The first PLAAF base I went on to was a training unit in Sichuan province. As we turned onto the line the first two Nanchangs were complete wrecks: yellowing glass and rotting flying control surfaces. As we went further down the line they started to improve until we came to complete examples with drip trays underneath. At the end by the headquarters building were aircraft with FULL covers on, wings, cockpit and fuselage. It looked, and it was confirmed by later visits to other units that aircraft were flown until they dropped, Xmas tree-ed until there was no more and just left there. Meanwhile they moved to the next aircraft in the line and started again.