Created Wednesday, Feb 10th 2021 08:22Z, last updated Wednesday, Feb 10th 2021 11:30Z
On Feb 10th 2021 Indonesia's KNKT released their Preliminary Report.
The KNKT reported: "At the time of issuing this preliminary report, the memory unit of the Cockpit Voice Recorder (CVR) has not been recovered and the search is continuing."
The KNKT reported the sequence of events on board of the aircraft as known so far:
On 9 January 2021, a Boeing 737-500 aircraft, registration PK-CLC, was being operated by PT. Sriwijaya Air on a scheduled passenger flight from Soekarno-Hatta International Airport (WIII), Jakarta1 to Supadio International Airport (WIOO), Pontianak. The flight number was SJY182. According to the flight plan filed, the fuel endurance was 3 hours 50 minutes.
At 0736 UTC (1436 LT) in daylight conditions, Flight SJY182 departed from Runway 25R of Jakarta. There were two pilots, four flight attendants, and 56 passengers onboard the aircraft.
At 14:36:46 LT, the SJY182 pilot contacted the Terminal East (TE) controller and was instructed "SJY182 identified on departure, via SID (Standard Instrument Departure) unrestricted climb level 290". The instruction was read back by the pilot.
At 14:36:51 LT, the Flight Data Recorder (FDR) data recorded that the Autopilot (AP) system engaged at altitude of 1,980 feet.
At 14:38:42 LT, the FDR data recorded that as the aircraft climbed past 8,150 feet, the thrust lever of the left engine started reducing, while the thrust lever position of the right engine remained. The FDR data also recorded the left engine N1 was decreasing whereas the right engine N1 remained.
At 14:38:51 LT, the SJY182 pilot requested to the TE controller for a heading change to 075 degrees to avoid weather conditions and the TE controller approved the request.
At 14:39:01 LT, the TE controller instructed SJY182 pilot to stop their climb at 11,000 feet to avoid conflict with another aircraft with the same destination that was departing from Runway 25L. The instruction was read back by the SJY182 pilot.
At 14:39:47 LT, the FDR data recorded the aircraft's altitude was about 10,600 feet with a heading of 046 degrees and continuously decreasing (i.e., the aircraft was turning to the left). The thrust lever of the left engine continued decreasing. The thrust lever of the right engine remained.
At 14:39:54 LT, the TE controller instructed SJY182 to climb to an altitude of 13,000 feet, and the instruction was read back by an SJY182 pilot at 14:39:59 LT. This was the last known recorded radio transmission by the flight.
At 14:40:05 LT, the FDR data recorded the aircraft altitude was about 10,900 feet, which was the highest altitude recorded in the FDR before the aircraft started its descent. The AP system then disengaged at that point with a heading of 016 degrees, the pitch angle was about 4.5 degrees nose up, and the aircraft rolled to the left to more than 45 degrees. The thrust lever position of the left engine continued decreasing while the right engine thrust lever remained.
At 14:40:10 LT, the FDR data recorded the autothrottle (A/T) system disengaged and the pitch angle was more than 10¢X nose down. About 20 seconds later the FDR stopped recording. The last aircraft coordinate recorded was 5°57'56.21" S 106°34'24.86" E
At 14:40:37 LT, the TE controller called SJY182 to request for the aircraft heading but did not receive any response from the pilot. At 14:40:48 LT, the radar target of the aircraft disappeared from the TE controller radar screen.
At 14:40:46 LT, the TE controller again called SJY182 but did not receive any response from the pilot. The TE controller then put a measurement vector on the last known position of SJY182 and advised the supervisor of the disappearance of SJY182. The supervisor then reported the occurrence to the operation manager.
The TE controller repeatedly called SJY182 several times and also asked other aircraft that flew near the last known location of SJY182 to call the SJY182. The TE controller then activated the emergency frequency of 121.5 MHz and called SJY182 on that frequency. All efforts were unsuccessful to get any responses from the SJY182 pilot.
About 1455 LT, the operation manager reported the occurrence to the Indonesian Search and Rescue Agency (Badan Nasional Pencarian dan Pertolongan/BNPP).
At 1542 LT, the Air Traffic Services (ATS) provider declared the uncertainty phase (INCERFA) of the SJY182. The distress phase of SJY182 (DESTRESFA) was subsequently declared at 1643 LT.
The captain (54, ATPL, 17,904 hours ttoal, 9,023 hours on type) was assisted by a first officer (34, CPL, 5,107 hours total, 4,957 hours on type). The aircraft, manufactured on May 31st 1994, had accumulated 62,983 flight hours in 40,383 flight cycles since new. The aircraft's tech log showed two recent entries:
DMI number list 07956
On 25 December 2020 during preflight check, the engineer found the first officer's Mach/Airspeed Indicator malfunctioned. The engineer then transferred the defect into the DMI list number 07956 due to unavailability of spare part. According to the Sriwijaya Air Boeing 737 Minimum Equipment List (MEL), the item was classified as repair category C8.
On 4 January 2021, the first officer's Mach/Airspeed Indicator was replaced and test result was satisfied. As such, the DMI number list 07956 was closed.
DMI number list 07958
On 3 January 2021, the pilot reported that autothrottle was unserviceable. The 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, the pilot reported that autothrottle was unserviceable. The engineer tried cleaning the autothrottle computer's electrical connector but the problem remained and it was transferred to DMI number list 07958.
On 5 January 2021, the engineer rectified the problem as stated in the DMI number 07958 by cleaning autothrottle Takeoff and Go Around (TOGA) switch and conducted a BITE test on the autothrottle computer. The BITE test result was good and the DMI was then closed.
With respect to the weather the KNKT reported: "The superimposed ADS-B-based flight profile with radar weather image at 1438 LT provided by the BMKG indicated that the radar intensity level along the flight profile was not more than 25 dBz, which means that the flight path did not indicate any significant development of clouds."
The KNKT reported Indonesia's DGCA undertook these safety actions:
On 11 January until 3 February 2021, the Directorate General of Civil Aviation (DGCA) conducted special inspection to all Boeing 737-300/400/500 air in Indonesia. The areas of the inspection were as follow:
- Airworthiness Directive (AD) compliances;
- routine and major inspection implementations;
- continuing analysis surveillance program implementation including the handling of repetitive defects;
- pilot training program implementation, including weather avoidance and upset recovery training program;
- pilot proficiency check implementation;
- flight duty time limitation and pilot recent experience;
- implementation of DGCA Circular regarding COVID-19 pandemic.
On 29 January and 4 February 2021, the DGCA initiated a discussion with aircraft operators and approved maintenance organizations related to the handling of repetitive problem.
On 28 January 2021, the DGCA initiated a discussion with aircraft operators on the implementation of upset prevention and recovery training (UPRT) program.
Sriwijaya undertook the following safety actions:
The Quality Maintenance Division of Sriwijaya Air issued a quality notice on 18 January 2021 to maintenance control center and engineers for ensuring:
- the repetitive defect handling must be conducted in accordance with the Safety Circular from the DGCA and Company Maintenance Manual;
- to follow the procedure described on the Aircraft Maintenance Manual (AMM), Fault Isolation Manual (FIM) and Illustrated Part Catalog (IPC) for troubleshooting;
- to fill the Aircraft Maintenance Log in accordance with the Quality Procedure Manual (QPM);
- to follow part robbing procedure as describe in the QPM and Aircraft Maintenance Procedure Manual (AMPM).
The Chief Pilot of Sriwijaya Air issued the following notice to pilots on 20 January 2021:
This notice reach you as a call toward the safe flight. With recent tragedy, we urge all pilots to raise awareness and keep the highest professionalism and discipline on your duty. This can be fulfilled with many guidance that we had:
- Follow Operating Experience guidance.
- Review Training Aid.
- Awareness of aircraft position, attitude, aircraft systems by active monitoring the state of aircraft on every phase of flight.
- Awareness of aircraft configuration, thrust lever position/power setting and flight control system modes, anytime airplane deviate from its intended state must be corrected immediately.
- Cockpit crew is responsible for entering clear and accurate write-ups of any discrepancies, including any incident or anomaly observation in AML, use of FRM (737NG) and/or describe discrepancy information comprehensively.
On 28 January 2021, the Standard, Quality, and Training Division of Sriwijaya Air included the upset recovery training as part of the training syllabus in the next Line Oriented Flight Training (LOFT) – Pilot Proficiency Check (PPC).
On 2 February 2021, the Quality and Safety Division of Sriwijaya Air issued safety recommendations to its Operation Directorate and Technical Directorate. (details in the appendices of the preliminary report)
(Editorial Remark: there is no mention of any manual control inputs by the crew in the entire preliminary report, there is also no information about the left engine parameters)
Weather radar with Mode-S flight path superimposed (Graphics: KNKT):
Extension of wreckage field and positions of FDR, CVR (without memory module) and pingers (Graphics: KNKT):
