All 88 passengers and crew died when Flight 261 nosedived into the Pacific off the California coast. So far only four bodies have been recovered.

On Saturday, a private memorial service was held at Pepperdine University's seaside chapel in Malibu, some 35 miles (56 kilometres) along the coast from the crash site.

While family members mourned, navy crews were continuing to map the plane's wreckage on the seabed 10 miles offshore.

They are using a sonar device on board the deep-diving robot that recovered the flight data and cockpit voice recorders - the so-called black boxes.

US crash investigators say work is proceeding rapidly, thanks to calm seas and a relatively small debris area, and that mapping of the site is expected to be completed by Monday.

Click here for a graphic of the last minutes of Flight 261

On Friday, investigators unearthed a new clue from one the black boxes detailing the last minutes of the flight crew's conversation.

The tape revealed that a loud noise had been heard on the plane minutes before it crashed.

The noise was one of two revealed by analysis of the cockpit voice recorder, said John Hammerschmidt, who heads the National Transportation Safety Board's (NTSB) investigation.

He said experts examining the tape reported that 12 minutes before the recording ended with the MD-83 jetliner going into its fatal plunge, the pilots lost control of the aircraft but regained it after a minute or so.

"After recovery from this loss of vertical control, a flight attendant advised the crew that she had heard a loud noise in the rear of the aircraft," Mr Hammerschmidt told a news briefing.

"The crew acknowledged that they had heard it, too.

"Slightly more than one minute before the end of the recording, a loud noise can be heard on the recording and the airplane appears to go out of control," he said.

Mr Hammerschmidt declined to speculate as to what might have caused the noise.

The NTSB has previously said that radio transmissions and eyewitness reports from other commercial pilots in the area show the plane turned upside down or "corkscrewed" into the water following a series of increasingly desperate manoeuvres that lasted at least half an hour.

Rescuers have now retrieved parts of the wrecked plane, including an intact section of the tail and a piece of fuselage. Several large pieces of debris were also located using underwater robots.

The plane - en route from Mexico to Seattle via San Francisco - had been heading for an emergency landing at Los Angeles when it crashed.

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