More than two decades after September 11, 2001, nearly every American knows the basic outline of what happened that morning. Nineteen al-Qaeda hijackers boarded four commercial airliners. American Airlines Flight 11 and United Airlines Flight 175 were flown into the World Trade Center. American Airlines Flight 77 struck the Pentagon. United Airlines Flight 93 crashed in Pennsylvania after passengers fought back. The official 9/11 Commission concluded that the 19 hijackers had boarded those four transcontinental flights with the intention of transforming them into weapons. Yet there is another story from that morning, one that has remained largely outside the familiar 9/11 narrative. It concerns a Boeing 767 sitting at John F. Kennedy International Airport, preparing for a cross-country journey to Los Angeles, and a group of crew members who eventually came to believe that their airplane may also have been marked for hijacking. That aircraft was United Airlines Flight 23.
The theory received renewed attention when TMZ spent six months investigating the flight for the documentary “TMZ Investigates 9/11: The Fifth Plane.” Originally broadcast in 2023 and later made available on YouTube, the program interviewed Flight 23’s captain, flight attendants, a United Airlines dispatcher and others connected to the events of that morning. TMZ presented their testimony as evidence of a haunting possibility: that the four hijacked planes everybody remembers might not have been the entire plan. Flight 23, the documentary asks, may have been intended to become another weapon before an extraordinary sequence of events prevented it from leaving the ground.
It is an explosive suggestion, but an important distinction needs to be made from the beginning. The publicly available evidence does not establish that United Flight 23 was definitely a fifth aircraft selected by al-Qaeda. The official 9/11 Commission account says that 19 hijackers were waiting to board four flights on the morning of September 11. What the United 23 story provides instead is a collection of witness recollections, unusual incidents and unresolved questions that the surviving crew members believe deserve far more attention than they have received.
United Flight 23 was scheduled to depart JFK for Los Angeles at approximately 9:00 that morning. Like the four aircraft that were successfully hijacked, it was a long-distance flight carrying a significant fuel load. Captain Tom Mannello remembered the beginning of the day as completely ordinary. The atmosphere among the crew was relaxed. Passengers were boarding. Preparations were being made for the long journey west. Nothing initially suggested that Flight 23 was about to become connected, even indirectly, to one of the darkest mornings in modern American history.
But several passengers began attracting the attention of the cabin crew.
According to accounts presented by TMZ, four passengers seated in first class seemed unusual to the flight attendants. Two additional passengers in business class also caused concern. One business-class passenger was reportedly sweating heavily even though the cabin was not particularly warm. By itself, that would prove nothing. People become nervous on airplanes for countless reasons. But after September 11 unfolded, seemingly meaningless details would take on a much darker significance for those who had been there.
The most memorable confrontation occurred in first class and began over something almost absurdly ordinary: airline food.
The purser discovered that several passengers did not eat meat, while the aircraft had only two fruit plates available. She considered delaying departure briefly so additional food could be obtained. According to her recollection, at least one passenger reacted strongly. The passengers were apparently uninterested in eating. What mattered to them, according to the crew’s account, was getting the plane into the air. TMZ reported the purser recalling one passenger insisting that they did not need food and simply wanted the aircraft to take off.
In almost any other context, it might have been remembered as nothing more than an impatient traveler arguing with a flight attendant.
But this was September 11, 2001.
As Flight 23 moved away from the terminal and joined the traffic heading toward departure, another Boeing jet was already speeding toward Manhattan.
At 8:46 a.m., American Airlines Flight 11 struck the North Tower of the World Trade Center. Initially, confusion spread through the aviation system. Controllers, airline employees and officials were trying to determine whether the collision had been an accident. Seventeen minutes later, at approximately 9:03 a.m., United Airlines Flight 175 slammed into the South Tower. Whatever uncertainty remained disappeared instantly. America was under attack.
United 23 was still on the ground.
The timing may have saved everyone aboard.
The aircraft had taxied toward departure but never reached the sky. As the magnitude of the unfolding emergency became apparent, JFK stopped normal operations. Flight 23 was ordered back to the terminal. The passengers were removed, the aircraft was emptied, and the door was secured. What might have happened if the plane had departed minutes earlier can never be known.
To the crew, however, the strangest events were only beginning.
According to witnesses interviewed for the TMZ investigation, approximately 20 minutes after the evacuated airplane had been locked, people outside noticed what appeared to be two uniformed individuals moving through its passenger cabin. That immediately raised an obvious question: how could anyone be inside an aircraft that was supposed to have been empty and secured?
Authorities returned to the plane.
When they entered, investigators reportedly discovered that a hatch connecting the passenger cabin to the lower portion of the aircraft was open. TMZ reported that the discovery alarmed investigators and became part of the FBI’s interest in Flight 23.
That hatch would eventually become one of the central mysteries in the fifth-plane theory.
Captain Mannello has suggested that the individuals allegedly seen inside could have been attempting to retrieve something from the aircraft. Perhaps weapons. Perhaps documents. Perhaps some other evidence that would have connected the passengers to the attacks unfolding elsewhere.
But that remains speculation.
No publicly available evidence identified by TMZ proves what those individuals were doing aboard the aircraft, whether they had legitimate access to it, or whether anything was actually removed. The documentary presents the unexplained activity as suspicious, and given the extraordinary circumstances surrounding that morning, it is understandable why crew members remember it so vividly. But describing an unanswered question is different from proving the answer.
Then came another disturbing discovery.
According to TMZ’s investigation, box cutters were discovered in the first-class seat pockets of another Boeing 767 parked near Flight 23. Box cutters occupy a particularly sinister place in the history of September 11 because small cutting weapons were associated with the hijackings. The neighboring aircraft apparently was not scheduled to depart during the critical period, leading Mannello to wonder whether the weapons might have been intended for Flight 23 and mistakenly placed aboard the wrong aircraft.
Again, that theory has never been publicly proven.
But imagine the perspective of the crew. They had encountered passengers behaving in ways that seemed unusual. Some had been extremely eager for the flight to depart. Their plane was stopped from taking off only because the largest aviation emergency in American history was developing around them. After evacuation, people were allegedly seen inside the supposedly secured aircraft. A hatch was discovered open. Then the crew learned that box cutters had reportedly been discovered aboard a nearby aircraft.
Individually, each incident might have an innocent explanation.
Together, they became much harder for the crew to forget.
Federal investigators apparently considered the situation serious enough to question the Flight 23 crew. According to the flight attendants interviewed by TMZ, FBI agents questioned them and took them to a Port Authority lineup in an attempt to identify passengers who had attracted their attention.
That detail matters because it shows that the suspicions surrounding Flight 23 were not created entirely decades later for television. Law-enforcement officials were investigating something associated with the flight in the immediate aftermath of September 11. What remains unclear from the publicly available record is what those investigators ultimately concluded.
The discrepancy between the seriousness remembered by the crew and the limited place Flight 23 occupies in the official public history is one reason the story continues to fascinate people.
The 9/11 Commission was created to provide a comprehensive examination of the attacks, including failures involving intelligence, aviation security, border control, law enforcement and government preparedness. Its final report described in extraordinary detail how the 19 identified hijackers prepared for their mission and boarded four aircraft. United Flight 23 did not become part of the central public narrative in the same way.
For some people, that absence itself looks suspicious.
But absence from a major report is not automatically evidence of a cover-up.
Investigators working after September 11 were confronted with thousands of tips, suspicious incidents, false alarms and potential connections. A claim can be investigated seriously and still fail to produce enough evidence to become part of the final historical conclusion. The FBI interviewing witnesses does not by itself prove that their initial suspicions were ultimately confirmed.
Still, the people who were aboard Flight 23 have every reason to ask what investigators discovered.
One of the most compelling elements of the documentary is that its central figures are not internet theorists who became interested in Flight 23 decades later. They were members of the crew who were physically there that morning.
Captain Tom Mannello has said that for years he resisted believing his aircraft had been targeted. According to TMZ, hearing the complete recollections of other crew members during production caused him to reconsider what happened. Eventually, he became convinced that the collection of events could not simply be dismissed as coincidence.
Flight attendants interviewed for the documentary expressed similar beliefs.
Their testimony carries emotional weight, but eyewitness confidence and historical proof are not necessarily the same thing. Memories can evolve over decades, particularly memories formed during traumatic events. Witnesses can accurately remember what they saw while still being mistaken about what those events ultimately meant.
That tension is precisely what makes the Flight 23 mystery compelling.
The strongest version of the theory argues that the aircraft was intended to be the fifth hijacked plane of September 11. Under this scenario, a group aboard Flight 23 was prepared to seize the Boeing 767 after takeoff. Weapons may already have been hidden on the aircraft or intended to be placed there. The passengers’ apparent impatience to leave the ground reflected knowledge that timing was essential. When JFK stopped departures following the World Trade Center attacks, the mission collapsed before it could begin. Someone connected to the plot then entered the evacuated aircraft through its lower compartment to remove evidence.
It is a dramatic reconstruction.
It also requires assumptions for which conclusive evidence has not publicly emerged.
There is no publicly established identification of the suspicious passengers as members of al-Qaeda’s 9/11 operation. There is no publicly demonstrated chain connecting the box cutters found on the neighboring aircraft to Flight 23. There is no confirmed public evidence showing that people seen moving through Flight 23 after evacuation were terrorists or accomplices. And the official 9/11 Commission narrative states that the operational teams on September 11 consisted of 19 hijackers aboard four flights.
Yet even the official history demonstrates that the wider plot was more complicated than the final 19 men who boarded those aircraft.
The September 11 conspiracy evolved over years. Khalid Sheikh Mohammed’s concept for attacking the United States underwent numerous changes before the operation took its final form. Additional individuals had been considered or connected to the broader conspiracy at various stages, and Zacarias Moussaoui became widely known as the alleged “20th hijacker,” although his precise intended role was debated. Testimony before the 9/11 Commission discussed Moussaoui in connection with the plot even though he was in custody before the attacks occurred.
That broader history makes the possibility of abandoned, backup or incomplete elements of the operation worthy of investigation. It does not prove the Flight 23 theory, but it demonstrates why asking whether the final four aircraft represented every aviation scenario ever contemplated by the conspirators is a legitimate historical question.
There is also the extraordinary chaos of that morning to consider.
The 9/11 Commission concluded that the aviation and national-defense systems were profoundly unprepared for suicide hijackings involving passenger aircraft used as weapons. Officials had to improvise while multiple aircraft were missing, communications were confused and inaccurate reports circulated across government agencies.
Against that background, it is possible to understand how Flight 23 might have generated an investigation that later received little public attention without requiring a deliberate government conspiracy. Investigators had to determine whether countless suspicious people, bags, vehicles, aircraft and reports had any genuine relationship to the attacks.
But from the perspective of the Flight 23 crew, the unanswered questions remain deeply personal.
Why did the FBI question them?
Who exactly were the passengers who attracted their attention?
What happened to those passengers after evacuation?
Why were witnesses reportedly shown a lineup?
Who were the uniformed people allegedly observed inside the supposedly empty plane?
Why was the internal hatch open?
What was the explanation for the box cutters allegedly discovered aboard a neighboring Boeing 767?
And most importantly, did federal investigators eventually determine that all of these events were unrelated coincidences, or did they discover something that has never been fully explained publicly?
Those questions are much stronger than simply declaring that the government “does not want people to know” about a fifth plane. Claims of intentional suppression require evidence of their own. Neither silence nor the absence of Flight 23 from the best-known sections of the 9/11 Commission Report automatically proves that officials deliberately concealed a confirmed fifth hijacking plot.
What can be said with confidence is that Flight 23 became the subject of serious suspicion among members of its crew, that FBI interviews and identification efforts were described by those witnesses, and that multiple unusual incidents were later investigated by TMZ.
The documentary ultimately succeeds not because it proves every element of the fifth-plane theory, but because it reopens a story many Americans had never heard.
There is something inherently unsettling about contemplating how close Flight 23 may have come to departing JFK. If the theory is wrong, then the passengers and crew were simply caught in the enormous shadow of a catastrophe taking place around them, and ordinary coincidences acquired sinister meaning because of what happened elsewhere.
If the theory is correct, however, the consequences are chilling.
A Boeing 767 loaded for a transcontinental flight could have been sitting only minutes from takeoff while another team prepared to reproduce what was already happening above the East Coast. The decision to halt operations at JFK would then have done something far greater than prevent another airplane from entering chaotic airspace. It would have unintentionally stopped another attack before it began.
Perhaps that is why the Flight 23 story continues to generate such fascination.
September 11 has been investigated more extensively than almost any terrorist attack in history. Thousands of pages of documents, hearings, intelligence reports and testimony have reconstructed the conspiracy in extraordinary detail. The identities and movements of the 19 hijackers have been traced across continents. Their flight training, hotels, ticket purchases and final movements were examined. Investigators reconstructed how the teams assembled and how four aircraft were selected and seized.
Yet historical investigations rarely answer every question.
Some evidence disappears. Some witnesses remember events differently. Investigative files remain classified or difficult to obtain. Leads that initially appear significant eventually prove unrelated. Other leads remain unresolved. More than two decades later, the dividing line between genuine mystery and speculation can become increasingly difficult for the public to see.
That is why the Flight 23 story should be approached with both curiosity and caution.
It would be irresponsible to declare that a fifth hijacking has been definitively proven when the available evidence does not establish that conclusion. It would be equally dismissive to pretend the testimony of the pilot, flight attendants and dispatcher has no historical value simply because their experience did not become part of the most familiar version of September 11.
The surviving crew members are not claiming to have reconstructed every element of an al-Qaeda operation. They are describing what they witnessed and explaining what those events now mean to them.
For Captain Mannello, the collection of circumstances eventually became too significant to dismiss. For the flight attendants, memories of suspicious passengers, an interrupted departure, FBI questioning and the strange activity surrounding their aircraft remained with them long after September 11 disappeared from their daily professional lives.
Their central question is remarkably simple.
Were they supposed to be next?
More than twenty-five years after the attacks, there is still no publicly established answer proving that United Flight 23 was the fifth plane. The documented historical record remains centered on four hijacked aircraft and 19 hijackers. But the unanswered details surrounding Flight 23 explain why the question has survived.
A plane bound for Los Angeles was preparing to leave New York at almost exactly the moment America came under attack. Several passengers caught the crew’s attention. Some allegedly seemed unusually determined to get airborne. The aircraft was stopped from departing because JFK shut down. People were later reportedly observed inside the evacuated plane. A hatch was found open. Federal agents questioned the crew and reportedly asked them to identify suspicious passengers. Box cutters were discovered aboard another nearby aircraft, according to the documentary’s account.
Every one of those details may have an explanation.
The unsettling part is that the public still does not have a single explanation tying all of them together.
And so United Flight 23 occupies an unusual place in the history of September 11: not one of the four planes that changed America forever, but an aircraft that never left the ground and whose crew members have spent years wondering whether that fact saved their lives.
The official history tells us what happened to four airplanes that morning.
The mystery of Flight 23 is about what might have happened to a fifth.
And that distinction may be the most haunting part of the entire story. The four aircraft that were successfully hijacked left enormous trails of evidence behind them: passenger manifests, cockpit communications, radar data, phone calls from passengers, airport surveillance footage and, ultimately, the destruction caused at their final destinations. United Flight 23 left behind something completely different. It left questions. Because it never became airborne, there was no hijacking to reconstruct, no crash site to examine and no final moments from which investigators could work backward. If there really had been an abandoned plan involving Flight 23, investigators would have been searching for evidence of a crime that never fully occurred.
That creates an unusual problem. How do authorities prove that an attack was going to happen when the suspected attackers never had the opportunity to carry it out?
The answer may depend almost entirely on intelligence gathered afterward: identities, travel records, financial transactions, telephone contacts, immigration files and connections between suspicious passengers and known extremists. Those are precisely the kinds of records that the public has never seen in any comprehensive form regarding the individuals who reportedly drew the attention of Flight 23’s crew.
That missing information is one reason speculation has survived.
If the suspicious passengers were eventually investigated and completely cleared, releasing documentation explaining that conclusion could seemingly end much of the controversy. If they were connected to something more significant, however, the story would immediately become one of the most important unresolved chapters of September 11.
Neither conclusion has been publicly established.
There is another possibility as well. Investigators may simply never have been able to determine exactly what happened.
The hours immediately following the attacks produced unprecedented confusion throughout the United States aviation system. Airports were shut down. Thousands of aircraft had to be landed. Passengers poured into terminals. Federal investigators rushed to identify possible accomplices while simultaneously trying to understand how four aircraft had been seized without warning.
In that environment, suspicious behavior was everywhere.
Reports circulated about possible additional hijackers, unexplained luggage, suspicious vehicles and potential secondary attacks. Some reports proved significant. Many did not. Investigators faced the enormous task of separating genuine evidence from coincidence, fear and misinformation.
Flight 23 could have been one of those unresolved leads.
But for the crew members, the possibility that their experience was simply another false alarm is difficult to reconcile with the combination of events they remember.
The timing is particularly difficult to ignore.