Nurcahyo Utomo, the KNKT acting chief of the air transportation accident investigation sub-committee, confirmed that the Airbus A320 PK-XC aircraft stalled according to the last data captured by the flight data recorder (FDR), thereby revealing the results of the investigation into the incident.
"Manual control of the aircraft by the crew later caused it to run into a condition known as upset condition and stall as captured until the end of the FDR recording. This was beyond the pilots capability," he explained.
Nurcahyo noted that the aircraft had stalled due to bad weather.
"The aircraft could not nosedive as its rear end had lost power to rise," he clarified.
He said the aircraft had departed from the Juanda Airport in Surabaya, East Java, at 5:35 hours local time, and since 6:01 hours local time, the FDR had recorded master cautions activation due to a "rudder travel limiter" (RTL) trouble on four instances.
"The trouble caused the activation of the electronic centralized aircraft monitoring (ECAM) system marked by AUTO FLT RUD TRV LIM SYS reading," he affirmed.
Based on the message, the crew accordingly took steps described in the ECAM, he remarked.
"The trouble in the RTL system is not a dangerous thing," he added.
He stated that on the fourth instance of the RTL trouble at 6:15 hours local time, the FDR recorded a reading that was different from the previous three signs but was similar to an incident that had occurred on December 24, 2014, wherein the aircraft was still on the ground and its Circuit Breaker (CB) from the Flight Augmentation Computer (FAC) was being reset.
Nurcahyo revealed that following the fourth instance of the problem, the crew activated the fifth warning sign showing a message on the ECAM reading AUTO FLT FC 1 FAULT and the sixth reading AUTO FLT FAC 1+2 FAULT on ECAM.
"After the messages, the auto-pilot and auto-thrust features did not work and the fly-by-wire system changed from normal law to alternate law, with some protection features being inactive," he pointed out.
He said the aircraft was manually controlled by the crew, causing it to enter into the "upset condition," meaning out-of-normal condition of 25 degrees nose up and 10 degrees nose down.
The aircraft was flying at a height of 32 thousand feet above sea level and was carrying 156 passengers, two pilots of which one was the captain pilot who acted as the monitoring pilot and a co-pilot acting as the pilot flying the aircraft, four cabin crew, and a technician.(*)