The International Group for Historic Aircraft Recovery (TIGHAR) believes it has the key to unlock the decades-old mystery of what happened to famed aviator Amelia Earhart and her navigator Fred Noonan in their planned circumnavigation of the globe in 1937. TIGHAR’s The Earhart Project analyzed dozens of radio transmissions received by radio amateurs and other short-wave listeners during the frantic search to locate Earhart’s plane when she did not make her scheduled arrival at Howland Island. Many theories have sprung up over the years to explain the mysterious disappearance, but a TIGHAR research paper entitled The Post-Loss Radio Signals, published in July by The Earhart Project, maintains that “the patterns and relationships emerging from the data show that TIGHAR has answered the 81-year-old question: ‘What really happened to Amelia Earhart?’”

The Earhart Project “is testing the hypothesis that Amelia Earhart and Fred Noonan landed, and eventually died, on Gardner Island, now Nikumaroro in the Republic of Kiribati,” its website says.

In July 1937, a young teenager named Betty Klenck, listening to short-wave bands on her family’s radio, intercepted and transcribed pleas for help that TIGHAR calls “a remarkable record of perhaps the last communication” from Earhart and Noonan and “leave little doubt” that the 15-year-old heard a genuine distress call from the pair, transmitted from the aircraft Electra. Klenck’s notebook, discovered in 2000, inspired TIGHAR’s effort to catalog all reception reports.

TIGHAR analyzed nearly 60 other reception reports made in the wake of Earhart’s failure to arrive on Howland Island. The vast majority, TIGHAR said, came from government or commercial operators as well as “licensed amateurs” working for the US Interior Department on Howland and Baker Islands, listening on Earhart’s primary, harmonically related frequencies of 3,105 and 6,210 kHz. TIGHAR contends that higher-order harmonics of the primary frequencies enabled the “accidental” reception of Earhart’s transmissions at greater distances, since those higher-frequency signals would be more prone to ionospheric propagation.

Reports came from the Pacific and the continental US, but poor reception appears to have precluded efforts to pin down the downed plane’s coordinates, although Earhart did report that she was on the 157°/337° track to Howland and down “on an uncharted island” that was “small, uninhabited.” The radio transmissions became progressively more desperate, with Earhart reporting that Noonan was injured and subsequently delirious. The commander of the US Coast Guard vessel Itasca, which was involved in the search, discounted the contemporary radio reception reports, saying that all available land areas had been searched. He expressed doubt that Earhart and Noonan had made any radio transmissions at all after the plane disappeared on July 2, 1937.

The bulk of the paper — published on July 24, which would have been Earhart’s 121st birthday — is devoted to “Post-Loss Radio Signals and Analysis 2.0” by TIGHAR Senior Researcher Richard Gillespie and Robert Brandenburg.

A study in Forensic Anthropology published earlier this year, Amelia Earhart and the Nikumaroro Bones: A 1941 Analysis versus Modern Quantitative Techniques, by Richard L. Jantz, claims that an analysis of bones found on Nikumaroro in 1940 prove that Earhart died as an island castaway. The study determined that the bones were a most likely Earhart’s, contradicting a contemporary conclusion that the bones were those of a male.