Indonesian budget carrier Adam Air is close to signing a deal with a salvage firm to retrieve the black box of one of its planes which crashed on New Year's Day with 102 people aboard, the airline's head said on May 25.

A U.S. navy ship with specialised equipment detected signals in January suspected to be from the plane's flight recorder, when the ship was part of the search for the missing Boeing 737-400.

Wreckage from the plane showed up in waters some weeks after the crash, but the black box has never been retrieved, making it difficult to determine the cause of the accident.

"We have a deal with U.S.-based Phoenix International to retrieve the black box. The plan will go ahead in early July," Adam Air chief executive Adam Suherman told Reuters.

He added that "retrieving the black box would not only serve the interest of Adam Air but would serve the interest of the aviation community in general."

Experts said in January that retrieving the flight recorder, set up to give off a signal for 30 days to aid detection, may be difficult and it could be lying in waters as deep as 1,700 metres (5,600 ft).

Locating the black box may be even tougher now as it may have shifted or may be buried under sediment.

The 17-year-old plane was heading from Surabaya in East Java to Manado in northern Sulawesi when it vanished in bad weather. The plane made no distress call, although the pilot had reported concerns over crosswinds.