Here’s what you’ll learn when you read this story:

• The disappearance of the British South American Airways Star Dust airliner in 1947 is one of aviation’s most enduring mysteries.
• The wreckage was eventually found 50 years later on Mount Tupungato, but experts don’t know what to make of the aircraft’s final message: STENDEC.
• Theories suggest it is a scrambled up message that’s meant to read “DESCENT” or possibly a mistranslation of the callsign for the Los Cerrillos Airport.

The history of aviation is filled with mysteries. Whatever happened to Amelia Earhart? Who (and where) is D.B. Cooper? Whatever happened to all those once-famous passenger airlines that just seemed to disappear without a trace? While these questions are certainly head-scratchers for the history books, only one of them involves a cryptic, seven-letter message that has stumped investigators and cryptography experts for 80 years.

On August 2, 1947, a British South American Airways (BSAA) Avro Lancastrian airliner named Star Dust left from Morón Airport in Buenos Aires, Argentina, en route to Los Cerrillos Airport in Santiago, Chile. By all accounts, the trip was a routine flight filled with six passengers and five crew, including a former Royal Air Force (RAF) pilot with World War II combat experience. The nearly four-hour flight was largely uneventful and at 5:41 p.m. local time, the Star Dust transmitted its arrival time in morse code to the Santiago airport as 5:45 p.m. But it never arrived.

While the fight might have been routine, the terrain between Buenos Aires and Santiago is anything but. Santiago rests as the very base of the Andean mountain range, which dominates the western portion of South America, so approaching it over the Andes requires a rapid, steep descent that’s often turbulent. But the plane was up for the job. Retrofitted from the RAF’s Lancaster bomber, it could fly higher and farther than any airliner in the world at the time, according to BBC. When the pilots reported their arrival time, their message read (in morse code), “ETA SANTIAGO 17.45 HRS STENDEC.” When the Chilean Air Force radio operator asked for clarification regarding the last word, the aircraft responded “STENDEC. STENDEC.” And then there was silence. The plane never arrived.

A search-and-rescue crew found no evidence of the plane near Santiago and couldn’t find wreckage high in the Andes, either. Incredibly, the plane was just gone.

“The mystery remained in my mind for the last half a century,” Frank Taylor, a BSAA pilot who participated in search operations for the Star Dust, told BBC in 2000. “In fact, I can safely say I had given up hope of ever hearing they’d found the aircraft.”

Then, the impossible happened. In 1998, two Argentine mountaineers found the wreckage of a Rolls-Royce Merlin engine—the exact model used by the Avro Lancastrian airliner—along with shreds of clothing on the slopes of Mount Tupungato 50 miles east of Santiago. Two years later, an Argentine Army expedition found more wreckage, along with human remains that were eventually confirmed (via DNA testing) to be from passengers on board the flight. With the plane finally located, investigators slowly pieced together the mystery. They theorized that the plane likely lost ground visibility in cloudy conditions and flew into a jet stream. The resulting headwind slowed down the plane enough to confuse the pilots, who descended too early and crashed into the mountainside.

However, the mystery of what STENDEC means remains open. One simple theory is that it means DESCENT, as the word is anagram of the transmission, and it’s possible the radio operator was suffering from hypoxia. Another theory is that it’s a mistranslation of “SCTI AR,” which uses the same dot-dash sequence as STENDEC. “SCTI” was the International Civil Aviation Organization (ICAO) station identifier for Los Cerrillos airport and “AR” is commonly used to signal “end of message.”

Although it’s unlikely we’ll ever know for sure, the story of the Star Dust is still unfolding, because reduced glaciation in the Andes will eventually reveal more of the wreckage over time.