Hull Losses per 100,000 Departures This popular performance measure(used by boeing among others)defines a serious accident as one in which the aircraft is sufficiently damaged that it cannot fly again (i.e a hull loss ) In(wisely)using departures in the denominator, the ratio gives us the probability that a given flight will end in the aircraft s immobilization There is, however, only a limited connection between the fate of the aircraft and the fate of the passengers. There are some events(e.g. clear air turbulence) that can cause deaths while doing little damage to the airframe. But more important is the wide variation in outcomes across hull losses, as is illustrated by two such losses near Los Angeles in early 2000 Southwest airlines, boeing 737, Burbank, California Passengers Aboard: 137 Passengers Killed Alaska airlines. MD-80. off Malibu. California Passengers aboard: 83 Passengers Killed There have been many instances in which a plane landed with substantial damage but, because of superb emergency procedures, all passengers were evacuated before the plar was engulfed in flames and became a hull loss. Such a rescue is irrelevant to the hull- loss ratio, but it hardly seems so to an assessment about the mortality risk of air travel Death risk per Flight Discussions such as those above lead to a conclusion: To evaluate passenger death risk, the most fruitful approach might be to estimate that quantity directly rather than deal with proxy measures. A useful statistic arises if one considers an appropriate set of past flights(e.g. UK domestic jet flights over 1990-99)and asks the question: If a passenger had chosen one such flight completely at random, what is the probability Q that he would have perished in an accident? (By flight, we mean a nonstop trip from one point to another. )Q is the product of the chance that the flight selected suffers some passenger deaths and the conditional probability that the passenger is among the victims given that deaths occur. If the flights are numbered 1 to N, then Q follows the rule Q=∑xN(1) Here the summation is from 1 to N, and xi is the fraction of passengers on flight i who do not survive it. ( For the overwhelming majority of flights, xI=0; for a flight in which 20% of the passengers are killed, xi=0.2.)3 Hull Losses per 100,000 Departures This popular performance measure (used by Boeing among others) defines a serious accident as one in which the aircraft is sufficiently damaged that it cannot fly again (i.e. is a hull loss). In (wisely) using departures in the denominator, the ratio gives us the probability that a given flight will end in the aircraft’s immobilization. There is, however, only a limited connection between the fate of the aircraft and the fate of the passengers. There are some events (e.g. clear air turbulence) that can cause deaths while doing little damage to the airframe. But more important is the wide variation in outcomes across hull losses, as is illustrated by two such losses near Los Angeles in early 2000: Southwest Airlines, Boeing 737, Burbank, California Passengers Aboard: 137 Passengers Killed: 0 Alaska Airlines, MD-80, off Malibu, California Passengers Aboard: 83 Passengers Killed: 83 There have been many instances in which a plane landed with substantial damage but, because of superb emergency procedures, all passengers were evacuated before the plane was engulfed in flames and became a hull loss. Such a rescue is irrelevant to the hull￾loss ratio, but it hardly seems so to an assessment about the mortality risk of air travel. Death Risk per Flight Discussions such as those above lead to a conclusion: To evaluate passenger death risk, the most fruitful approach might be to estimate that quantity directly rather than deal with proxy measures. A useful statistic arises if one considers an appropriate set of past flights (e.g. UK domestic jet flights over 1990-99) and asks the question: If a passenger had chosen one such flight completely at random, what is the probability Q that he would have perished in an accident? (By flight, we mean a nonstop trip from one point to another.) Q is the product of the chance that the flight selected suffers some passenger deaths and the conditional probability that the passenger is among the victims, given that deaths occur. If the flights are numbered 1 to N, then Q follows the rule: Q =
xi/N (1) Here the summation is from 1 to N, and xi is the fraction of passengers on flight i who do not survive it. (For the overwhelming majority of flights, xI = 0; for a flight in which 20% of the passengers are killed, xi = 0.2.)