Originally Posted by airmen, referring to TCAS
they saved already my live once at least!
There is a phenomenon here worth thinking about. When I voiced some of my concerns about TCAS on a pilot's mailing list some years ago, I was deluged with affidavits from pilots who claimed that TCAS had saved their lives. If all of these claims had been true, that would have amounted to some 20 or so midair collisions in a sample of a few hundred pilots (the members of the mailing list) over the course of, say, ten years. Let's assume 10 "life-savers", that is, otherwise-midairs, for 500 pilots in 10 years. That is an average of one "midair collision" per 500 pilots per year.
There are about 15,000 aircraft from Airbus, Boeing, MD, Lockheed still in service (calculated from figures in Flight International, 24-30 October 2006). So that's not counting the "commuters", or the Tupolevs. Those aircraft are in service, let's say, 14 hours per day, for a total of 210,000 hours per day, or 5,880,000 hours in 28 days. Duty rosters take 100 flight hours for a pilot in 28 days to be relatively high, but let's use this figure, since it will lead to a conservative estimate. It means there are about 59,000 captains needed to fly those 5,900,000 hours every 28 days. With one "midair" per 500 captains per year, and accounting for the fact that it takes 2 captains to have a "midair", we come to a figure of 59 "midairs" per year.
Compare this with actual midairs amongst airline transport aircraft. 1959 Grand Canyon, 1976 Zagreb, 1978 San Diego, 1985 Cerritos. And then, since the advent of TCAS, 1995 Namibia (involving a German military machine which I do not believe was TCAS-equipped), 1996 New Delhi, 2002 Überlingen and 2006 Amazonas. That is 4 before the advent of TCAS (mandated 1991, I believe) and 4 since (16 years).
Those crediting TCAS with all these "saves" need to explain why, before the advent of TCAS, there were a statistically-negligible number of collisions in the history of airline flying, and upon the introduction of TCAS there are suddenly almost 60 per year. Even considering the growth of air travel, that is an unbelievable jump.
The obvious answer is, of course, that most of those "saves" would not have resulted in collisions, despite what their pilots thought or think.
Consider the following, as a thought experiment. Up to the Congressional mandate for TCAS, there were three collisions involving airliners in the U.S.: 1959 Grand Canyon, 1978 San Diego and 1985 Cerritos. Suppose TCAS initiated RAs, not for 2 TCAS-equipped aircraft, but only when one had TCAS and the other only Mode C. That would have satisfied the issue worrying the Congresspeople, namely incursions of GA aircraft into zones of intensive airline operations, and it would have saved one of the midairs since (Überlingen). The other three midairs in the TCAS era occurred to non-TCAS-using aircraft.
Let us compare TCAS with another highly-lauded system for avoiding accidents, GPWS/EGPWS. Also a system introduced primarily by one manufacturer (again Honeywell). And in contrast to TCAS addressing a real, continuing problem which still leads to many aircraft losses per year, namely CFIT. EGPWS is essentially a private development (stemming from the work of Don Bateman and colleagues).
It is interesting in this regard to notice how TCAS is self-advertising and EGPWS not. A pilot can say "TCAS saved me" without it reflecting on himher self, but rather on some air traffic controller establishment somewhere. No pilot can say "EGPWS saved me" without someone else asking how heshe lost situational awareness in the first place (with rare exceptions in which it is clear how, such as with British Mediterranean at Addis Ababa).
So the statistics were never there to say "TCAS is a good thing", and it is self-advertising, through pilot "save" stories. But there are smart people in aerospace who, no matter whether they think TCAS is a net gain or a net problem, are able to look at the facts and the situation just the same as I am now. Airline CEOs, for example. So the question is: why are collision avoidance mechanisms still being promoted, researched and supported to such a great extent?
I think there are two reasons. One is that they are one attempt at a solution to a problem which no one knows yet how to assess accurately, namely the avoidance of midair collisions, and no one is willing to risk misjudging (underestimating) the likelihood of those. The other reason is that effective on-board systems make collision avoidance a contract between the two (or more) aircraft involved, which transfers the costs of collision avoidance away from large ATC organisations. Since the airlines and their passengers ultimately fund these organisations, one could see the financial benefits to airlines of bringing this function in-house (after the initial cost of installing the equipment, which has n any case been mandated). Add to this that collision avoidance is one of the brakes on moving to "free flight" (self-routing IFR at high altitudes), which airlines believe would bring them great cost reductions, and one can see that TCAS+free flight is a politically sellable package which could reduce the costs of air travel even further. Without some ATC-independent collision-avoidance system regarded as effective, this move could not happen, and TCAS is the only technology in town.
PBL