By: Chris Kilroy

United Airlines Flight 175 is seen on its collision course with the south tower of the World Trade Center (top), and on impact. (File Photos/AP)

September 11, 2001 brought the costliest man-made tragedy in the history of civilization to the United States of America.

On this Tuesday morning, nineteen anti-American terrorists hijacked four commercial airliners - two of United Airlines, and two of American Airlines - with the intention of crashing them into prominent United States buildings. They were devestatingly successful.

American Airlines Flight 11
North Tower, World Trade Center, New York City

American Airlines Flight 11, operated by a Boeing 767-223ER (N334AA) on the morning of September 11, departed Runway 4R at Logan International Airport in Boston, Massachusetts for the 5+ hour flight to Los Angeles, California at 7:59am local time.

On board the aircraft were 81 passengers (including five hijackers), nine flight attendants, and the two pilots.

Shortly after its departure, Flight 11 disappeared from FAA radar screens, and ceased responding to radio calls from air traffic controllers.

At 8:24am, the Captain of another aircraft on the air traffic control frequency, United Airlines Flight 175, reported that "we heard a suspicious transmission on our departure from BOS. Sounds like someone keyed the mike and said everyone stay in your seats." Less than ninety seconds later, UA175 flight would suffer the same fate.

The North WTC Tower begins to collapse. (File Photo/AP)

At 8:45am, the aircraft was flown into the side of the North 110 floor tower - between the 80th and 90th floors - of the World Trade Center Plaza in New York City's financial district.

The aircraft impacted the tower at an estimated 350 knots. This fact, combined with the large amount of burning jet fuel, led to severe structural damage within the tower, which caused its eventual collapse some 104 minutes later at 10:29am local time.

United Airlines Flight 175
South Tower, World Trade Center, New York City

United Airlines Flight 175, operated by a Boeing 767-222 (N612UA) on the morning of September 11, departed Runway 9 at Logan International Airport in Boston, Massachusetts for the 5+ hour flight to Los Angeles, California at 8:14am local time.

On board the aircraft were 56 passengers (including five hijackers), seven flight attendants, and the two pilots.

Shortly after its departure, moments after its crew had reported suspicious radio transmissions from another flight to Boston ARTCC center, Flight 175 disappeared from FAA radar screens, and ceased responding to radio calls from air traffic controllers.

At 9:03am, with hundreds of cameras around Manhattan focused on the World Trade Center complex, the aircraft was flown into the South 110 floor tower, between the 65th and 75th floors. Images of the collision were broadcast live around the world as television networks covered the previous aircraft collision some eighteen minutes earlier.

Similar to AA11, the aircraft is estimated to have impacted the structure at approximately 350 knots, and the structural damage caused to the tower by the impact caused it to collapse 47 minutes later at 9:50am.

American Airlines Flight 77
Pentagon (DOD Building), Washington, D.C.

The damage at the Pentagon Building. (File Photo/AP)

American Airlines Flight 77, operated by a Boeing 757-223 (N644AA) on the morning of September 11, departed Runway 30 at Washington Dulles International Airport for the 4+ hour flight to Los Angeles, California at 8:10am local time.

On board the aircraft were 58 passengers (including five hijackers), four flight attendants, and the two pilots.

Shortly after departure, the aircraft disappeared from FAA radar screens and ceased responding to air traffic control radio transmissions.

The aircraft was turned around and flown back toward Washington, D.C. from the north. The aircraft then reportedly proceeded to descend over the White House, enter a tight 270° turn, and fly toward the U.S. Department of Defense Building (Pentagon) in northern Virginia.

Witnesses reported that the aircraft clipped trees and lightposts as it descended at a high rate of speed, before impacting the the south-west face of the Pentagon Building.

United Airlines Flight 93
Somerset, Pennsylvania

United Airlines Flight 93, operated by a Boeing 757-222 (N591UA) on the morning of September 11, departed Newark International Airport near New York for the 5+ hour flight to San Francisco, California at 8:01am local time.

On board the aircraft were 37 passengers (including four hijackers), five flight attendants, and the two pilots.

Unlike the other aircraft hijacked this day, UA93 proceeded normally on course for over an hour, being hijacked at approximately 9:35am somewhere near Cleveland, Ohio while cruising at 35,000 feet.

The aircraft's course was presumably changed to proceed to Washington, D.C. Investigators believe that the aircraft had a target of either the White House or the Capitol Building. It never made it that far.

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During the initial takeover, two Flight Attendants were reportedly killed near the front of the aircraft, while the remaining persons aboard the plane were herded toward the rear portion of the passenger cabin. Throughout the ordeal, these passengers and crewmembers were permitted to use cellular phones as well as the onboard AirFone system to contact loved ones.

As word spread of the three other hijackings, and their end result, a group of passengers aboard UA93 began to develop a plan to regain control of the aircraft from the four hijackers. A GTE AirFone operator, speaking with one of the passengers on board, reported that the passenger had told her that the passengers had voted on whether to obey the hijackers, or challenge them, and that the vote had been to attempt to regain control of the plane.

The AirFone operator then heard one of the passengers say "Let's roll," and the phone dropped to the floor. Staying on the line, she would later recall hearing sounds of loud comotion, yells and screams for the next several minutes, followed by the line going dead.

United Flight 93 had crashed into a field in south-western Pennsylvania.

The Human Toll

Although the exact number of casualties as a result of the September 11 terrorist attacks will never be known, below are known details concerning fatalities: *

American Airlines Flight 11: 81 passengers, 9 flight attendants, 2 pilots
United Airlines Flight 175: 56 passengers, 7 flight attendants, 2 pilots
American Airlines Flight 77: 58 passengers, 4 flight attendants, 2 pilots
United Airlines Flight 93: 37 passengers, 5 flight attendants, 2 pilots

World Trade Center: 524 confirmed casualties, 3,822 missing
Pentagon (DOD) Building: 125 confirmed casualties

* Figures accurate as of Nov 9, 2001

The Financial Toll

Damages resulting from the September 11 terrorist attacks are expected to approach US$30 Billion, making the attacks the costliest man-made tragedy in history.

The airline and travel industries were hit particularly hard following the attacks, with commercial passenger traffic in the United States dropping nearly 40% between September 10 and October 10, 2001, and world-wide traffic decreasing some 18%. The airline industry predicts that traffic will not return to pre-attack levels until nearly 2007.

The Aftermath

No one can say with any certainty what the lasting effects of the September 11 terrorist attacks will be. Below are changes that have been instituted within the airline industry since the attacks.

- Numerous changes within airport buildings, including regulations that restrict curb-side baggage checkin, and prohibit non-passengers from passing the security checkpoints. Airports being patrolled by National Guard troops.

- U.S. airlines have fortified cockpit doors, most often with stronger materials, and metal bars, to prevent intruders from gaining access to the cockpit.

- Aircraft which either report a problem, or fail to respond to air traffic controllers, have been escorted back to airports for landing by military fighter jets.

- President Bush has announced that high-ranking military officers have been granted the authority to down any aircraft deemed a threat to persons/structures on the ground.

- An Airport Security Bill is currently under debate in Congress. The U.S. Senate passed a bill that would federalize all airport security workers and operations, while the House of Representatives later passed a bill that would maintain the current system of using civilian employees, while instituting Federal oversight of operations and employee performance. A compromise is expected to be agreed upon, and receive President Bush's signature, making it law.