It's been a year since Malaysia Airlines Flight 370 and the 239 souls aboard it disappeared without a trace, and if the fates of scores of commercial, private and military planes that have vanished around the globe since 1948 are any indication, the world may never know what became of the jetliner.

“Every flight that has disappeared had its own story."

- David Cenciotti, The Aviationist

Whether in remote areas of the ocean or rugged mountain regions where snow or forests hide wreckage from view, planes have been disappearing for decades, leaving authorities, aviation experts and victims' families with no answers. The biggest ocean search in human history has failed to turn up even a confirmed trace of the plane, which had left Kuala Lumpur for Beijing and is believed to have gone down in a remote part of the Indian Ocean after the pilot inexplicably turned off the communication system and made an unplanned U-turn. The disappearance is the deadliest and most recent in a long line of aviation mysteries that experts say may never be solved.

Aviation Safety Network, which tracks missing planes, documents 85 passenger, cargo, and military transport aircraft that have gone missing without a trace since 1948, along with eight maritime patrol aircraft, five corporate jets and six air taxis. In each case, not a single piece of wreckage, oil slick or body has been found.

“Every flight that has disappeared had its own story,” said David Cenciotti, editor of TheAviationist.com, one of world's most-read aviation blogs.“Some may have been hijacked and may have landed on a hidden or remote airfield. Others may have simply crashed in bad weather in remote locations, or at sea, after flying several minutes, if not hours off track, hence search-and-rescue teams have looked for them in the wrong place.”

In 1948, the first of two British South American Airways Avro Tudor passenger planes disappeared on flights to Bermuda. The other plane was lost a year later and no trace of either aircraft or the 51 people aboard them ever turned up. The strange disappearances helped propel the myth of the Bermuda Triangle, which had captivated the nation just three years earlier when the area claimed five Navy torpedo bombers with a 14-member crew along with an aircraft sent to find them.

Prior to MH370, the costliest airplane disappearance came in 1962, when a Flying Tiger Constellation leased by the U.S. military vanished over the Pacific while traveling from Guam to the Philippines. Despite a massive search, no trace of wreckage or any of the 92 soldiers and crew aboard were ever found.

“The subsequent search covered 144,000 square miles using 48 aircraft and 8 surface vessels, but nothing was found,” said Harro Ranter, CEO of the Aviation Safety Network. “This was a very extensive search operation, possibly the largest area searched for a missing plane prior to the search for MH370.”

Other notable aviation mysteries that may never be solved include:

  • 1956: A nuclear B-47 Stratojet disappeared over the Mediterranean Sea along with its crew and two nuclear weapons.
  • 1979: A Varig Brazilian Airlines plane carrying $1.2 million worth of artwork vanished with its crew after leaving Japan’s Narita International Airport.
  • 2003: A Boeing 727-233 left Quatro de Fevereiro Airport in Luanda, Angola, without certified pilots, clearance or communicating with the tower and disappeared over the Atlantic Ocean. It was never found, despite a worldwide search.

More recently, and just prior to the disappearance of MH370, a Beech 1900 vanished somewhere over Africa. Neither the sole occupant, U.S. pilot Jerry Krause, nor any trace of wreckage was ever found.

“There was a thunderstorm in the area as the airplane was descending towards São Tomé,” Ranter said, noting at the time of disappearance, there was one pilot on board. “The plane had still not been traced by mid-May 2013.”

Krause's family is still trying to find out what happened.

There is hope for closure. In many cases, debris from missing planes is discovered years later, Ranter said. He cited a BSAA Avro Lancastrian that vanished between Montevideo, Uruguay, and Santiago, Chile, in 1947 was located in January 2000, and the wreckage of an Indian Air Force An-12 transport plane was found in August 2013, 45 years after it disappeared with 102 passengers on board.

These disappearances are a reminder that, in spite of modern equipment on the ground, planes are not continuously tracked because of poor or no radar coverage over large parts of the planet, said Cenciotti, adding that it is really difficult to find the wreckage of a plane once it crashed in an unknown location on land or, even worse, at sea.

Peter Bartos, a retired U.S. Air Force pilot, said prior to the 1980s, searches were hampered by a combination of navigation and communication equipment limitations, poor radar surveillance and weather forecasting, and large areas of blue ocean without communications links to land.

“Weather forecasting was a black art and routine access to satellite imagery was almost non-existent,” Bartos said.

Flying Air Force fighter aircraft crossing the Atlantic or Pacific, and even flying along the Mediterranean Sea, in the late 1980s to early 1990s, Bartos said he encountered huge stretches of distance where he was without any two-way communications to land.  

“That's why we flew with tanker aircraft -- militarized airliner with extra gas -- to provide that tenuous communications link and extra gas should we experience aircraft malfunctions,” Bartos said.

Even today there are huge areas where radar coverage is nonexistent, said Bartos, who now works for Northrop Grumman.

“Given the sheer volume of air traffic over land, it's not too surprising that there could have been a few disappearances of aircraft, especially in remote regions where air traffic control isn't as tightly regulated or well-equipped as in the United States or Western Europe,” Bartos said.

Much can be done to prevent another MH370, Cenciotti said. Current airplanes make several different kinds of services available to passengers such as interactive media, movie, games, music, and Internet and telephone, with the latter using satellite channels.

This link could be used to stream Cockpit Voice Recorder and Flight Data Recorder data - or just a subset of flight parameters - to reduce transmissions and save money, and report the black boxes position coordinates to ground stations in real time, Cenciotti said.

Another option is to make Underwater Locator Beacons more powerful and capable to operate for longer periods, since they currently are limited to 30 days, Cenciotti added.

In the case of a deliberate action by the pilot or passengers to take a plane down, as is suspected in the MH370 case, airlines could block the ability to switch off communication and navigation systems to make the plane almost invisible to radars.

“Since we can’t be completely dependent on aircrews to track airplanes wherever they fly, any ‘new’ system should be designed in such a way pilots can’t switch it off,” Cenciotti said.

So what did happen to Malaysian airliner?

The MH370 Search Strategic group, coordinated by Australian Transport Safety Bureau, has performed an extensive investigation, analyzing signals transmitted by the aircraft’s satellite communications terminal to Inmarsat’s Indian Ocean Region satellite.

The June 26, 2014, report shows the aircraft continued to fly for several hours after loss of contact, changed course shortly after it passed the northern tip of Sumatra, Indonesia, and traveled in a southerly direction until it ran out of fuel in the southern Indian Ocean west of Australia. Another report, released Sunday, exactly one year after the crash, by The Malaysian ICAO Annex 13 Safety Investigation Team for MH370, had similar findings, and also detailed in its 548 pages the incredible delays that occurred before a search-and-rescue operation was launched.

As with the 84 other unsolved aviation mysteries, Cenciotti is not confident answers are coming soon.

"It's impossible to say anything sensible about what happened to MH370,” he said.