Grounding Boeing 737 Max airplanes might actually harm safety

See Turbulence At Boeing by David Henderson. Excerpt:

"Some airlines have few 737 Max airplanes and won’t be much affected by the prohibition on flying. Other airlines, such as Air Canada, have a large number of such planes, not in absolute terms but as a percentage of their fleet. According to its website, Air Canada’s fleet has 172 airplanes that carry 150 passengers or more. Of these, 24, or 14 percent, are 737 Max 8s. Air Canada is scrambling to adjust. When I called last Friday to inquire about seat choice for a trip this summer, the person who answered explained that my 42-minute wait on the phone was due to that scramble.

Imagine, as seems reasonable, that Air Canada adjusts by replacing some of the 737 Max 8s with smaller airplanes, such as its Embraer 190. This would make sense if some 737 Max 8s had, say, 50 seats going empty. Then it might need to drop frequency on shorter routes flown by the Embraer. Other airlines, in the United States and elsewhere, might make similar decisions.

The shorter the route dropped, the more likely it is that some people who would have otherwise flown would, instead, drive.

There’s the rub. Ample data show that for a given passenger, the probability of dying in a car is two orders of magnitude higher than the probability of dying on a commercial flight going the same distance. Specifically, for U.S. commercial airlines between 2000 and 2010, a time that includes 9/11, there were 0.2 deaths per 10 billion passenger miles. For U.S. driving, by contrast, in 2000 there were 150 deaths per 10 billion passenger miles. That’s a ratio of 750 to 1. It’s true that driving has gotten safer, but so has commercial airline travel. For any given year, therefore, my two orders of magnitude comparison is reliable.

That means that grounding the 737 Max 8, if it causes some flights to be cancelled, could well cause more deaths on roads than the number of airline passengers’ lives it saves. This conclusion follows directly if everyone who gets bumped from a short flight drives instead and if the 737 Max 8 is not more dangerous than the other aircraft. But it follows even if we weaken both of those assumptions. Let’s say that as few as 10 percent of people bumped from short-haul trips drive instead. And let’s even grant that the 737 Max 8s are more dangerous, even 5 times as dangerous.

Then do the math. Ten percent of people drive, thus choosing an option that’s 750 times as risky per mile as flying. But even if the 737 Max 8 is 5 times as dangerous as the average commercial airplane, those 10 percent are choosing an option that is 150 times as dangerous as the grounded 737 Max 8. Since 10 percent choose to drive, that’s 15 more deaths in driving (10 percent of 150) per death saved by not flying. That’s not a good deal for passengers."