A final report into the 1 January 2007 crash of an Adam Air Boeing 737-400 in Indonesia has determined that the aircraft plunged into the sea from cruise after the pilots became preoccupied with an inertial reference system (IRS) malfunction and lost control.

The airline, which last week was grounded for safety violations, is also criticised for not providing adequate training to its pilots and for not taking numerous IRS faults in its 737 fleet seriously enough. Indonesia’s aviation regulator is also criticised in the report for deficiencies in its oversight of the airline.

Indonesia’s National Transportation Safety Committee (NTSC) issued its final report today following a long-running investigation that was made difficult by the limited amount of wreckage that was recovered and the fact that the digital flight data recorder (DFDR) and cockpit voice recorder (CVR) were not retrieved from the sea bed for nearly nine months, until late in August.

The 737, registered as PK-KKW, was operating as domestic flight DHI574 on 1 January last year between Surabaya and Manado when it disappeared from radar after cruising at 35,000ft (10,668m). On board were 102 passengers and crew, all of whom were killed in the crash. The first pieces of wreckage were only found nine days after the aircraft disappeared.

In its final report, the NTSC cites repeated errors by the crew in the flight’s final moments and criticises the airline for not providing its pilots with adequate training to prevent what happened from occurring.

“The CVR revealed that both pilots were concerned about navigation problems and subsequently became engrossed with troubleshooting inertial reference system anomalies for at least the last 13min of the flight, with minimal regard to other flight requirements,” it says.

The DFDR analysis showed the aircraft was cruising with the autopilot engaged when the captain noticed there was a navigation problem between the two IRS’, “specifically a significant difference in distance”, says the NTSC.

The crew then set the number two, or right, IRS mode selector unit to “attitude” mode and the autopilot disengaged, after which the aircraft began a slow roll to the right. However there were limited attempts by the pilots to take corrective action – even after a “bank angle” alert sounded as the aircraft’s roll exceeded 35° right.

“The DFDR data showed that roll rate was momentarily arrested several times, but there was only one significant attempt to arrest the roll. Positive and sustained roll attitude recovery was not achieved. Even after the aircraft had reached a bank angle of 100°, with the pitch attitude approaching 60° aircraft nose down, the pilot did not roll the aircraft’s wings level before attempting pitch recovery in accordance with standard operating procedures,” says the report.

“The aircraft reached 3.5g, as the speed reached Mach 0.926 during sustained nose-up elevator control input while still in a right bank. The recorded airspeed exceeded Vdive (400 kcas), and reached a maximum of approximately 490 kcas just prior to the end of recording.”

It says that around 20sec before the end of the recorded data, the aircraft suffered a “significant structural failure” due to speeds that were beyond the 737’s design limitations, but by that time it was already in a “critically uncontrollable state”.

“This accident resulted from a combination of factors, including the failure of the pilots to adequately monitor the flight instruments, particularly during the final 2min of the flight,” says the NTSC.

“Preoccupation with a malfunction of the inertial reference system diverted both pilots’ attention from the flight instruments and allowed the increasing descent and bank angle to go unnoticed. The pilots did not detect and appropriately arrest the descent soon enough to prevent a loss of control.”

Source: flightglobal.com's sister premium news site Air Transport Intelligence news

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Source: FlightGlobal.com