In this Oct. 24, 2006, police investigate the wreckage of...

In this Oct. 24, 2006, police investigate the wreckage of a 2005 Chevrolet Cobalt that crashed in St. Croix County, Wisconsin, killing three teens. The vehicle's ignition was found in the “accessory” position and the air bags did not deploy. Credit: AP

When Ford Motor Co. recalled 600,000 sport-utility vehicles recently, it became the fourth carmaker this year to acknowledge an issue with malfunctioning air bags.

So far in 2014, automakers in the U.S. have recalled about 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 buggy software could delay air bags from activating in a rollover. In March, Nissan Motor Co. 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 Co. 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 non-deployment for at least a decade, the top U.S. auto regulator is under increasing pressure from safety advocates to better understand a technology that gets more complicated with each new wave of models.

Impala Deaths

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.

Crude Technology

While not mandated for all light vehicles until 1999, front air bags began appearing in 1970s iterations of the Oldsmobile 88 and 98, Cadillac DeVille and Buick LeSabre. The devices were much simpler then. In a severe crash, a ball bearing was forced down a tube, completing an electrical circuit and deploying the bag.

The technology was crude but continued saving drivers decades later, according to Doug Campbell, who helped design the first GM air bags and is now president of the Automotive Safety Council, an industry group.

Automakers added more air bags to protect passengers when a vehicle is hit from the side and then modified them to inflate longer so people are less likely to be ejected in a rollover. Some bags shoot up from the console between front seats to protect drivers and passengers when cars are T-boned from the opposite side. Ford has even added air bags in the seat belts to prevent chest injuries during an accident.

Multiple Sensors

In the milliseconds following an accident, multiple sensors determine if the crash is coming from the front, back, side or is the result of a rollover. The 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 if 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.

Front-End Crash

Now carmakers and regulators are focusing on air bags that fail to deploy. Thirty of 42 complaints NHTSA has received from consumers about air bags in 2014 models involved software issues or non-deployment, a Bloomberg News analysis shows. The complainants said nine people were injured as a result. Owners identities aren’t revealed for privacy reasons.

The Newton, Pennsylvania, owner of a 2014 Ford Expedition told regulators that in a front-end crash on March 14 all of the air bags except the driver’s air bag deployed.

The owner of a 2014 Kia Soul told a NHTSA representative that they crashed into the rear end of another car in Deland, Florida, while driving about 50 miles (80 kilometers) per hour and the air bags did not deploy. The driver sustained back and neck injuries. In another crash, the driver of a 2014 Jeep Compass described a head-on crash at 40 mph where air bags didn’t activate.

Many of the complaints about air bag passenger sensors related to Nissan models, including ones recalled in March. An owner of a 2014 Altima in Oak Grove, California, said his passenger seat sometimes didn’t recognize the presence of his 110-pound girlfriend. The Basking Ridge, New Jersey owner of a 2014 Infiniti QX60, a luxury Nissan model, cited a similar issue with her sons.

Complicated Logarithms

Because air-bag systems employ multiple sensors and complicated logarithms, investigators struggle to determine the cause when they don’t work properly. While GM has said Cobalt air bags failed to deploy in the fatal crashes because the ignition key slipped into the “accessory or off” position, it’s still unclear why they didn’t activate in at least five crashes when the ignition switch was “on.”

“We’re definitely investigating that,” said Lance Cooper, a Georgia lawyer whose 2011 wrongful death suit against GM helped uncover the switch defect. “There is certainly a question about the manner in which these bags are designed and deploying, because even in certain accidents where the key was in the run position, bags weren’t deploying.”

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