Problems with a glitch-prone rudder component and the way pilots tried to respond were major factors in the crash of an Indonesian AirAsia jet last year that killed all 162 people on board, investigators said on Tuesday (Dec 1).
Flight QZ8501 crashed into the Java Sea on Dec 28, less than halfway into a two-hour flight from Indonesia's second-biggest city of Surabaya to Singapore.
In their first public report, Indonesian investigators did not pinpoint a single reason why the Airbus A320 disappeared from the radar. But they laid out a sequence involving the faulty component, maintenance and crew actions.
Here's a quick look at the key findings of the report.
1. The soldering on a tiny electronic part in the Rudder Travel Limiter (RTL) was cracked, causing it to send four warning signals to the pilots. The RTL controls the rudder, a part of the aircraft's tail.
2. The crew resolved the issue the first three times, but on the fourth, the pilots tried to reset the system.
3. One or both pilots apparently removed and re-inserted circuit breakers to the flight computers. This led to a power cut and the autopilot was turned off.
4. The rudder turned 2 degrees left, sending the aircraft into a 54-degree roll.
5. With no autopilot, the less experienced co-pilot took over the plane. He appeared "startled" and "disorientated" as the aircraft banked sharply. He kept pulling the nose up until the plane stalled, a state in which it lost lift.
6. The captain shouted "Pull Down", a command investigators called "confusing" as a clearer order to point the nose lower and stop stalling would be "Push Down" or "Push Forward". The captain did not take back control as a senior pilot seated at the controls is required to do in such an emergency.
7. The plane entered "a prolonged stall condition that was beyond the capability of the flight crew to recover".
8. The plane reached an altitude of 38,000 feet before falling at a maximum speed of 20,000 feet per minute. There were "about five minutes" from the time it stalled to the moment of impact.
9. The cracked soldering in the RTL had malfunctioned 23 times over the previous year. The problem had generated maintenance reports. In the three months prior to the crash, the recorded reports came at increasingly closer intervals.
10. Bad weather did not play a role in the crash.
SOURCES: REUTERS, AGENCE FRANCE-PRESSE