United Flight 23: The Unanswered Story of 9/11’s Alleged ‘Fifth Plane’

As four hijacked airliners carried out the devastating attacks of September 11, 2001, another transcontinental jet was waiting to depart New York. More than two decades later, crew members believe their aircraft may also have been targeted. But how much of the United Flight 23 story is documented—and how much remains speculation?

The terrorist attacks of September 11, 2001, claimed 2,977 innocent lives and changed aviation forever.

Four commercial airliners were hijacked that morning. American Airlines Flights 11 and 77 and United Airlines Flight 175 were deliberately flown into the World Trade Centre and the Pentagon, while United Flight 93 crashed in Pennsylvania after its passengers and crew fought back against the hijackers.

However, a fifth aircraft has since become the subject of an enduring and deeply unsettling question.

United Airlines Flight 23 was preparing to fly from New York’s John F Kennedy International Airport (JFK) to Los Angeles (LAX) when the attacks began. The Boeing 767 had already left its gate and was waiting to depart when New York’s airspace was closed.

Its crew subsequently reported several incidents they considered suspicious. The FBI investigated, passengers were sought and questioned, and the 9/11 Commission examined at least some of the allegations.

Yet no publicly released evidence has established that Flight 23 formed part of al-Qaeda’s operation.

United 23 Prepares To Depart

United Flight 23 was scheduled to leave JFK at approximately 0900hrs local time on September 11.

The aircraft is understood to have been Boeing 767-222 N602UA, an early example of the twin-engine widebody carrying United’s internal fleet number 6002. The jet was one of the first 767s built and was delivered to the airline in January 1983.

Around 160 passengers were reportedly on board, together with Captain Thomas “Tom” Mannello, First Officer Carol Timmons and six cabin crew members.

Like the four aircraft that were hijacked, Flight 23 was operating a transcontinental service and would have departed with a significant fuel load for the journey to California.

Mannello later remembered an otherwise normal morning at JFK. As the aircraft was being pushed back, a member of the ground crew asked whether he had heard about a fire at the World Trade Centre.

At 0846, American Airlines Flight 11 had struck the North Tower. However, the nature of the unfolding attack was not yet understood, and Mannello initially assumed that a light aircraft had been involved in an accident.

Flight 23 was cleared to taxi but joined an unusually long queue of around ten aircraft. Mannello recalled being positioned behind an Icelandair Boeing 757, with no aircraft taking off or landing.

That delay would prove crucial.

At 0903, United Flight 175 struck the South Tower. It was now clear that the United States was under attack.

‘Beware Any Cockpit Intrusion’

United dispatcher Ed Ballinger was responsible for 16 transcontinental flights that morning, including Flights 23, 93 and 175.

After learning what had happened in New York, Ballinger began sending an urgent Aircraft Communications Addressing and Reporting System—or ACARS—message to the crews under his control.

Flight 23 reportedly received the warning at approximately 0920hrs:

“Beware any cockpit intrusion—two aircraft in NY hit World Trade Centre.”

The message prompted an immediate response on the flight deck.

Mannello retrieved the cockpit crash axe, while Timmons used the pilots’ luggage to barricade the cockpit door against the surrounding bulkhead. They also kept a fire extinguisher close at hand as a possible defensive weapon.

At the time, reinforced and permanently locked cockpit doors had not yet been introduced. Standard hijacking procedures relied on cooperation and negotiation, with pilots expected to comply with demands and focus on landing the aircraft safely.

No one yet understood that the hijackers intended to use passenger aircraft as weapons.

Mannello instructed the cabin crew not to attempt to enter the cockpit. A flight attendant then reported that several passengers in the forward cabin had become increasingly agitated about the delay.

First Officer Timmons recalled the message during a 2011 interview: there were men in first class who were extremely unhappy that the aircraft was not taking off.

Shortly afterwards, the crew heard that JFK was being closed and its control facilities evacuated. The pilots began coordinating with other aircraft to find a safe route back to the terminal.

As Flight 23 taxied towards its gate, Mannello and Timmons could see thick smoke rising from Lower Manhattan.

The aircraft eventually returned to Gate 2 at Terminal 7, where its passengers and crew disembarked.

The Suspicious Passengers

The first reports about Flight 23 appeared within days of the attacks.

On September 14, CBS and the Associated Press reported that the FBI was investigating whether an altercation aboard the flight could have been connected to an aborted hijacking attempt.

According to the contemporary account, three men refused to leave Flight 23 after being told that it had been cancelled. Their disagreement with a crew member allegedly became heated, and airport security was summoned.

By the time officers reached the gate, the men had disappeared into the crowds evacuating JFK.

A later review by 9/11 Commission staff found supporting evidence for part of this story.

According to a surviving Commission email, a United employee telephoned the Port Authority police at 1111hrs on September 11 to report three Arab men who were refusing to leave a cancelled flight. An officer was dispatched 17 minutes later, but the individuals had gone by the time the officer arrived.

That delay must be considered within the extraordinary circumstances of the morning. Many Port Authority officers had reportedly left the airport to respond to the unfolding disaster at the World Trade Centre.

What Happened To The Men?

The suggestion that the Flight 23 passengers vanished and were never identified does not appear to be entirely accurate.

On September 13, four Saudi citizens were identified at JFK as possible customers from the cancelled flight. They had reportedly arrived from Saudi Arabia early on September 11 and returned to the airport two days later seeking refunds and new flights to California or Boston.

The men were detained and questioned by the Joint Terrorism Task Force.

All four carried Saudi passports and US visas. One possessed identification from Embry-Riddle Aeronautical University and a Virginia driving licence, while another carried a Mayo Clinic card. The FBI prepared individual interview reports—known as 302s—for each man.

Their names remain redacted from the publicly available copy of the Commission document.

There are inconsistencies within that document. It incorrectly describes Flight 23 as flying to San Francisco rather than Los Angeles and says United operated from Terminal 6 instead of Terminal 7, as identified by Mannello and contemporary reports.

It also describes the four men as “possible” Flight 23 customers, meaning it does not conclusively establish that all four were the passengers reported by the crew.

Contemporary news reports stated that approximately a dozen Middle Eastern travellers detained during security alerts at JFK and LaGuardia were eventually cleared of involvement in the attacks. One of the three men associated with Flight 23 was reportedly stopped after returning to JFK and attempting to board American Airlines Flight 299 to San Jose.

No public evidence has subsequently connected any of these individuals to al-Qaeda.

The Crew’s Documentary Testimony

Interest in Flight 23 was revived by the 2023 television documentary TMZ Investigates: 9/11: The Fifth Plane, which was later shown in the UK as 9/11: Mystery of the Fifth Plane.

The programme brought together Mannello, members of the cabin crew, dispatcher Ed Ballinger and other aviation figures to examine whether the aircraft could have been another intended target.

Mannello told the documentary:

“I now believe that it is more likely than not that we were the fifth aeroplane.”

Flight attendant Sandy Thorngren recalled noticing a passenger in business class who appeared extremely nervous and was sweating heavily despite the cool temperature inside the aircraft.

In first class, purser Deborah described a group that included a well-built man in a tan suit, a young boy, another man who appeared to act as a bodyguard, and a person wearing a niqab.

Thorngren and fellow flight attendant Barbara Brockie Smaldino said they came to believe the niqab-wearing passenger may have been male because of the person’s large, hairy hands. This was their personal impression; it was never officially established.

The group had apparently requested meat-free meals. Deborah tried to get additional fruit plates, but one passenger became insistent that they did not want to wait for food and wanted the aircraft to depart.

One of the adults also reportedly asked whether the young boy could visit the cockpit. Such requests were not unusual before September 11, but the crew understandably viewed the incident very differently after learning how the other aircraft had been seized.

Thorngren also recalled a passenger asking during the evacuation whether the White House had been hit. The precise timing and context of that remark have not been independently corroborated.

It is important to acknowledge that the descriptions changed between different accounts. 

Contemporary reports referred to three adult men, while later recollections mentioned four young men, a family group, a veiled passenger and one or two additional men in business class.

These may have been separate groups of passengers. They may also reflect the difficulty of reconstructing a traumatic, chaotic event many years later.

People Seen Inside The Empty Aircraft

The documentary introduced an even more disturbing allegation.

After Flight 23 was emptied, searched, and supposedly secured, people on the ground allegedly saw one or two uniformed individuals moving through its cabin.

When investigators examined the aircraft, they reportedly found a floor panel leading into the electronics and avionics compartment beneath the cabin open. The 767’s electronics bay can also be accessed externally from beneath the aircraft.

Members of the crew came to suspect that someone had entered the aeroplane after its evacuation, possibly to remove weapons or other evidence.

An unnamed flight attendant later told investigative website Florida Bulldog that she had returned to the aircraft for a bottle of water after believing everyone had left. She claimed that two unidentified men then emerged from the rear galley.

According to her account, a mechanic later confronted the men before they apparently escaped through the lower compartment.

These are serious claims, but no publicly available police report, maintenance log, photograph or FBI document has been released to substantiate them. Mannello did not witness the alleged intrusion himself and learned about the open panels from others.

During an unprecedented evacuation, mechanics, security personnel and emergency responders may also have had legitimate reasons to enter an abandoned aircraft.

The incident therefore remains unexplained rather than proven evidence of terrorist activity.

Box Cutters On The Wrong Aircraft?

Perhaps the most compelling element for Mannello was something he says happened several days later.

A United manager allegedly contacted him and asked for the fleet number of the aircraft that had operated Flight 23. Mannello identified it as 6002.

He was reportedly told that box cutters had been discovered inside first-class seat pockets aboard another United aircraft parked nearby. That aeroplane was identified as 6001.

Mannello began to wonder whether someone had intended to conceal the weapons aboard Flight 23 but had accidentally placed them on the wrong aircraft.

The theory would also explain anyone entering Flight 23 after its evacuation: they might have been trying to remove equipment or evidence after the operation failed.

However, the theory depends upon several unconfirmed assumptions.

There is no publicly released evidence report identifying the neighbouring aircraft, recording precisely where the box cutters were discovered or connecting them to any Flight 23 passenger.

Box cutters and small knives were found aboard several other aircraft during the security searches that followed September 11. Contemporary reports confirmed discoveries aboard Delta jets in Boston and Atlanta. A subsequently released FBI document also described a box cutter found beneath a seat on an American Airlines aircraft that had operated between San Diego and JFK on September 10.

Investigators considered whether weapons might have been placed aboard aircraft in advance, but the origins of those particular items were never publicly established.

Their discovery shows why Mannello’s concerns cannot simply be dismissed. It does not, however, prove that the box cutters on the neighbouring United aircraft were intended for Flight 23.

The Unclaimed Luggage

Another frequently repeated claim is that unclaimed baggage belonging to the suspicious passengers contained box cutters and documents connected to al-Qaeda.

The public evidence is again indirect.

Aviation author Lynn Spencer said senior FAA officials and airport managers told her that suspicious items had been discovered in baggage associated with Flight 23.

Ballinger also told 9/11 Commission investigators that he had received reports from United personnel—including the airline’s chief pilot—that several Muslim passengers had not collected their bags and that the luggage contained incriminating information.

Ballinger believed that the warning he sent to Flight 23 may have prevented another hijacking.

But he had not searched the baggage himself. His knowledge was secondhand, and Mannello disputed other parts of what he was told. For example, Ballinger heard that the crew had invented a mechanical problem to return to the terminal, whereas Mannello said no such deception occurred.

No baggage inventory, photograph, forensic examination or FBI report has been made public. The claim that al-Qaeda documents were found therefore remains unverified.

The FBI Investigation

Mannello said the FBI interviewed the entire crew on September 12.

His own interview reportedly lasted between three and four hours. He recalled an agent saying that investigators had identified seven Arab or Muslim passengers aboard the flight. Three—a couple and their young child—were apparently not considered suspicious, leaving four men whom investigators wanted to locate.

Timmons later summed up the crew’s experience succinctly: “The FBI asks questions. They don’t tell you things.”

The documentary claimed that flight attendants were also taken to an identification lineup to see whether they could recognise the passengers.

The crew never received a detailed public explanation of what investigators ultimately concluded.

In 2022, Florida Bulldog submitted a Freedom of Information Act request for the FBI’s Flight 23 records. The Bureau confirmed that responsive documents existed but refused to release them, stating that they were relevant to a “pending or prospective law enforcement proceeding.”

That response has sometimes been portrayed as confirmation that the FBI was still investigating a fifth hijacking team. It does not necessarily mean that.

It confirms that the FBI possesses Flight 23 material and considered it relevant to some form of enforcement proceeding in 2023. It does not reveal whether that proceeding concerned the flight itself, the wider 9/11 investigation, alleged Saudi support networks or related litigation.

No prosecution or official finding concerning Flight 23 has been announced since.

The 9/11 Commission

United 23 does not appear in the final 9/11 Commission Report.

That omission has fuelled claims that the incident was ignored or concealed. Surviving Commission records, however, show that staff were aware of the flight and investigated at least part of the story.

They examined Port Authority records, investigated the four Saudi travellers and recorded that the FBI had interviewed them. The Commission also questioned Ballinger and documented his belief that his warning might have saved Flight 23.

No one has officially explained why the incident was excluded from the final report. The most reasonable inference is that investigators found insufficient evidence to connect it to the confirmed plot.

Former Commission staff member Miles Kara later said his reconstruction of the attacks left no room for a fifth aircraft. He believed the suspicious passengers may have panicked and fled during the airport evacuation.

That was Kara’s assessment, not a formal Commission finding, and he was not personally responsible for investigating Flight 23.

Al-Qaeda’s Earlier Plans

It is known that Khalid Sheikh Mohammed, the principal architect of the attacks, initially proposed a far more ambitious operation involving ten aircraft.

Nine would have been crashed into targets on both American coasts, including government buildings, nuclear facilities and prominent West Coast landmarks. Mohammed intended to land the tenth aircraft and deliver a speech to the media.

Al-Qaeda’s leadership considered the proposal too complicated, and the operation was substantially reduced.

By August 2001, the Commission’s reconstructed evidence pointed to four assigned hijacking teams. All 19 tickets were purchased between August 25 and September 5, and the men gathered near Boston, Newark and Washington ahead of the attacks.

The often-mentioned “20th hijacker,” Mohammed al-Qahtani, was not assigned to a fifth aircraft. Investigators believe he was intended to complete the team aboard Flight 93 but was refused entry to the United States in August 2001.

No fifth pilot, additional team, ticket purchases, financial trail, communications or target connected to United 23 have been publicly identified.

Its scheduled departure also presents a problem for the theory. The four hijacked aircraft were due to leave between 0745 and 0810, allowing the attacks to begin before airlines and authorities understood what was happening.

Flight 23’s 0900 departure left it vulnerable to precisely the disruption that prevented it from taking off.

None of this proves that another attack was impossible. It does mean that Flight 23 does not fit comfortably within the final operation reconstructed from al-Qaeda communications, financial records and the hijackers’ movements.

A Mystery, Not An Established Fifth Aircraft

The concerns of Flight 23’s crew deserve to be treated seriously and respectfully.

They were sitting aboard a fuelled transcontinental airliner as four similar aircraft were hijacked and hundreds of people were being killed only a few miles away. They had incomplete information, an unsecured cockpit door and no idea how many other aircraft might be under threat.

Mannello, Timmons and their cabin crew reacted quickly to protect the cockpit and everyone on board. Whatever the truth behind the passengers’ behaviour, their decisions were entirely appropriate in the circumstances.

The crew’s subsequent trauma was also real. Several struggled to return to flying, and some left the industry earlier than planned. Timmons died in August 2020, before the latest television investigation was produced.

Nevertheless, testimony must be separated from corroborated evidence.

We know that Flight 23 existed, taxied for departure and received Ballinger’s warning. We know that several passengers caused concern, that the Port Authority received a call and that the FBI questioned both crew members and possible passengers. We also know the 9/11 Commission investigated the incident, though it omitted it from its final report.

What we do not have is publicly released evidence connecting those passengers to al-Qaeda or showing that weapons, incriminating documents or a fifth hijacking team were assigned to the aircraft.

United Flight 23 can therefore be accurately described as a flight investigated at the time as a possible aborted hijacking.

Whether it really was intended to become the fifth aircraft of September 11 remains one of the day’s unresolved questions.

© Confessions of a Trolley Dolly