Even with the discovery of the two "black boxes," it may be a long time before investigators figure out what caused a China Eastern Airlines Boeing 737-800 to crash last week, killing all 132 people on board.
The first black box was discovered two days after the March 21 disaster, and the second was discovered six days later, on Sunday. According to experts, it may take weeks or months to evaluate their contents and begin to uncover solutions.
WHAT EXACTLY IS A BLACK BOX?
Most commercial jetliners are equipped with two recorders to aid investigators in determining the cause of accidents. They are generally orange, despite their name, to make them easier to find.
The cockpit voice recorder records the voices of the pilots and other passengers in the cockpit, as well as audio alarms and the sound of engines or switches being adjusted. It records for at least two hours before beginning to record over itself.
Flight data recorders continuously record at least 88 items of information, such as airspeed, altitude, direction, and whether the plane's nose is pointed up, down, or level. They can also record the position of the wing flaps and whether or not the plane is on autopilot. Typically, they capture 25 hours of data.
Flight recorders used to utilise magnetic tape but are now digital, allowing them to carry more data.
WHAT HAVE INVESTIGATORS DISCOVERED?
The cockpit voice recorder was found first, followed by the flight data recorder. Soil covered the two orange cylinders, which were the size of a large, elongated cannister. The second was discovered beneath 1.5 metres (5 feet) of earth.
The outside of the cockpit voice recorder was damaged, according to officials, but there was no word on whether the recording was intact. In Beijing, both will be studied and assessed.
WHAT CAN CRASH INVESTIGATORS LEARN FROM THE RECORDERS?
The recorders can tell investigators what the pilots were doing prior to the disaster, if they were aware of any concerns, and how the engines and other equipment were performing. They are especially critical in the aftermath of tragedies such as the China Eastern accident, in which no survivors were recovered and air traffic controllers received no communication from the pilots.
The flight recorder from the Lion Air Boeing 737 Max tragedy in Indonesia in 2018 revealed that pilots tried to maintain the plane's nose up, opposing an automatic system that pulled it down. Four months later, an Ethiopian Airlines 737 Max crashed in a same fashion. The jet, which is a different model than the 737-800, was grounded as a result of the disasters.
WHAT WILL THE INVESTIGATION LOOK LIKE?
The investigation will be led by China. It will include a representative from the National Transportation Safety Board of the United States, as well as representatives from Boeing and CFM, the General Electric Co.-Safran joint venture that produced the engines. The NTSB stated that discussions with China were underway to address COVID-19 quarantine regulations.
Investigators will examine at the plane's maintenance history, the pilots' training and records, and weather data. They will look for clues in the wreckage. The magnitude of the debris field is also essential. When wreckage is dispersed over a vast region, it may suggest that the plane was breaking up before impacting the ground.