Image caption There are several theories about what happened to Amelia Earhart on her last flight

An expedition to find out what happened to celebrated US pilot Amelia Earhart is returning to Hawaii without the evidence it was looking for.

The International Group for Historic Aircraft Recovery (Tighar) believes Earhart and her navigator crashed on a Pacific island and died soon after.

The $2.2m (£1.4m) expedition was searching for evidence of the wreckage in the waters around Nikumaroro.

Amelia Earhart was the first woman to fly solo across the Atlantic, in 1932.

"This is just sort of the way things are in this world," Tighar president Pat Thrasher said.

"It's not like an Indiana Jones flick where you go through a door and there it is. It's not like that - it's never like that."

Next year Tighar is planning a return voyage to the island, where they believe Earhart may have survived for a short time.

'Nightmare terrain'

The research team collected video and sonar data, and is expected to begin analysing it on the return journey to Hawaii, Ms Thrasher said.

Amelia Earhart Born in Kansas in 1897

First woman to fly solo across the Atlantic Ocean

Helped form the Ninety-Nines, a professional aviation group for women, and became their first president

Held multiple speed records

Updates from her husband, Ric Gillespie, who founded Tighar, suggested the search was cut short to five days from 10 because of "nightmare terrain", and accidents with equipment.

On 2 July 1937, Amelia Earhart and her navigator Fred Noonan took off from Papua New Guinea in their Electra 10E aircraft, en route to Howland Island.

Many experts think a navigational error caused the pair to run out of fuel over the sea. They were never seen again.

They were three-quarters of the way through an unprecedented circumnavigation of the globe around the equator.

On 3 July, the USS Colorado departed from Hawaii in search of Earhart and Noonan.

The research team set sail 75 years to the day after search teams went looking for the pair.

Tighar's expedition had the approval of the US state department and Secretary of State Hillary Clinton.

Artefacts that could have belonged to Earhart and Noonan have been found on earlier visits to the island and a photograph of the coast from October 1937 could show a blurred image of part of the plane.