If the plane finishes handling with a delay, the game offers you a chance to erase the delay for silver planes. You can either click finish handling, but you will get a delayed handling, which can even lead to contract cancellation if it happens often, or you can flip the switch above the button, spend (in this case 40) silver planes and then click the button and the handling will be considered on time.
This is not a bug, but intended behaviour, to offer you a way to erase the delay, which in this case is most likely caused by what you’ve described in your other report: Qantaslink DH8B
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