Communication during the September 11 attacks

AT&T
Company type	Public
Industry	Telecommunications
Key people	Alexa Graf (spokesperson)
Products	Landline and mobile phone services

Communication challenges had a major impact on the response efforts during the September 11 attacks in 2001. Many communication systems were either destroyed, overwhelmed, or failed to operate as required.

Attackers

The perpetrators of the September 11, 2001 terrorist attacks mainly relied on in-person meetings for coordination, minimizing their use of electronic communications. This deliberate "radio silence" strategy helped them evade detection.

Federal government

According to the 9/11 Commission staff, multiple federal communication breakdowns occurred during and following the attacks. A significant issue arose during an "Air Threat Conference Call" initiated by the National Military Command Center (NMCC) after two aircraft struck the World Trade Center, but prior to the assault on The Pentagon. Crucially, this call did not include the Federal Aviation Administration (FAA) air traffic control command center, which possessed vital hijacking information.

The report explains:

Efforts to connect with the FAA were hindered by technical difficulties and challenges in obtaining secure contact numbers. NORAD requested FAA involvement on three occasions before 10:03 a.m. to receive hijacking updates; however, FAA participation only began at 10:17 a.m. The FAA representative present lacked hijacking experience, access to key decision makers, and critical intelligence available to senior FAA officials. There was no indication that NORAD’s senior commanders engaged with FAA headquarters to improve situational awareness or coordinate a unified response. Instead, lower-level personnel acted independently—the FAA’s Boston Center bypassed its chain of command to communicate directly with the NEADS. Meanwhile, top Defense Department officials depended on the NMCC’s Air Threat Conference, where FAA involvement was minimal.^[1]^{: p. 21}

First responders

Following the 1993 World Trade Center bombing, radio repeaters were installed within the tower complex to support communication for the New York City Fire Department. However, fire chiefs stationed at their command post in the North Tower lobby mistakenly believed these repeaters were non-functional and therefore did not utilize them, although some firefighters did. When police issued evacuation orders due to risks of tower collapse, fire officials were not informed. Additionally, fire commanders on site initially underestimated the severity when the South Tower fell.

Despite establishing an Office of Emergency Management (OEM) in 1996 to enhance interagency coordination, communication between the New York City Police Department and fire department command units remained limited. OEM’s emergency operations center, located on the 23rd floor of 7 World Trade Center, was evacuated after fires caused by debris ultimately led to its destruction at 5 p.m., further impairing coordination efforts.

In the weeks after the attacks, volunteer amateur radio operators provided vital emergency communication support in Lower Manhattan and at the Pentagon.

Victims

During and following the attacks, cell phones and onboard credit card phones were crucial for passengers who used them to contact family members and authorities. Prominent individuals who made such calls include Sandra Bradshaw, Todd Beamer, Tom Burnett, Mark Bingham, Jeremy Glick, and Barbara Olson. Passengers aboard United Airlines Flight 93 utilized these communications to evaluate their situation and organize a counterattack, which resulted in the plane crashing before reaching its intended destination—likely preventing damage to important government facilities.

The 9/11 Commission Report documented that thirteen passengers from Flight 93 placed over thirty calls to relatives and emergency responders, supported by multiple cell towers. Calls were also recorded from passengers on American Airlines Flight 11, Flight 175, and Flight 77; among these were two calls from flight attendants Betty Ong (Flight 11) and CeeCee Lyles (Flight 93).

AT&T spokesperson Alexa Graf described it as almost coincidental that many calls successfully connected. Specialists confirmed that cell phones could function during various phases of flight, with success rates differing during takeoff and landing.

After impact with the towers, many individuals inside made final phone calls to loved ones or emergency services. More than nine hours of 9-1-1 call recordings were later released following requests from The New York Times and families of victims. In 2001, mobile phones in the U.S. generally lacked camera features that became widespread later in that decade.

General public

Following the attacks, cell phone networks throughout New York City and the surrounding Tri-State region experienced an immediate and significant overload, with call volumes surging to twice their usual levels. This surge caused widespread failure across East Coast cellular systems. Verizon's landline services in downtown Manhattan were disrupted for several weeks due to severed subscriber cables and the closure of the 140 West Street switching center. Additionally, trunk line cuts diminished communication capacity between Brooklyn and Manhattan.

Cellular network difficulties continued until September 14, 2001, when 36 mobile cell towers on wheels (COWs) were deployed in Lower Manhattan to assist FEMA and ensure vital telephone connectivity for emergency responders engaged in rescue and recovery operations.

The collapse of the North Tower (One World Trade Center) resulted in the loss of transmission towers used by three major television networks, severely limiting their ability to broadcast. WNYC’s FM transmitter was destroyed, but the station maintained its AM broadcasts and utilized NPR’s New York offices to continue programming.

WPIX’s satellite feed froze on the final image transmitted from the WTC mast—a distant view of the burning towers—which remained visible across North America until alternative transmission methods were established. Both WCBS-TV channel 2 and WXTV-TV channel 41 continued broadcasting; WCBS operated a full-power backup transmitter located at the Empire State Building. On that day, WCBS was also simulcast nationally on Viacom’s VH1 network and provided airtime to stations that had lost their transmitters until they could restore service.

Due to comprehensive media coverage, the Emergency Alert System was not activated. In response to the crisis, AT&T waived charges for domestic calls made from New York City area codes (212, 718, 917, 646, 347) during the days immediately following September 11.

Radio communications

Radio communications during the September 11 attacks played a vital role in managing coordination among NYPD, FDNY, Port Authority Police, and emergency medical teams.

Although improvements had been made after the 1993 World Trade Center bombing, investigations revealed that communication systems still lacked full interoperability. Infrastructure damage and system failures occurred during the attacks, while simultaneous transmissions overwhelmed channels between command personnel and field units.

Background

The sequence of key events is as follows:

08:46 hrs.: American Airlines Flight 11 strikes the North Tower (1 World Trade Center).
09:03 hrs.: United Airlines Flight 175 hits the South Tower (2 World Trade Center).
09:58 hrs.: The South Tower collapses, 55 minutes post-impact.
10:28 hrs.: The North Tower collapses, 102 minutes after impact.

The National Commission characterized the attack's magnitude as unprecedented. Within seventeen minutes—from 8:46 to 9:03 am—over a thousand police officers, firefighters, and EMS personnel arrived at the scene. Some estimates indicate that between 2,000 and 3,000 responders participated in rescue efforts—a scale rarely seen by most agencies.

Significant confusion marked the response. The National Institute of Standards and Technology (NIST) determined that commanders lacked sufficient situational awareness and that interagency communication was inadequate. For instance, while NYPD’s 9-1-1 center advised callers to remain in place according to fire management protocols, responders on location instructed evacuation. The 9/11 Commission noted that NYPD and FDNY dispatch centers were inundated with unprecedented call volumes and were not fully integrated with field operations.

Challenges with radio communication included coverage gaps within buildings, congested channels, and failures of internal systems. Many off-duty personnel self-deployed without radios, limiting centralized command control. Although spare radios were available in caches, insufficient quantities and configuration issues hampered their effective deployment.

NIST reported that radio traffic initially peaked at five times normal levels early in the incident before settling at approximately three times normal volume. Recordings of FDNY dispatches reveal delays in responding to calls; numerous emergency calls were either disconnected or met with busy signals. This communication overload adversely affected coordination during critical phases of the emergency response.

Voice radio communication systems

According to NIST findings, approximately one-third of radio transmissions during the peak communication period were either incomplete or difficult to understand. Visual evidence from documentary footage reveals that tactical channels frequently became congested, with multiple simultaneous conversations occurring on certain frequencies.

Despite these challenges, the radio networks at the World Trade Center site generally enabled effective communication among users. The 2002 documentary 9/11 by Gedeon and Jules Naudet features handheld radio audio recorded during the event, capturing exchanges from the North Tower lobby command post. Furthermore, 26 Red Book CDs containing FDNY transmissions related to initial dispatches and tower failures were analyzed, alongside oral histories from fire personnel debriefed after the incident. These materials confirm that although technical difficulties were present, fire chiefs and units frequently maintained successful communication.

NYPD and Port Authority Police Department radio systems in 2001

In 2001, the New York Police Department utilized Ultra High Frequency (UHF) radios operating across 35 citywide radio zones. Most handheld devices supported a minimum of 20 channels, facilitating communication throughout the city. UHF signals offer superior penetration through buildings compared to the Very High Frequency (VHF) band employed by FDNY radios but have a shorter range over open spaces. The Commission's report did not identify any technical shortcomings in the NYPD system.

The Port Authority Police Department (PAPD) relied primarily on low-power UHF systems typically confined to individual locations, with the exception of a single Port Authority-wide channel. It remains uncertain whether these channels were interstitial frequencies limited to 2 watts output or leaky cable systems designed for indoor use. The report highlighted seven site-specific PAPD channels; radios programmed for one location generally could not operate at others, and not all radios contained every channel. This restriction has since been resolved, with all units now capable of functioning across all sites.

Fire Department and EMS dispatch channels

Recordings from Citywide, Brooklyn, and Manhattan Fire and Emergency Medical Services channels were examined, showing overall reliable system performance. However, the audio coupling point for the Manhattan Fire logging recorder diminished clarity of the dispatcher’s voice. Among these recordings, an anonymous fire dispatcher known as Dispatcher 416 is prominently featured.

In 2001, FDNY utilized five repeater channels: one each dedicated to Manhattan, Brooklyn, Queens; Bronx and Staten Island shared a frequency differentiated by distinct Private Line (PL) tones; plus a citywide channel. Additionally, FDNY radios included five simplex channels for direct communication.

Observations from that year revealed that the citywide EMS channel frequently experienced voting due to signal noise and interference sources such as frequency-shift keying (FSK) paging signals or intermittent microwave radio links causing audio disruptions. Despite these dropouts, dispatchers generally maintained comprehension of radio communications.

Port Authority fire repeater system (Repeater 7)

The Port Authority’s repeater system—referred to as Port Authority Channel 30—was intended to enhance communications within the towers but failed to perform as expected on September 11. Installed in 1994 following the 1993 WTC bombing at the Port Authority police desk in WTC Building 5, news reports indicated that this system was turned off due to technical issues. The Commission report noted that disabling it was routine because it interfered with other Fire Department radios. A Fire Department member suggested that aircraft impact caused its malfunction. Evidence points to the remote control console in the North Tower lobby command being nonoperational while the repeater itself remained functional.

Analysis of logging recorder audio reveals early attempts from the North Tower lobby command post to operate a remote control unit for transmitting on this channel, with multiple unsuccessful tries cycling through all eight function tones. A statement such as "... the wireline isn't working," reflects perceived problems. The audio confirms that the transmission path was live; however, it is uncertain if function tones successfully activated the transmitter.

Some personnel misinterpreted remote control unit failure as a complete channel outage; nevertheless, other fire units continued using the repeater inside the South Tower until its collapse. The Commission report suggests potential causes for lobby command issues include technical faults, volume control misadjustments, or failure to press enable buttons—highlighting user interface complexities. Effective backup systems should be continuously active, user-friendly, and routinely tested.

Audio recordings also captured transmissions originating from an external agency—likely based in New Jersey—via a repeater on Port Authority Repeater 7’s frequency. This unintended interference may have resulted from leaving the repeater continuously enabled. The external agency’s traffic appeared on the same input frequency and CTCSS tone as Repeater 7. Accidental button presses may have temporarily placed the base station into monitor mode allowing outside transmissions; subsequent function tones would have restored normal operation.

Fire Department Communication System

According to an oral history interview, UHF radios provided by the Port Authority were commonly utilized inside the World Trade Center (WTC) during emergencies. Firefighters arriving at the site received these radios, which reportedly "functioned throughout," implying that FDNY radios had recognized coverage limitations within the towers. The 9-11 Commission characterized FDNY radios as having "underperformed" during the incident. While FDNY radios operated on VHF frequencies (150 MHz), the Port Authority radios employed UHF bands, which offer superior penetration in steel-structured buildings due to their shorter wavelengths. Since the Port Authority system was designed specifically for the WTC site, it delivered better coverage than the broader citywide FDNY network.

At least four distinct radio channels were active at the WTC:

Channel 5 (potentially "Command 5") served Command functions in both Towers.
Tactical 1 was designated for Operations in the North Tower.
Tactical 3 handled Operations in the South Tower.
Repeater 7 (Port Authority Repeater) was used by certain units operating in the North Tower.

An officer referenced a "Command 3" channel related to the North Tower; however, it remains uncertain whether this referred to Tactical 3 or a separate frequency.

Video footage depicts FDNY personnel using radios within the WTC lobby with seemingly adequate reception, corroborated by oral testimonies that confirm partial radio effectiveness. Nonetheless, handheld radios can experience signal overload when multiple devices transmit simultaneously nearby, resulting in weaker transmissions being lost. Despite appearances, FDNY radios—originally designed in 1976—were susceptible to interference from modern digital cellular repeaters operating at high power levels in lower Manhattan, generating a challenging radio frequency environment that impaired their performance.

An audio review of 26 FDNY recordings shows transmissions were mostly clear and understandable, with dispatchers responding appropriately, indicating a generally reliable radio infrastructure. Coverage issues likely existed but might have been alleviated if higher-power Command Post radios had been deployed. Some transmissions probably failed to reach receivers due to interference. The cellular network was operating near maximum capacity on that day, creating a "perfect storm" of radio frequency interference beyond what the aging FDNY equipment could effectively manage.

Recorded audio reveals heavily used channels with overlapping conversations on Tactical 1, reflecting typical congestion during major incidents when radio resources are heavily taxed. NIST found that approximately one-third of fire department transmissions were either incomplete or unintelligible. Some personnel mistakenly selected incorrect channels—such as attempting to contact dispatch on Repeater 7—possibly due to confusion caused by smoke or darkness preventing clear visibility of radio controls.

FDNY operated a communications van designated as "Field Comm." A backup van was deployed because the primary unit was out of commission; regrettably, this backup vehicle was destroyed during the event, resulting in loss of tactical channel audio recordings.

FDNY Radio Programming

A significant challenge with FDNY fire communication systems involved recurring unit ID data bursts transmitted at the end of each transmission. These bursts assist in identifying and locating firefighters who may be in distress and automatically display unit IDs at dispatch consoles—relieving dispatchers from manual entry—but they also produce audible interruptions. Radios are programmed to send unit IDs on tactical channels; however, disabling encoders where not needed can save valuable air time equivalent to two to three syllables per push-to-talk activation.

Certain vehicle radios likely utilized "status buttons" that sent brief data bursts to update dispatch on unit status. Although these cause momentary voice interruptions, they reduce overall channel usage compared to verbal status reports like "Engine fifty on scene."

Tactical 1

Tactical 1 functioned as the main simplex communication channel within the North Tower but was limited in range, extending only as high as approximately the 30th floor. Some personnel opted to switch to Repeater 7 for enhanced coverage; however, this channel was often underutilized compared to the heavily burdened Tactical 1 frequency. Audio evidence confirms that Tactical 1 experienced significant congestion while Repeater 7 remained relatively idle.

The 9-11 Commission documented the creation of a portable repeater system known as "the post," intended to boost weak radio signals at major incidents by being positioned near the scene to improve communication reach.

Command channel

The command channel utilized by officers was identified in records as Channel 5 or Command 5. It reportedly featured a repeater, though it remains uncertain whether this was a citywide system, installed in the Field Comm van, or housed within a battalion chief’s vehicle. Unfortunately, recordings from this channel were lost when the Field Comm van was destroyed. Nonetheless, both documentary sources and oral histories confirm that the channel was effectively employed.

Interoperability

The federal 9/11 Commission Report underscored significant shortcomings in communication capabilities among police, fire, and EMS agencies during the WTC event. The report and subsequent media discussions highlighted the lack of direct radio communication across these departments—police units could not contact fire personnel, nor could ambulances communicate directly with police. Commission member Lee Hamilton stressed this critical deficiency in multiple interviews related to a 2006 analysis of the WTC incident.

Aviation assets

Hamilton noted that during the event, the Police Department helicopter was unable to alert Fire Department units about the imminent collapse of the towers due to communication obstacles. According to the NIST report, this helicopter might have been able to provide several minutes’ advance warning—potentially sufficient for evacuating some of the lower floors. Although this warning was transmitted on at least one police radio channel, there is no proof it was further disseminated.

FDNY operates at least two communications vans; one was deployed at the WTC site. The primary FDNY van had the capability to communicate with NYPD helicopters; however, on September 11, 2001, only the secondary van—which lacked this functionality—was in operation.

Generally speaking, many U.S. emergency helicopters are equipped with radios capable of accessing multiple conventional two-way radio systems if frequencies and signaling tones are programmed in advance for rapid use. The Commission report did not indicate that NYPD helicopters had such multi-channel access.

Cross-department

Introducing cross-agency communication presents considerable challenges in training and incident command, adding layers of complexity when managing large-scale emergencies. Command and safety oversight can be compromised if firefighters switch to EMS channels and become unreachable, potentially prompting unnecessary rescue operations. Likewise, patient care may be hindered if EMS dispatchers cannot contact ambulances on fire department frequencies. New York City Police Commissioner Raymond Kelly stated on the Charlie Rose program that existing radio systems functioned adequately during the WTC event and that the interoperability recommended by the 9-11 Commission was not essential.

Necessity for NYPD/FDNY Interdepartmental Connectivity?

Challenges in communication between departments existed well before the World Trade Center tragedy. During the Oklahoma City bombing, firefighters were alerted to evacuate due to a potential second explosive device, but this crucial information failed to reach police and EMS personnel because of communication breakdowns.

In the aftermath of Hurricane Katrina, a Louisiana wildlife sergeant publicly emphasized on national television the inability to establish contact with other agencies involved in recovery operations, highlighting severe systemic failures as a major concern.

Interoperability difficulties extend beyond technological limitations and are often influenced by cultural factors. For instance, during a manhunt, officers from three distinct police departments did not coordinate on a unified radio channel due to misconceptions regarding radio compatibility, indicating gaps in training or technical understanding. Reports indicate this situation has improved over time.

In another case, despite comprehensive interoperability training, certain firefighting staff preferred to remain on their dedicated channels. This behavior illustrates that interoperability obstacles arise not only from technology but also from operational habits. Modifications to the ICS framework or command post arrangements might produce better results than solely upgrading equipment. Even when frameworks are in place, interoperability issues can continue.

Is ICS a Component of the Solution?

The Incident Command System (ICS) functions by having units communicate through their designated representatives at the command post or division level, who then coordinate requests across various departments. For example, when a fire unit requires paramedic ambulance support, the request is passed to their fire officer who incorporates it into the overall operational picture and liaises with EMS. Maintaining awareness of the evolving situation is vital for effective command during large-scale events, as circumventing incident commanders can compromise the command hierarchy.

Trunked Networks, Commercial Radios, and Interagency Netting

Certain contemporary trunked radio systems provide dynamic regrouping, which allows dispatchers to assemble units from multiple agencies into a shared talk group during emergencies. However, this capability depends on proximity to infrastructure and compatible systems—conditions rarely met across different agencies. An informal survey involving three agencies revealed minimal knowledge or utilization of this feature, implying limited practical benefit without consistent training and exercise.

Numerous agencies enhance their communication capabilities with commercial two-way radios such as Nextel; however, these systems do not match the coverage or reliability standards of public safety trunked networks. They are appropriate for routine communications but unsuitable for critical life-threatening situations. Even trunked networks can suffer from congestion during major disasters due to limited channel availability.

NYPD Chief Charles Dowd reportedly regarded trunking as unnecessary since NYPD operates an extensive conventional repeater network with ample UHF channels. With sufficient channel capacity, trunking—and its associated busy signals—becomes redundant; users simply wait for their turn to transmit, ensuring clear communication without relying on complex technologies.

Mobile data terminals

Every 911 ambulance and FDNY vehicle is outfitted with mobile data terminals (MDTs) that connect directly to the computer-aided dispatch (CAD) system. These devices provide real-time job information and unit assignments, enhancing communication efficiency and alleviating congestion on voice radio channels.

During the events of September 11, some MDTs experienced operational failures. At 09:11:14, Division 3 reported that its terminal displayed incomplete unit rosters, compelling the Chief to manually document unit details. This manual process occupied the Manhattan Fire radio channel for nearly one minute, causing delays in other transmissions. Comparable malfunctions were observed in several instances.

The exact reasons behind these MDT disruptions have not been definitively identified but are thought to involve factors such as:

Radio network saturation caused by an exceptionally high volume of data requests.
Data transmission bottlenecks occurring between radio modems and the CAD system backend.
Elevated retransmission rates of data packets due to weak signal strength and error correction mechanisms.
Interference arising between voice and data radio systems under heavy operational loads.

MDTs play a vital role in minimizing dispatcher workload and reducing voice channel traffic. Nonetheless, during periods of intense call volume, data system failures can overwhelm both dispatch functions and communication networks, underscoring the necessity for resilient and high-capacity systems.

New York City Council investigation

Council member Eric Gioia of New York City proposed an initiative to examine the FDNY’s radio communication breakdowns that occurred during the September 11 attacks.

↑ Cite error: Invalid <ref> tag; no text was provided for refs named Improvising a Homeland Defense

[Improvising_a_Homeland_Defense-1] Cite error: Invalid <ref> tag; no text was provided for refs named Improvising a Homeland Defense

[1]