A combination of pilot failure and problems with navigation equipment were to blame for a plane crash in Indonesia that killed 102 people last year, the country's transport safety body said on Tuesday.

An analysis of the plane's cockpit voice recorder (CVR) revealed that a faulty Inertial Reference System, a navigation device, had diverted the pilots' attention from flight instruments, Indonesia's National Transport Safety Committee said in its report.

The Boeing 737-400 plane, operated by budget carrier Adam Air, crashed into the sea off Sulawesi island on New Year's day in 2007. All 102 people on board are presumed dead.

The report said maintenance records showed the plane had 154 recurring defects related to the navigation system during the two months before the crash.

"The CVR revealed that both pilots were concerned about navigation problems and subsequently became engrossed with trouble shooting the Inertial Reference System anomalies for at least the last 13 minutes of the flight, with minimal regard to other flight requirements," the report said.

Committee chairman Tatang Kurniadi said flight recorder data indicated a significant structural failure before the plane crashed.

"The pilots' failure was the last stage in the process after the plane entered a critical altitude," he told a news conference announcing the results of the investigation.

Another committee investigator, Mardjono Siswosuwarno, said the plane broke into pieces when it hit the sea.

The transport ministry grounded all Adam Air flights last week over safety concerns after another of its aircraft was involved in a non-fatal incident this month.

Adam Air said this month that a leasing firm had seized more than half its fleet of 22 planes after the airline defaulted on payments.

Indonesia's airline industry has grown rapidly in the past decade following liberalization, with the launch of new players and a wider choice of routes across the sprawling archipelago.

However, the world's fourth-most populous country has suffered a string of airline disasters in recent years, raising concerns about safety standards and prompting the European Union to ban all Indonesian airlines from its airspace.