In the event of an engine failure , for instance , it could use its navigational map to locate a suitable area to put down .
比如，如果一台引擎发生故障，无人机需要使用其航行图来找到合适地点降落。
Every helmsman checks his compass-a chinese invention used for the first time in history as a navigational tool on this voyage-and sets a southerly tack as far as the singapore strait then west into the indian ocean .
