The first indication is that Tuesday afternoon's crash occurred after the metro system staff had switched to manual scheduling following a signalfailure.
暗示星期二下午这场事故发生的第一个信号就是,地铁系统员工在信号指示失败后立刻转为手动操作。
3
In this case the controller sends out a FAILUREsignal to the coordinator, thus invoking the compensatory activities in reverse order.