When radio contact with a Malaysia Airlines plane was lost in March 2014, it was en route from Kuala Lumpur to Beijing, China. Most recently, she was spotted on military radar over the Andaman Sea heading out into the Indian Ocean.
And because the jet disappeared over the sea, the GPS device in the black box would have been of limited use.
GPS devices transmit on two channels and use electromagnetic radiation in the frequency bands 1,575.42 MHz and 1,227.60 MHz. This corresponds to the radio wave frequency called UHF (Ultra High Frequency), but radio waves at these wavelengths are transmitted very poorly in water.
The black box emits sar high frequency sound for 30 days after a plane crash.
Instead of GPS devices, there are usually sound transmitters in the black boxes. They activate if they come into contact with water and send a signal once per second for at least 30 days.
These are high-frequency sounds with a frequency of 37.5 kHz. For comparison, the human ear can detect up to 20 kHz (kHz), while dogs can hear up to 45 kHz.
The high-frequency sound travels much better through water than radio waves and can be detected up to three kilometers away – but it was not enough to locate the wreckage of the Malaysian jet.
A new box comes off the plane
However, that tragedy has led to the creation of a new type of registration box. The new model is called ADFR (Automatic Deploy Flight Recorder) and is released from an aircraft that crashes into the sea and then floats on the surface. From there, the device then sends a message via satellite and this greatly increases the chances that the box will be found.
For the technicians who investigate plane crashes, it is very important to have access to the so-called black boxes – which are actually orange in color.
The devices record, among other things, flight altitude, direction, speed and engine condition and record pilots’ conversations.
