Here are some things you might not know about black boxes.

They’re not black. Black boxes are the same colour as the Golden Gate Bridge in San Francisco. 【小题1】. The Golden Gate Bridge is a darker shade, while the international orange used for black boxes is much brighter.

A black box comes in two parts. The black box is made up of two separate pieces of equipment: the flight data recorder (FDR) and a cockpit voice recorder (CVR). They are compulsory on any commercial flight or corporate jet. They are usually kept in the tail of an aircraft. 【小题2】. The FDRs record things like airspeed, altitude, vertical acceleration and fuel flow. The CVRs track not only the crew’s interactions with each other and air traffic control, but also background noise that can give vital clues to investigators.

【小题3】. Black boxes start emitting (发出) a pulse if their sensors touch water. They work to a depth of just over four kilometers and can “ping” once a second for thirty days before the battery runs out. If a flight crashed into the ocean, it might take search teams a few years to find and raise the black boxes. However, they are worthy of the time. 【小题4】.

They’re almost undestroyable. The FDRs are usually double-wrapped in titanium or stainless steel. 【小题5】. The crucial part that contains the memory boards can bear a 227 kg weight with a pin attached to it, which is dropped onto the unit from a height of three meters. Researchers try to crush it, destroy it in an hour of 1,100 degrees Celsius fire, submerge it in a pressurized salt water tank and immerse it in jet fuel.