A few months ago, a near-collision between two Boeing 757s off the coast of Hawaii was in the headlines. This event was particularly noteworthy because of the emergency descent made by United Airlines Flight 1205, which descended over 600 feet in a matter of seconds, terrifying passengers and sending items flying in the cabin. The pilots on the United flight were alerted to the oncoming traffic, and took action based on their Traffic Collision Avoidance System (TCAS).
History of mid-air incidents and TCAS mandate
Although TCAS systems are a (relatively) recent development in airline cockpits, the need for such systems was recognized long ago. On June 30,1956, a mid-air collision occurred at 20,000 feet between a United Airlines DC-7 and a TWA Lockheed 1049 over the Grand Canyon in northern Arizona. This incident, which resulted in 128 fatalities, served as a wake-up call for the aviation industry. Prior to the collision, “big sky theory” was the prevailing notion – that two aircraft flying in three-dimensional space were very unlikely to collide. Following this incident (which also led to the creation of the FAA), research began on developing collision avoidance systems.