"All I know is that I will be going back there to look for that wreck, come hell or high water and whether America believes me or not, I don't really care," Billings e-mailed this week from Singapore.
If all goes well, he'll return "later this year," he said.
Wilmington's Ric Gillespie, the man behind July's 3-1/2 week expedition, finds the New Britain theory implausible, saying Earhart simply didn't have enough fuel to fly near Howland Island - halfway to Hawaii - then turn around and reach New Britain.
"It's physically impossible," he said.
His Delaware-based group, TIGHAR, is also on the trail of plane wreckage - about 400 miles southeast of Howland, off the coast of a coral atoll called Nikumaroro, known as Gardiner Island in Earhart's day.
In March, Secretary of State Hillary Clinton publicly expressed her enthusiasm for TIGHAR's latest expedition, after a closer look at some 1937 negatives showed something - landing gear? - sticking out of the water off the coral atoll's coast.
No wreckage was noticed during the expedition itself, which used two sophisticated underwater devices to collect sonar data and high-resolution video. But post-trip scrutiny by forensic imaging specialist Jeff Glickman found a "debris field" - possible Electra wreckage - at the spot of the jutting object in the old photo.
Over the weekend, TIGHAR released a photograph - one frame from the video - showing objects identified as possible airplane parts, including a pulley, a fender and a wheel. TIGHAR hopes to release video soon, which will provide a better look, Gillespie said.
Another voyage to Nikumaroro, though, will be needed to retrieve the submerged objects and confirm exactly what they are.
"They are coral lumps," he e-mailed. ". . . It's a wonder they didn't pick out Fred's suspenders!"
The Gillespie group's website, www.TIGHAR.org, documents the discovery of all sorts of tantalizing clues during nine expeditions to Nikumaroro.
But Billings isn't swayed. "It is only a Hypothesis," he contends.
He counters his skeptics, including Gillespie, by saying that the strength of Earhart's radio transmissions doesn't prove she got close to Howland; she could have made her fuel last a long longer, especially with a tail wind; the numbers on the map almost certainly refer to her plane; and the engine wasn't from a B-17 that exploded over New Britain in 1942.
"The B-17E 41-2429 in the area was powered by Wright Cyclone 9-Cylinder Radial Engines of 1100 H.P. and I have seen one of these Wrights sitting in a river bed," he wrote, adding that he could help anyone seeking to recover any remaining crew members' bodies.
Billings, 72, who has made more than a dozen trips to New Britain, believes he's narrowed the Electra's location down to a couple of acres near two rivers - and hopes to find it this year and prove his theory to the world.
"Recognition of the aircraft as 'the' Electra is fairly easy. It is a unique aircraft and carries many, many distinctive features," he said, citing its fuselage tanks, as well as a variety of identifying numbers.
"Certainly the bulk of the aircraft and the engines will still be there, no question," he said.
His evidence is laid out on his New Britain Project website, www.electranewbritain.com.
For every searcher so far, though, proof has proved elusive.
Douglas Westfall, author of The Hunt For Amelia Earhart, sides with those who think she was lost at sea, because the extensive search at the time found nothing.
"There are three main hypotheses," he said, "for the disappearance of Amelia Earhart: Splash and sink, crash and land, or fly into the hands of the Japanese military. I'm a splash and float kind of guy."
Among the more wild ideas: She was an American spy. She became a Tokyo Rose, broadcasting war propaganda for the Japanese. A New Jersey woman, Irene Bolam, sued an author whose book accused her of secretly being Earhart.
Gillespie acknowledges he has yet to find the indisputable, "any-idiot artifact," though he's gathered many clues that fit together like a puzzle.
A Navy pilot reported seeing signs of habitation on Gardiner Island a week after the disappearance.
In 1940, 13 human bones, a woman's shoe and an empty sextant box were found on the rarely inhabited island. Although a physician initially determined they were male, the doctor's recorded measurements better fit a 5-foot-7 woman of European descent, according to a forensic anthropologist.
A zipper piece, a broken pocket knife, a shard of a cosmetics jar, pieces of shoes, a chunk of rouge are all consistent with Earhart and her belongings.
In 1937, dozens of reports surfaced of distress calls from someone saying she was Earhart, and one, picked up by a Florida girl who took notes, quoted the transmitter as repeating something that sounded like "New York City."
A freighter called the Norwich City was abandoned on the beach at Nikumaroro in 1929, and the rusting hulk remained visible for decades.
TIGHAR even found some bone fragments, and hopes another round of DNA analysis will finally make an identification.
Contact staff writer Peter Mucha at 215-854-4342 or firstname.lastname@example.org.