Boeing said on Wednesday that it had received a $2 billion contract to continue providing logistics support for the U.S. military’s fleet of C-17 transport planes through 2017.

The contract includes support for the aircraft, forecasting, purchasing and material management under a Performance-Based Logistics program that began in 1988.

Boeing said the sustainment program, which has expanded to 246 aircraft from 42, helps lower costs through economies of scale.

Under performance-based logistics contracts, customers receive an agreed level of system readiness instead of paying for a specified number of spare parts.