What floors were hit in the twin towers? American Airlines Flight 11 struck the North Tower between floors 93 and 99 at 8:46 a.m. on September 11, 2001, while United Airlines Flight 175 struck the South Tower between floors 77 and 85 at 9:03 a.m. The two impacts occurred at different heights and affected different portions of the buildings, helping shape what happened during the minutes that followed.
The floor ranges are among the most important details for understanding the September 11 attacks at the World Trade Center. Both the North Tower and South Tower were 110-story buildings, but the planes struck them at substantially different levels. The North Tower was hit higher, while the South Tower was struck lower and suffered particularly severe structural damage in the impact area.
Which Floors Were Hit in the North Tower?
The North Tower, officially known as 1 World Trade Center, was struck by American Airlines Flight 11 at 8:46 a.m. The aircraft entered the building in the area of floors 93 through 99.
Flight 11 was a Boeing 767 carrying passengers and crew after being hijacked. The aircraft approached Lower Manhattan from the north and struck the North Tower’s north face.
The impact damaged the building’s exterior columns, floor systems and interior structural components. Aircraft debris also traveled through portions of the building, while aviation fuel spread across several floors and ignited.
Because the impact occurred between floors 93 and 99, people working above the damaged area were effectively cut off from the building’s stairways. This became a critical factor in the loss of life in the North Tower.
The North Tower eventually collapsed at 10:28 a.m., approximately 102 minutes after Flight 11 struck the building.
The distinction between the impact floors and the floors affected by fire is important. The aircraft did not simply damage one floor. Its large mass and high speed caused extensive damage across multiple levels, while the resulting fires affected additional areas around and beyond the immediate impact zone.
Which Floors Were Hit in the South Tower?
The South Tower, officially known as 2 World Trade Center, was struck by United Airlines Flight 175 at approximately 9:03 a.m.
Flight 175 hit the South Tower between floors 77 and 85. The impact occurred on the building’s south face and caused extensive damage to structural columns, floor framing and other components.
The South Tower was struck 17 minutes after the North Tower. By that time, people in and around the World Trade Center had already witnessed the first crash and were beginning to evacuate.
The lower impact position in the South Tower meant that more people were potentially located above the damaged floors. However, the timing of the second attack also meant that some occupants had already begun leaving the building before Flight 175 arrived.
The South Tower collapsed at 9:59 a.m., less than an hour after it was struck.
This made it the first of the two towers to collapse even though it was hit second.
Twin Towers Impact Floors at a Glance
The two aircraft strikes can be summarized simply:
| Tower | Aircraft | Approximate impact time | Floors struck |
|---|---|---|---|
| North Tower (WTC 1) | American Airlines Flight 11 | 8:46 a.m. | 93–99 |
| South Tower (WTC 2) | United Airlines Flight 175 | 9:03 a.m. | 77–85 |
The difference is significant. Flight 11 struck the North Tower roughly 14 floors higher than Flight 175 struck the South Tower.
Both aircraft were Boeing 767-200ER aircraft. The buildings were designed as 110-story towers with a structural system that incorporated a dense exterior column network, a central core and lightweight floor trusses.
The aircraft impacts caused damage well beyond the visible holes in the exterior walls. Structural columns were severed or damaged, floor systems were disrupted, and fireproofing was stripped from structural steel in areas affected by the aircraft.
Why Did the Exact Impact Floors Matter?
The floors hit by the aircraft were important because the impacts disrupted both the physical structure and the ability of people to escape.
In the North Tower, the aircraft destroyed all three stairways serving the floors above the impact area. As a result, occupants above the impact zone could not descend through the stairwells.
The National Institute of Standards and Technology determined that approximately 1,355 people were trapped in the upper floors of the North Tower when it collapsed.
The situation in the South Tower was different.
The aircraft destroyed or severely damaged two of the building’s three stairways in the impact area. However, the third stairway remained passable through part of the damaged region. Eighteen people above the impact zone were able to escape through that stairway.
The difference illustrates why the exact floor and location of an aircraft impact mattered. The number of floors above the impact point, the location of the damage, the condition of the stairwells and the timing of evacuation all affected the chances of survival.
The Fires Spread Across Multiple Floors
The aircraft impacts were only the beginning of the structural disaster.
Both Boeing 767s were carrying large quantities of aviation fuel. After the crashes, fuel and burning aircraft debris spread through portions of the buildings and ignited extensive fires.
The fires were not confined to a single impact floor. They spread across multiple floors and heated structural components that had been damaged or stripped of fireproofing during the impacts.
This distinction is essential when discussing what floors were hit in the twin towers. The published impact ranges identify where the aircraft physically struck the buildings, but the resulting fires and structural damage extended beyond those precise levels.
NIST’s investigation found that the combination of aircraft damage, dislodged fireproofing and subsequent multi-floor fires weakened the towers’ structural systems.
The aircraft impact alone did not cause either tower to collapse immediately. The towers remained standing for a period after the crashes, despite enormous structural damage.
Why the South Tower Collapsed First
One of the most frequently misunderstood details of the attacks is that the South Tower collapsed first even though it was struck second.
Flight 175 hit the South Tower at approximately 9:03 a.m. The building collapsed at 9:59 a.m., giving it a survival time of less than one hour after the impact.
The North Tower was struck at 8:46 a.m. but remained standing until 10:28 a.m.
NIST’s investigation found that the South Tower experienced particularly severe damage to its core and structural systems. The aircraft also extensively damaged fireproofing, while persistent fires developed in areas affected by the impact.
Heat weakened structural members and caused portions of the floor system to sag. The weakened floors pulled perimeter columns inward, contributing to the failure that initiated the collapse.
The North Tower followed a different progression. Its fires and structural damage eventually weakened critical parts of the building until the upper portion began descending and the collapse progressed through the structure.
How Many Floors Were Above the Impact Zones?
The Twin Towers each contained 110 stories, making the impact levels important for understanding how many occupants were located above and below the damaged areas.
In the North Tower, the impact zone at floors 93 through 99 left approximately the top 11 floors above the primary impact range.
In the South Tower, the impact zone at floors 77 through 85 left a much larger section of the building above the primary impact range, extending through the upper floors.
However, the number of floors above the impact zone should not be interpreted as a simple measure of the number of people trapped there. Occupancy varied from floor to floor, and people moved through the buildings throughout the morning.
The World Trade Center complex had thousands of occupants at the time. Many people began evacuating after the first plane struck, while others initially remained at their workplaces or received instructions that affected their decisions.
The Difference Between Impact Floors and Collapse Floors
Another important distinction is that the floors where the planes struck were not necessarily the exact floors where the towers’ final collapse began.
The aircraft impacts occurred at floors 93–99 in the North Tower and floors 77–85 in the South Tower.
NIST’s investigation found that collapse initiation occurred at or near the fire and impact regions after the structural systems had been weakened by the combined effects of impact damage and fire.
In other words, the planes created enormous initial damage, but the towers did not immediately collapse at the moment of impact.
The subsequent fires played a major role in reducing the strength and stability of damaged structural components. As the fires continued, heated floor systems sagged and exerted forces on perimeter columns. Structural failure eventually began in the regions affected by the impacts and fires.
This explains why simply identifying the floors struck by the aircraft does not tell the entire story of how the towers collapsed.
What Happened to People Below the Impact Floors?
The difference between occupants above and below the impact areas became particularly important during evacuation.
People below the aircraft impact zones generally had access to functioning stairways and could descend toward the ground.
NIST reported that approximately 99 percent of occupants located below the impact floors successfully evacuated.
That figure demonstrates how important the location of the aircraft strikes was to evacuation outcomes. Although the impacts caused catastrophic destruction, the portions of the buildings below the impact zones retained enough usable egress capacity for most occupants to escape.
The situation above the impact zones was dramatically different because the aircraft damage destroyed or blocked critical escape routes.
The South Tower’s surviving stairway provided a narrow path for a small number of people above the impact area. In the North Tower, the destruction of all stairways above the impact zone prevented those occupants from reaching the ground.
The Two Impact Zones in Historical Context
The floor numbers also help explain why the two attacks looked different in photographs and videos.
The North Tower was struck near its upper section, with Flight 11 entering between floors 93 and 99.
The South Tower was struck substantially lower, between floors 77 and 85. The aircraft’s approach and the location of the impact produced a large opening and extensive structural damage that could be seen from Lower Manhattan.
Both towers were enormous structures, and the aircraft penetrated far into the buildings rather than simply creating holes in their exterior walls.
The crashes damaged exterior columns, floor framing and core structural components. The resulting fires then affected structural elements over several floors.
Latest Verified Understanding of the Impact Floors
The established floor ranges have not changed: Flight 11 struck the North Tower at floors 93 through 99, while Flight 175 struck the South Tower at floors 77 through 85.
Modern technical understanding of the attacks comes from extensive investigations, including structural analysis, photographs, videos, recovered steel, emergency communications and computer modeling.
The National Institute of Standards and Technology concluded that the towers’ collapses resulted from the combined effects of aircraft impact damage and the subsequent large, multi-floor fires. The investigation found that the aircraft impacts damaged structural columns and dislodged fireproofing, leaving portions of the structures more vulnerable to heat.
This remains the established engineering explanation for the collapse of the Twin Towers.
Final Thoughts
The answer to what floors were hit in the twin towers is precise: American Airlines Flight 11 struck the North Tower across floors 93 through 99, while United Airlines Flight 175 struck the South Tower across floors 77 through 85. Those different impact levels shaped the structural damage, evacuation conditions and events that followed.
The floor numbers are more than historical coordinates. They help explain why evacuation conditions differed between the two towers, why the South Tower collapsed first despite being struck second, and how aircraft damage and subsequent fires combined to produce the catastrophic structural failures of September 11, 2001.
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