Reports of a missing Boeing 737-500 in Indonesia.

BZ · 10-01-2021 10:08am

L1011 wrote: »

Blue Air were the biggest operator with them recently - post COVID I don't know if they still have them. Some ACMI operators probably still do

The newest are younger than the oldest NGs and its still in manufacturer support

Blue Air only showing 2 of 7 active since covid kicked in. Pretty popular among corporate charter companies. KlasJet, AirX and Oryxjet have a couple between them. Nearest large operator to Europe would be Utair in Russia who have a sizeable fleet.

Tenger · 10-01-2021 12:57pm

Debris and bodies found by divers;

https://www.telegraph.co.uk/news/2021/01/09/plane-crash-boeing-737-jet-indonesia-flight-sj182-jakarta/

The Daily Mail claims to have an eye witness;
https://www.dailymail.co.uk/news/article-9129007/Boeing-737-passenger-jet-VANISHES-sea-falling-10-000ft.html

10-01-2021 3:45pm

Hotblack Desiato wrote: »

26000 feet per minute is a phenomenal rate of descent, it implies a major departure from normal flight and the aircraft was close to being nose-down for whatever reason.

If it broke up or exploded in mid-air it would take longer than that for the bits to descend because they're no longer aerodynamic and not under power

So this implies the aircraft was intact and under power and went pretty much straight down basically

It's like as if full power had been applied for the downward trajectory.

10-01-2021 3:54pm

I see from a translation from kompas.com that the copilot was formerly in Air Force. He had originally been assigned a different route according to what he had told her by phone, so wife was very shocked to be informed he was on the ill-fated flight.

10-01-2021 4:15pm

Another piece of translation via Google Translate from the Indonesian language:

"At 14:40 WIB, the Jakarta Approach saw the Sriwijaya SJY 182 plane not heading for 075 degrees but to the Northwest (North West), therefore it was asked by ATC to report the direction of the plane.

Not long after, within seconds, the Sriwijaya SJY 182 aircraft disappeared from radar. The operations manager coordinates directly with: Basarnas, destination airports, and other related agencies."

Going by this the aircraft was already on a course which had not been authorised. It should have been turning around in a north-easterly direction after departure, but it went in a roughly northerly direction without the approved starboard turn. Something was amiss from earlier on.

23-01-2021 4:10pm

Interesting to read this:

https://www.reuters.com/article/us-indonesia-crash-idUSKBN29R0HG

JAKARTA (Reuters) - Indonesia's air accident investigator is probing whether a problem with the autothrottle system, that controls engine power automatically, contributed to the Sriwijaya Air crash on Jan. 9 that killed all 62 people on board, an official said on Friday.

National Transportation Safety Committee (KNKT) investigator Nurcayho Utomo said a problem with the Boeing 737-500's autothrottle system was reported after a flight a few days earlier.

"There was a report of malfunction on the autothrottle a couple of days before to the technician in the maintenance log, but we do not know what kind of problem," he told Reuters. "If we find the CVR (cockpit voice recorder) we can hear the discussion between the pilots, what they talked about and we will know what is the problem."

It remains unclear whether a problem with the autothrottle system contributed to the crash, Utomo said, adding he could not recall any other issues raised in the maintenance log.

It is acceptable for a plane to fly with an autothrottle system that is not working because pilots can control it manually instead, he said.

Sriwijaya said he was unable to comment on technical matters involving the investigation before an official statement was made by KNKT. A preliminary report is expected to be issued within 30 days of the crash, in line with international standards.

The plane's flight data recorder (FDR) has been recovered and read by investigators but an underwater search for the CVR's memory unit at the crash site in the Java Sea is continuing.

Citing sources close to the investigation, the Wall Street Journal (WSJ) on Thursday reported the FDR data showed the autothrottle system was not operating properly on one of the plane's engines as it climbed on departure from Jakarta.

Instead of shutting off the system, the FDR indicated the pilots tried to get the stuck throttle to function, the WSJ said. That could create significant differences in power between engines, making the jet harder to control.

Could we have had a reverse (with the fault itself OR foostering to control it) on #2 that set the aircraft off in its downward trajectory to the right? There will be a preliminary report within a month.

lintdrummer · 23-01-2021 8:38pm

On another aviation forum there has been speculation about the auto throttle since before the media began reporting it.
I'm not familiar with the 737 but from what I understand it involves a clutch mechanism in the throttle system of the classics.
The hypothesis is that a failure can conceivably occur where one of the throttles gets stuck at a lower power setting while the other is free to demand full power. With all the automatics in, the asymmetry will be corrected to a point with aileron input. The rudder is not strictly autopilot controlled, rather it's a yaw damper system so it would not deflect much in this scenario.
If the pilots don't notice the asymmetry in the throttle levers or the control column then this will continue until the autopilot reaches the limit of it's aileron authority. It will then 'give up' and disconnect. You could then find yourself with an airplane that is way out of trim and with the startle effect you could be in a large bank and deteriorating upset scenario.

It's all speculation but there is history of such events and it seems to be a plausible scenario. With the FDR data already downloaded, we should find out exactly what happened within the next few weeks.

23-01-2021 10:43pm

lintdrummer wrote: »

On another aviation forum there has been speculation about the auto throttle since before the media began reporting it.
I'm not familiar with the 737 but from what I understand it involves a clutch mechanism in the throttle system of the classics.
The hypothesis is that a failure can conceivably occur where one of the throttles gets stuck at a lower power setting while the other is free to demand full power. With all the automatics in, the asymmetry will be corrected to a point with aileron input. The rudder is not strictly autopilot controlled, rather it's a yaw damper system so it would not deflect much in this scenario.
If the pilots don't notice the asymmetry in the throttle levers or the control column then this will continue until the autopilot reaches the limit of it's aileron authority. It will then 'give up' and disconnect. You could then find yourself with an airplane that is way out of trim and with the startle effect you could be in a large bank and deteriorating upset scenario.

It's all speculation but there is history of such events and it seems to be a plausible scenario. With the FDR data already downloaded, we should find out exactly what happened within the next few weeks.

Interesting insight. It looked like something was perhaps insidiously developing, then catastrophe. Hopefully improvements in training/checklists will help prevent future such scenarios if throttle symmetry becomes a concrete part of observations in all airlines, and moreover, techniques to assuredly deal with such scenario.

billy few mates · 24-01-2021 12:53am

lintdrummer wrote: »

On another aviation forum there has been speculation about the auto throttle since before the media began reporting it.
I'm not familiar with the 737 but from what I understand it involves a clutch mechanism in the throttle system of the classics.
The hypothesis is that a failure can conceivably occur where one of the throttles gets stuck at a lower power setting while the other is free to demand full power. With all the automatics in, the asymmetry will be corrected to a point with aileron input. The rudder is not strictly autopilot controlled, rather it's a yaw damper system so it would not deflect much in this scenario.
If the pilots don't notice the asymmetry in the throttle levers or the control column then this will continue until the autopilot reaches the limit of it's aileron authority. It will then 'give up' and disconnect. You could then find yourself with an airplane that is way out of trim and with the startle effect you could be in a large bank and deteriorating upset scenario.

It's all speculation but there is history of such events and it seems to be a plausible scenario. With the FDR data already downloaded, we should find out exactly what happened within the next few weeks.

The autothrottle is designed to disengage in the event of a throttle split above a certain value or in the case of a jammed (or stiff) throttle cable run so it's not possible for it to apply assymetric power to any great extent before it drops out.
Even when it is engaged the crews can still override the servos through a clutch system that allows them to manually position the thrust levers even if the auto throttle system is controlling them.
This looks more like a catastrophic failure, loss of major component or inadvertent thrust reverser deployment even though that should not be possible due to the introduction of T/R synch locks in the aftermath of the Lauda 767 crash a number of years ago.
Or possibly even deliberate or terrorist action.

lintdrummer · 24-01-2021 2:11pm

billy few mates wrote: »

The autothrottle is designed to disengage in the event of a throttle split above a certain value or in the case of a jammed (or stiff) throttle cable run so it's not possible for it to apply assymetric power to any great extent before it drops out.
Even when it is engaged the crews can still override the servos through a clutch system that allows them to manually position the thrust levers even if the auto throttle system is controlling them.
This looks more like a catastrophic failure, loss of major component or inadvertent thrust reverser deployment even though that should not be possible due to the introduction of T/R synch locks in the aftermath of the Lauda 767 crash a number of years ago.
Or possibly even deliberate or terrorist action.

I'd be inclined to discount deliberate or terrorist action due to the timing of the event. It's so soon after takeoff that it's unlikely the opportunity for someone to breach the cockpit arose. Equally unlikely that one of the crew had left the cockpit at that stage.

24-01-2021 2:39pm

A very different beast, the little Let 410 was discovered to have a potential fault causing prop reverser to be inadvertently deployed, causing at least one fatal accident.

https://www.flightglobal.com/safety/new-engine-control-to-lower-l-410-thrust-reverse-risk/133961.article

Pilots have also been made aware to respond quickly to any such future incidence. Being taken by surprise by such a happening would be disastrous if the engine weren't put out of action immediately.

mr.anonymous · 10-02-2021 8:06pm

Preliminary report released by Indonesia's KNKT.

Throughout the last moments the left thrust lever reduces and the aircraft rolls to the left. Not recovered by the crew. Autothrottle seems to be a focus of the investigation. No CVR recordings yet as the memory module hasn't been found.

10-02-2021 10:29pm

mr.anonymous wrote: »

Preliminary report released by Indonesia's KNKT.

Throughout the last moments the left thrust lever reduces and the aircraft rolls to the left. Not recovered by the crew. Autothrottle seems to be a focus of the investigation. No CVR recordings yet as the memory module hasn't been found.

There seems to be a *suggestion* of the possibility of the Captain having potentially been incapacitated at a critical moment. The Chief Pilot of the airline has emphasised how all pilots need to be on the ball regarding the aircraft engine performance at all times irrespective of distractions.

General Disarray · 12-02-2021 5:38am

[Deleted User] wrote: »

There seems to be a *suggestion* of the possibility of the Captain having potentially been incapacitated at a critical moment. The Chief Pilot of the airline has emphasised how all pilots need to be on the ball regarding the aircraft engine performance at all times irrespective of distractions.

I read it as "not concentrating" rather than incapacitated.

With the left engine thrust reducing, the resultant roll to the left will be counteracted by the autopilot. Eventually, the autopilot servos will reach the end of their travel and can't cope anymore. At this point, the autopilot will automatically disengage. This will be followed by an immediate sharp roll to the left.
If the crew haven't been properly monitoring the aircraft, which they obviously weren't or the situation wouldn't have developed, they would now be suddenly startled by the disengagement and the quick roll to the left.

Reports of a missing Boeing 737-500 in Indonesia.

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