美国有线新闻 CNN 埃航和狮航客机坠毁事故有相似之处 波音MCAS系统备受争议（在线收听）

Up next, the U.S. Justice Department is trying to determine if any laws were broken in the certification process for certain passenger planes. The model is Boeing 737 Max series. One of these planes crashed in Indonesia last October. Another crashed in Ethiopia earlier this month. Everyone aboard both flights was killed, and the 737 Max jets have been grounded world wide. U.S. investigators are looking into everything from how the plane was certified as safe to how it was marketed. Meantime, Boeing has developed a software patch and a pilot training program to address some of the issues with the Max aircraft.

OREN LIEBERMANN: One of the most important concepts in aviation is the angle of attack. In simple terms, it's the difference between the angle of the wings and the direction in which the plane is flying. Imagine a plane that's about to land. Its nose is pointed up, but the plane is still moving down towards the runway. That difference there is the angle of attack, sometimes called alpha. If the angle gets too big, if it exceeds a critical angle of attack, a plane stalls. Airliners have an angle of attack sensor. It's connected to the instruments and systems inside the plane.

One of these is Boeing's new MCAS system on its 737 Max series of airliners. MCAS is an automated anti-stall system. This system is the focus of the investigation into October's Lion air crash. And experts say there are similarities between it and the Ethiopian Airlines crash. If the MCAS system senses a high angle of attack, it will push down the nose to avoid a stall. But if the angle of attack sensor is malfunctioning, and gives a faulty reading, the system could force the plane to dive with potentially disastrous consequences.