The National Transportation Safety Committee (NTSC) has blamed the Adam Air accident off South Sulawesi on Jan. 1, 2007, which killed 102 people, on pilot errors and problems with navigational equipment.
The committee quoted technical log (pilot reports) and maintenance records showing between October and December, 2006, there were 154 recurring defects, directly and indirectly related to the Boeing 737-400 aircraft's inertial reference system, mostly the left system.
"The preoccupation (of pilots) with the malfunction of the inertial reference system diverted both pilots' attention from the flight instruments, allowed the increasing descent and left the bank angle unnoticed," the report stated.
Consequently, the pilots did not detect and appropriately arrest the descent soon enough to prevent loss of control, the committee added.
The Boeing 737, registered PK-KKW, departed from Djuanda airport in Surabaya early on Jan.1, 2007 for Manado in North Sulawesi, but the plane disappeared off the radar a few hours later while cruising at 35,000 feet.
Following an extensive land, sea and air search, the wreckage was located in the water and on the shores along the coast near Pare-Pare, nine days after the aircraft went missing.
The search was suspended when it was determined that the wreckage was located in the ocean at a depth of some 2,000 meters, requiring specialized recovery equipment not available in the region.
The flight recorders--a digital flight data recorder and cockpit voice recorder--were recovered in late August, 2007, after four days of salvage operations.
The transport ministry grounded all Adam Air planes last week over safety concerns after another of its Boeing 737-400 aircraft was involved in a non-fatal incident at Hang Nadim airport on Batam island early this month.
The accident was the latest in a string of airline crashes over the past few years that prompted the European Union to effectively ban all Indonesian airplanes from its airspace as of July, 2007.
Adam Air itself had been plagued with a series of accidents over the past few years. Just one month after the Sulawesi crash, an Adam Air Boeing 737 jetliner carrying 148 passengers buckled its fuselage in a hard landing, also at Djuanda airport.
In 2006, the airline was also involved in a strange accident in which one of its aircraft strayed off-course on a flight from Jakarta to South Sulawesi, although it eventually landed safely on the island of Sumbawa, east of Bali.
The report said the cockpit voice recorder of the plane revealed both pilots were concerned about navigation problems and subsequently became engrossed with troubleshooting inertial reference system anomalies for at least the last 13 minutes of the flight, with minimal regard to other flight instruments.
"The data flight recorder showed that even after the aircraft had reached an angle of 100 degrees, with the pitch attitude approaching 60 degrees aircraft nose down, the pilot did not roll the aircraft wings' level before attempting pitch recovery in accordance with standard procedure," the committee said.
Committee chairman Tatang Kurniadi said the flight recorder data indicated a significant structural failure occurred before the plane crashed.
"The pilots' failure was the last stage in the process after the plane entered a critical altitude," Kurniadi said as quoted by Reuters at a news conference announcing the results of the investigation.
"There was no evidence that the pilots were appropriately controlling the aircraft even after the bank angle alert sounded as the aircraft's roll exceeded 35 degrees right bank," the report said.
The flight safety watchdog concluded there was no evidence that Adam Air included component reliability in its reliability control program, to ensure the effectiveness or airworthiness of aircraft components for the fleet at the time of the accident.
"The accident thus resulted from a combination of factors including the failure of pilots to adequately monitor the flight instruments, particularly during the final two minutes of the flight," the committee pointed out.