Amelia Earhart standing in front of the Lockheed Electra in which she disappeared in July 1937. (Photo: Smithsonian Institution)

The unexplained disappearance of Amelia Earhart, the pioneering aviatrix who set out in 1937 to circumnavigate the globe and lost contact over the South Pacific, has long grabbed the attention of aviation fans and conspiracy theorists alike. But new research, presented Friday by researchers from The International Group for Historic Aircraft Recovery, uses digitized information management systems, antenna modeling software and radio wave propagation analysis programs to re-examine the 120 known reports of radio signals alleged to have been sent from Earhart's aircraft during the search and rescue period between July 2, 1937 and July 18, 1937.

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Researchers concluded that 57 of the distress calls were credible, which gives them several clues about what may have happened to Earhart and her navigator, Fred Noonan, on that fateful summer day.

"Amelia Earhart did not simply vanish on July 2, 1937," Richard Gillespie, executive director of TIGHAR, told Discovery News. "Radio distress calls believed to have been sent from the missing plane dominated the headlines and drove much of the US Coast Guard and Navy search."

"When the search failed, all of the reported post-loss radio signals were categorically dismissed as bogus and have been largely ignored ever since," Gillespie said.

A series of distress calls made in the wake of her disappearance were sent over her Electra radio on frequencies that would have been rare for others to use in that time period. "Earhart's Electra was the only plausible central Pacific source of voice signals on 3105 kHz," said Gillespie.

These transmissions join a host of recent discoveries of artifacts that have been tied to Earhart's time as a castaway in the South Pacific, as reported by the Christian Science Monitor, including "a bone-handled pocket knife of the type known to have been carried by Earhart, part of a man's shoe, part of a woman's shoe, a zipper of the kind manufactured in the 1930s, a woman's compact, and broken pieces of a jar appearing to be the same size and unusual shape as one holding "Dr. Berry's Freckle Ointment." (Earhart was known to dislike her freckles.)"

Though small items have turned up, Earhart's Lockheed Electra aircraft still remains missing.

"The Electra hasn't yet been found, because the ocean is 17,000 feet deep around Howland Island, and only recently has technology allowed the construction of underwater vehicles that can endure the pressure at that depth," writes Susan Butler for the Daily Beast. Butler wrote the 1997 biography of Earhart, "East to the Dawn: The Life of Amelia Earhart."

Earhart's final in-flight transmission to the Howland Island Coast Guard station hints at her possible landing point, which may have been Gardner Island, an uninhabited island now called Nikumaroro in the in the Republic of Kiribati.

The transmissions give the team some idea of where Earhart and Noonan may have been on the island. In order to use the radio, the engine would have to be on, which meant that the propeller would need to be free from water or obstacles to spin. The team used tidal records to verify that the transmissions of credible signals came in during periods where the water level was low enough to operate the engine.

TIGHAR researchers will return to the South Pacific in July and use submersibles to try to find the aircraft Earhart and Noonan piloted onto the island.