Paris (AFP) - When investigators arrive at an aviation crash site, one of their first priorities is to locate the plane's black boxes, two pieces of equipment that can hold vital clues on what caused the aircraft to go down.
Despite the name, these two boxes -- consisting of the flight data recorder and the cockpit voice recorder -- are in fact bright orange with reflective stripes, and all commercial planes are obliged to have them on board.
The digital flight data recorder gathers information about the speed, altitude and direction of the plane with enough storage for 25 hours of data, while the cockpit voice recorder keeps track of conversations and other sounds in the pilots' cabin.
The treasure trove of data they provide helps explain nearly 90 percent of all crashes, according to aviation experts.
Egyptian authorities were quick to announce they had found both black boxes of Russia's Kogalymavia flight 9268 after it crashed in the Sinai Peninsula Saturday shortly after taking off from the resort of Sharm el-Sheikh, killing all 224 people on board the St Petersburg-bound Airbus A321.
But, crucially, the officials did not specify which condition the boxes were in.
Analysing the data can take "days or even weeks" depending on what state the boxes are in, according to an expert who worked on the 2004 investigation of a Boeing 737 that plunged into the Red Sea after taking off from Sharm el-Sheikh, with the loss of all 148 lives on board.
The initial reading of the black box data relating to Saturday's crash should allow investigators to determine "relatively quickly" whether or not the plane was hit by a missile or if, for example, there was an intruder in the cockpit, the source said.
But he stressed that usually no findings are released publicly until all of the information has been examined in detail.
- Black boxes past and future -
Introduced in the 1960s, flight recording devices are housed in boxes built to survive extreme shocks, fire and lengthy submersion underwater.
They each weigh seven to 10 kilograms (15 to 22 pounds) and can survive as deep as 6,000 metres (almost 20,000 feet) underwater or an hour at 1,100 degrees Celsius (2,012 degrees Fahrenheit). To make them easier to find, they are fitted with a beacon which can emit a signal for one month.
In January 2004, the black boxes of the Egyptian charter flight that crashed off the coast of Sharm el-Sheikh were found after a two-week search, 1,022 metres below water.
In 2011, after 23 months submerged at a depth of 3,900 metres in the Atlantic Ocean, the black boxes of doomed Air France flight AF447 travelling between Rio and Paris were retrieved, with the data intact, allowing investigators to determine the causes of the June 1, 2009 crash.
Long-haul Airbus A350 and A380 passengers jets will soon come equipped with ejectable black boxes that can float, making them easier to find in an air crash at sea.