Investigators found out that the Inertial Reference System (IRS) failure and the unsuccessful attempts of the pilots to recover it as the main cause of the crash of a plane of budget airline Adam Air that killed all 102 people on board in New Year in 2007 at the waters of central Indonesia, local media reported on March 25.

But, the National Transport Safety Committee's chief Tatang Kurniadi refused to categorize the failure of pilot attempt as human error.

The Boeing 737 with registration number of PK-KKW departed from Djuanda Airport at Surabaya of East Java province to Sam Ratulangi Airport at Manado of Nort Sulawesi province.

It disappeared from radar while cruising at 35,000 feet, Kurnaidi said.

"This accident resulted from a combination of factors including the failure of the pilots to adequately monitor the flight instruments. Preoccupation with a malfunction of the Inertial Reference System diverted both pilot's attention from the flight instruments and allowed the increasing descent and bank angle to unnoticed," he told a joint press conference at the transport ministry office.

Kurniadi said that the pilots did not detect and appropriately arrest the descent soon enough to prevent loss of control.

"The Cockpit Voice Recorder revealed that both pilots were concerned about navigation problems and subsequently become engrosses with trouble shooting Inertial Reference System (IRS) anomalies for at least the last 13 minutes of the flight, with minimal regard to other flight requirements. This included identification and attempts at corrective actions," said Kurniadi.

The aircraft reached 3.5 g, as the speed reached March 0.926 during sustained nose-up elevator control input while still in a right bank, he said.

The recorded airspeed exceeded Vdive (400 kcas), and reached a maximum of approximately 490 kcas just prior to the end of recording, said Kurniadi.

Another investigator Santoso Sayogo said that the aircraft felt with very high speed to the sea and broken into very small pieces.

Several weeks after the accident, one of Adam Air's plane suffered from the fuselage that was torn in half after a hard landing and earlier this month another Adam Air's plane skidded off runway injuring five people.

The series of accidents have led the ministry to ban the airline from flying, as investigators found that it had not met with the standard of safety.

The carrier had not conducted an upgrading of pilot skills regularly, said Bambang Erfan, an official of the ministry.

Plane is a preferred transport mean in the sprawling archipelago country, but lack of safety standard has triggered many accidents recently that killed hundreds of lives.

It led the European Union to impose air travel ban on 51 airlines in Indonesia on July 6 last year, including Adam Air, and extended the ban on November 28 after revoking its ban on Pakistan International Airlines (PIA) and Blue Wing Airlines of Surinam.

Indonesia, which has been struggling to exit from the ban. The country now is under the monitoring of the group for the possibility of revoking the ban.

The aviation authorities from Indonesia and EU have agreed to cooperate for accomplishment of the flight safety standard in Indonesia after the group authorities said in January that a lot has to be done by Indonesia to fully meet with the air safety standard.