Following a tragic incident earlier this week in Louisville, Kentucky, that resulted in at least 12 fatalities, FedEx and UPS have decided to temporarily halt operations for their McDonnell Douglas (MD-11) cargo aircraft fleets.

UPS stated that MD-11s constitute roughly 9 percent of its airline fleet. “We are grounding these aircraft effective immediately and have taken this step proactively based on the aircraft manufacturer’s recommendation,” the company announced. Additionally, UPS emphasized, “The safety of our employees and the communities we operate in remains our top priority.”

FedEx echoed this sentiment, informing The Hill that it too has grounded its MD-11 fleet. “We are conducting a comprehensive safety review as advised by the manufacturer,” FedEx stated.

The company further added, “We are enacting contingency plans across our integrated air-ground network to reduce disruptions. Our focus is on maintaining the highest safety and service standards for our customers and team members.”

“We are immediately implementing contingency plans within our integrated air-ground network to minimize disruptions,” the company continued. “Our teams are focused on delivering the highest standards of safety and service for our customers and team members.”

Boeing, the manufacturer of the MD-11 aircraft, made this recommendation to FedEx and UPS “in an abundance of caution and we will continue coordinating with the Federal Aviation Administration [FAA] on this matter.”

“Boeing’s Safety Review Board assessed all available information and concluded further engineering analysis was needed,” Boeing officials told The Hill. “We recommended temporarily pausing fleet operations, so the analysis and any necessary corrective actions could be completed.”

The aviation accident at the UPS Worldport, located at Louisville Muhammad Ali International Airport, killed a dozen people, including one child, on Tuesday. Just after takeoff, a UPS cargo plane’s left wing caught on fire and an engine fell off just before it crashed and exploded, officials revealed.

The investigation is ongoing.

The incident is expected to delay shipping, though experts told the Associated Press that the impact should be lessened before peak holiday season.

“I understand the circumstance and will gladly receive it when it arrives,” Tom Goldsby, professor of supply chain management at the University of Tennessee in Knoxville, told the AP. “People and businesses don’t have a lot of understanding (about the supply chain).”

He added, “We just don’t expect our logistics operations to have a calamity or even a bad day.″