Sunday, 28th of December, 2014
Indonesia AirAsia Flight 8501, an international scheduled passenger flight from Surabaya-Juanda Airport (SUB/WARR), Indonesia, to Singapore-Changi International Airport (SIN/WSSS), Singapore, operated with an Airbus A320-216, registration PK-AXC, stalled and crashed into the Karimata Strait, Indoensia.
The six crew and 156 passengers perished. (162 fatalities)
The crash of Flight 8501 is the third deadliest aviation accident on Indonesian soil. It is also the second deadliest crash involving the Airbus A320.
The flight took off from runway 10 at Surabaya-Juanda Airport (SUB) at 05:35 hours local time (22:35 UTC). The airplane turned left, tracking 329° over the Java Sea. The planned cruising altitude of FL320 was reached about 05:49. At 06:00 the Electronic Centralized Aircraft Monitoring (ECAM) amber advisory AUTO FLT RUD TRV LIM 1 appeared. One minute later a failure on both Rudder Travel Limiter Units triggered a chime and master caution light. The ECAM message showed “AUTO FLT RUD TRV LIM SYS” (Auto Flight Rudder Travel Limiter System). The pilot in command read and performed the ECAM action to set the Flight Augmentation Computer (FAC) 1 and 2 push-buttons on the overhead panel to OFF then to ON one by one. Both Rudder Travel Limiter Units returned to function normally.
Upon entering the Jakarta Flight Information Region (FIR) over the TAVIP waypoint at 06:11 the flight contacted Jakarta ACC. The flight stated that they were deviating to the left of their planned route along airway M635 to avoid clouds and requested a climb to FL380. The requested climb was not possible due to other traffic but the flight was cleared to climb to FL340.
At 06:13, a single chime sounded and the amber ECAM message “AUTO FLT RUD TRV LIM SYS” was again displayed. This was the third failure on both Rudder Travel Limiter Units on this flight. The pilots performed the ECAM actions and the system returned to function normally.
At 06:15, the fourth failure on both Rudder Travel Limiter Units occurred and triggered ECAM message “AUTO FLT RUD TRV LIM SYS”, chime and master caution light.
At 06:16 the flight was cleared by Jakarta Radar to climb to FL340 but there was no reply. The Jakarta Radar controller then called the pilot for several times but received no reply.
Meanwhile on the flight deck, the pilot in command decided not to follow the same ECAM actions as before to rectify the failure. He had recently observed a ground engineer resetting the FAC Circuit Breakers (CB) to rectify the rudder travel limiter failure and assumed he could use the same method in flight. This action however was not allowed in flight. The consequences of resetting FAC CBs in flight are not described in Airbus documents. It requires good understanding of the aircraft system to be aware of the consequences.
Following a reset of the circuit breakers, several master cautions were triggered in relation to FAC’s 1 and 2.
After electrical interruption the autopilot and the auto-thrust then disengaged. Flight control law reverted from Normal Law to Alternate Law. The aircraft started to roll to the left up to 54° angle of bank. Nine seconds after the autopilot disengaged, the right side-stick activated. The delayed response of the pilot flying was likely due to his attention not being directed to the PFD as many events occurred at this time. He may have been startled when he realized the unusual attitude of the aircraft.
After the right side-stick activated, the aircraft roll angle reduced to 9° left. This rapid right rolling movement might cause an excessive roll sensation to the right. The pilot flying may have experienced spatial disorientation and over-corrected by shifting the side stick to the left which caused the aircraft rolled back to the left up to 50°
The input on his side-stick was mostly pitch up and the aircraft climbed up to approximately 38,000 feet with a climb rate of up to 11,000 feet per minute.
The aircraft pitch reached 24° up. The pilot in command then stated: “pull down…pull down” however the input on the pilot flying’s side stick was backward and increased resulting in the AOA increasing up to a maximum of 48° up.
At 06:17:17 the stall warning activated and continued until the end of the CVR recording.
In a response the pilot in command applied nose down commands with his side stick while the pilot flying’s side stick input was mostly at maximum pitch up until the end of the recording
At 06:17:41 the aircraft reached the highest altitude of 38,500 feet and the largest roll angle of 104° to the left. The aircraft then lost altitude with a descent rate of up to 20,000 feet per minute.
At approximately 29,000 feet the aircraft attitude was wings level with pitch and roll angles of approximately zero with the airspeed varied between 100 and 160 knots. The Angle of Attack (AOA) was almost constant at approximately 40° up. The aircraft then lost altitude with an average rate of 12,000 feet per minute until the aircraft impacted the sea.
On December 30 pieces of debris and bodies were recovered from the sea. On January 12 and 13, 2015 the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) were retrieved. On January 14 the main fuselage was located by a Singapore Navy ship.
“- The cracking of a solder joint of both channel A and B resulted in loss of electrical continuity and led to RTLU failure.
– The existing maintenance data analysis led to unresolved repetitive faults occurring with shorter intervals. The same fault occurred 4 times during the flight.
– The flight crew action to the first 3 faults in accordance with the ECAM messages. Following the fourth fault, the FDR recorded different signatures that were similar to the FAC CB’s being reset resulting in electrical interruption to the FAC’s.
– The electrical interruption to the FAC caused the autopilot to disengage and the flight control logic to change from Normal Law to Alternate Law, the rudder deflecting 2° to the left resulting the aircraft rolling up to 54° angle of bank.
– Subsequent 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.”