The wreckage of a Pan American Airways plane has been found 74 years after it plunged into the Atlantic Ocean in a crash that prompted mandatory airline safety briefings.

The Clipper Endeavor was found 2,000ft (610m) below sea level off the coast of Puerto Rico with a sonar-equipped drone. It went down on 11 April 1952 following multiple-engine failure shortly after take-off.

Everyone onboard survived the impact – but passengers struggled to locate life vests and rafts as the plane rapidly sank. Of the 69 passengers and crew onboard, just 17 survived.

The disaster led to sweeping reforms in aviation safety, including compulsory pre-flight safety briefings on every commercial flight.

The expedition to find the wreckage was led by the Air/Sea Heritage Foundation in partnership with the Discovery Channel's Expedition Unknown show and several other organisations.

Last month, explorers discovered the ruins of the Douglas DC-4 aircraft using an autonomous sonar drone that detected the aircraft's fuselage and tail.

"We are all stunned and elated ​by this ​discovery, yet also humbled ⁠to remember what happened in that place so long ago," said Russ Matthews, president of ​the Air/Sea Heritage Foundation.

The plane had been carrying 64 passengers and five crew to New York when the pilot was forced to make a violent water landing.

The confusion that ensued became a "catalyst" for modern regulations mandating better flotation equipment on planes and preflight briefings on how to use it, aviation safety expert John Cox told AP.

Today, before every commercial flight, cabin crew are required to outline where a plane's exits are, as well as the location of life vests and how to inflate them.

"Every time you step onboard an airplane today, you are safer because of what happened to Clipper Endeavor and her passengers three-quarters of a century ago," said Expedition Unknown host Josh Gates.

Matthews, a maritime explorer and historian, first became interested in the crash in 2019, after reading about a luggage tag from the flight that had washed ashore in Florida.

He said in a statement that he had been "astonished that such an important story had largely faded from public memory".

He then began piecing together the aircraft's final moments using reports from the Civil Aeronautics Board, the predecessor to the US Federal Aviation Administration.

The breakthrough came after researchers uncovered records from a public hearing in Puerto Rico, including a map drawn by air force pilots who had witnessed the crash, which helped narrow down the search area.

Researchers used historical records and weather data from the time of the crash to identify the 10 square nautical miles of Atlantic Ocean seabed where the wreckage was likely resting.

An attempt to locate the wreckage in 2024 was abandoned due to poor weather – but Matthews said his team had been determined to return before the 75th anniversary of the crash.

A drone found the wreckage – which had broken into two sections – during its first pass of the search area on 2 June.

A follow-up photographic survey confirmed the wreckage was of the Clipper Endeavor, providing images that revealed the Pan Am logo and aircraft's name were still visible on the fuselage.

"To have a front-row seat to an expedition like this as it's unfolding is tremendous, and so I feel really lucky that we were able to be a part of it," said Gates, who was aboard the surface ship when the wreckage appeared on screen.

The discovery could offer fresh hope for the families of passengers of other planes that are presumed to have crashed in the ocean, such as Malaysia Airlines Flight 370.

It disappeared 12 years ago with 269 people onboard and, despite numerous searches in the Indian Ocean, has not yet been located.

The discovery of the Clipper Endeavor will be featured in a special episode of Expedition Unknown this Autumn.