10 Unsolved Airplane Mysteries

The disappearance of Malaysia Airlines Flight 370 captured global attention in early 2014. The plane mysteriously deviated from its scheduled route between Kuala Lumpur and Beijing, vanishing somewhere over the Indian Ocean, with all 239 passengers and crew members on board [source: Associated Press].

As this article was being finalized, search teams were still tasked with scouring an area exceeding 22,000 square miles (57,000 square kilometers) in the Indian Ocean. The chances of finding the plane seem slim, let alone solving the enigma of its disappearance [source: Associated Press].

It's astonishing to consider that a plane could go missing today, with all the technology at our disposal. For instance, air traffic controllers can monitor planes using two different radar systems when they fly over land.

When an aircraft flies over the ocean, beyond the reach of ground radar, it uses a different system, Automatic Dependent Surveillance, which sends a signal to satellites to report its location. Aircraft are also designed to alert the Aircraft Communications Addressing and Reporting System in the event of mechanical failures. Investigators suspect that in the case of MH 370, these systems were intentionally disabled, possibly by saboteurs [source: Topham].

While the Malaysia Airlines mystery remains deeply perplexing, it is not unique. Since 1948, over 100 other aircraft have vanished mid-flight, never to be found, according to data from the Aviation Safety Network, an international body that monitors airline accidents, hijackings, and safety concerns [sources: Topham, ASN]. Other planes have crashed under circumstances that remain unexplained. Here’s a look at 10 of the most mysterious aviation cases in history.

10: Amelia Earhart Disappears

In June 1937, renowned aviator Amelia Earhart embarked on her quest to become the first woman to fly around the world, a journey covering 29,000 miles (46,671 kilometers). By July 2, she had completed all but the final 7,000 miles (11,265 kilometers), when she and her navigator Fred Noonan departed from Lae, Papua New Guinea, on a 2,556-mile (4,114-kilometer) flight to Howland Island, a small island in the Pacific.

A U.S. Coast Guard cutter, the Itasca, was stationed just off the coast, and two other vessels were placed along the flight path to mark Earhart's plane's route. However, the plane encountered overcast skies and sporadic rain, making celestial navigation, Noonan's preferred method, challenging. The following morning at 7:42, the Itasca intercepted a radio message from Earhart: "We must be on you, but we cannot see you. Fuel is running low." About an hour later, Earhart radioed, "We are running north and south" [source: AmeliaEarhart.com].

That was her final transmission, and her plane never reached its destination. Rescuers conducted what was then the largest search effort in aviation history, covering 250,000 square miles (647,497 square kilometers) of ocean in a failed attempt to locate her. Some believe the plane crashed into the ocean and the passengers perished; others suggest they survived the crash but succumbed to dehydration on a deserted island, or that they were captured by the Japanese, who mistook them for spies [source: Roach and Than]. To this day, the fate of Earhart and Noonan remains unsolved.

9: What Does STENDEC Mean?

In August 1947, a British airliner carrying 11 people took off from Buenos Aires bound for Santiago, Chile, and mysteriously disappeared just moments before its scheduled landing. The only clue left behind was an enigmatic Morse code message: "STENDEC," which was repeated three times in the plane’s final transmission.

Fifty-three years later, in 2000, a team of searchers finally discovered the missing aircraft, which had crashed into a mountain approximately 31 miles (50 kilometers) from its intended destination. A glacier had trapped the plane in ice. After examining the engines, investigators found no signs of mechanical failure but proposed another theory. They believed the plane had ascended to higher altitudes to avoid bad weather and encountered a jet stream, a high-speed wind not yet understood at the time. This jet stream likely slowed the aircraft, causing it to descend too early, resulting in the plane veering toward the mountain. However, the final message sent by the plane remains a mystery, continuing to elude the numerous attempts to decode it [sources: BBC News, BBC News].

8: Was It an Alien Spacecraft?

In January 1948, Capt. Thomas Mantell, a Kentucky Air National Guard pilot, along with other pilots, took off from the Fort Knox airfield in P-51 Mustang fighters, chasing a swiftly moving, circular object heading west. The other pilots abandoned the pursuit when the large metallic object ascended to an altitude of 22,500 feet (6,858 meters), well above the danger zone for flying without oxygen, which starts at 14,000 feet (4,267 meters). However, Mantell continued his chase of the mysterious craft. His plane ultimately fell from the sky and crashed in Kentucky.

The official explanation was that Mantell lost consciousness due to oxygen deprivation, but questions linger about why he pursued the object so intently and what exactly he was following. Initially, Air Force officials suggested he had mistakenly pursued the planet Venus, but some witnesses believed he encountered a spacecraft or another UFO. The object is now thought to have been a Skyhook weather balloon used in a secret project to measure radiation levels [sources: National Guard History eMuseum, Randle].

7: The Missing H-bomb

In February 1958, while on a routine training mission off the coast of Georgia, a B-47 bomber collided with an F-86 fighter jet whose pilot failed to spot the bomber on his radar. The crash caused the fighter's left wing to break off and severely damaged the bomber's fuel tanks. The bomber's pilot, Air Force Col. Howard Richardson, faced a tough decision. His aircraft was carrying a 7,000-pound (3,175-kilogram) H-bomb, and Richardson feared that the bomb might detach from the damaged plane during the landing attempt.

To prevent this from happening, Richardson chose his only alternative and jettisoned the bomb into the waters off Tybee Island, Georgia, before safely landing at Hunter Air Force Base near Savannah. Despite a two-month search by the Navy, the bomb was never found, and for many years, its location remained a mystery. The Air Force claims the bomb poses minimal risk if left undisturbed [source: NPR].

6: The Vietnam War Casualties Who Never Got to Vietnam

These lost servicemen's names have never been included on the Vietnam Veterans Memorial in Washington. Strangely, no government agency — whether the Army, Air Force, Pentagon, State Department, National Archives, or CIA — claims to have any records related to the mission. In March 1962, Flying Tiger Line Flight 739, carrying 93 U.S. military advisers, three South Vietnamese officers, and 11 crew members, mysteriously disappeared between Guam and the Philippines while en route to Vietnam. Despite extensive searches, no wreckage was found, although some witnesses reported seeing a vapor trail and an explosion in the sky the night it vanished [source: Burke].

Some suggest the aircraft was brought down by Viet Cong sabotage, potentially making the passengers the first casualties of the Vietnam War. Others propose that it was shot down by friendly fire. Oddly, at least three soldiers confided to their families that they had a foreboding feeling that they wouldn't return from this mission alive [source: Burke].

5: An Artistic Disappearance

In January 1979, a Boeing 707 cargo plane, carrying 153 artworks by the renowned Brazilian-Japanese artist Manabu Mabe, valued at approximately $1.2 million, departed from Narita International Airport in Tokyo. The flight, operated by Varig Airlines, was slated to make a stop in Los Angeles before continuing to Rio de Janeiro.

However, the plane never reached its intended destination. About 30 minutes after takeoff, while still north of Tokyo, air traffic controllers lost contact with the pilot. Despite extensive search efforts, no trace of the plane, its cargo, or its six crew members has ever been discovered [sources: ASN, Hastings].

4: Mechanical Failure or Suicide?

The incident stirred international debate. On October 30, 1999, EgyptAir Flight 990, bound for Cairo, took off from Kennedy Airport in New York with 217 people aboard. The flight was commanded by senior pilot Ahmad al-Hai, with experienced co-pilot Gameel al-Batouti assisting him.

The aircraft reached an altitude of 33,000 feet (10 kilometers) and flew without incident for 30 minutes, before tragically plunging into the Atlantic Ocean, 60 miles (97 kilometers) south of Nantucket, Massachusetts. All aboard perished in the crash [source: Langewiesche].

What led to the disaster? Egyptian authorities attributed the accident to mechanical failure, insisting that suicide is forbidden in Islam. However, the U.S. National Transportation Safety Board (NTSB) concluded that the co-pilot intentionally caused the crash, noting that the autopilot was disabled, the plane was in a controlled dive, and the co-pilot repeatedly muttered, "I rely on God." The NTSB's final report pointed to the co-pilot's "manipulation of the airplane controls," a finding that Egypt continues to challenge [source: Wald].

An EgyptAir pilot later informed the FBI that Batouti had recently been demoted following allegations of sexual misconduct. It was suggested that he may have crashed the plane in a tragic act of suicide or as an act of revenge against his supervisor, who was a passenger aboard the flight [source: Wald].

3: The Stolen Airliner

In May 2003, a Boeing 727, owned by a leasing company based in Florida, was undergoing maintenance at an airport in Luanda, Angola. Unexpectedly, the plane rolled onto a runway without permission from the control tower and took off in a haphazard manner, with its lights off and no transponder signal.

Onboard were Ben Charles Padilla, a skilled mechanic and flight engineer overseeing the repairs, along with his newly hired assistant, John Mikel Mutantu, from Congo. Neither man was trained to fly a 727 – Padilla had only a private pilot's license, and Mutantu had no flying qualifications. Both men, along with the plane, vanished without a trace and were never found.

Initially, authorities suspected terrorism or an insurance fraud scheme. However, they now believe the incident may have involved a hijacking carried out for financial gain [source: Wright].

2: The Ghost Plane

One of the most chilling episodes in aviation history occurred in August 2005, when Helio Airways Flight 522 was on a brief flight from Cyprus to Greece. The plane veered slightly off its course, and despite 19 radio requests for clarification, there was no response.

Eventually, two F-16 fighter jets caught up with the aircraft and discovered the situation. The pilots saw that the captain's seat was vacant, while the co-pilot appeared unconscious, with his oxygen mask hanging loose from the ceiling. Meanwhile, the passengers were frozen in their seats due to the temperatures reaching minus 58°F (minus 50°C).

The fighter jets followed the "ghost plane" as it continued flying on autopilot until it ran out of fuel and crashed into a hill. The Greek authorities' official investigation suggested that the pilots had mistakenly set the plane's pressurization system to manual after takeoff, which prevented the cabin from automatically repressurizing when it lost pressure. Furthermore, the crew failed to recognize the signs of pressure loss — and lack of oxygen — until it was too late. However, this explanation leaves some questioning whether the plane was haunted [sources: Daily Mail, Krisch].

1: Was a Sleepy Pilot to Blame?

Much like the infamous disappearance of Malaysia Airlines Flight 370, Air France Flight 447 vanished over an area of the ocean where radar coverage was nonexistent. In June 2009, this Airbus A330-200, carrying 216 passengers and 12 crew members, disappeared while en route from Rio de Janeiro to Paris.

For several days, the fate of the aircraft remained unknown. Even after wreckage was located and recovered, the circumstances surrounding its disappearance remained unclear. Despite the plane being equipped with the latest in tracking and communication technology, no distress signal had been sent at any time. Two years later, the plane's black boxes were finally retrieved from the ocean [source: Smith].

According to a 2012 report from French air safety investigators, the crash was likely caused by a series of unusual errors. Ice crystals formed on a probe, causing it to give faulty speed readings and disengage the autopilot. The co-pilots, who were in charge during the captain's break, became confused by the malfunction. When the captain returned 90 seconds later, the plane was already in a stall that he could not recover from. The aircraft crashed two minutes and thirty seconds later [source: BEA].

The delay in the captain’s response to the co-pilots' desperate calls for assistance remains unexplained. Media reports mentioned that the captain was traveling with a female companion and had only slept for one hour the night before [sources: Battiste, Smith].