Loss of control Accident Boeing 737-524 (WL) PK-CLC, Saturday 9 January 2021
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Date:Saturday 9 January 2021
Time:14:40
Type:Silhouette image of generic B735 model; specific model in this crash may look slightly different    
Boeing 737-524 (WL)
Owner/operator:Sriwijaya Air
Registration: PK-CLC
MSN: 27323/2616
Year of manufacture:1994
Total airframe hrs:62983 hours
Cycles:40383 flights
Engine model:CFMI CFM56-3B1
Fatalities:Fatalities: 62 / Occupants: 62
Other fatalities:0
Aircraft damage: Destroyed, written off
Category:Accident
Location:19 km NE of Jakarta-Soekarno-Hatta International Airport (CGK) -   Indonesia
Phase: En route
Nature:Passenger - Scheduled
Departure airport:Jakarta-Soekarno-Hatta International Airport (CGK/WIII)
Destination airport:Pontianak Airport (PNK/WIOO)
Investigating agency: NTSC
Confidence Rating: Accident investigation report completed and information captured
Narrative:
Sriwijaya Air flight 182 crashed into the sea, shortly after departure from Jakarta-Soekarno-Hatta International Airport, Indonesia. All 56 passengers and 6 crew members died in the accident.
The aircraft, a Boeing 737-500 registered PK-CLC, arrived at Jakarta-Soekarno-Hatta International Airport at 12:11 hours local time after a flight from Pangkal Pinang. The subsequent flight for the aircraft, SJ182, was due to depart at 13:40.
Weather at the airport was poor with heavy rainfall and low clouds due to a thunderstorm in de vicinity. This caused a delay in departure. At 14:18 the aircraft was cleared to taxi to runway 25R. Take-off from runway 32R was commenced at 14:35 (07:35 UTC).
At 14:36:46, the pilot contacted the Terminal East (TE) controller and was cleared for an unrestricted climb to FL290. Five seconds later, at altitude of 1,980 feet, the Autopilot (AP) system engaged.
At 14:38:42, as the aircraft climbed past 8150 feet, the thrust lever of the left engine started reducing, while the thrust lever of the right engine remained in position. FDR data showed that the left engine N1 was decreasing whereas the right engine N1 remained the same.
Nine seconds later flight requested a heading change to 075° to avoid weather conditions, which was approved by the TE controller.
At 14:40:05, the aircraft reached the highest altitude of about 10,900 feet. The autopilot system disengaged at that point with a heading of 016°, the pitch angle was about 4.5° nose up, and the aircraft rolled to the left to more than 45°. The thrust lever position of the left engine continued decreasing while the right engine thrust lever remained in position.
Five seconds later the the autothrottle (A/T) system disengaged and the pitch angle was more than 10° nose down. The aircraft had entered a high speed descent and impacted the surface of the sea about 20 seconds later.
The wreckage was located and appeared to be distributed across an area of about 80 by 110 meters on the seabed at a depth of approximately 16 meters.

The Indonesian NTSC reported on February 10 that the aircraft had a repeating issue the autothrottle in the days before the accident.
On 3 January 2021, a pilot reported that the autothrottle was unserviceable. An engineer rectified the problem by cleaning the autothrottle computer’s electrical connector. After re-installation, the Built-in Test Equipment (BITE) test result was good.
On 4 January 2021, a pilot again reported that the autothrottle was unserviceable. An engineer tried cleaning the autothrottle computer’s electrical connector but the problem remained and it was transferred to the Deferred Maintenance Items.
On 5 January 2021, an engineer rectified the problem by cleaning the autothrottle Takeoff and Go Around (TOGA) switch and conducted a BITE test on the autothrottle computer. The BITE test result was good.

Contributing Factors:
- The corrective maintenance processes of the A/T problem were unable to identify the friction or binding within the mechanical system of the thrust lever and resulted in the prolonged and unresolved of the A/T problem.
- The right thrust lever did not reduce when required by the A/P to obtain selected rate of climb and aircraft speed due to the friction or binding within the mechanical system, as a result, the left thrust lever compensated by moving further backward which resulted in thrust asymmetry.
- The delayed CTSM activation to disengage the A/T system during the thrust asymmetry event due to the undervalued spoiler angle position input resulted in greater power asymmetry.
- The automation complacency and confirmation bias might have led to a decrease in active monitoring which resulted in the thrust lever asymmetry and deviation of the flight path were not being monitored.
- The aircraft rolled to the left instead of to the right as intended while the control wheel deflected to the right and inadequate monitoring of the EADI might have created assumption that the aircraft was rolling excessively to the right which resulted in an action that was contrary in restoring the aircraft to safe flight parameters.
- The absence of the guidance of the national standard for the UPRT, may have contributed to the training program not being adequately implemented to ensure that pilots have enough knowledge to prevent and recover of an upset condition effectively and timely.

METAR:

07:00 UTC / 14:00 local time:
WIII 090700Z 30007KT 4000 VCTS RA FEW016CB OVC018 25/24 Q1007 NOSIG

07:30 UTC / 14:30 local time:
WIII 090730Z 30006KT 5000 -RA FEW017CB OVC018 25/24 Q1006 NOSIG

08:00 UTC / 15:00 local time:
WIII 090800Z 28008KT 4000 -RA BKN016 OVC018 26/24 Q1006 NOSIG

Accident investigation:
cover
  
Investigating agency: NTSC
Report number: KNKT.21.01.01.04
Status: Investigation completed
Duration: 1 year and 10 months
Download report: Final report

Sources:

Antara
Flightradar24 track

Statistics

  • worst accident in 2021
  • 3rd worst accident of this aircraft type
  • 3rd worst accident of this aircraft type at the time

Location

Images:


photo (c) Leslie Snelleman; Balikpapan-Sepingan Airport (BPN/WALL); 09 November 2017


photo (c) M. Gabriel Miolo; Makassar-Sultan Hasanuddin International Airport (UPG/WAAA); 11 September 2018


photo (c) Christoper Gramen; Jakarta-Soekarno-Hatta International Airport (CGK/WIII)


photo (c) Axel Anderson; Jakarta-Soekarno-Hatta International Airport (CGK/WIII); 03 January 2021

Revision history:

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