Context of '(9:04 a.m.) September 11, 2001: WTC 7 Alarms Activate; OEM Calls for Air Security and Warned of Plane Heading for New York' This is a scalable context timeline. It contains events related to the event (9:04 a.m.) September 11, 2001: WTC 7 Alarms Activate; OEM Calls for Air Security and Warned of Plane Heading for New York. You can narrow or broaden the context of this timeline by adjusting the zoom level. The lower the scale, the more relevant the items on average will be, while the higher the scale, the less relevant the items, on average, will be.
 The hole caused by the Flight 11 crash. [Source: Reuters]Flight 11 slams into the WTC North Tower (Building 1). Seismic records pinpoint the crash at 26 seconds after 8:46 a.m. [CNN, 9/12/2001; New York Times, 9/12/2001; North American Aerospace Defense Command, 9/18/2001; USA Today, 12/20/2001; Federal Emergency Management Agency, 5/1/2002, pp. 1-10; USA Today, 8/13/2002; Associated Press, 8/21/2002; Newsday, 9/10/2002; New York Times, 9/11/2002] The NIST report states the crash time to be 8:46:30. [National Institute of Standards and Technology, 9/2005, pp. 19  ] The 9/11 Commission Report states the crash time to be 8:46:40. [9/11 Commission, 7/24/2004, pp. 7] Investigators believe the plane still has about 10,000 gallons of fuel (see 8:57 a.m. September 11, 2001). [New York Times, 9/11/2002] The plane strikes the 93rd through 99th floors in the 110-story building. No one above the crash line survives; approximately 1,360 people die. Below the crash line, approximately 72 die and more than 4,000 survive. Both towers are slightly less than half full at the time of the attack, with between 5,000 to 7,000 people in each tower. This number is lower than expected. Many office workers have not yet shown up to work, and tourists to the observation deck opening at 9:30 A.M. have yet to arrive. [USA Today, 12/20/2001; National Institute of Standards and Technology, 9/2005, pp. 20-22 ] The impact severs some columns on the north side of the North Tower. Each tower is designed as a “tube-in-tube” structure and the steel columns which support its weight are arranged around the perimeter and in the core. The plane, which weighs 283,600 lb and is traveling at an estimated speed of around 430 mph (see October 2002-October 2005), severs 35 of the building’s 236 perimeter columns and damages another two. The damage to the South Tower’s perimeter will be similar (see 9:03 a.m. September 11, 2001). [National Institute of Standards and Technology, 9/2005, pp. 5-9, 20, 22 ] The perimeter columns bear about half of the tower’s weight, so this damage reduces its ability to bear gravity loads by about 7.5 percent. [National Institute of Standards and Technology, 9/2005, pp. 6 ] The actual damage to the 47 core columns is not known, as there are no photographs or videos of it, but there will be much speculation about this after 9/11. It will be suggested that some parts of the aircraft may have damaged the core even after crashing through the exterior wall. According to the National Institute of Standards and Technology (NIST): “Moving at 500 mph, an engine broke any exterior column it hit. If the engine missed the floor slab, the majority of the engine core remained intact and had enough residual momentum to sever a core column upon direct impact.” [National Institute of Standards and Technology, 9/2005, pp. 107 ] According to NIST’s base case computer model, three of the core columns are severed and another ten suffer some damage. [National Institute of Standards & Technology, 9/2005, pp. 189 ] If this is accurate, it means that the impact damage to the core reduces the Tower’s strength by another approximately 7.5 percent, meaning that the building loses about 15 percent of its strength in total. This damage will be cited after 9/11 by NIST and others researchers as an event contributing to the building’s collapse (see October 23, 2002 and October 19, 2004). In addition, some of the fireproofing on the steel columns and trusses may be dislodged. The original fireproofing on the fire floors was mostly Blazeshield DC/F, but some of the fireproofing on the flooring has recently been upgraded to Blazeshield II, which is about 20 percent denser and 20 percent more adhesive. [National Institute of Standards & Technology, 9/2005, pp. xxxvi, 83 ] Photographs and videos of the towers will not show the state of fireproofing inside the buildings, but NIST will estimate the damage to it using a computer model. Its severe case model (see (October 2002-October 2005)) will predict that 43 of the 47 core columns are stripped of their fireproofing on one or more floors and that fireproofing is stripped from trusses covering 60,000 ft2 of floor area, the equivalent of about one and a half floors. NIST will say that the loss of fireproofing is a major cause of the collapse (see April 5, 2005), but only performs 15 tests on fireproofing samples (see October 26, 2005). [National Institute of Standards and Technology, 9/2005, pp. 23 ] According to NIST, more fireproofing is stripped from the South Tower (see 9:03 a.m. September 11, 2001).
 Paul Worcester. [Source: Paul Blackmore / Cape Cod Times]Senior commanders at Otis Air National Guard Base in Cape Cod, Massachusetts, become aware of the attacks on the World Trade Center from television coverage, and one commander then orders the base’s battle staff to assemble. The commanders have just been in the first of the base’s regular Tuesday morning meetings, which ended at 8:55 a.m. They are taking a short break before the next meeting, which is scheduled for 9:00 a.m., and are apparently unaware that a plane has crashed into the WTC.
Wing Commander Sees Burning WTC on Television - One of those in the meeting was Lieutenant Colonel Paul Worcester, the logistics group commander of the 102nd Fighter Wing, which is based at Otis. As Worcester walks past the break room he notices that everyone inside it is fixated on the television. He goes in to find what they are watching and gets his first sight of the coverage of the burning North Tower. Worcester finds it odd that a plane could have hit the WTC, and thinks to himself: “On such a clear day, planes don’t just go astray. That just doesn’t happen.” Although he is aware that the base’s two F-15s that are kept on alert have been scrambled in response to a suspected hijacking (see 8:46 a.m. September 11, 2001), he does not connect this with what he is seeing on television.
Commanders See Second Attack - Worcester is joined in the break room by more of the senior commanders. They watch as the live television coverage shows Flight 175 crashing into the South Tower (see 9:03 a.m. September 11, 2001), and all of them then realize that America is under attack. One commander immediately shouts out, “We need to go to battle staff!” The senior commanders disperse and head toward the adjacent operations building, where they will reconvene in the battle cab of the installation operations center (see Shortly After 9:03 a.m. September 11, 2001). A voice sounds out over the base’s loudspeakers: “The commander has ordered the 102nd core battle staff to assemble. Please report to the operations building immediately.”
Unit Mobilizes for War - Subsequently, as author Lynn Spencer will describe: “Under the leadership of the [102nd Fighter] Wing commander, the various subordinate group commanders cross-brief on scramble activity, training flight issues, available munitions, personnel available to begin uploading more fighters to combat-ready status, security force increases, and more. In short, they begin to mobilize the wing for war, keeping NEADS [NORAD’s Northeast Air Defense Sector] in the loop on their preparations.” [Spencer, 2008, pp. 87-88, 153-154]
Base Learned of First Hijacking 20 Minutes Earlier - The 102nd Fighter Wing of the Massachusetts Air National Guard, which is based at Otis Air Base, is responsible for protecting the Northeast United States, including New York, Washington, and Boston. Its mission includes defending the region against terrorist attacks. [Cape Cod Times, 9/12/2001; Cape Cod Times, 9/12/2001] On a typical day, it has about a dozen pilots on duty. [Cape Cod Times, 9/15/2001] It is equipped with 18 F-15 fighter jets, two of which are kept on 24-hour alert, ready to be in the air within five minutes of being called upon. [Boston Globe, 9/15/2001; Cape Cod Times, 9/21/2001] These were the two jets that launched at 8:46 a.m. in response to the hijacking of Flight 11. [9/11 Commission, 7/24/2004, pp. 20] The base was notified about this first hijacking shortly after 8:34 a.m. (see (Shortly After 8:34 a.m.) September 11, 2001). [Spencer, 2008, pp. 27-28] Why the senior commanders did not initiate their crisis response at that time is unclear.
 Flight 175 hits the WTC South Tower. The picture was taken from a traffic helicopter. [Source: WABC 7/ Salient Stills]Flight 175 hits the South Tower of the World Trade Center (Tower Two). Seismic records pinpoint the time at six seconds before 9:03 a.m. (rounded to 9:03 a.m.). [New York Times, 9/12/2001; CNN, 9/12/2001; CNN, 9/17/2001; North American Aerospace Defense Command, 9/18/2001; USA Today, 12/20/2001; Federal Emergency Management Agency, 5/1/2002, pp. 1-10; Associated Press, 8/21/2002; USA Today, 9/2/2002; New York Times, 9/11/2002] According to the NIST report, the crash time is 9:02:59. [National Institute of Standards and Technology, 9/2005, pp. 38 ] According to the 9/11 Commission Report, the crash time is 9:03:11. [9/11 Commission, 7/24/2004, pp. 8] Millions watch the crash live on television. The plane strikes the 77th through 85th floors in the 110-story building. Approximately 100 people are killed or injured in the initial impact; 600 people in the tower eventually die. The death toll is far lower than in the North Tower because about two-thirds of the South Tower’s occupants have evacuated the building in the 17 minutes since the first tower was struck. [USA Today, 12/20/2001; National Institute of Standards and Technology, 9/2005, pp. 5-9, 41 ] The combined death toll from the two towers is estimated at 2,819, not including the hijackers. [Associated Press, 8/21/2002] The impact severs some columns on the south side of the South Tower. Each of the Twin Towers is designed as a “tube-in-tube” structure and the steel columns which support its weight are arranged around the perimeter and in the core. The plane, which is traveling at an estimated speed of around 500 mph (see October 2002-October 2005), severs 33 of the building’s 236 perimeter columns and damages another one. [National Institute of Standards and Technology, 9/2005, pp. 39 ] The perimeter columns bear about half of the tower’s weight, so the damage to them reduces the tower’s ability to bear gravity loads by about 7.1 percent. [National Institute of Standards and Technology, 9/2005, pp. 6 ] The actual damage to the 47 core columns is not known, as there are no photographs or videos of it, but there will be much speculation about this after 9/11. It will be suggested that some parts of the aircraft may be able to damage the core even after crashing through the exterior wall (see 8:46 a.m. September 11, 2001). [National Institute of Standards and Technology, 9/2005, pp. 107 ] According to NIST’s base case model, five of the core columns are severed and another five suffer some damage. [National Institute of Standards & Technology, 9/2005, pp. 235 ] This may reduce the tower’s ability to bear loads by a further approximately 8 percent, meaning that the aircraft impact accounted for a loss of about 15 percent of the building’s strength. This damage will be cited as an event contributing to the building’s collapse after 9/11 (see October 23, 2002 and October 19, 2004). NIST’s base case estimate of damage to the North Tower’s core will be similar, even though the aircraft impact there was dissimilar (see 8:46 a.m. September 11, 2001). Flight 11 hit the North Tower’s core head on, whereas Flight 175 only hits the corner of the South Tower’s core. [National Institute of Standards and Technology, 9/2005, pp. 20-23, 38-41 ] In addition, some of the fireproofing on the steel columns and trusses may be dislodged (see 8:46 a.m. September 11, 2001). [National Institute of Standards & Technology, 9/2005, pp. xxxvi, 83 ] Photographs and videos of the towers will not show the state of fireproofing inside the buildings, but the National Institute of Standards and Technology (NIST) will try to estimate the damage to fireproofing using a series of computer models. Its severe case model (see (October 2002-October 2005)) will predict that 39 of the 47 core columns are stripped of their fireproofing on one or more floors and that fireproofing is stripped from trusses covering 80,000 ft2 of floor area, the equivalent of about two floors. NIST will say that the loss of fireproofing is a major cause of the collapse (see April 5, 2005), but only performs 15 tests on fireproofing samples (see October 26, 2005). [National Institute of Standards and Technology, 9/2005, pp. 41 ] According to NIST, less fireproofing is stripped from the North Tower (see 8:46 a.m. September 11, 2001).
The second plane hitting the World Trade Center (see 9:03 a.m. September 11, 2001) causes internal alarms to go off in WTC Building 7, located just a few hundred feet away from the Twin Towers. The alarms warn there is no water pressure and that the building’s emergency power generator has been activated. Office of Emergency Management (OEM) staff, based in Building 7, immediately request air security over New York. They are told that federal support is on its way, but the Federal Aviation Administration instructs them to use NYPD and Port Authority Police Department air assets to clear the airspace around the WTC. They are also warned that the Kennedy Airport control tower is reporting an unaccounted for plane heading towards New York. A report by the Mineta Transportation Institute will claim that this plane is Flight 93, which later crashes in Pennsylvania. [Jenkins and Edwards-Winslow, 9/2003, pp. 16] However, Flight 93 is still flying west at this time, and only reverses course and heads towards Washington at around 9:36 a.m. (see (9:36 a.m.) September 11, 2001). According to at least one person at the scene, WTC 7 is evacuated around this time due to the reports of this incoming third plane (see (9:03 a.m.) September 11, 2001). [Jems And FireRescue Supplement, 3/2002, pp. 68 ] The jet fuel that spilled from Flight 175 when it hit the South Tower (see 9:03 a.m. September 11, 2001) has mostly burned up by this time. The National Institute of Standards and Technology (NIST), which later investigates the collapses, will say the “initial jet fuel fires themselves lasted at most a few minutes.” [National Institute of Standards and Technology, 9/2005, pp. 183 ] Engineering professor Forman Williams will say the jet fuel “burned for maybe 10 minutes.” [Popular Mechanics, 3/2005] Flight 175, a Boeing 767, had a capacity of 23,980 gallons, but was only carrying about 9,100 gallons of fuel when it hit the WTC. NIST will estimate that less than 1,500 gallons were consumed in a fireball inside the tower and 910 to 2,275 gallons were consumed in the fireballs outside the building. Approximately 6,100 gallons therefore splashed onto the office furnishings and started fires on various floors. However, after the jet fuel is used up, office fires burn until the building collapses. NIST will calculate that there were about four pounds per square foot of combustibles in the office space, or about 60 tons per floor. Offices in the WTC actually had fewer combustibles than other similar spaces due to the small number of interior walls and limited bookshelf space. NIST will later find that only three of sixteen perimeter columns it recovers reached a temperature of 250°C and neither of the two core columns it retrieves reached this temperature. NIST will also find that none of the samples it acquires reached a temperature above 600°C (see August 27, 2003). While steel does not melt until its temperature is about 1,600°C, it may begin to lose significant strength at over 500°C. [National Institute of Standards and Technology, 9/2005, pp. 29, 38, 42, 77 ] The jet fuel also burned up in the North Tower about 10 minutes after it was hit (see 8:57 a.m. September 11, 2001). When a group of firefighters reach the bottom impact floor in the South Tower just before collapse, they only find two isolated fires (see 9:52 a.m. September 11, 2001). The FAA’s Cleveland Center notifies United Airlines’ headquarters, near Chicago, that Flight 93 is not responding to attempted radio contacts. [9/11 Commission, 8/26/2004, pp. 39 ] Cleveland Center made its last normal communication with Flight 93 at 9:27 (see 9:27 a.m. September 11, 2001). [9/11 Commission, 7/24/2004, pp. 28] After the hijacking began at around 9:28, the controller handling Flight 93, John Werth, tried unsuccessfully to re-establish contact with it. [Gregor, 12/21/2001 ; CBS News, 9/10/2006] The lack of response from Flight 93, combined with the plane’s turning to the east (see (9:36 a.m.) September 11, 2001), will lead United to believe, by 9:36 a.m., that it has been hijacked. [9/11 Commission, 7/24/2004, pp. 456] Having followed a seemingly normal course until now, after reaching the Cleveland area, Flight 93 suddenly makes a sharp turn to the south. It then makes another turn back eastward, cutting through West Virginia’s Northern Panhandle before re-entering Pennsylvania. [Washington Post, 9/12/2001; Pittsburgh Post-Gazette, 9/13/2001; 9/11 Commission, 8/26/2004, pp. 41 ] Having thus turned 180 degrees, it now heads toward Washington, DC. [CNN, 9/13/2001]  Stacia Rountree. [Source: Vanity Fair]Colin Scoggins, the military liaison at the FAA’s Boston Center, contacts NORAD’s Northeast Air Defense Sector (NEADS) and incorrectly notifies it that another aircraft, Delta Air Lines Flight 1989, is a possible hijacking. [9/11 Commission, 2004; Vanity Fair, 8/1/2006] Boston Center previously called NEADS at 9:27 and said that Delta 1989 was missing (see 9:27 a.m. September 11, 2001). [North American Aerospace Defense Command, 9/11/2001; 9/11 Commission, 5/23/2003]
NEADS Technicians Respond - At NEADS, Stacia Rountree, the ID technician who takes Scoggins’s call, announces to her colleagues: “Delta ‘89, that’s the hijack. They think it’s possible hijack.… South of Cleveland.” The plane’s transponder is still on, and she adds, “We have a code on him now.” Rountree’s team leader, Master Sergeant Maureen Dooley, instructs: “Pick it up! Find it!” The NEADS technicians quickly locate Delta 1989 on their radar screens, just south of Toledo, Ohio, and start alerting other FAA centers to it. [Vanity Fair, 8/1/2006; Spencer, 2008, pp. 177] NEADS mission crew commander Major Kevin Nasypany will be notified by his staff of the suspected hijacking at about 9:41 or 9:42 a.m. [9/11 Commission, 1/22/2004 ] NEADS never loses track of Delta 1989. It will follow it on radar as it reverses course over Toledo, heads east, and then lands in Cleveland (see (10:18 a.m.) September 11, 2001). [9/11 Commission, 7/24/2004, pp. 28] It will order Air National Guard fighter jets from Selfridge and Toledo to intercept the flight (see (9:55 a.m.) September 11, 2001 and 10:01 a.m. September 11, 2001). [Spencer, 2008, pp. 178-179] But it will soon learn that Delta 1989 is not in fact hijacked. [9/11 Commission, 7/24/2004, pp. 28]
Cleveland Center, Not Boston, Handling Delta 1989 - Although Boston Center notifies NEADS of the suspected hijacking, Delta 1989 is in fact being handled by the FAA’s Cleveland Center. [USA Today, 8/13/2002; 9/11 Commission, 7/24/2004, pp. 10-12] Cleveland Center air traffic controllers suspected that Delta 1989 had been hijacked at around 9:30 a.m. (see (9:28 a.m.-9:33 a.m.) September 11, 2001), but apparently only informed the FAA’s Command Center, and not NEADS, of this. [USA Today, 8/13/2002] To explain why Boston Center alerts NEADS to the flight, the 9/11 Commission will later comment that, “Remembering the ‘we have some planes’ remark” (see 8:24 a.m. September 11, 2001), the Boston Center simply “guessed that Delta 1989 might also be hijacked.”
Similar to First Two Hijacked Planes - Like Flights 11 and 175, the two aircraft that have crashed into the World Trade Center (see 8:46 a.m. September 11, 2001 and 9:03 a.m. September 11, 2001), Delta 1989 took off from Boston’s Logan Airport. [9/11 Commission, 7/24/2004, pp. 27-28] According to the New York Times, it left there at about the same time as Flights 11 and 175 did, meaning around 8:00 to 8:15 a.m. [New York Times, 10/18/2001; 9/11 Commission, 7/24/2004, pp. 32] Like those two aircraft, it is a Boeing 767. [USA Today, 8/13/2002; 9/11 Commission, 7/24/2004, pp. 27-28] But, unlike those flights, its transponder has not been turned off, and so it is still transmitting a beacon code. [9/11 Commission, 7/24/2004, pp. 28; Vanity Fair, 8/1/2006] It is unclear what Delta 1989’s intended destination is. According to some accounts, like Flights 11 and 175 were, it is bound for Los Angeles. [Associated Press, 9/11/2001; New York Times, 10/18/2001; USA Today, 8/13/2002; Arizona Daily Star, 9/24/2007; Spencer, 2008, pp. 167] Other accounts will say that its destination is Las Vegas. [9/11 Commission, 7/24/2004, pp. 28; Vanity Fair, 8/1/2006] Personnel at NEADS are apparently informed that Las Vegas is the intended destination. Around this time, one member of staff there tells her colleagues that the flight is “supposed to go to Vegas.” [North American Aerospace Defense Command, 9/11/2001]
One of Numerous Incorrect Reports - The 9/11 Commission will comment: “During the course of the morning, there were multiple erroneous reports of hijacked aircraft (see (9:09 a.m. and After) September 11, 2001). The report of American 11 heading south was the first (see 9:21 a.m. September 11, 2001); Delta 1989 was the second.” [9/11 Commission, 7/24/2004, pp. 28]
The FAA’s Command Center in Herndon, Virginia, provides updates to FAA headquarters in Washington, DC, about the problems with Flight 93. At 9:41 a.m., John White, a manager at the Command Center, is talking to Doug Davis, the special assistant for technical operations in air traffic services at FAA headquarters. White says that Flight 93 has reversed course from its intended flight path (see (9:36 a.m.) September 11, 2001), its transponder signal has been lost (see (9:40 a.m.) September 11, 2001), and it is now descending and heading east. From 9:42 a.m., one of the Command Center managers (exactly who is unstated) gives the headquarters several updates on Flight 93’s progress and location. At 9:46 a.m., White tells Jeff Griffith, the FAA’s deputy director of air traffic, that Flight 93 is “29 minutes out of Washington, DC, and tracking toward us.” Two minutes later, in another conversation with Griffith, White confirms that Flight 93 has reversed course and is heading toward Washington. [Federal Aviation Administration, 10/21/2002; 9/11 Commission, 8/26/2004, pp. 43-44 ] The air traffic control tower at Pittsburgh International Airport is evacuated, because of concerns that Flight 93, which is heading in the direction of the airport, could crash into it. [Federal Aviation Administration, 9/17/2001 ; Pittsburgh Post-Gazette, 9/23/2001; Federal Aviation Administration, 3/21/2002, pp. 11-13 ; Lancaster New Era, 11/3/2006]
Cleveland Center Notifies Pittsburgh Tower - At 9:44 a.m., an air traffic controller at the FAA’s Cleveland Center calls the Pittsburgh Airport control tower and notifies it of the loss of radio contact with Flight 93, and the loss of a secondary radar return from that aircraft (see (9:40 a.m.) September 11, 2001). The Cleveland Center controller also says Flight 93 has made an unanticipated turn (see (9:36 a.m.) September 11, 2001), and its flight path will take it close to Pittsburgh Airport, if not directly over it. [Federal Aviation Administration, 3/21/2002, pp. 11-12 ] The controller at the Pittsburgh tower who answers the call, apparently Paul Delfine, begins tracking Flight 93’s primary target on radar, and calls over his operations supervisor, Mal Fuller. [Federal Aviation Administration, 9/17/2001 ; Lancaster New Era, 11/3/2006]
Supervisor Orders Evacuation - Delfine points to a plane—which Fuller only later learns is Flight 93—on a radar scope. He tells Fuller it was hijacked over Cleveland, and controllers don’t know where it is heading. Fuller will later recall: “In two sweeps of the radar, I could tell it was going very fast. It was headed directly for the control tower.” Fuller is aware of the attacks on the World Trade Center and the Pentagon, and, at 9:49, gives the order, “Evacuate the facility.” [Pittsburgh Post-Gazette, 9/23/2001; Lancaster New Era, 11/3/2006] By 9:51, the facility has been evacuated. [Federal Aviation Administration, 9/17/2001 ] However, one controller refuses to leave his post and remains in the tower. [Spencer, 2008, pp. 193-194]
Employees Do Not See Flight 93 Overhead - Some of the evacuated employees are so upset that they immediately head home. Others mill around in a parking lot. Fuller will later guess that Flight 93 passed directly overhead as he was heading outside, but he assumes it was too high for anyone to see it. He will recall: “We watched and watched and watched. We never saw anything.” [Lancaster New Era, 11/3/2006]
Controllers Return to Facility - Minutes after evacuating, at 9:56 a small number of tower controllers will volunteer to return to their facility. Once back inside, they find that Flight 93’s track is no longer visible on their radar screens. At 10:05 a.m., tower personnel will contact the FAA’s Herndon Command Center to explain why they evacuated. They say they did so because there had been an aircraft, thought to be Flight 93, which appeared to be on a collision course with the tower, and this aircraft allegedly had a bomb on board. [Federal Aviation Administration, 9/17/2001 ; Federal Aviation Administration, 3/21/2002, pp. 12-13 ] Around the time the Pittsburgh Airport control tower evacuates, while Flight 93 is heading east, NEADS battle commander Colonel Robert Marr hears that the FAA’s Cleveland Center is being evacuated (see (Between 9:45 a.m. and 12:00 p.m.) September 11, 2001). [Filson, 2003, pp. 73]  F-16 Fighting Falcons from the 127th Wing at Selfridge Air National Guard Base. [Source: John S. Swanson / US Air Force]NORAD’s Northeast Air Defense Sector (NEADS) contacts Selfridge Air National Guard Base in Michigan to arrange for two of its F-16 fighter jets that are out on a training mission to intercept a suspicious aircraft. Accounts will conflict over whether this aircraft is Flight 93 or Delta Air Lines Flight 1989, which is wrongly thought to have been hijacked. [Associated Press, 8/30/2002; ABC News, 9/11/2002; Vanity Fair, 8/1/2006; Spencer, 2008, pp. 178] Delta 1989 was flying about 25 miles behind Flight 93 when air traffic controllers mistakenly suspected it might be hijacked (see (9:28 a.m.-9:33 a.m.) September 11, 2001), and since then it has been instructed to land at Cleveland Hopkins Airport in Ohio (see (9:42 a.m.) September 11, 2001). [USA Today, 8/13/2002; USA Today, 9/11/2008] Flight 93 is currently flying east across Pennsylvania. [National Transportation Safety Board, 2/19/2002 ] NEADS has already tried getting fighter jets from a unit in Duluth, Minnesota, sent after Delta 1989, but the unit was unable to respond (see (Shortly After 9:41 a.m.) September 11, 2001). [9/11 Commission, 1/22/2004 ; 9/11 Commission, 1/23/2004 ]
NEADS Calls Selfridge Base - A NEADS weapons technician now calls the 127th Wing at Selfridge Air National Guard Base. He knows the unit has two F-16s in the air on a training mission. Although these jets are unarmed and only have a limited amount of fuel remaining, the commander at the Selfridge base agrees to turn them over to NEADS. [Spencer, 2008, pp. 178] The commander says: “[H]ere’s what we can do. At a minimum, we can keep our guys airborne. I mean, they don’t have—they don’t have any guns or missiles or anything on board.” The NEADS technician replies, “It’s a presence, though.” [Vanity Fair, 8/1/2006]
Fighters May Have to Crash into Hijacked Plane - Military commanders realize that, without weapons, the Selfridge fighter pilots might have to slam their jets into a hijacked plane to stop it in its tracks. Colonel Robert Marr, the NEADS battle commander, will later reflect, “As a military man, there are times that you have to make sacrifices that you have to make.” [ABC News, 8/30/2002; ABC News, 9/11/2002] However, the Selfridge jets never have to intercept either of the two suspect aircraft, and instead are able to head back to base. [Filson, 2003, pp. 70; Wolverine Guard, 9/2006 ]
Selfridge Called due to Concerns about Delta 1989? - According to author Lynn Spencer, the NEADS weapons technician’s call to the Selfridge unit is made in response to a report NEADS received about the possible hijacking of Delta 1989 (see 9:39 a.m. September 11, 2001). [Spencer, 2008, pp. 178] Vanity Fair magazine and the 9/11 Commission will also say NEADS calls the Selfridge unit in response to this report about Delta 1989. [9/11 Commission, 7/24/2004, pp. 28; Vanity Fair, 8/1/2006]
NORAD Commander Gives Different Account - However, Larry Arnold, the commander of the Continental United States NORAD Region, will suggest the Selfridge unit is called due to concerns about both Delta 1989 and Flight 93. He will say: “We were concerned about Flight 93 and this Delta aircraft [Flight 1989] and were trying to find aircraft in the vicinity to help out. We didn’t know where it was going to go. We were concerned about Detroit… and the fighters up there were out of gas with no armament.” [Filson, 2003, pp. 71]
NEADS Commander Claims Fighters Sent toward Flight 93 - Robert Marr will give another different account. He will claim that NEADS contacts the Selfridge base solely because of its concerns over Flight 93. He tells author Leslie Filson that before Flight 93 reversed course and headed back east (see (9:36 a.m.) September 11, 2001), NEADS thought it was “headed toward Detroit or Chicago. I’m thinking Chicago is the target and know that Selfridge Air National Guard Base has F-16s in the air.” NEADS contacts “them so they could head off 93 at the pass.” [Filson, 2003, pp. 68] Marr will tell the 9/11 Commission that the Selfridge F-16s are going to be “too far from Cleveland to do any good,” and so he believes NEADS directs them to intercept Flight 93. [9/11 Commission, 1/23/2004 ] (Presumably, he means the jets cannot be responding to Delta 1989, which has been told to land in Cleveland [USA Today, 9/11/2008] )
9/11 Commission Disputes Arnold's and Marr's Accounts - The 9/11 Commission will reject Arnold’s and Marr’s accounts. It will state, “The record demonstrates, however, that… the military never saw Flight 93 at all” before it crashes, and conclude, “The Selfridge base was contacted by NEADS not regarding Flight 93, but in response to another commercial aircraft in the area that was reported hijacked (Delta Flight 1989, which ultimately was resolved as not hijacked).” [9/11 Commission, 8/26/2004, pp. 101 ] Lt. Col. Doug Champagne, the pilot of one of the Selfridge F-16s, will recall that “he and his colleague never received orders to intercept [Flight 93] in any way.” [Mount Clemens-Clinton-Harrison Journal, 9/6/2006] Reports based on interviews with the two Selfridge pilots will make no mention of the jets being directed to intercept Delta 1989 either (see (9:56 a.m.-10:29 a.m.) September 11, 2001). [Filson, 2003, pp. 68-70; Wolverine Guard, 9/2006 ; Mount Clemens-Clinton-Harrison Journal, 9/6/2006]
 The South Tower of the World Trade Center collapses. [Source: Associated Press]The South Tower of the World Trade Center tilts to the southeast and then collapses. It was hit by Flight 175 at 9:03 a.m., 56 minutes earlier (see 9:03 a.m. September 11, 2001). [Washington Post, 9/12/2001; New York Times, 9/12/2001; MSNBC, 9/22/2001; USA Today, 12/20/2001; Associated Press, 8/21/2002; ABC News, 9/11/2002; National Institute of Standards and Technology, 9/2005, pp. 44 ] The first sign of the collapse is visible on floor 82. [National Institute of Standards and Technology, 9/2005, pp. 87 ] The angle of the tilt will be disputed after 9/11 (see September-November 2005), as will the time it takes the towers to fall to the ground (see September 12, 2001-September 2005). [Scientific American, 10/9/2001; Eagar and Musso, 12/2001; PBS Nova, 5/2002; National Institute of Standards and Technology, 8/30/2006]
United Airlines issues a press release confirming that Flight 93 has crashed. Flight 93 went down in Pennsylvania shortly after 10:00 a.m. (see (10:06 a.m.) September 11, 2001). The release states: “United Airlines has confirmed one of its flights has crashed near Pittsburgh, Pennsylvania. United Flight 93, a Boeing 757 aircraft, is the flight number involved. The flight originated in Newark and was bound for San Francisco.” The release adds, “United is deeply concerned about a further flight, United Flight 175, a Boeing 767, which was bound from Boston to Los Angeles.” [United Airlines, 9/11/2001] Although Flight 175 hit the World Trade Center at 9:03 (see 9:03 a.m. September 11, 2001), United Airlines will not publicly confirm it has crashed until 11:53 a.m. (see 11:53 a.m. September 11, 2001). United Airlines finally issues a press release confirming that Flight 175 has crashed, nearly three hours after this aircraft hit the World Trade Center (see 9:03 a.m. September 11, 2001). The release states, “United Airlines has now confirmed that two of its aircraft have crashed.” These include “United Flight 175, a Boeing 767 aircraft, [that] departed from Boston at 7:58 a.m. local time, bound for Los Angeles, with 56 passengers onboard, two pilots and seven flight attendants.” [United Airlines, 9/11/2001] United Airlines previously issued a press release, at 11:17, confirming the crash of Flight 93 (see 11:17 a.m. September 11, 2001), but this had stated that the airline was, at that time, only “deeply concerned” about Flight 175. [United Airlines, 9/11/2001] However, at 9:22, the United Airlines System Operations Control manager had issued an advisory to all the airline’s facilities, stating that Flight 175 had been in an accident in New York (see 9:22 a.m. September 11, 2001). [9/11 Commission, 8/26/2004, pp. 26 ] And Colin Scoggins, the military liaison at the FAA’s Boston Center, will later claim that United confirmed to the center that Flight 175 was down, “within two or three minutes” (see (9:06 a.m.) September 11, 2001). [Vanity Fair, 8/1/2006] One of the key variables in the computer simulations used by the National Institute of Standards and Technology (NIST) (see (October 2002-October 2005)) to explain the WTC collapses is the speed of the aircraft that hit the towers. However, there is no consensus on how fast the planes were traveling. The first estimate was contained in an initial research paper by engineers Zdenek Bazant and Yong Zhou, who stated that the planes were traveling at 342 miles per hour. [Bazant and Zhou, 1/2002 ] However, the Federal Emergency Management Agency (FEMA) and American Society of Civil Engineers (ASCE) report said that the plane that hit the North Tower was traveling at 470 miles per hour, whereas the plane that hit the South Tower was traveling at 590 miles per hour (see May 1, 2002). [Federal Emergency Management Agency, 5/1/2002, pp. 31] NIST initially estimates speeds of 435 miles per hour for the plane that hit the North Tower and 497 miles per hour for the plane that hit the South Tower. These estimates closely match figures produced by the Massachusetts Institute of Technology, which finds speeds of 429 miles per hour and 503 miles per hour for the two planes. However, NIST is dissatisfied with these results and does a second study, which finds speeds of 466 and 545 miles per hour. It then uses speeds of 472 and 570 miles per hour in its severe case model, on which its final report is based. In this model, the simulation of the planes traveling faster means greater damage to the towers’ structure, making them more unstable. [Kausel, 5/2002 ; National Institute of Standards & Technology, 9/2005, pp. 152-165 ; National Institute of Standards and Technology, 9/2005, pp. 109 ]  Matthys Levy. [Source: PBS]A report is made publicly available, which the Engineering News-Record calls the “most comprehensive study yet on the destruction of the World Trade Center.” The study was commissioned by WTC leaseholder Silverstein Properties Inc. to support a $7 billion insurance claim, and conducted by a team of engineers from several leading firms, including Weidlinger Associates, LZA Technology/Thornton-Tomasetti, and ARUPFire. It is intended to build on a previous study sponsored by FEMA (see May 1, 2002). The report’s findings are based on an analysis of original structural drawings, thousands of photos, and dozens of videos. Investigators used fire evaluation techniques and powerful computer software to simulate the condition of each tower at critical times between the planes’ impacts and the towers’ collapses. The earlier FEMA investigators had no access to such computer modeling. Matthys Levy, the chairman of Weidlinger Associates and one of the engineers on the study team, says, “The buildings had tremendous reserve capacity and that was reflected in all of the elements we analyzed. In fact, because there were so much excess capacity, the columns even in the impact floors did not buckle immediately, but failed as the result of the fire.” The report states that failure of the WTC’s steel floor supports (“trusses”) did not contribute to the collapses. Instead, the collapses were caused by the failure of steel structural columns that were either destroyed when the planes hit or lost fireproofing, leaving them vulnerable to the weakening effects of the ensuing fires. It says that debris and dust distributed by the plane crashes inhibited the fires, such that the average air temperatures on the impact floors were between 400 and 700°C (750-1,300°F): significantly lower than those associated with typical “fully developed” office fires. However, says Matthys Levy, “By the time the temperature inside the buildings reached 400 degrees, the steel would have lost approximately 50% of its strength. Eventually, gravity took over and the towers began to fall.” Then, according to the analysis led by researchers from LZA Technology/Thornton-Tomasetti, “Once collapse initiated in each tower, essentially all of the interior structure of the tower fell straight down with floors pancaking on top of one another. The network of perimeter steel columns and spandrels acted like a chute to funnel the interior contents into the tower footprint.” According to the computer simulations, the damage to the South Tower’s steel core columns was so severe that the tower should have collapsed immediately after the plane hit. Civil engineer John Osteraas says this incorrect result casts doubt upon some of the study’s predictions. The report concludes that the collapse of the South Tower did not cause or contribute to the subsequent collapse of the North Tower, thus supporting Silverstein Properties’ claim that the terrorist attack represented two occurrences, entitling it to two $3.5 billion insurance policy limits. A separate study commissioned by the insurers contradicts this (see October 23, 2002). The Silverstein report apparently does not examine the collapse of WTC Building 7, a 47-story skyscraper that also collapsed on 9/11 (see (5:20 p.m.) September 11, 2001). It has been passed on to the National Institute of Standards and Technology (NIST), which is undertaking its own investigation of the WTC collapses (see August 21, 2002). [New York Times, 9/30/2002; Business Insurance, 10/23/2002; Silverstein Properties, Inc., 10/23/2002 ; Engineering News-Record, 10/25/2002; New York Times, 10/29/2002; Engineering News-Record, 11/4/2002; Real Estate Weekly, 4/30/2003]
 Shyam Sunder. [Source: NIST]The National Institute of Standards and Technology (NIST) releases nearly 500 pages of documents, detailing the latest findings of its investigation of the WTC collapses on 9/11. These include its hypotheses for the collapse sequences of each of the Twin Towers; details of their analysis of interviews with nearly 1,200 building occupants, emergency responders, and victims’ relatives; and information from their analysis of the emergency response and evacuation procedures. Their investigation into the collapses is based upon an analysis of thousands of photos and videos, examination of many of the elements used to construct the towers, and computer-enhanced modeling of the plane impacts and the spreading of the fires. Their hypothesis is that the towers collapsed ultimately due to the fires they suffered: As the fires burned, the buildings’ steel core columns buckled and shortened. This shifted more load to the buildings’ perimeter columns, which were already affected by the heat of the fires, and caused them to give way under the increased stress. Investigators have conducted a test with a reconstructed section of the WTC floor, and found that the original fireproofing was sufficient to meet the New York City building code. They say that had a typical office fire occurred in the towers, without the structural damage and the loss of some fireproofing caused by the plane impacts, it is likely the buildings would have remained standing. Lead investigator Dr. Shyam Sunder says, “The buildings performed as they should have in the airplane impact and extreme fires to which they were subjected. There is nothing there that stands out as abnormal.” NIST’s theories of why the WTC buildings collapsed conflict with an earlier investigation by FEMA, which claimed the collapse of the North Tower had begun in its core, rather than its perimeter columns (see May 1, 2002). [National Institute of Standards and Technology, 10/19/2004; New York Times, 10/20/2004]
The National Institute of Standards and Technology (NIST), which is conducting an investigation into the WTC collapses on 9/11, releases three new reports. Investigators say that the Twin Towers would probably have remained standing if the fireproofing material that surrounded the buildings’ structural steel had not been stripped away when the planes hit. Their report states that “[t]he jet fuel, which ignited the fires, was mostly consumed within the first few minutes after impact. The fires that burned for almost the entire time that the buildings remained standing were due mainly to burning building contents and, to a lesser extent, aircraft contents, not jet fuel.” However, they claim, without the loss of fireproofing during the planes’ impacts, the heat from the fires would have been insufficient to cause the buildings to collapse. They say that although the architects had in 1964 tested the impact of a Boeing 707 airplane crashing into the 80th floor of one of the towers, they never envisioned the intense fires that ensued. NIST also reports that the time taken by survivors from the North Tower to descend a flight of stairs was about double the slowest evacuation speed estimated in a standard fire engineering text. They state: “approximately 87 percent of the WTC tower occupants, including more than 99 percent below the floors of impact, were able to evacuate successfully.” However, they say, if each tower had been full when they were hit, as many as 14,000 people could have died. [National Institute of Standards and Technology, 4/5/2005; Associated Press, 4/5/2005; New York Times, 4/5/2005; Associated Press, 4/6/2005] National Institute of Standards and Technology (NIST) releases a 12-page appendix to its final reports on the WTC collapses (see October 26, 2005) detailing tests it conducted on samples of the type of fireproofing used in the WTC. An earlier NIST report had concluded that loss of fireproofing was a major factor in the collapses (see April 5, 2005). The appendix was not included in earlier drafts of the report (see June 23, 2005) [National Institute of Standards and Technology, 6/23/2005 ; National Institute of Standards & Technology, 9/2005, pp. 263-274 ; National Institute of Standards and Technology, 9/2005, pp. 149 ] NIST conducted a series of fifteen tests. In the tests projectiles were fired at fireproofing mounted on 12 inch x 12 inch plates, and steel bars with a one inch diameter. The fireproofing used in the tests was Blazeshield DC/F, one of the two grades of fireproofing used on the impact floors. In thirteen of the tests the projectiles were buckshot, which was fired at the steel samples from a modified shotgun at a distance of 29.5 ft. The other two tests used steel bolts and hexagon nuts, fired with less velocity and at closer range. According to NIST, “The test results support the assumption that, within the debris field created by the aircraft impact into WTC 1 and WTC 2, the SFRM [i.e., fireproofing] used for thermal insulation of structural members was damaged and dislodged.” [National Institute of Standards & Technology, 9/2005, pp. 83, 263-274 ]
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