What Happened? — The Twin Towers, 11 September 2001
On the morning of 11 September 2001, New York began its working day beneath a clear blue sky.
Within less than two hours, both towers of the World Trade Center would be gone.
Nearly 3,000 people would be dead across New York, Washington and Pennsylvania. Thousands more would be injured, and the consequences of that morning would reshape international politics, security, intelligence and warfare for decades.
The images became some of the most recognisable in modern history.
But behind those images lies a sequence of events that unfolded with extraordinary speed.
The Hijackings
Nineteen members of the terrorist organisation al-Qaeda boarded four commercial airliners departing from airports on the eastern side of the United States.
All four aircraft were scheduled for long-distance flights and therefore carried substantial quantities of fuel.
Shortly after take-off, the attackers seized control of the aircraft.
The four flights were:
American Airlines Flight 11
Boston to Los Angeles.
United Airlines Flight 175
Boston to Los Angeles.
American Airlines Flight 77
Washington Dulles to Los Angeles.
United Airlines Flight 93
Newark to San Francisco.
The aircraft themselves had become the weapons.
8:46 a.m. — The North Tower
At approximately 8:46 a.m., American Airlines Flight 11 struck the North Tower of the World Trade Center.
The Boeing 767 hit the building at high speed between approximately the 93rd and 99th floors.
The impact tore through the structure, destroyed escape routes and ignited major fires fuelled partly by aviation fuel carried aboard the aircraft.
At first, many people watching from elsewhere in New York believed they were witnessing a terrible aviation accident.
Emergency services were immediately dispatched.
Firefighters, police officers and paramedics began moving towards the World Trade Center while thousands of occupants attempted to evacuate.
Inside the North Tower, however, everyone above the impact zone was effectively trapped.
The aircraft had destroyed or blocked all three stairways through the impact area.
9:03 a.m. — The South Tower
Seventeen minutes later, any belief that the first collision had been an accident disappeared.
At approximately 9:03 a.m., United Airlines Flight 175 struck the South Tower.
Television cameras were already focused on the burning North Tower.
Millions of people therefore watched the second aircraft hit almost in real time.
The United Airlines Boeing 767 entered the South Tower at an angle, striking roughly between the 77th and 85th floors.
The United States was clearly under attack.
Inside the Towers
Thousands of people were attempting to escape.
Many occupants below the impact zones successfully reached the ground through stairwells.
Firefighters were simultaneously climbing upwards.
They carried heavy equipment while office workers descended past them.
Radio communications were difficult. Information available to those inside the buildings was incomplete, confused and constantly changing.
In the South Tower, one stairway — Stairwell A — remained partly passable through the damaged area. A small number of people from above the impact zone managed to escape through it.
In the North Tower there was no equivalent route.
People trapped high in the buildings faced smoke, fire and unbearable heat.
Some appeared at broken windows seeking air.
Others attempted desperately to attract attention from rescuers hundreds of feet below.
Some fell or jumped from the towers.
These remain among the most distressing aspects of the disaster.
Washington
The attack was not confined to New York.
At approximately 9:37 a.m., American Airlines Flight 77 struck the Pentagon in Arlington, Virginia.
The aircraft crashed into the western side of the building, killing everyone aboard along with people inside the Pentagon.
The attacks were now directed against both symbolic economic and military targets.
The White House, Capitol and other government buildings were evacuated.
American airspace began moving towards an unprecedented shutdown.
9:59 a.m. — The South Tower Falls
The South Tower had been struck second.
It collapsed first.
At approximately 9:59 a.m., only 56 minutes after the impact of Flight 175, the tower suddenly began to fail.
Its upper floors appeared to tilt before disappearing into the structure beneath them.
Within seconds, the 110-storey skyscraper collapsed to the ground.
An immense cloud of dust and debris swept through surrounding streets.
People fled through lower Manhattan.
Emergency responders who had been operating inside and around the building were caught in the collapse.
To millions watching television, the sight appeared almost impossible.
One of the tallest buildings in the world had simply disappeared.
Flight 93
Passengers aboard United Airlines Flight 93 had begun receiving information through telephone calls about what had happened in New York and Washington.
They realised their aircraft was probably intended to strike another target.
Passengers and crew attempted to retake control of the aircraft.
At approximately 10:03 a.m., Flight 93 crashed into a field near Shanksville, Pennsylvania.
Everyone aboard was killed.
Investigators concluded that the hijackers probably intended to strike a major government target in Washington.
The actions of those passengers and crew prevented the aircraft from reaching it.
10:28 a.m. — The North Tower Falls
The North Tower remained standing for approximately 102 minutes after the impact of Flight 11.
Firefighters and emergency personnel were still inside.
At approximately 10:28 a.m., it collapsed.
Again, the failure took only seconds.
Another enormous debris cloud spread through lower Manhattan.
The familiar skyline of New York had changed forever.
Why Did the Towers Collapse?
The aircraft impacts caused catastrophic structural damage, but neither tower collapsed immediately.
The collisions severed and damaged structural columns, stripped fireproofing from parts of the steel framework and spread burning aviation fuel across several floors.
The aviation fuel itself did not need to melt the structural steel.
It ignited widespread fires involving normal office contents and materials.
As those fires continued, structural components heated and weakened.
Floors began to sag.
The redistribution of loads placed increasing stress on already damaged structural elements.
Eventually, critical parts of each building could no longer support the weight above them.
Once collapse began, the enormous mass of the upper sections falling onto the floors beneath produced forces far beyond those floors’ capacity to withstand.
Progressive collapse followed.
World Trade Center 7
Later that afternoon another major building in the World Trade Center complex collapsed.
World Trade Center 7 was a 47-storey building located north of the main towers.
It had not been struck by an aircraft.
It had, however, suffered structural damage from debris when the North Tower collapsed, and fires burned uncontrolled inside the building for several hours.
At approximately 5:20 p.m., WTC 7 collapsed.
Its failure later became the subject of considerable speculation and conspiracy theories.
The National Institute of Standards and Technology concluded after investigation that fire-induced structural failures led to the progressive collapse.
The Rescue Operation
Even as the towers were burning, thousands of emergency personnel had entered the area.
Many continued climbing upwards while occupants came down.
The New York City Fire Department suffered catastrophic losses.
A total of 343 FDNY firefighters died.
Members of the New York Police Department and Port Authority Police Department were also killed in large numbers.
In the immediate aftermath, rescuers searched the ruins for survivors.
The site became known simply as Ground Zero.
For days, and then weeks, crews worked amid twisted steel, dust, smoke and fire.
Very few survivors were recovered from deep inside the collapsed structures.
The Human Cost
The attacks of 11 September killed 2,977 victims, excluding the 19 hijackers.
People from more than 90 countries died.
The victims included office workers, airline passengers and crew, visitors, firefighters, police officers and other emergency personnel.
For many families, grief was made more difficult because remains were never recovered or could not initially be identified.
The human cost also continued long after the attacks.
Thousands of survivors and emergency responders were exposed to dust and contaminants released during the collapse and subsequent recovery work.
Respiratory illnesses, cancers and other medical conditions have since affected many who worked or lived around the site.
Deaths associated with 9/11 therefore did not end on the day itself.
What Went Wrong Before the Attacks?
Subsequent investigations revealed that American intelligence and law-enforcement agencies possessed fragments of information relating to al-Qaeda and some of the future hijackers before 11 September.
The problem was not the complete absence of intelligence.
It was the failure to bring separate pieces of information together.
Agencies did not always share information effectively.
Warnings about al-Qaeda’s intention to attack the United States existed, but the precise plan was not understood.
Some hijackers had previously attracted official attention.
Others entered or remained within the United States despite information that, viewed retrospectively, appeared significant.
The official 9/11 Commission later described failures involving imagination, policy, capabilities and management.
No single warning identified the complete operation in sufficient detail to allow authorities simply to stop it.
But opportunities existed that, had information been handled differently, might have changed events.
The Response
The attacks produced an immediate transformation in American policy.
On 7 October 2001, the United States and its allies began military operations in Afghanistan.
The Taliban government had provided sanctuary to al-Qaeda and its leader, Osama bin Laden.
The conflict would become America’s longest war.
The attacks also transformed aviation security.
Cockpit doors were strengthened.
Passenger and baggage screening changed.
Intelligence organisations were reorganised.
New security agencies and surveillance programmes were created.
International cooperation against terrorist networks expanded dramatically.
The political consequences extended far beyond Afghanistan.
The attacks became part of the justification used in the wider American-led War on Terror, including the invasion of Iraq in 2003, although Iraq was not responsible for the 11 September attacks.
Osama bin Laden
Al-Qaeda leader Osama bin Laden became the principal target of the international search that followed.
He avoided capture for almost ten years.
On 2 May 2011, US special operations forces raided a compound in Abbottabad, Pakistan.
Bin Laden was killed during the operation.
His death ended the search for the man regarded as the architect of the attacks.
It did not end the consequences of what had happened.
A Morning That Divided History
The extraordinary thing about 11 September is how little time separated normality from catastrophe.
At 8:45 that morning, thousands of people were beginning an ordinary working day.
By 10:30, both towers of the World Trade Center had collapsed.
The Pentagon had been struck.
Four passenger aircraft had been destroyed.
The United States had closed its airspace.
And the world had changed.
Twenty-five years later, the photographs remain familiar.
The aircraft approaching the towers.
The fireballs.
The smoke rising over Manhattan.
The figures at the windows.
The firefighters climbing stairways while everyone else was coming down.
The towers collapsing into streets filled with people.
Yet the story should never become merely a collection of unforgettable images.
Behind every window was a person.
Behind every telephone call was a family.
Behind every name on the memorial was a life that had begun that morning without any knowledge that history was about to arrive.
That is ultimately what happened on 11 September 2001.
Not simply the destruction of two buildings.
It was the loss of thousands of individual lives in less than two hours — and the beginning of consequences that are still being felt today.
Read the Full Investigation
The Twin Towers — 102 Minutes That Changed the World examines the events of 11 September 2001 in far greater detail: the hijackings, the aircraft, the towers, the people trapped inside, the emergency response, the intelligence failures, the investigations and the questions that followed.
Available now through Billy’s Book Club and Amazon Kindle.