What happened? MH370 and other aviation mysteries

The puzzling disappearance of a Malaysian jetliner in 2014 is not the first time a plane has vanished without a trace.

Here are six other cases of plane disappearances and disasters, some of which remain unsolved.

Malaysia Airlines Flight 370

The Boeing 777 passenger jet vanished about an hour into its flight from the Malaysian capital of Kuala Lumpur to Beijing. There was no distress call before it lost contact over the sea between Malaysia and Vietnam.

International search teams combed the Indian Ocean for months, but have found no clues. Three pieces of the aircraft found later do not explain what caused it to crash.

Air France Flight 447

That was the last contact with the plane. Its last known position – two to four days by ship from the nearest ports – complicated the searches.

It took almost two years before the bulk of the wreckage, the majority of bodies, and the voice and data recorders were recovered.

French authorities said ice crystals disrupted the system used to determine the plane’s airspeed, causing the autopilot to disconnect. The plane plunged into the ocean.

Company-owned Boeing 727

A company-owned Boeing 727 vanished while flying from the Angolan capital of Luanda to Burkina Faso on May 25, 2003.

The plane, which reportedly sat unused for months before its unexpected departure, took off with its lights off and a dysfunctional transponder, according to Air & Space. Witnesses said the plane taxied erratically and did not communicate with the flight tower before takeoff.

There are conflicting reports on the number of people in the jet, but flight engineer Ben Charles Padilla is believed to be one of them. Some reports say he was alone, while others say three people were aboard.

The plane has not been heard from since. Its whereabouts are unknown to this day.

EgyptAir Flight 990

The passenger jet made a rapid descent, plunging almost 14,000 feet in 36 seconds.

The Boeing 767, en route to Cairo from New York City, crashed into the Atlantic Ocean off the Massachusetts coast in October of that year.

Though its debris was later found in the Atlantic Ocean, speculation remains on what caused the crash.

Theories include a possible suicide by the pilot or co-pilot, complete with tales of a chaotic struggle for controls in the cockpit. Egyptian authorities have said a mechanical failure was to blame.

1996: TWA FLIGHT 800

The Paris-bound plane exploded in midair shortly after takeoff from New York City, killing all 230 people aboard.

Witnesses said they saw a streak of light and a fireball, leading to suspicions that terrorists struck the plane with a rocket. Others blamed a meteor or a missile.

The National Transportation Safety Board ruled that the explosion was caused by an electrical short circuit, which detonated the fuel tank and caused the Boeing 747 to break into pieces in the waters off Long Island.

Despite the explanation, conspiracy theories of a government coverup abounded.

BSAA ‘Stardust’

A British South American Airways (BSAA) Avro Lancastrian, nicknamed “Stardust,” disappeared after taking off from Buenos Aires to Santiago on August 2, 1947. There were 11 people on board.

After searches for the plane named Stardust turned up nothing for more than 50 years, conspiracy theorists jumped into action. But theories of aliens, among others, were invalidated in 2000, when the wreckage of the plane was found buried deep in a glacier in the Argentine Andes.

The crash on August 2, 1947, killed 11 people, the BBC reported.

Stardust’s final Morse code transmission was the word “STENDEC.” The meaning of the word remains a mystery.

Flight 19 Navy Bombers

Flight 19 refers to five Navy bombers that disappeared off the Florida coast on December 5 of that year.

A flight instructor flew one plane, and qualified pilots were in the others, according to the Naval History and Heritage Command.

Radio transmissions indicated that the instructor got lost when compasses malfunctioned over the Bermuda Triangle. Radio contact was lost before the exact problem was determined, and no traces of the planes were ever found.

Adding to the mystery, a search aircraft sent to look for Flight 19 also disappeared. The patrol plane, which took off later that day, has not been seen or heard from since.

Flight 19 was reported in the area informally known as the Bermuda Triangle.

1942: British fighter

Its pilot was never heard from again, and the damaged P-40 Kittyhawk was presumed lost forever.

But in 2012, an oil company worker discovered it seven decades after the accident. Surprisingly, it was extraordinarily well-preserved, and most of its fuselage, wings, tail and cockpit instruments were intact.

Back then, experts say, planes flew with basic supplies, so its pilot’s chances of survival were not good.

1937: Amelia Earhart

The disappearance of Amelia Earhart is possibly the most famous unsolved aircraft mystery.

The groundbreaking aviator was on her most ambitious flight, vying to become the first woman to fly around the world.

In 1937, she attempted the voyage in her twin-engine Lockheed Electra. With about 7,000 miles left to go, she made a challenging landing at Howland Island in the mid-Pacific.

Her radio transmissions became unclear, and the last thing she reported over her radio was, “We are running north and south,” according to an online biography.

After spending $4 million and searching 250,000 square miles of ocean, the United States called off its search.

Many theories exist today, but her fate and that of navigator Fred Noonan remain unknown. This year, new footage emerged of her preparing for the doomed flight.

CNN’s Mariano Castillo contributed to this report