UPS and FedEx announced on Friday that they have temporarily grounded their McDonnell Douglas MD-11 aircraft fleets. This decision comes “out of an abundance of caution” following a directive from the Federal Aviation Administration (FAA) issued the next day. The FAA’s order mandates that these planes remain out of service until they undergo thorough inspections and any potential issues are addressed.

The catalyst for this precautionary move was an incident in Louisville, where the MD-11 jet’s left engine detached during takeoff.

According to the FAA, “This condition could result in the loss of continued safe flight and landing,” and they warned that similar problems “are likely to exist or develop in other products of the same design.”

The tragic crash at UPS Worldport on Tuesday resulted in the deaths of 14 individuals, including the three pilots onboard. The flight was en route to Honolulu.

As per company statements, MD-11 aircraft constitute approximately nine percent of UPS’s airline fleet and four percent of FedEx’s fleet.

“We made this decision proactively at the recommendation of the aircraft manufacturer,” UPS said in a statement.

“Nothing is more important to us than the safety of our employees and the communities we serve.”

FedEx said in an email that it was grounding the aircraft while it conducts “a thorough safety review based on the recommendation of the manufacturer”.

Boeing, which merged with McDonnell Douglas in 1997, said in a statement on its website that it “recommended to the three operators of the MD-11 Freighter that they suspend flight operations while additional engineering analysis is performed”.

Western Global Airlines is the only other U.S. cargo airline that flies MD-11s, according to aviation analytics firm Cirium.

The airline has 16 MD-11s in its fleet but 12 of them have already been put in storage.

The company did not immediately respond to an email seeking comment outside of business hours.

Boeing announced in 1998 that it would be phasing out its MD-11 jetliner production, with final deliveries due in 2000.

The UPS cargo plane, built in 1991, was nearly airborne Tuesday when a bell sounded in the cockpit, National Transportation Safety Board member Todd Inman said earlier this week.

For the next 25 seconds, the bell rang and the pilots tried to control the aircraft as it barely lifted off the runway, its left wing ablaze and missing an engine, and then ploughed into the ground in a spectacular fireball.

The cockpit voice recorder captured the bell, which sounded about 37 seconds after the crew called for takeoff thrust, Inman said.

There are different types of alarms with varying meanings, he said, and investigators haven’t determined why the bell rang, though they know the left wing was burning and the engine on that side had detached.

Inman said it would be months before a transcript of the cockpit recording is made public as part of that investigation process.

Jeff Guzzetti, a former federal crash investigator, said the bell likely was signalling the engine fire.

“It occurred at a point in the takeoff where they were likely past their decision speed to abort the takeoff,” Guzzetti told The Associated Press after Inman’s news conference.

“They were likely past their critical decision speed to remain on the runway and stop safely. … They’ll need to thoroughly investigate the options the crew may or may not have had.”

Dramatic video captured the aircraft crashing into businesses and erupting in a fireball.

Footage from phones, cars and security cameras has given investigators evidence of what happened from many different angles.

Flight records suggest the UPS MD-11 that crashed underwent maintenance while it was on the ground in San Antonio for more than a month until mid-October.

It is not clear what work was done.

The UPS package handling facility in Louisville is the company’s largest.

The hub employs more than 20,000 people in the region, handles 300 flights daily and sorts more than 400,000 packages an hour.

UPS Worldport operations resumed on Wednesday night with its Next Day Air, or night sort, operation, spokesperson Jim Mayer said.