THEY vanished without a trace.
What happened to Malaysia Airlines Flight 370 at the weekend was exceptionally rare, but it has happened before.
The Boeing 777 passenger jet vanished just two hours into a flight from Kuala Lumpur on its way to Beijing.
There was no distress call and now grave fears are held for the crew and 239 passengers on board, including six Australians.
It often takes time for investigators to get to the bottom of aviation disasters.
In 2009, it took five days for search and rescue teams to find Air France Flight 447 from Rio De Janeiro to Paris after the Airbus A330 plunged into the Atlantic Ocean, killing all 228 on board.
It took another three years for investigators to report that ice crystals had most likely blocked the plane’s air speed sensors, eventually leading to the plane to stall.
There have been several other ‘ghost flights’ in aviation history which have blinked off the radar completely.
Sometimes it takes decades for wreckage to be found and many remain lost to this day. These are their stories.
Flying Tiger Line Flight 739
What happened to Flying Tiger Line Flight 739 in March 1962 remains one of world’s most enduring aviation mysteries.
The US military flight was chartered to transport more than 90 military personnel from Guam to the Philippines but it never arrived at Clark Air Force Base.
More than 1300 people were involved in a US military search for the wreckage but nothing was found. There was no distress call and only a few believed to have witnessed its demise.
The crew of a Liberian tanker ship claim to have spotted an explosion in the sky at the approximate time and location where the flight would have passed over.
Crew members said they witnessed an “intensely luminous” light in the sky, with two flaming objects falling into the sea.
The plane, which was eventually meant to carry the troops to Vietnam, is understood to have gone down somewhere in the western Pacific Ocean.
The US Civil Aeronautics board ruled it was “unable to determine the probable cause of the incident.”
The jets lost to the Bermuda Triangle
It is the vast expanse of ocean between Florida and the islands of Bermuda and Puerto Rico that cannot shake the legend.
In the first half of the 20th century several planes and boats disappeared in the Carribean region, including a pair of British South American Airways passenger jets in 1948 and 1949.
More than 51 passengers and crew were lost in the Star Tiger and Star Ariel incidents which happened almost a year apart.
No wreckage was ever found from the Tiger which was lost on January 30 1948 or the Ariel, last heard from on January 17 1949.
A 2009 BBC investigation theorised that the Tiger may have run out of fuel too quickly while a technical error may have ignited the Ariel.
The official UK investigation team into the Tiger incident confessed they were “baffled” by its disappearance.
“It may truly be said that no more baffling problem has ever been presented,” investigators wrote.
The UK team suggested the Tiger incident may have been caused by a “mechanical incident” or, more ominously, “some external cause (that) may overwhelm both man and machine”.
“What happened in this case will never be known and the fate of Star Tiger must remain an unsolved mystery,” the concluded.
A communication bungle meant search and rescue teams were not hailed until more than seven-and-a-half hours after the Ariel vanished, meaning it had likely sunk.
The STENDEC mystery: One last Morse broadcast
“STENDEC”. That was the last message air traffic controllers received from the Star Dust aircraft, which vanished in a snowstorm over the Andes Mountains on August 2 1947.
Chile’s Santiago airport received the Morse code transmission “ETA SANTIAGO 17.45 HRS STENDEC” four minutes before it was scheduled to land that day.
The controller responded that he did not understand the acronym at the end of the message but “STENDEC” was never clarified by the pilot, fuelling conspiracy theories about UFOs.
The wreckage of the aircraft, which was operated by British South American Airways, was not found for more than half a century.
In 1998, a pair of Argentinian rock climbers ascending Mount Tupungato discovered engine wreckage and returned to Santiago to report their alarming find.
An Argentian army expedition in 2000 discovered additional wreckage as well as a human remains, including a hand and part of a torso.
Experts believe the vehicle crashed into the side of the mountain, likely causing an avalanche to bury the aircraft.