1. Plane type: TWA Flight 553 was a McDonnell Douglas DC-9 aircraft which, at the time, was the latest in larger regional aircraft.
Introduced in 1965, the original DC-9 could seat up to 90 passengers.
Historically, the DC-9 was one of the most reliable aircraft. The final DC-9 was built in 1982 and was officially retired by all major commercial airlines in 2014.
Flight 553 had 21 passengers and 4 crew members onboard during its last flight.
PHOTOS: Historical pictures of TWA Flight 553 crash in Urbana
2. Crash report: TWA Flight 553 crashed outside of Urbana after colliding with a single-pilot Beechcraft aircraft, killing 26 people, including all 21 passengers and 4 crew members aboard Flight 553 and the pilot of the Beechcraft.
Prior to the crash, the radar controller in Dayton noticed and notified the TWA flight about another plane in the airspace ahead and slightly to the right. The captain of the TWA flight acknowledged the transmission four seconds later as it descended from 20,000 feet to 3,000 feet in preparation for landing.
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The NTSB report determined probable causes of the crash as the failure of the TWA crew to see and avoid the small, private plane, as well as environmental conditions and the excessive speed of the TWA flight.
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3. Aftermath: The most immediate result was a rule issued in December the year of the crash that limited the speed of aircraft flying below 10,000 feet.
The Urbana crash, along with a crash near Hendersonville, N.C., resulted in Congressional hearings on aviation safety.
In 1970, NTSB recommended new procedures that included the development of Collision Avoidance Systems for commercial aircraft and larger general aviation aircraft and the recommendation of Pilot Warning Systems development.
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