Tuesday, September 6, 2011
When Airplanes Collide: Avoiding The Unexpected
With midair collisions showing no sign of decreasing, “See and Avoid” is more important than ever
The 2010 Nall Report on aviation safety sheds light on GA midair collisions, which occur most often in good weather. In fact, 87% of them happen in day VFR conditions. They account for nearly 42% of descent/approach accidents, and most often occur near the airport. Most aircraft involved in midair collisions are engaged in recreational flying, and not on any kind of flight plan. Collisions happen mostly on weekends, with the vast majority occurring near nontowered airports and below 1,000 feet. They occur mostly from behind, or at a slight angle, not head-on.
Since 2000, the number of midair collisions annually has remained in the teens and 20s, though 2009 was an unusually quiet year with 10 of them. Compared to other accident causes, midair collisions are relatively rare, but when they do occur, they’re almost always fatal (seven out of the 10 in 2009). Given the lethality of these types of accidents, all pilots should have traffic avoidance on their minds. Today, we have two methods of avoiding midair collisions; one is the “see and avoid” concept, and the second is the Traffic Collision Avoidance System (“TCAS” for short).
“See and avoid” refers to 14 CFR Part 91.113 (b) that commands, in part, “… vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft.” The responsibility is on each pilot to see and steer clear of the other to avoid a midair collision. The problem is that this regulation gives no instructions or guidelines on how to specifically accomplish this “vigilance.”
Many of the procedures we follow today regarding traffic avoidance were enacted by the FAA in the 1950s after several high-profile midair collisions involving great fatalities. The most famous occurred in 1956 when 128 people died after a Douglas DC-7 operating as United Airlines flight 718 struck a gleaming TWA Lockheed Constellation named Star of the Seine over the Grand Canyon, shearing off the Connie’s tail and the DC-7’s wing, sending them both spiraling into the desert below. The public demanded modernization of the ATC system and greater safety oversight, resulting in sweeping changes.
The 1978 collision of a Boeing 727 and a Cessna 172 over San Diego, and the 1986 crash of a DC-9 after it hit a single-engine piper over Cerritos, Calif., galvanized the public further, and pressured the industry to enhance safety and modernize the air-traffic-control system, resulting in the 1986 Airport and Airway Safety Expansion Act. These changes paved the way for the ATC system and procedures we fly with today. For 25 years, we’ve been using mostly visual techniques, which rely heavily on our own physiology.
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