U.S. auto safety regulators have granted BMW a five-month extension to complete repairs on Takata Airbags.

U.S. auto safety regulators have granted BMW of North America a five-month extension to complete repairs on some of its vehicles affected by the Takata airbag inflator recalls after replacement inflators from an alternative supplier failed in testing.

The National Highway Traffic Safety Administration says BMW now has until May 31, 2020, to replace all defective PSDI-4 driver-side inflators from Takata, according to a copy of the extension order provided to Automotive News by the agency. They were installed in 420,000 BMW vehicles, including 2002-06 3-series models, 2002-03 5-series models, and 2003-04 X5s.

About 1.8 million Takata inflators in BMW vehicles are covered by the Takata recalls and need to be replaced. The extension only applies to vehicles with the PSDI-4 inflators.

The extension also pushes back deadlines this year for BMW’s ramp-up of replacement parts to supply recall demand at dealerships, including next week’s March 31 deadline aimed at providing parts to about 100,000 of the vehicles. That deadline is now Aug. 31.

Those 100,000 BMW vehicles are among a larger group of vehicles from the 12 automakers involved that NHTSA views as being most at risk of an inflator rupture, a defect that can spray vehicle occupants with metal shards and has been linked to 10 deaths worldwide.

In November, NHTSA set deadlines for the 12 automakers to amass replacement supplies and complete the repairs, grouping vehicles into four risk-based groups.

Automakers face a March 31 deadline to amass enough supply of replacement to meet demand for the riskiest group, vehicles from the 2008 model year or prior that are located in hot, humid climates.

NHTSA spokesman Bryan Thomas said the agency expects all other automakers involved in the recalls will meet the March 31 deadline.

The extension delays the already lengthy timeline of replacing the roughly 1.8 million inflators in BMW vehicles, but Thomas said it was granted in the interest of safety.

“We’re only going to put in safe inflators,” Thomas told Automotive News. “We’re not going to encourage or allow manufacturers to put unsafe inflators into their vehicles”

The delay underscores the challenges and complexity of the Takata recalls that have dogged the industry for years and will continue for years to come as some 29 million inflators in as many as 25 million vehicles are replaced.

According to NHTSA, BMW experienced an “unexpected failure” during “robustness” tests of inflators to replace the Takata PSDI-4 inflators that were being sourced from an alternative supplier to Takata.

After the failure, BMW halted production of the alternative supplier’s inflators while it worked on a solution. The automaker told NHTSA it would be unable to meet the March 31 deadline, according to a copy of the agency’s order granting BMW’s requested deadline extension.

BMW had contracted an alternative supplier to make replacements for the “batwing” PSDI-4 driver-side inflators that could be used for the life of the vehicle. In the interim, BMW had been repairing some of its affected vehicles using Takata-made replacements that would need to be replaced later, Thomas said.

NHTSA views those as a “safer” alternative to the original inflators that had been in use for years, even if they must be replaced again, because they hadn’t been exposed to the years of hot and humid climates that raises the risk of a rupture. Other automakers have been installing Takata-made replacements that may need to be replaced down the road, as well.

“We’re not calling them safe, but they’re an interim step until they can get sufficient supply,” of replacement inflators that will be safe long-term, Thomas said.

You can reach Ryan Beene