Why can the black box be

Malaysia's Prime Minister on March 24 held a press conference claiming that the MH370 aircraft carrying 239 people crashed into the Indian Ocean.The mystery of the incident will likely only be revealed until the search teams recover the black boxes of the subsea aircraft.

However, aviation experts warn, black boxes cannot always bring us the correct answer about the fate of missing aircraft. On each aircraft, there are two same devices called black boxes , including the Cockpit Recorder (CVR) and the Flight Data Recorder (FDR) , but they all have limitations.

The CVR device only records the last 2 hours

Listening to the final moments of the Air France 447 flight crashed in the Atlantic in 2009, has helped uncover mistakes in driving crews, resulting in accidents. Such cockpit recording data will be an invaluable tool to help investigating agencies determine whether the aircraft MH370 is a victim of a technical error or a human plot. They can also help investigating agencies reconstruct the flight path of MH370.

However, things won't be simple even if the authorities find the black boxes. CRV continuously records what happens in the cockpit during flight. According to American company Honeywell Aerospace, the maker of black boxes for missing aircraft, the CRV device only retains the last 2 hours of recording as current regulations. However, in the case of flight MH370, important events may have happened long before the accident took place.

Short battery life

Black boxes emit a ping sound, the operation is triggered by immersion in the water and can be detected by a microphone device, signal analysis. Both the cockpit recorder and flight data recorder have their own ping sounding department.

After nearly two years of trouble finding the black box of Air France 447, the new regulations of the world air have asked the department to poke the black box for 90 days to search teams. More time if there is a risk. However, the missing Malaysian aircraft has not yet updated the life of the department to ping that level. The battery of these parts in the black box MH370 flight has a very short life, only 30 days. Search teams currently only have 12 days to trace the ping. The only consolation is that, even if the battery runs out, the data of the black boxes remains intact.

Black boxes are relatively small in size

Black boxes are fastened to the tail of the aircraft to avoid head injury accidents that are easy to occur. They are small in size, equivalent to a shoe box. According to Dr. Guy Gratton of Brunel University's Flight Safety Laboratory, despite being strikingly orange, seeing black boxes in the middle of the ocean is not easy. The search often has to focus on finding the location of the plane crash, before proceeding to determine the location of the black box by receiving ping sound. If the department says that the ping stops working, the investigating agency will need other search techniques, such as magnetic detection.

Black box does not float

The black box is made of aluminum and is designed to withstand strong impacts, large fires or high pressure, so it is quite heavy, about 10kg despite its small size. That means, the black box will sink very quickly when it falls into the water. Meanwhile, the Indian Ocean has very deep areas. The search area stretches more than 1,150 meters and is 7,000 meters deep, not to mention the rugged seabed terrain like the Alps. Therefore, investigators will have to consider that the black box may be outside the 'reach' of many underwater or ultrasonic sound locating devices.

Range of short ping sounds

Honeywell said the pings coming from the black box of the aircraft only had a range of about 1.6 km. That means, search aircraft need to move straight above the heads of the black boxes to 'hear' their pings. In addition, there are other factors that may obscure the signal: debris on the surface or if the black box is submerged in mud or sediment on the seabed. Experts say that in the case of black boxes deep in the seabed, the best way to find them could be devices using underwater stethoscope technology. Modern submarines of participating countries such as the US, China and Australia are also said to be able to 'hear' ping at many kilometers away.

An obstacle is also mentioned by experts, if ping sounds with a hot or colder layer above, they can be reflected or refracted, making it difficult to find.