I beg to differ about using statistics to make decisions about risk of dying, but agree to the conceptual and logistical difficulties. The reason statistics work with human behaviors like flying and crashing is that human behavior is statistically extremely lawful. We all tell ourselves that WE won't do something wrong, and can point out certain things that we probably WON'T do wrong, but there are so many ways to screw up that we can be 100% sure that we will NOT eliminate them all.



Many variables are useful predictors of aviation risk. Here's one of my favorite (and more depressing) ones given by Richard Collins in the Dec Flying issue: every year, about 1 out of 500 registered GA aircraft is involved in a fatal accident, including crashes and ground accidents involving propellers (1 in 442 to be "exact"). Collins compares this statistic to the corresponding one for automobiles to show that it is many times larger for planes - which we spend much less time in than our cars. Another number Collins gives shows that almost 1 out of 1000 current instrument pilots dies each year in a botched instrument flight in IMC (1 in 1281 to be "exact"). These numbers speak for themselves. Collins finds the flying risk from 5 to 21 times greater than the driving risk, depending on how risk is defined and measured, overall.



GA planes will never be as safe as cars due to the much greater energy levels in flying as compared to driving, but that doesn't mean that GA has to remain as marginally safe as it really is now. The solution is for plane and equipment makers to design out some of the human error, like using sensors, avionics, and autopilots to prevent pilots from trying to take off loaded with ice (which SEEMS to have just happened in a high profile case), or controlled flight into terrain on an instrument approach (ditto), or stalling on short final on an instrument approach (which killed Sen. Wellstone), or flying into a thunderstorm, or flying head-on at 340 knots into each other while receiving radar services and talking to ATC (24 Jan 2003 midair over Denver, CO, for example; see NTSB report at http://www.ntsb.gov/ntsb/brief.asp?ev_id=20030203X00145&key=1). Technology is the key to further reduction of these risks, along with common sense and good judgment - of course.

Chad's got it exactly right. There's no one "correct" measure and nothing based on a single exposure measure comes close to the truth due to the multiple exposure factors that must be taken into account. In GA, the number of real (as opposed to instructional) instrument approaches is more predictive of risk than distance or time alone by far. Yet the crude measures of "risk" that policy makers rely on invariably give only one - very misleading - measure such as miles, passenger miles, hours, takeoffs, etc. A simple thought experiment reveals the problem of using only distance or time alone. Given the astronomical miles traveled by the space shuttle, and the few miles travelled by skateboarders, one might compute the usual kind of policy making risk measure of accidents or fatalities per unit miles traveled and conclude that skate boarding is more risky than space shuttle flight - an absurd conclusion. A more meaningful comparison would be, if I take a skate board ride or a space flight, which is more likely to kill me and how much more likely. Alternatively, one might ask, how is my life expectancy likely to be affected if I choose the hobby of space flight as compared to skateboarding? The latter seems to me to be the only way to compare and even combine the multiple risk factors involved in even our most mundane choices like what to have for breakfast - or what not to have. If I choose to drive fast and aggressively, or fly with little regard for regulations and conventions, or to eat and drink with reckless abandon, or to work in a hazardous occupation, or to live in a dangerously polluted environment (like mine here in Washington, DC), or to carry a handgun (as opposed to keeping one where neither I nor anyone else can access it in the wrong frame of mind), then how much life expectancy will I have to pay the piper? And how much will those losses add up to across all involved parties for the policy makers to consider? Difficult but not impossible questions - and closely related to personal freedom.

Slow down, anonymous, you're getting a little reckless. No need to rush. We've all spent a lot of time thinking about these issues and made many valid points. My goal is to achieve breakthroughs by brain storming with others. PMT is no panacea. Get over it.

OK, here's my final answer. As Albert Einstein once said, a theory should be as simple as possible, but no simpler. All risk ratio concepts like fatalities/pmt and fatal accidents/vmt oversimplify, because they omit many nontrivial factors known to affect risk thereby reducing the comparison to a pseudo-scientific rhetorical exercise. With auto versus airline trips, for example, relevant factors for the auto trip include the mass and CG of the auto, whether it has airbags (front, side, curtain), whether occupants are belted, their age and gender (these are big factors), their fatigue level, their propensity towards speeding and aggressive driving, road conditions, weather, etc. With the airline trip, relevant factors include the airline, the aircraft, number of takeoffs and landings, pilots'skill and physiological state (eg, fatigued or ill), enroute and destination weather, and ground travel to/from origin and destination airports. All this is obvious, but ignored anyway in simplistic ratios used to supposedly compare risk across or even within travel modes.

This news clip on a new study is provocative and illustrative of the right way to approach risk. Finds among other things that the youngest drivers are 4 times more likely to be in auto accidents, and 3 times more likely to die in them, than adults. Taken out of context, the latter ratios are somewhat misleading, because the fatality risk is higher for boys than girls - the study may discuss this. Also, accident risk goes up with number of occupants for these young drivers - which, like the age and gender effects, has interesting ramifications for use of pmt as a measure of risk exposure. I'll try to get the study and see if they accounted for the dramatic improvements in crashworthiness and crash avoidance that have been designed into autos over this period when, concurrently, the regulations were changed to more graduated entry into driving. Most likely, both contributed to the improvements. I wonder if aviation might benefit from similar effort on both fronts, ie, more attention to design enhancements that help avoid or survive crashes and more graduated entry into the real world of flying.





Youngest Drivers' Death Rate Decreases



By Elizabeth Williamson

Washington Post Staff Writer

Thursday, February 24, 2005; Page B01





Fatal car crashes among the nation's youngest, most accident-prone drivers decreased sharply in the decade after most states enacted laws limiting their access to a driver's license, a new study shows.



Auto deaths involving 16-year-old drivers fell 26 percent between 1993 and 2003, a period when 46 states and the District enacted graduated licensing laws that allow fewer 16-year-olds to drive, according to the study released today by the Arlington-based Insurance Institute for Highway Safety.



Among 16-year-olds who have full driving privileges, the rate of fatal crashes has not fallen, and it remains higher than that of any age group. Researchers said the difference between the two groups points to the effect of the new laws, which keep most 16-year-olds from receiving unrestricted licenses and which are intended to curb risky practices, such as carrying teenage passengers and driving at night.



The study shows that "withholding a license is going to improve the crash picture among 16-year-olds," said Susan A. Ferguson, senior vice president for research at the institute and an author of the study. "That's a success story, because the fewer of them who drive, the fewer of them who die."



The dramatically higher crash and fatality rates for teenagers in their first year behind the wheel have prompted highway safety advocates to fight for laws that prevent them from driving unsupervised, at least until they turn 17. Sixteen-year-olds are four times as likely than adult drivers to become involved in a crash and three times as likely to die in one, national statistics show.



Motorists are at the greatest risk during their first year of driving -- with high speed, driver error and multiple passengers contributing to crashes, previous research cited by the Insurance Institute shows .



Although the rules vary by state, graduated licensing programs extend the learner's period, the time that teenagers must drive with an adult in the car. Further, they limit driving under conditions linked to crashes. The first graduated licensing program was introduced in Florida in 1996. By 2003, 47 jurisdictions had the programs, including the District, Maryland and Virginia.



Lawmakers are considering legislation to further restrict teenage drivers. In Maryland, the state Senate gave tentative approval yesterday to a bill that would prohibit new drivers from carrying passengers younger than 18 during the first six months of an 18-month provisional license. The measure, which is expected to win final approval today, has not cleared the House of Delegates.



In Virginia, the Senate and House have approved measures that would restrict cell phone use by teenage drivers, and are working to resolve differences between two versions of the bill.



According to the study, 938 16-year-old motorists nationwide were involved in fatal wrecks in 2003 -- more than one-fourth fewer than in 1993, when 1,084 died in such crashes. That is despite an 18 percent increase in the number of 16-year-olds in the nation, the study found. At the same time, the percentage of fully licensed 16-year-olds declined -- from 42 percent in 1993 to 31 percent in a decade.



Also striking, the institute's Ferguson said, was a 39 percent drop in fatal crashes involving a 16-year-old drivers carrying other teenage passengers.



"The probability of being in a crash increases with each additional in the car," she said. The figures show that "there's a fundamental change in the way young passengers are being transported."



In the region, crash rates among teenagers have been more erratic, pointing to differences in the graduated licensing programs, as well as the difficulty in drawing conclusions from relatively few accidents.



In 1993, there were 27 fatal crashes in Virginia that involved a 16-year-old driver, eight such crashes in Maryland and none in the District. In 2003, there were 12 fatal accidents involving 16-year-old drivers in Maryland, 16 in Virginia and one in the District.



This year, a string of deadly accidents involving new drivers has moved legislators to try to toughen the region's licensing laws, and to place new restrictions on the youngest drivers -- an effort that Ferguson applauds.



"I think there's clearly more we need to do," she said.

It's interestng to compare the safety-relevant features of cars made in the 1960's to those made today. In spite of the bright engineering making mass-produced autos available to nearly everyone, they didn't even put in seat belts. Many minor crashes by today's standards killed people back then, eg, hitting a pole at 30 mph. But have aircraft designs changed accordingly over the same period? Hardly. Then they did have lap belts, and now they have shoulder belts - which make a big difference in survivability - but that's about it. My guess is that arrogant American engineers (or CEOs) will again wait for a Japanese company to solve the obvious problems, eg, integrating autopilots, gps, airspeed gauges, fuel burn, etc, to "discourage" and even prevent recurrent causes of crashes like flying too low and/or too slow on instrument approaches, VFR into IMC loss of control or CFIT, etc.



Why should we "good" pilots care? Two reasons: (1) we're not always as good as we may have been led to believe and should value our own lives and those of our family and friends, and (2) the cost of aviation will drop drop substantially with a growing GA market as more people fly who won't now because they've made a legitimate life decision to exclude that unacceptable risk.

Hey folks - read the Nall Report and do the math. It makes things pretty clear. GA flying is many times more dangerous than driving. Also consider that the fatality rate is even higher than the Nall numbers report since the total GA flight hours come from what pilots report and most exagerate their flight time. Richard Collins talked about this years ago and, to his credit, was brutally honest about aviation safety (unlike some in av media).
A lot of the dead pilots in these accident stats probablythought of themselves the same way most us do - that they are conservative, proficient and well trained aviators.

I love general aviation more than most things but I never BS people and preach about how safe it is.

Also just to add ... with the exception of twin engine training, I think the training period is very safe and that it's the initial few hundred hours that are the most dangerous, particularly for people who can't fly enough hours to retain proficiency.

thanks, John in Brisbane

I'm a pilot with 3500 hours.

Of course flying isn't safer than driving... at 3 times the speed, there is 9 times the kinetic energy to deal with in a crash. Aircraft by design are lightweight, and therefore much less crashworthy than an automobile even if the energy were the same.

The failure modes in an automobile are much more benign also. Unless you happen to be driving through a very bad neighborhood at just the wrong moment, the consequences of an engine failure, even well managed are much riskier in an aircraft than in a car. An engine failure 30 seconds after liftoff in an airplane is exponentially more dangerous than the same event in a car.

Factor in weather and the relative complexity of flying as compared to driving and it's a wonder that the stastics aren't much worse than they are.

This should not be surprising to anyone, airplanes leave the ground and cars do not.

Most of the risk in driving is uncontrollable by the driver, such as the risk of colliding with another driver who is intoxicated, or distracted. In flying we get to choose our level of risk for the most part -- given a good attitude, good training, and a little experience, and much (but not all) of the risk can be mitigated -- this is not possible to teh same extent in an automobile.

Finally, let me comment on the passenger miles vs hours flown vs miles flown discussion. For the individual on the aircraft, it seems to me that the sensible denominator is "per departure". In other words, if I, today, buckle myself into this vehicle, what are the odds that I will DIE before I get out of it. This is the most personal and immutable of the stastics, and really it is the only one that an individual cares about. GA doesn't fare particularly well in this category. If 400 people get on an airplane and it flys 3000 miles in one hop, you can see that your actual risk of NOT walking out of the airplane you just walked into could be 800,000 (400*3000) times as much as this "passenger miles" value.

Fly because it's convenient, flexible, and fun, but don't kid yourself into thinking you're safer than driving.

Statistics ?in a day maybe a few thousands flight happening but in a day how many cars going to roads?Maybe billions tomes.It is something like every 1000 flights 1 crash and 1 million drive 1 crash and less fatal.Plus and more importantly car crushes happens mostly because of driver mistake while airplanes due to technical problem.