Are bigger planes more deadly?

By Ian

I have no idea, really, but in the course of some work I ran across the following chart and was instantly fascinated:

Airline Accident Trends 1945-2004

(Source: PDF) Note that these numbers exclude non-accident occurances such as bombing and hijacking.

The left hand ordinate is the number of fatalities, and the right-hand ordinate is the number of accidents. While the trend indicates that the number of accidents has been on quite a descent, what I find more interesting is that the ratio of accidents:fatalities converges, but doesn't (on average) reverse, 1985 and 1997. After an increase in the number of fatalities through to the mid 70s, the number has returned to numbers just below the 40s. But the number of accidents is almost a third of what it was during the same time.

Not being overly familiar with the aviation industry, the only trends I'm familiar with are the growth in plane size, and the alternating shift to, and now more recently from, hub-based route architecture. With larger planes, each accident will claim more lives. (Which is similar to my retort about people who talk incessantly about flying being safer than driving -- I've spent a good portion of my life on a plane and have never had a fear of flying, but when you have a car crash, you don't often lose 280 people at once. In the event of an accident, I'd much rather take my chances in an automobile. I don't think I have the luck to come out this well.) Any ideas?


Brandon Berg wrote:

What exactly are you asking? I assume that the severity of a crash can best be expressed as the proportion of occupants which it kills. That is, a crash can be said to be severe enough to kill 80% of those involved, rather than severe enough to kill 100 people regardless of the number involved. If this is true, then it seems obvious to me that if the number of passengers per flight doubles, then the number of fatalities per crash will double.

Another explanation could be an increase in the safety of smaller airplanes. Pareto's law seems to apply here; most of the fatalities come from a small minority of the crashes, while most of the fatal crashes involve small planes with fewer than 20-30 occupants. If these planes get safer while the safety of large passenger planes remains constant, then the number of fatal crashes will fall without significantly impacting the number of fatalities.

-- July 14, 2005 1:46 AM

GradStudent wrote:

I'm hoping that the scale on the right corresponds to the number of fatalities, an the scale on the left corresponds to accidents? I didn't think that about 1,000 people die every year due to airplane accidents?

-- July 14, 2005 2:49 AM

DrDan wrote:

I haven't looked at the pdf source file but most travel related injury and mortality analyses use an 'exposure' denominator that is usefullly able to be compared over time - for example, 'millions of kilometres travelled'. If you do it this way, it is possible to calculate deaths per million km travelled. In epidemiological terms this type of analysis tells us something of the level of 'exposure' to risk of injury/death. The big problem though in the real world is that nice denominator data are lacking...I am by no means critical of the graph - it is interesting. Keep up the nice work

-- July 14, 2005 5:14 AM

MCP [TypeKey Profile Page] wrote:

" but when you have a car crash, you don't often lose 280 people at once. In the event of an accident,"

Exactly. That is why I hate the standard "flying is safer than driving" line that cites vehicle rather than passenger miles. The odds of your plane crashing may be less than for your car but in the former case you have bought 300 tickets in a lottery you don't want to win instead of 2 or 3. Flying is probably still safer but I think the FAA and industry overstate the difference.

Of course the reason most people fear flying is the near certainty of death if something does go wrong and the lack of personal control.

-- July 14, 2005 5:39 AM

Ian wrote:

GS -- Unfortunately, the scale on the left is, in fact, the number of deaths. The number passed 500 in 2004, I believe.

DrDan -- I wasn't aware that such was the method for calculating "exposure." I'll have to look into it more, since it could provide some help on the work I'm doing. (I simply ran across this while looking for data on revenue per kilometer traveled, and hadn't really been thinking of fatalities at all, let alone per unit of travel). Many thanks.

-- July 14, 2005 9:46 AM

Brandon Berg [TypeKey Profile Page] wrote:

I didn't think that about 1,000 people die every year due to airplane accidents?

These are worldwide numbers, not just for the US. See the linked PDF for details.

-- July 14, 2005 1:43 PM

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