787 cockpit showing TCAS on the Multi-Function Display – Photo: AirlineReporter
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, â€œbig sky theoryâ€ 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.
American’s new Airbus A321 in flight – Photo: Eric Dunetz
A while back, I viewed a tweet about an Air Traffic Control (ATC) conversation in New York, where JFK ATC got a little bit confused about an aircraft type. Â American Airlines (AA) Flight 32 was incorrectly called a â€œheavyâ€ aircraft, likely because for so long that flight was operated by a Boeing 767-200. Â Ever since AA debuted their new Airbus A321 on the LAX-JFK route, this flight no longer needs to use the “heavy” designation, but that didn’t stop the ATC staff from using old habits. Â It made me question, at what point does an aircraft become â€œheavyâ€?
When aircraft are approaching or departing an airport, they must use special designations to help avoid the wake turbulence from other aircraft. Â Larger aircraft, like a 767 or an A340, need more space behind them to prevent the wake vortices generated by the larger wing span from impacting other aircraft. Â The bigger the aircraft, the longer the distance.
The dangers are real, as all over the world a number of incidents have occurred that can be attributed to a wake vortex. Â From the crash of an XB-70 in the 60’s to some involving more modern aircraft in the last 10 years (including an A380 in Sydney).