Indonesian safety officials have found a repetitive malfunction to be the original cause of problems for an Indonesia AirAsia Airbus A320 that crashed in December, though the inability of the pilots to control an upset situation appears to be a critical factor.
The aircraft crashed in the Java Sea on Dec. 28, during Flight QZ8501 from Surabaya, Indonesia, to Singapore. All 162 passengers and crew were killed. The flight was operated by the Indonesian affiliate of the AirAsia Group, and the incident prompted Indonesian authorities to conduct strict reviews of all local carriers.
In a final report released Dec. 1, Indonesia’s National Transportation Safety Committee found that cracking on a solder joint resulted in electrical interruption, triggering rudder travel limiter unit (RTLU) failures. This was causing master caution activation and electronic centralized aircraft monitoring (ECAM) warnings in the cockpit.
The problem had occurred repeatedly on the aircraft in the months prior to the crash, and had been resolved on the ground by resetting the flight-augmentation computer (FAC) and pulling circuit breakers. However, the unresolved core problem had caused the warnings to occur at shorter intervals. The issue was not identified as meeting the criteria for repetitive defects.
During the flight, master caution activation and ECAM warnings occurred three times, and the flight crew performed the required ECAM actions to return the system to normal functioning. However, on the fourth warning, the evidence suggests that the crew reset the FAC circuit breaker.
In turn, this disengaged the autopilot and auto-thrust, and flight control law switched from normal to alternate. The rudder deflected 2 deg., resulting in a 54-deg. roll to the left. The report indicates there was a confused response from the crew, and the stall warning was activated. After reaching its highest altitude of 38,500 ft.—with the roll reaching 104 deg. to the left—the aircraft dived at up to 20,000 ft. per minute. The pilots were able to level the wings, but the aircraft remained in a developed stall until impact.
“Flight crew action leading to inability to control the aircraft in the alternate law resulted in the aircraft departing from the normal flight envelope and entering prolonged stall condition that was beyond the capability of the flight crew to recover,” the report said.
The report found that the crew did not follow the “standard call-outs” for cockpit communications during the emergency, and also identified inadequate upset-recovery training for this type of situation.
The airline has already taken several measures following the earlier preliminary report. These include improvements to flight operations such as upset-recovery training as well as maintenance procedures related to repetitive problems, post-flight reports and troubleshooting manuals.
Beyond these actions, the report recommends that Indonesia AirAsia should “re-emphasize” the importance of the standard call-outs, and the taking-over control procedure in “various critical situations of flight.”
The report calls for Indonesia’s Directorate General of Civil Aviation to ensure: airline training is in accordance with standards; operators conduct simulator upset-recovery training; and maintenance systems have the ability to “detect and address all repetitive faults appropriately.”
There are also recommendations for Airbus: The manufacturer should consider developing a means for crew to “effectively manage multiple and repetitive master caution alarms to reduce distraction,” and should review the flight-crew training manual for standard call-outs for all phases of flight.