Yet this sobering discussion might be overwrought. For one thing, it ignores a central tendency of aviation history: Time and time again, mortal hazards to air travel have been rendered harmless because of advances in technology, training, and procedures.(How else could the First-World safety record be so astoundingly close to perfect? Fifteen years ago, for example, there was great concern about thunderstorm- induced wind shear, which had caused five disasters on US airlines in just over a decade a whole host of measures since then has vastly reduced the danger; indeed, some new planes automatically execute escape maneuvers at the first sign of wind shear Even for the specific dangers we discussed, there are hopeful elements to the story In the US, both the National Transportation Safety Board and the Federal Aviation Administration have identified runway collisions as the number-one threat to US aviation. In consequence, public and private organizations are exploring with great intensity a number of innovations--technological and otherwise-that might prevent collisions at airports. If there is validity to the truism that recognizing a problem is halfway to solving it, then runway collisions are at least 50% towards oblivion On Likewise, we expressed concern that free-flight could seriously complicate the work in ways that, in themselves, might reduce the risk of mid-air collisions For a simpe o air-traffic controllers. But free-flight would also change the geometry of flight path example, consider Figure 1, which concerns one plane traveling from a to B and another E-F-B and the second, path C-E-F-D. The planes could therefore come in close ath a from C to D. Under the present prescribed routings, the first plane might follow path A proximity along segment EF. If they could instead travel straight-line paths to their destinations, they should get nowhere close to one another Figure 1 goes here In any case, our risk analysis has been incomplete in a major respect. We have described menaces that caused scant fatalities in the 1990s but which could cause more deaths in forthcoming years. We have said nothing, however, about the complementary menaces that caused air crashes in the 1990s but might be less problematic in the future setbacks on some din provements to occur, overall mortality risk could go down despite It is useful in this connection to recall the only domestic-jet disaster in the 1990s in Western Europe. The crash resulted largely from confusion about how a cockpit display measured the plane's rate of descent: as an angle with the horizon or instead in meters per second. Travelers can rest assured that many cockpit displays are far easier to understand in the aftermath of the accident, and thus that a recurrence is not likely soon Indeed, there is now strong determination to identify ambiguities and other difficulties long before they result in accidents. Data from routine operations are9 Yet this sobering discussion might be overwrought. For one thing, it ignores a central tendency of aviation history: Time and time again, mortal hazards to air travel have been rendered harmless because of advances in technology, training, and procedures. (How else could the First-World safety record be so astoundingly close to perfect?) Fifteen years ago, for example, there was great concern about thunderstorm￾induced wind shear, which had caused five disasters on US airlines in just over a decade. A whole host of measures since then has vastly reduced the danger; indeed, some new planes automatically execute escape maneuvers at the first sign of wind shear. Even for the specific dangers we discussed, there are hopeful elements to the story. In the US, both the National Transportation Safety Board and the Federal Aviation Administration have identified runway collisions as the number-one threat to US aviation. In consequence, public and private organizations are exploring with great intensity a number of innovations—technological and otherwise—that might prevent collisions at airports. If there is validity to the truism that recognizing a problem is halfway to solving it, then runway collisions are at least 50% towards oblivion. Likewise, we expressed concern that free-flight could seriously complicate the work of air-traffic controllers. But free-flight would also change the geometry of flight paths in ways that, in themselves, might reduce the risk of mid-air collisions9 . For a simple example, consider Figure 1, which concerns one plane traveling from A to B and another from C to D. Under the present prescribed routings, the first plane might follow path A￾E-F-B and the second, path C-E-F-D. The planes could therefore come in close proximity along segment EF. If they could instead travel straight-line paths to their destinations, they should get nowhere close to one another. Figure 1 goes here In any case, our risk analysis has been incomplete in a major respect. We have described menaces that caused scant fatalities in the 1990’s but which could cause more deaths in forthcoming years. We have said nothing, however, about the complementary menaces that caused air crashes in the 1990’s but might be less problematic in the future. Were enough safety improvements to occur, overall mortality risk could go down despite setbacks on some dimensions. It is useful in this connection to recall the only domestic-jet disaster in the 1990’s in Western Europe. The crash resulted largely from confusion about how a cockpit display measured the plane’s rate of descent: as an angle with the horizon or instead in meters per second. Travelers can rest assured that many cockpit displays are far easier to understand in the aftermath of the accident, and thus that a recurrence is not likely soon. Indeed, there is now strong determination to identify ambiguities and other difficulties long before they result in accidents. Data from routine operations are