Two days after a UPS cargo plane crashed in Kentucky, the confirmed death toll has risen to 12, with nine people still unaccounted for.

Airlines stopped flying MD-11s mainly because the aircraft initially failed to meet its promised performance, particularly in range and fuel efficiency, which led to many airlines canceling orders or replacing them with more efficient planes such as the Boeing 777 and Airbus A330, according to the Infinite Flight blog.

Operations at the Worldport facility resumed Wednesday night, with the courier extending expected delivery times for some priority delivery services.

The United Parcel Service cargo plane that crashed Tuesday was 34 years old and needed a critical repair on its fuel tank in September.The MD-11 plane was grounded in San Antonio from Sept. 3 through at least Oct.

UPS said in a statement that it’s activating contingency plans to move shipments “as quickly as conditions permit,” though it did not release details. Supply chain experts say they believe the