航空业界正在努力理解为何一架客机与一架军用直升机会在半空中发生致命的相撞事故。一位专家形容，那是“全球控制最严的空域”。

Two American Airlines passenger planes bumped wings on a taxiway at the Ronald Reagan National Airport in Washington, D.C., on Thursday, the US Federal Aviation Administration (FAA) said. No injuries ...