Ever since flying machines began taking to the skies there have been instances of an airship or aircraft disappearing, sometimes with little or no trace, making it very difficult for investigators to ascertain exactly what happened.

Over the years flying has become considerably less risky and the odds of vanishing in an aircraft became increasingly slim in an ever-shrinking world where safety margins increased as aviation evolved into a mainstream industry, featuring vast enhancements in aircraft reliability, precision navigation, radar, and improvements to standard operating procedures.

Since more than seventy percent of the earth is covered by water, it’s no surprise most of the recorded aircraft disappearances involve a large body of it; some of the first attempts at transatlantic crossings, for example, fall into this category.

Charles Lindbergh conquered the Atlantic in 1927, but several other attempts that you probably haven’t heard about were not so successful. François Coli, Charles Nungesser, and their experience in the White Bird is a great example of such an attempt, and further testimony to the ocean being far from a hospitable place to go down in an airplane. Unforgiving, it will swallow an aircraft with ease and neglect to yield any clues in return.

According to the Aviation Safety Network’s accident database, a high percentage of all the aircraft disappearances reported occurred over the Atlantic and Pacific oceans during and shortly after World War II – mostly attributed to US Army Air Force or US Navy aircraft. Unfortunately, this made the 1940s and 50s a dark era for many a Douglas C-47 Skytrain or Consolidated PBY-5 Catalina–a number of which went missing without a trace.

Let’s take a look at 9 other unsolved aviation mysteries:

9) On March 10, 1956, 3 USAF personnel were lost when a Boeing B-47 Stratojet bound for Morocco from MacDill AFB vanished over the Mediterranean Sea near the Algerian coast. The aircraft was making the trip nonstop along with three other B-47s, which necessitated two aerial refueling. The four B-47s descended through a solid cloud layer to meet their KC-97 tanker, but only 3 B-47s made it through the cloud layer. Though they were not capable of detonation, the B-47 carried material for two atomic cores that were also lost, accounting for 2 of the US military’s “Broken Arrows.” No trace of aircrew nor aircraft was ever found despite an exhaustive search by several militaries.

8) On January 30, 1979, a Boeing 707 freighter operated by Brazilian airline Varig, went missing over the Pacific approximately 30 minutes after taking off from Tokyo’s Narita International Airport on its way to Los Angeles International. Aboard were 6 occupants and 153 paintings, worth over 1.2 million dollars (4.3 million in 2015 dollars). No emergency transmission was received, and no trace of the aircraft was ever found.

7) A Pakistan International Airlines Fokker F27 disappeared on August 25, 1989 while en route from Gilgit to Islamabad, with no trace of the aircraft ever found. This route took the flight over some of the most inhospitable terrain imaginable, the Himalayas. Remote mountainous areas like this have nasty a habit of hiding aircraft, as in the case of the British South American Airways flight that crashed into the Andes Mountains in 1947, and no evidence of the crash was found until 50 years later.

6) The Bermuda Triangle is also a well-known area where several aircraft have seemingly vanished. In late 1945, a flight of 5 TBM Avengers went missing after taking off from Fort Lauderdale, but two hours after departure the flight leader reported navigational instrument failure, which was also reported by the other Avengers in the flight. A Martin PBM Mariner amphibious search-and-rescue aircraft was launched to look for the stricken Avengers, but the Mariner soon disappeared as well, and was later believed to have suffered a catastrophic explosion in flight.

About 20 minutes after the Mariner took off, a tanker ship reported an airborne explosion and ensuing burning oil slick, but no conclusive evidence of the Mariner or the flight of 5 Avengers was ever found. A crashed TBM Avenger was found in the Florida Everglades in 1989, was thought to potentially be the flight leader’s aircraft, but the aircraft can no longer be located. These incidents, combined with the loss of other ships and aircraft in the area around the same time, including a pair of British South American Airways Avro Tudor passenger aircraft gave rise to the unfortunate legend of the Bermuda Triangle.

5) On June 5, 1969, a US Air Force RC-135E Rivet Amber, callsign IRENE 92, was enroute from Shemya AFB to Eielson AFB for maintenance when it reported vibration in flight, but the aircraft was under control. Later a transmission was made suggesting the crew was donning oxygen, and following a series of radio clicks no further contact was made with IRENE 92. No definitive cause, or trace of the aircraft was ever found, despite a 3-week effort. It was the only RC-135E ever built, with a very expensive (at $35 million in 1960 dollars) and very powerful (7 megawatts) Hughes phased-array radar system installed. Designed to track Soviet ballistic missiles, it could track a basketball-sized object from a distance of 300 miles and this system made it the most expensive aircraft in the USAF inventory at the time.

4) On March 16, 1962, a Lockheed L1049 Super Constellation operated by Flying Tiger Line disappeared while enroute from Guam to Clark AB in the Philippines while operating a Military Air Transport Service charter flight. A ship along the aircraft’s presumed flight path reported a large midair explosion, but an 8-day search yielded no evidence of aircraft or the 107 people onboard.

3) N844AA, a former American Airlines Boeing 727, took off from Luanda, Angola late in the evening on May 25, 2003, without any communication with air traffic control. The 727 headed southwest out over the Atlantic with both aircraft lighting and transponder off. Outfitted with large fuel tanks inside for delivering diesel fuel to the diamond mines in Angola, the 727’s unusual disappearance suggested theft and prompted serious investigation by various 3-letter agencies in the US, though that interest eventually waned.

2) Perhaps one of the most famous mysteries in all of aviation is the story of Amelia Earhart and Fred Noonan. The pair disappeared somewhere in the Pacific while attempting to follow the equator around the world in a Lockheed model 10 Electra. Recently discovered on a remote atoll in the south Pacific was a piece of sheet metal that had been installed on the aircraft while in Miami. This offered some additional clues into what might have happened to the pair while on their around-the-world flight, but is far from a definitive answer to the puzzle.

1) Aside from the disappearance of Amelia Earhart and Fred Noonan, Malaysian 370 is the obvious choice for the most widely-known disappearance of any aircraft in history. MH370, the Malaysian Airlines Boeing 777 that shocked the world when it vanished a year and a half ago enroute from Kuala Lumpur to Beijing, still has not been found despite a massive search effort that involved almost two dozen countries. Although the evidence thus far points to the aircraft running out of fuel over the Indian Ocean, the disappearance of Malaysian 370 raises questions of just how a modern airliner can completely vanish in the age of GPS and other technologies.

Another story for another time, perhaps. Recently though, a part of a wing washed up on Reunion Island near Madagascar and Malaysian officials quickly pronounced that the flaperon was from the missing 777, but other countries involved in the investigation have been considerably more cautious regarding the ongoing MH370 investigation.

The majority of these aviation mysteries will likely never be explained fully, or even to the extent that we as humans would find acceptable. A lot of the safety equipment and regulations in place today came about as a result of an accident or incident in the past, but that’s a tall order when there’s no wreckage to investigate.

One thing is certainly clear however: in this day and age it is extraordinarily difficult for an aircraft to simply disappear, and that’s a good thing!

(Featured Photo courtesy of the NAS Fort Lauderdale Museum)

This article was written by Jonathan Derden