Sriwijaya Air missing after take off from Jakarta 09JAN21

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TLspotting
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Re: Sriwijaya Air missing after take off from Jakarta 09JAN21

Post by TLspotting »

sn26567 wrote: 15 Jan 2021, 12:20 Indonesian divers have found the casing of Sriwijaya 737's second black box, the cockpit voice recorder, but the memory unit is missing!
And where is it ?

At the tech hangar or in the water ?
Hi. I'm Thibault Lapers. @ThibaultLapers & @TLspotting

Homo Aeroportus
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Re: Sriwijaya Air missing after take off from Jakarta 09JAN21

Post by Homo Aeroportus »

FR24 has released a more granular set of data.
The graph below shows the altitude and the heading during the last 90 seconds of the flight.

PK-CLC HDG vs ALT.png

The seven-second segment between 07:39:43 and 07:39:50 is when the heading was constant at 047, represented by the red line in the Google Earth snapshot below.

SJA182 Flight Path.jpg

They then departed that heading for a left-hand turn, at a rather low rate, and while still climbing from 10675ft to their max at 10900ft that they reached 17 seconds later.

Weird.

H.A.

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Re: Sriwijaya Air missing after take off from Jakarta 09JAN21

Post by Homo Aeroportus »

Going a bit further in analysing the FR24 data, leading to a possible cause of this accident. I say again, possible.

Nothing out of usual until reaching FL100 on a 047 heading. Then at 07:39:50 a left-hand turn is initiated, rather shallow.
It takes 17 seconds (time to reach the moment they start losing altitude) to achieve a change of heading of 24 degrees. This gives an average rate of turn of less than 1.5 deg/s. A Standard Rate Turn, i.e. to make a 180 in one minute, is 3°/s.

The graph below shows this change of heading and altitude.

PK-CLC Turn Rate.png
Left : 737-700 Right : 737-500

The Rate of Turn is calculated from the FR24 data but they report heading as an integer. Therefore, the first change is given to be from 047° to 046° in half a second, a RoT of 2°/second. This is purely theoretical as a change of heading is not sudden and the first two seconds of the graph may be disregarded.
Considering an initial RoT of 0.4°/s, and a speed of 287 kts (OK, FR24 reports ground speed but the TAS shouldn’t be much different) the resulting bank angle is about 6 degrees only, probably unnoticeable (horizon not visible in the climb) if the change of heading was unintentional.

The RoT creeps up to about 1°/s ten seconds later, bank angle 15°, and around 1.8°/s when hell broke lose and they start losing altitude with a bank angle of 25°.
But what causes this change of heading? Is it part of the chain of events that lead to the catastrophic outcome?
Maybe a serious incident that occurred 10 years ago can shed some light.

An Air Nippon (now ANA) 737-700 while cruising at FL410 suddenly nose-dived with a roll angle reaching 130° and ND pitch of -35°. They lost 6000ft before recovering.
The root cause of the severe incident is reported as : The pilot inadvertently operated the rudder trim switch while intending to unlock the flight deck door.

Link to the Japan Transport Safety Board : https://www.mlit.go.jp/jtsb/eng-air_report/JA16AN.pdf
Also reported here : https://www.aviation-accidents.net/air- ... ght-nh140/
In 2014, the FAA has issued a Special Airworthiness Information Bulletin accessible via EASA on : https://ad.easa.europa.eu/ad/NM-15-03
Boeing issued Service Letter 737-SL-27-238, “Inadvertent Activation of Rudder Trim,” dated September 19, 2012, to provide operators with additional information.

In the case of Air Nippon, the FO had transitioned from 737-500 to 737-700. The pedestal layout is significantly different between these two aircraft.
On the 735, the Rudder Trim button is further aft than the Door Lock Selector. This is the opposite on the 737-700.
B737 Pedestal. Left 737-700 Right 735.png

This difference between the Classic and the NG is explained by the fact that the Door Lock Button has been installed after the “9/11” under a Supplemental Type Certification and commonality between the two types was not deemed important. The resulting location of the Door Lock may also differ between companies.
Sriwijaya operates both the B737-500 and the B737-800.

It would be interesting to read the KNKT accident report on the SJA182.

H.A.

crew1990
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Re: Sriwijaya Air missing after take off from Jakarta 09JAN21

Post by crew1990 »

Homo Aeroportus wrote: 16 Jan 2021, 22:38 An Air Nippon (now ANA) 737-700 while cruising at FL410 suddenly nose-dived with a roll angle reaching 130° and ND pitch of -35°. They lost 6000ft before recovering.
The root cause of the severe incident is reported as : The pilot inadvertently operated the rudder trim switch while intending to unlock the flight deck door.
The plane crashed after 5 min after T/O so I don't think that in the case of Sriwijaya this mis-manipulation could be caused by trying to open the door. Usually on a normal flight, when the seat belt sign goes off, cabin crew prepare everything for the service and then call the flight deck prior to start the service as we have to call them every 20 minutes to ensure they are ok.

This is also at this moment that we usually bring them coffee before starting the service, so it's already around 8-9 min after take off that they actually unlock the door to let the cabin crew enter.

I don't see why after 5 min they would unlock the door.

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sn26567
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Re: Sriwijaya Air missing after take off from Jakarta 09JAN21

Post by sn26567 »

FDR data from Sriwijaya flight SJ182 shows autothrottle system was not operating properly on one of the engines as it climbed on departure from Jakarta.

https://www.airlive.net/breaking-fdr-da ... -properly/
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Re: Sriwijaya Air missing after take off from Jakarta 09JAN21

Post by sn26567 »

Indonesian investigators have released their preliminary report on the crash of SJ182. The report is a factual report only and does not draw any conclusions about the cause of the crash. The investigators note that the thrust lever of the left engine began decreasing as the aircraft climbed through 8,150 feet, while the thrust lever for the right engine remained at climb power. The thrust from the left engine continued to decrease as the aircraft climbed to 10,900 feet—the highest recorded altitude—at which point the autopilot disengaged and the aircraft rolled to the left more than 45°. The full preliminary report may be viewed here.
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