The Federal Aviation Administration has ordered all McDonnell Douglas MD-11 aircraft grounded pending further inspection, following UPS and FedEx each deciding to ground the planes that make up part of their cargo fleet.

The FAA's emergency directive on Saturday prohibits flight of MD-11 aircraft because it has "determined the unsafe condition is likely to exist or develop in other products of the same type design."

The grounding comes after a UPS MD-11 plane crashed shortly after takeoff in Louisville, Ky., last week, killing 14 people.

Though the MD-11s make up a small share of UPS and FedEx's cargo fleet, some aviation experts say that depending on how long the MD-11s are grounded, it could delay holiday deliveries.

The cause of the crash is still under investigation. Boeing on

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