Investing.com -- The Federal Aviation Administration approved Boeing's protocol on Monday for safely returning MD-11 airplanes to service in the U.S. after grounding the fleet in December.

The FAA had barred MD-11 flights following a fatal November crash of a UPS cargo plane in Kentucky that resulted in 15 deaths.

UPS decided to retire its entire MD-11 fleet following the crash. FedEx said it plans to resume operations of its 28 MD-11 aircraft later this month once the planes meet Boeing's maintenance requirements.