the track and taxied back to the gate.

The passengers departed and then the crew went through the plane to make sure it was completely clear because an engineer had been ordered to crash the plane.

About 20 minutes later, the FBI boarded the plane and discovered that four hatches in the cabin floor were open. The hatches lead to a compartment for the aircraft’s electronics. Inside this compartment there is also another hatch under the floor that allows access to the aircraft from the runway.

Purser Deborah said she was surprised when the FBI asked her about the open hatches.

“When they told me the hatches were open I couldn’t breathe. I tried to figure out how those hatches could be opened unless there was someone in electronics and they opened it after we got off the plane,” she said.

Pilot Tom Mannello suspected that someone might have been trying to get out of the aircraft “without being noticed” and had been trying to get on board to remove evidence.

“Whether it’s box cutters in the seats, knives or weapons, I have no idea, but someone could have gotten into the plane through the electronics compartment and into the cabin and removed whatever evidence they wanted and then just get off the plane.” ‘ he said.

On a Boeing 767 jet, the hatch at the bottom of the electronics compartment is located behind the front wheel. It can be opened from the catwalk with the turn of a handle. So someone can lift themselves inside with their arms or use a ladder.

Once inside the electronics compartment, a second hatch above allowed access to the main cabin of the aircraft. The hatch is next to the main entry door of the aircraft at the rear of the cabin.

WHY WERE FIRST CLASS BOX CUTTERS FOUND ON THE ADJACENT PLANE?

In its searches of other planes at JFK, the FBI discovered a pair of box cutters in the plane’s seat compartment next to United 23 in the terminal.

The plane’s tail number was just one digit away from the United flight, leading pilot Mannello to suspect that the blades were actually meant for his plane, but had been misplaced.

Mannello said he learned that the FBI had found the box cutters through a discussion with another pilot.

“If someone was on the ground cooperating with them, they just made a mistake and put the box cutters on the wrong plane,” he said.

I think those box cutters were for my plane, not the one next to me.

“It’s the only thing that makes me think there’s a good chance someone was planning to use our plane as a weapon of mass destruction.”

WHERE DID THE PASSENGERS GO?

The crew was taken to the Port Authority the next day by the FBI. The agents arrived at their hotel rooms and were interviewed individually.

They were later taken to see a line of people at the Port Authority, but none of them could identify any of the people behind the window.

Thorgren said he told them he was suspicious of the four people in first class and the sweaty man in the shop.

Pilot Mannello said that during his interview with the feds, they said they had seven people on their radar. The FBI did not elaborate on the four gentlemen in first class, but Mannello recalled that the agent referred to all of them as “Arabs.”

“I think he suggested that they were going to be questioned,” Mannello said.

The pilot said he doesn’t understand why the FBI never explained what it found about United 23. The agency did not respond to a request for comment from the filmmakers.

Mannello said: “Nobody reached out with what I think is a simple statement: ‘No, these were innocent people on the flight, forget it.’ I don’t know why that information can’t be released.

“If they were involved, then I could understand why that information isn’t published.”

He said, “Now I think it was more likely that we were the fifth plane.”