Black boxes, or flight recorders, are electronic devices that record information on an airplane to be used in the event of a severe incident such as a crash. Usually, an aircraft carries two types of recorders.

　　The first, a flight data recorder, makes a record of instructions sent to a plane's electronic systems; the second, a cockpit voice recorder, makes a record of conversations, radio communications and other sounds in the cockpit. Sometimes, the recorders are part of the same unit.

　　Black boxes, which are actually bright orange, are designed to withstand extreme forces and temperatures, and are usually located in the tail of the aircraft, where they are least likely to encounter an impact.

　　黑匣子的工作原理

　　Clues to missing flight

　　The recorders could offer clues about what happened to Malaysia Airlines Flight 370, which disappeared enroute from Kuala Lumpur to Beijing on March 8, with 239 people on board. Investigators have been searching for the plane in the southern Indian Ocean west of Australia, where satellite data suggests the aircraft may have crashed.

　　The black boxes emit underwater locator beacon signals, or pings, at depths of up to 20,000 feet (6,000 meters), for up to 30 days before their batteries die.

　　An Australian navy ship picked up signals with the same frequency as those emitted by the missing plane's black boxes in the northern part of the search area, officials announced Monday (April 7), according to CBS News. The ship Ocean Shield heard the pings from a towed pinger locator. The first series of pings lasted two hours and 20 minutes, and a second signal lasted for 13 minutes.

　　A Chinese ship also reported hearing pings consistent with a plane's recorder signals on Friday and Saturday (April 4 and 5), according to Xinhua, China's official news agency. This ship heard pings about 345 miles (555 kilometers) away from those detected by the Australian ship.

　　Awaiting confirmation

　　But investigators have yet to confirm the pings came from the missing aircraft. Sea life (such as whales) and shipping noise can trigger false alerts. Last week, a British Royal Navy ship called the H.M.S. Echo detected signals that sounded like those from a black box, Australian officials reported, but the signals were false, according to The New York Times.

　　The Australian and Chinese ships will attempt to detect the pings again. If they do, they will probably deploy underwater robots to search for plane wreckage on the seafloor, a mission that could take many days, investigators said. The black box pinger has a range of only a few miles. And the black box itself is small and doesn't float, so it could be tough to locate.

　　Finding the flight recorders and the plane's wreckage would provide confirmation that the flight crashed, but the recordings themselves may not be able to resolve the causes of the crash.

　　The flight voice recorder only stores the most recent two hours of flight, but the key events in the Malaysia Airlines flight may have taken place earlier, officials have said. The flight data recorder would be much more useful, however, because it may allow investigators to reconstruct the flight path, a former pilot told BBC News.

　　据Livescience网站报道，搜寻船只探测到疑似客机黑匣子的脉冲信号，这是失联航班MH370谜团中一个重大突破。但是黑匣子到底如何工作？

　　黑匣子，或称飞行记录器，是一个电子设备，用于在飞机上记录信息以备重大事故时使用，如坠机。通常飞机会装有两种类型的记录器。

　　一种是飞行数据记录器，记录发送到飞机电子系统上的指令；另一种是驾驶舱话音记录器，记录舱内对话，无线电通信以及其他声音。有时候，这两种记录器是同一设备的不同部分。

　　黑匣子实际上是亮桔色，可以承受极端力量和温度。黑匣子通常位于机尾，那里受到直接冲击的可能性最小。

　　失联航班线索

　　这两个记录器可以提供与载有239名乘客的马来西亚航班370的相关线索：飞机为何会在吉隆坡飞往北京的途中失联？在澳大利亚以西的南印度洋海域已经展开调查，那里的卫星数据显示飞机可能已经坠毁。

　　黑匣子可在深达2万英尺（约6000米）的水下发出水下定位信标信号，或者说脉冲信号。电量可维持30天。

　　据哥伦比亚广播公司新闻4月7日消息，当天澳方官员宣布，一艘澳大利亚军舰在搜寻区域北部接收到失联客机黑匣子频率相符的水下信号。这艘“海洋之盾”号军舰由一个拖曳式“黑匣子”水下探测设备监听到信号。第一次信号持续了大约2个小时20分钟，第二次信号持续了13分钟。

　　中国官方通讯社新华社报道，一艘中国船只也报告称于周五和周六（4月4日和4月5日）监听到与飞机记录器频率一致的脉冲信号。这艘船只监听到信号的地点离澳方船只相距555千米。

　　等待确认

　　但是调查员还在确认这些信号是否来自失联航班。海洋生物（例如鲸鱼）以及船舶噪音同样可引发错误的警报。上周，一艘名为英国皇家海军“回声号”军舰探测到疑似黑匣子发出的脉冲信号，而据《纽约时报》报道，澳大利亚官方报告称这个信号并非黑匣子所发出。

　　调查人员说，澳大利亚以及中方军舰尝试再次探测到脉冲信号。如果再次探测到信号，他们可能将部署水下机器人在海底搜寻飞机残骸，这一任务可能需要很多天。黑匣子脉冲发射器的发射范围只有几英里。并且黑匣子本身很小，不会漂浮,所以很难找到它。

　　找到黑匣子和飞机的残骸可以确认飞机坠毁，但记录本身可能无法提供坠机的原因。

　　官方称，飞机语音记录器仅储存航班最近两个小时的飞行记录，但马来西亚航空公司失联航班上的关键事件可能在此之前就已经发生。一位前飞行员告诉BBC记者，飞行数据记录器将更有用，因为它能让调查人员重构飞行路径。