NAS - UNITED STATES BEST PRACTICE
We found the following extracts relating to TCAS on an open website in the United States of America. We are not aware of any published standards within the airspace design world that would contemplate allowing aircraft to get as close as 501 feet horizontally and 201 feet vertically as a matter of normal operational or system design. TCAS is a last line of defence – not a design aid.
Center for Advanced Aviation System Development (CAASD) at the MITRE Corporation (
www.caasd.org/proj/tcas/)
“….The Traffic Alert and Collision Avoidance System, or TCAS, is an instrument integrated into other systems in an aircraft cockpit. It consists of hardware and software that together provide a set of electronic eyes so the pilot can "see" the traffic situation in the vicinity of the aircraft. Part of the TCAS capability is a display showing the pilot the relative positions and velocities of aircraft up to 40 miles away. The instrument sounds an alarm when it determines that another aircraft will pass too closely to the subject aircraft. TCAS PROVIDES A BACKUP TO THE AIR TRAFFIC CONTROL SYSTEM’S REGULAR SEPARATION PROCESSES…..”
“…..From its inception, TCAS has dramatically improved pilots' chances of successfully averting the threat of a mid-air collision. Pilots have come to rely on TCAS to give them the crucial data to avoid collisions. AS THEIR LAST LINE OF DEFENSE, TCAS gives pilots the edge needed to ensure that their crew and passengers have the safest flight possible……”
“……As CAASD's Dr. Andrew Zeitlin points out, "Because of the pilots' normal workload, WE DON'T EXPECT THEM TO SPEND ALL OF THEIR TIME LOOKING AT THE SCREEN. It's there when needed, but more important, it speaks up and advises them as they need to make a maneuver to avoid a collision…."
“……..On August 31, 1986, while TCAS was still in development, a collision occurred over Cerritos, California, involving an Aeromexico DC-9 and a small Piper aircraft carrying a family of three. The DC-9 was descending toward Los Angeles International Airport in clear skies, flying at 6,500 feet. The Piper hit the DC-9's tail, causing both aircraft to plummet from the sky…….The accident resulted in the deaths of all 67 people aboard the two planes, as well as 15 people on the ground. In the aftermath of this accident, Congress passed a law requiring the FAA to mandate the use of TCAS. By 1993, all carrier aircraft operating within U.S. airspace with more than 30 passenger seats were equipped with TCAS II. Aircraft with 10 to 30 seats were required to employ TCAS I…….”
“…..Based on the likelihood of incursions into a protected zone around aircraft with a radius of 500 feet and a height of 200 feet -- defined as Critical Near Mid-Air Collisions (NMACs) -- McLaughlin concluded that "TCAS should reduce NMAC probability by at least 90 to 98 percent," depending on whether one or both aircraft in an encounter are equipped with TCAS……”
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