As the expedition to Nikumaroro nears an end, hopes to identify pieces of Amelia Earhart's plane are waning.
A difficult environment and a number of technical issues have plagued the underwater search in the waters off the tiny uninhabited island between Hawaii and Australia where the legendary aviator may have landed and died as a castaway 75 years ago.
Carried out by The International Group for Historic Aircraft Recovery (TIGHAR), the hunt is due to end in the next few hours.
"After discussion and analysis of the results so far, they have decided that there is very little point in extending the trip," Patricia Thrasher, TIGHAR's president, said.
She added that the problem is the nature of the reef slope.
It's a vertical cliff from 110 feet down to 250 feet, with a shelf that runs along that contour from the spot where an unidentified object was photographed three months after Earhart's disappearance to the wreck of the British steamer SS Norwich City, which went aground on the island's reef in 1929.
"The airplane could have come to rest there briefly and lost pieces, but they have not found anything at all on that ledge. From there the cliff goes almost vertically down to 1,000 to 1,200 feet, with another ledge," Thrasher said.
TIGHAR researchers will spend the rest of the time searching that area.
"That is where the Norwich City wreckage came to rest, so maybe that's where the airplane stopped," Thrasher said.
Disappointingly, two promising targets identified a couple of days ago, turned out to be a large coral boulder and a much degraded piece of the Norwich City's keel.
Thrasher admitted that the question of searching for an airplane in such a difficult environment -- filled with nooks and crannies and caves and projections-- is even more basic than "what ledge" or "how far down."
"Given what we now know about this place, is it reasonable to think that an airplane which sank here 75 years ago is findable? It would be easy to go over and over and over the same territory for weeks and still not really cover it all. The aircraft could have floated away, as well," Thrasher said.
Nevertheless, TIGHAR has collected an enormous amount of data, which is certainly of great value to anyone doing ocean and reef research in that area.
"We won't know exactly how much, or what it all means, until it's integrated and analyzed...We have no idea what might be discovered as we pull together all the pieces without the fog of war to distract us," Ric Gillespie, TIGHAR's executive director, said.
Click here for more background and updates on TIGHAR's expedition to Nikumaroro.
This story was provided by Discovery News.