Years ago, Mr. Cox said, he descended in a Boeing 737 about Orlando International Airport when the system warned him and his co-pilot about traffic in the neighborhood. The pilots looked around at another plane, but saw nothing. Then TCAS gave an urgent instruction: “Climb.” Mr. Cox said they did that and later saw a smaller plane among them. A collision would have been catastrophic, he said.
After a series of collisions, culminating in the crash of a passenger beam and smaller aircraft in 1986 near Cerritos, California, in which 82 people were killed, the Congress instructed the Federal Aviation Administration to require TCAs on all major commercial planes. However, it is optional for military planes, and it is not clear whether the army helicopter was involved in the crash on Wednesday.
However, that crash took place at a relatively low height, where the most critical collision avoidance instructions of TCAs would have been limited by design, said Mr. Cox and other safety experts. While Jets is approaching an airport, they are probably closer together than at higher heights. As a result, the system limits the warnings that IT problems can prevent to cause confusion and to hinder safety.
The automatic dependent security broadcast
In recent years, the FAA of all passenger airlines and many other aircraft needs to use a different system, called the automatic dependent surveillance broadcast. The technology broadcasts the location, height, speed and other data from aircraft on which it is installed every second. These broadcasts can be picked up by other aircraft or equipment on the ground.
Air traffic controllers and many pilots for passenger plane rely on the information received from ADS-B systems using devices that can offer detailed maps of aircraft in an area. That information is useful when visualizing what is happening in the air, but the system usually does not indicate the kind of reports that TCAS is doing. Nevertheless, ADS-B is useful for pilots, especially when they fly in bad weather conditions or at times when visibility is low, Dr. Hassan Shahidi, the president of the non-profit Flight Safety Foundation.
