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Bloomberg News
So far in 2014, U.S. automakers have recalled about 6.6 million vehicles for defects that could prevent air bags from deploying properly in a crash.

4th recall tests faith in air bags

Complexity of software, defects can hurt function

– When Ford recalled 600,000 sport utility vehicles last week, it became the fourth carmaker this year to acknowledge an issue with malfunctioning air bags.

So far in 2014, automakers in the United States have recalled 6.6 million cars and trucks, more than a third of the total, for defects that could prevent air bags from deploying properly in a crash. At Ford, engineers found faulty software could delay air bags from activating in a rollover. In March, Nissan recalled almost 1 million cars, including the 2014 Altima, because software sometimes thinks a passenger seat is empty, leading to an air bag failure.

A technology that’s saved thousands of lives has become a preoccupation for carmakers and regulators ever since General Motors acknowledged air bags failed to deploy in accidents linked to 13 deaths. While a defective ignition switch was responsible in those cases, software is often the culprit, a byproduct of cars’ growing complexity. Some models now feature 11 computer-controlled air bags that protect everything from the head to knees and must deploy at exactly the right moment.

“The more situations you’re trying to cover, the more complex your algorithms get, and the harder it is to know that it’s going to do the right thing,” said David Zuby, chief research officer for the Insurance Institute for Highway Safety. “It’s hard to test everything and the real world is a lot more complicated than the test laboratory.”

While the National Highway Traffic Safety Administration has been studying air bag nondeployment for at least a decade, the top U.S. auto regulator is under pressure from safety advocates to better understand a technology that gets more complicated with each new wave of models.

Last month, the Center for Auto Safety asked NHTSA to investigate reports that a software fault can misread a passenger’s weight and render air bags inoperative in 2003-2010 Chevrolet Impalas. At least 143 people have died in frontal crashes when an Impala’s air bag didn’t deploy, said Donald Friedman, a safety consultant, who cited data collected from NHTSA’s fatal-crash database. Other automakers may be using the same technology, Friedman said.

GM said it was cooperating with the regulator and would take action if needed.

Despite its flaws, the air bag is widely considered a successful technology, having saved an estimated 37,000 lives from 1986 through 2012, according to NHTSA. In most cases, the technology works as advertised, said Dan Edmunds, an auto engineer at, which helps drivers assess models.

In the milliseconds after an accident, multiple sensors determine whether the crash is coming from the front, back or side or is a result of a rollover. Results are communicated to a computer controller, which in turn activates the air bags. Sensors located on the front bumper, inside the car, on the doors or elsewhere measure the force. Another one tries to determine whehter the vehicle is tipping.

Ironically, the technology’s growing complexity reflects in part an American hostility toward regulation. Because some drivers can’t be counted on to wear seat belts, air bags need to include measures to keep folks safe if they don’t buckle up.

Early on, air bags gained a reputation for occasionally killing the people they were designed to protect. From 1990 through the early 2000s, about 300 people, mostly small adults and children, died when air bags deployed with excessive force. That number was reduced to zero by 2008 as more sophisticated air bag controls were introduced, according to NHTSA.