Investigation Summary
Flight 175 departed Boston at 08:14 EDT. Approximately 28 minutes into the flight, hijackers led by Marwan al-Shehhi breached the cockpit, killed the pilots, and took control of the aircraft. Unlike the hijackers of Flight 11, the Flight 175 team did not disable the transponder, allowing air traffic controllers to track the aircraft's erratic path and descent. During the hijacking, passengers and crew members made phone calls to family and authorities, reporting the deaths of the pilots and the dire situation in the cabin. The aircraft narrowly avoided two mid-air collisions with Delta Flight 2315 and Midwest Express Flight 7 before being steered into the South Tower at 09:03 EDT, traveling at approximately 510 knots (590 mph).
Final Conclusions
The 9/11 Commission Report concluded the crash was a coordinated terrorist act. The structural damage from the high-speed impact, combined with the intense heat from the ignition of approximately 10,000 gallons of jet fuel, compromised the South Tower's steel structure, leading to its total collapse at 09:59 EDT.
Video Analysis
No video analysis linked for this case file yet.
Systems & Failure Modes
Transponder
The device remained on, allowing ATC to track the aircraft's position and altitude throughout the hijacking.
Cockpit Door
Standard non-reinforced doors of the era allowed hijackers to force entry using knives and threats.
Interesting Facts
- 01It is the second-deadliest plane crash in aviation history.
- 02The aircraft struck the South Tower at a speed of approximately 590 mph (950 km/h).
- 03The impact was the only one of the four 9/11 attacks to be broadcast live on television.
- 04The transponder remained active throughout the hijacking, unlike American Airlines Flight 11.
- 05The aircraft was carrying approximately 10,000 gallons of jet fuel at the time of impact.
Safety Actions & Advisories
Reinforced Cockpit Doors
The FAA mandated the installation of hardened, bulletproof cockpit doors on all commercial airliners to prevent unauthorized entry.
TSA Creation
The Aviation and Transportation Security Act was passed, creating the TSA and federalizing airport screening.
Flight Deck Officer Program
Legislation was enacted to allow trained pilots to carry firearms in the cockpit for self-defense.