Aircraft crashing into buildings
Endro SUNARSO, ASIS-CPP?, PMI-PMP?, FSyl, F.ISRM
Effective security professional with extensive experience in corporate & physical security operations & management across APAC & ME.
Some of the first suicide aircraft attacks of the 20th century involved the Japanese military in the WWII. The first Kamikaze (suicide) attacks occurred during the Battle of Leyte Gulf (23–26 Oct 1944) when pilots in aircraft loaded with bombs,?torpedoes &/or other explosives would attempt to crash their aircraft into enemy ships.
Pilot murder-suicides, where it has been concluded through post-accident analysis & investigation that the pilot deliberately crashed a commercial aircraft killing the pilot & all others on board have occurred in 6 instances over the past 30 years.?
On 11 Sept 2021, 19 terrorists from Al-Qaeda, 15 were nationals from an US ally, Saudi Arabia, commandeered 4 commercial aircraft to be used in suicide attacks on the World Trade Centre, the Pentagon & an unknown target. The commercial aircraft flown into the World Trade Center & the Pentagon have proven to be a highly successful method of attack. Although not a suicide bomb in the conventional sense the force of impact, combined with the resulting ignition of aviation fuel, causes a highly catastrophic explosive event.
Two decades after the 11 Sept 2001 terrorist attacks, aviation remains a staple target for terrorists. Although fatal hijackings & attacks on aircraft occurred well before these attacks, 9/11 sparked the international community into launching new aviation security, procedures, regulations & operations.
Aviation security experts acknowledge that prior to 9/11, no one envisioned suicide terrorists wanting to use commercial airplanes as weapons & being willing to kill themselves in order to kill hundreds of innocent people. Now, counterterrorism & homeland security official work to imagine the unimaginable & enhance defenses to prevent the ever-changing & growing threats to aviation security.
Why do structures to collapse?
Buildings are exceeding attractive targets for terrorist attack & explosives the favorite means of delivering it. A structure's response to attack varies according to its method of construction. A structure that is framed with robust individual members, strong but ductile connections to tie the members together & good fire protection will provide the greatest resistance to such attacks.
Nearly every large building has a redundant design that allows for loss of one primary structural member, such as a column. However, when multiple members fail, the shifting loads eventually overstress the adjacent members and the collapse occurs like a row of dominoes falling down.
Newer structures after 9/11 usually have a strong skeleton made of steel or reinforced concrete, with non-structural panels being used to close the space between the members. Members are able to resist both tension & compression, support the structure & crucially, are tied together to form a frame. The frame members have strength in tension & are able to resist sideways force much better, whilst presenting a smaller surface area to the blast. The pressure wave may blow away the infill panels between members but the frame is likely to survive. If a frame member is in distress or destroyed completely, the structural loads can be automatically redistributed amongst the remaining members, bridging the new gap from above, below & alongside.
But there are some caveats to the otherwise good resistance of a framed structure to a terrorist attack.
The 1st caveat is the way the frame is tied together. If the frame joints are inadequate, the structure will behave like a house of cards. Individual parts may remain intact but the frame will disintegrate allowing a partial or complete collapse.
The 2nd caveat is an attack that creates a fire. It is known that structural steel begins to soften around 425°C & loses about half of its strength at 650°C. The melting point of steel is about 1,500°C. Normal building fires & hydrocarbon (jet fuel) fires generate temperatures up to about 1,100°C. The aircraft that hit the WTC were loaded with about 10,000 gallons of jet fuel each. About 25% of this quantity was consumed in the initial blast & resulting fireball. Another 25% of the fuel is believed to have flowed down through elevators & utility shafts in the buildings. The remaining 50% of the fuel burned off within the first few minutes (5-8 minutes) of the aircraft impact (Rehm et al.2002, FEMA 2002). Although the jet fuel had burned off in the first few minutes, it acted as a catalyst in igniting the combustible materials & in generating massive fires at several floors simultaneously. This generated fire conditions significantly more severe than those anticipated in typical building fires (Yong and Kodur 2000, FEMA 2002). The maximum fire temperatures attained in the WTC fires were in the range of 1,000° to 1,100°C. These temperatures were not significantly different from other typical office building fires. However, the rise in fire temperatures was much faster than those in typical building fires & represented typical hydrocarbon fires with temperatures reaching about 800°C in the first 3-4 minutes (ASTM 1993).?NIST reported maximum upper layer air temperatures of about 1,000°C in the WTC towers. Members bend & joints are weakened, leading to the failure of a frame that could otherwise resist a large explosion or kinetic energy attack at a lower temperature. Contrary to many early media reports, the steel did not melt. The melting point for steel varies with the alloy & is in the range of 1,500-1,600°C. Since the fire temperatures did not reach this level, it is unlikely that there was any melting of steel.?
In the 1993 attack, the North Tower survived a very large explosion in the underground car park despite severe local damage. The vehicle-borne improvised explosive device (VBIED), weighed more than 1,000 pounds & caused extensive damage to 7 of the building’s floors, 6 of which were below grade. A blast crater measured 130?feet in width by 150?feet in length.
However, in the 9/11 attack, both towers were destroyed when burning aviation fuel from 2 deliberately crashed aircraft took away the strength of the frames after little over an hour. Here, the energy released by the fuel overwhelmed fire protection designed for a more normal fire, which was also damaged by the impact of the aircraft. According to Kodur & Harmathy 2002, steel-framed buildings depend on fire proofing for its ability to resist the impact of fire. The adhesion & cohesion of sprayed fiber & the cementatious materials, is a problem when subjected to significant impact loads (Morse 2002). In the twin towers the impact of aircraft mechanically damaged much of the spray-applied fire protection, originally present on the structural steel frame, to an extent that much of the steel in the immediate fire area was unprotected (FEMA 2002, Glover 2002).
Prior to 9/11 no fire-protected steel framed building had ever totally collapsed. What made the difference at the WTC was how a combination of fire & impact damage triggered progressive collapse. The intense heat from the fires attacked the structural system & over a period of time, resulted in sufficient additional damage to the structural system to initiate a progressive sequence of failures that eventually culminated in the total collapse of both towers.?The extreme heat from the fires might have caused the steel floors to expand & bow, which may have caused the support columns to bend inward & buckle. Heat also may have caused the steel flooring to separate from the columns, or the columns themselves may have heated up & buckled outward.
The 3rd caveat is an explosion or kinetic energy attack occurring high up a structure. Whilst the majority of the frame might resist the attack, the members & floors close to the attack may be seriously overloaded. An explosion may force the floor above upwards in a direction that it was not designed to resist. If the explosion breaks this floor slab & detaches it from the frame it can fall downwards. The kinetic energy of the falling slab might then break the weakened floor below. The increasing momentum of these 2 falling floors could then be sufficient to break an otherwise undamaged floor below, producing progressive collapse where all the floors collapse progressively downwards, leaving the outer frame standing but the infilling floors destroyed. There is little doubt that the collapse of the upper floors of the WTC towers brought down both structures. The impact was equivalent to dropping a 25-story building straight down. It was like a pile driver, which is why it collapsed as it did.
A similar effect occurs when the frame itself is overloaded. This occurred to the frame of the WTC where the kinetic energy of the collapsed upper floors falling & impacting on the undamaged frame below the aircraft impact area was sufficient to overload it. This resulted in the collapse of the undamaged structure lower down. It also explains why the structure collapsed vertically downwards on itself, rather than falling over.
The 9/11 commission (formally known as The National Commission on Terrorist Attacks Upon the United States) issued its report with 37 recommendations to help prevent future strikes on the US. These recommendations were unanimously approved by the panel's 5 Republican & 5 Democratic commissioners. The report detailed the planning & execution of the?Al-Qaeda?attacks, the response of the intelligence & policy?communities?to the intelligence warnings of an attack in the preceding months, & the response of the national security system to the attacks when they occurred. The commission concluded that the?CIA & FBI had inadequately assessed the threat posed by Al-Qaeda & had not taken sufficient steps to disrupt its planning. The report said that the most important failure in both the intelligence & policy communities was one of imagination, in understanding the depth of the threat Al-Qaeda posed.
Below is a partial list of aircraft crashing into other buildings.
New York, USA
In July 1945, bad weather & extremely low fog caused a U.S. Army Air Corps?B-25 bomber heading to Newark from the Northeast collided with the 79th floor of the Empire State Building, killing at least 14 & injuring dozens.
(B-25 Mitchell bomber)
The B-25 Mitchell bomber crashed into the 79th floor of the 1,250-foot Empire State Building at 0952 hour, killing at least 14 including the 3 men aboard the plane & injured 24, 6 seriously.
The resulting terrific explosion jolted thousands in midtown offices. So great was the plane’s impact that one of its motors, hurled loose with projectile speed, tore nearly 100 feet through 7 walls of the 79th floor & melted the suspension cables of 3 elevators before it landed with a final explosion on the roof of an adjacent 17-story building.
Florida, USA
On Jan 2002, Charles J. Bishop, a high-school student stole a?Cessna 172 light aircraft & crashed it into the side of the?Bank of America Tower?in downtown?Tampa, Florida. The impact killed the teenager & damaged an office room, but there were no other injuries.
Bishop had been inspired by the?Sept 11 attacks. He had left a suicide note crediting?Osama bin Laden?for the attacks & praising it as a justified response to actions against Palestinians & Iraqis.?Officials could find any evidence & terrorism as a motive was ruled out .
Milan, Italy
On 18 April 2002, at 1715 hours, Luigi Marco Fasulo, an amateur pilot from Italy & Switzerland, took off from Magadino airport in Switzerland in his Rockwell Commander 112TC for Milan.
(Rockwell Commander 112TC)
At approximately 1745 p.m., the aircraft crashed into the Pirelli skyscraper causing the death of the pilot, the death of 2 Lombardy Region employees & injured 60 people. This crash initially led to a speculation of a terrorist attack. Subsequently, it emerged that the pilot apparently had a past of illegal activities & financial problems.
At the end of 2002, an enquiry established that the cause of the accident was probably an undercarriage failure, as indicated by the pilot himself to the control tower, as well as the pilot's inability to handle critical flight situations.
Tehran, Iran
In Dec 2005, it was reported that an Iranian military plane carrying dozens of journalists crashed into a crashed into a 10-storey apartment building?in a residential area of?Tehran, killing at least 116 people. All 94 passengers & crew on the C-130 transport plane died. Several children were among the dead in the building.
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Austin, USA
In Feb, 2010, Andrew Joseph Stack III deliberately crashed his single-engine?Piper Dakota light aircraft?into Building I of the Echelon office complex in?Austin, Texas,?killing himself & another.?13 others were injured, 2 severely. The 4-story office building housed an IRS field office along with private businesses. Prior to the crash, Stack had posted a?suicide note to his website, expressing his disillusionment with corporations & government agencies such as the IRS.
North Carolina, USA
In Sept 2021, a Cessna Citation 560X jet took off just before 1000 hours from the Robertson Airport heading for the Dare County Regional Airport in Manteo, North Carolina, Along the way, it crashed into the building at Trumpf Inc., a manufacturing company.
(Cessna Citation 560X)
Hang-gliders & light aircraft are probable methods of delivering a suicide attack & suicide bombers have been trained in numerous Western countries to fly light & commercial aircraft. An Ultralight is an ideal aircraft as it does not carry sufficient metal for radar detection & when laden with explosives, could be used to attack vital economic, political & military targets. Hot air balloons, parachutes & paragliders are also feasible methods of attack. Terrorist attacks are classified as low probability, high impact events.
Black Swans & Gray Rhinos
Black Swans are surprising, high-impact events produced by complex systems of non-linear interactions that are inherently unpredictable. This term used to describe unanticipated events has seeped into public consciousness since the publication of The Black Swan: The Impact of the Highly Improbable by Nassim Nicholas Taleb, 2007. According to Taleb, a Black Swan event has 3 characteristics:
Strategic surprise, the realization that one’s knowledge & assumptions are wrong & the adversary has an upper hand, is a national security nightmare (Amidon, 2005; Defense Science Board, 2015; Handel, 1984). Examples would be Pearl Harbor, Sputnik, the Cuban Missile Crisis & the Sept 11 2001 attacks.
Gray Rhinos are surprising events whose indicators exist & should have been obvious but were missed because we were not looking or properly assessing them.?
The coordinated attacks of 9/11 involved long term planning, split second timing & an innovative use of existing resources. There are plenty of small airfields with parked aircraft & helicopters where security is lax. As such it is not that difficult to someone to gain access to a small aircraft or helicopter, pack it with explosives & use it as a missile against a specific target. Furthermore, there are many people who are trained to fly & own aircraft. Therefore, it is not that difficult to crash an aircraft into a building. Ms Cathleen Berrick, director of Homeland Security & Justice Issues told the Senate Commerce Committee during a Nov 5 2003 hearing on aviation security that 70 general aviation aircraft have been stolen in the last 5 years, “indicating a potential weakness that could be exploited by terrorists.”
The US General Accounting Office (GAO) reported that although strict security guidelines are in place for the nation’s major commercial airports requiring screening of passengers & baggage, no such measures are required for the nation’s 19,000 general aviation airports, making them vulnerable to terrorist use. This is generally the case with all other countries. The 2,000-foot, grass strip, public use airport that is privately owned, simply does not have the same needs as a large general aviation airport.
The metal detectors & X-ray machines so familiar at airport concourses are basically the only line of protection for airlines. The vulnerability of general aviation stems from the fact that pilots & passengers are not screened before takeoff & the contents of general aviation planes are not screened at any point. Because of lax security measures, such planes could easily be rented with just a credit card or simply stolen. Such vulnerability was demonstrated in Jan 2002 when a teenage flight student stole & crashed a single-engine airplane into a Tampa skyscraper.
In May 2003, the US Department of Homeland Security issued a warning to the general aviation community that terrorists were interested in using small planes packed with explosives to attack targets. The basis of the warning came on the heels of a foiled plot to fly “obtain a small fixed-wing aircraft or helicopter [loaded with] with explosives” & crash it into the US Consulate in Karachi, Pakistan.” Of course, this runs contrary to the view of terrorism that we commonly get from Hollywood.
The vast majority of terrorist attacks rely on unsophisticated, readily accessible weapons. Based on Global Terrorism Database (GTD) data, 80% of all attacks rely on explosives & firearms. For the most part, the explosives used are relatively common, especially dynamite & grenades. Similarly, the most common firearms are also widely available, including especially shotguns & pistols. Fortunately, sophisticated weapons, including chemical, biological, radiological & nuclear (CBRN) weapons are the rare exception.
References
Amidon, M. (2005). Groupthink, Politics, and the Decision to Attempt the Son Tay Rescue. Parameters, 35, 119- 131. Retrieved from https://www.carlisle.army.mil/usawc/Parameters/Articles/05autumn/amidon.pdf?
ASTM, 1993, “Standard Test Methods for Determining Effects of Large Hydrocarbon Pool Fires on Structural Members and Assemblies,” American Society for Testing and Materials.
ASTM, 2000, “Standard Test Methods for Fire Tests of Building Construction and Materials,” American Society for Testing and Materials.?
Defense Science Board. (2015). Strategic Surprise. Office of the Under Secretary of Defense for Acquisition, Technology, and Logistics Washington, D.C.
Eagar, Thomas W. and Christopher Musso (2001). "Why Did The World Trade Center Collapse? Science, Engineering, And Speculation". JOM 53.12 :8-11.
Federal Emergency Management Agency (FEMA), "World Trade Center Building Performance Study: Data Collection, Preliminary Observations and Recommendations", Report 403, FEMA, Washington D.C., 2002.
Glover N.J., 2002, "Collpase Lessons", Fire Engineering, October 2002.?
Gregory H. Urich, Analysis of Mass and Potential Energy in the World Trade Center Twin Towers, B.S. Electrical and Computer Engineering.
Handel, M. I. (1984). Intelligence and the problem of strategic surprise. Journal of Strategic Studies, 7(3), 229- 281. doi:10.1080/01402398408437190.
Irfanoglu,?Ayhan and Christoph M. Hoffmann. "Engineering Perspective Of The Collapse Of WTC-I". J. Perform. Constr. Facil. 22.1 (2008).?
Kenedi C, Friedman SH, Watson D, Preitner C. Suicide and murder-suicide involving aircraft.?Aerosp Med Hum Perform.?(2016) 87:388–96. doi: 10.3357/AMHP.4474.2016.
Kodur, V. R.; Harmathy, T. Z. "Properties of building materials" SFPE Handbook of Fire Protection Engineering, 3rd edition, P.J. DiNenno, National Fire Protection Association, Quincy, MA, pp. 1.155-1.181, 2002.
Morse, R.G. "Fire Proofing at the WTC Towers". Fire Engineering, October 2002.
Panagiotis and Asif Usmani. "The World Trade Center 9/11 Disaster And Progressive Collapse Of Tall Buildings". Fire Technol 49.3 (2012).
Quintiere J.G., Marzo, M.D.; and Becker. R, "A Suggested Cause of the Fire-Induced Collpase of the World Trade Towers"; Fire Safety Journal; 2002.?
Rehm, R.G.; Pitts, W.M; Baum, H.R.; Evans, D.D.; Prasad, K.; Mcgratten K.B.; and Forney, G.P. "Initial Model for Fires in World Trade Center Towers", Proceedings (in press) 7th International Association of Fire Safety Science Symposium (Worcester, MA., U.S.A.), 2002.
Taleb, Nicholas N. 2010. The Black Swan: The Impact the Highly Improbable. 2nd ed. New York: Random House.
Wang, Y.C.; Kodur, V.R. "Research toward the use of unprotected steel structures" ASCE Journal of Structural Engineering,126(12), 2000.
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Endro Sunarso is an expert in Security Management, Physical Security & Counter Terrorism. He is regularly consulted on matters pertaining to transportation security, off-shore security, critical infrastructure protection, security & threat assessments, & blast mitigation.
Besides being a Certified Protection Professional (CPP?), a Certified Identity & Access Manager (CIAM?), a Project Management Professional (PMP?) & a Certified Scrum Master (CSM?), Endro is also a Fellow of the Security Institute (FSyl) & the Institute of Strategic Risk Management (F.ISRM).
Endro has spent about 2 decades in Corporate Security (executive protection, crisis management, critical infrastructure protection, governance, business continuity, loss mitigation, due diligence, counter corporate espionage, etc). He also has more than a decade of experience in Security & Blast Consultancy work, initially in the Gulf Region & later in South East Asia.