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737-500 missing in Indonesia

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737-500 missing in Indonesia

Old 11th Feb 2021, 16:29
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Teddy Robinson

I don't know where that summary came from but it is wrong in several important respects. Instead of re-quoting misinformation we should (and can) quote directly from the report.


1.6.3 Maintenance Log Examination
The Aircraft Maintenance Log (AML) recorded that the aircraft had two Deferred
Maintenance Items (DMIs) related to the first officer’s Mach/Airspeed Indicator and
the other to autothrottle system. The details were as follows:

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.
There were three attempts to fix the autothrottle.

1.1 History of the Flight
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), Jakarta 1 to Supadio International Airport (WIOO),
Pontianak2. The flight number was SJY182. According to the flight plan filed, the
fuel endurance was 3 hours 50 minutes.

At 0736 UTC (1436 LT3) 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 N14 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 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 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, 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.

At 14:40:10 LT, the FDR data recorded the autothrottle (A/T) system disengaged and
the pitch angle was more than 10 nose down. About 20 seconds later the FDR
stopped recording. The last aircraft coordinate recorded was 557'56.21" S
10634'24.86" E
There was one occurrence of thrust lever decreasing, which continued for over a minute without apparent correction.
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Old 11th Feb 2021, 16:30
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Originally Posted by FlyingStone View Post
.........At higher speed, the engine failure with regards to controllability isn't a problem..........Asymmetric thrust can be easily recognised by progressively increasing deflection of the control column towards the live engine, and the autopilot will put in quite a lot of force/deflection before it gives up.
Except this crew apparently didn't recognise a thrust lever stagger, a big N1 difference, and the yokes a long way out of horizontal.

Knowing that their auto-thrust had been faulty, PF must have had their hand on the thrust levers, one would hope? Something else must have been going on, hence the CVR is needed.

I've got experience of both and both need to be watched like a hawk. The only difference is that with one you can rest your hands gently on the control column and thrust levers and look out the window, and with the other one you need to have your eyes glued to the FMA and N1/EPR to see if something untoward is going on.
Obviously we should regularly look at our FMA and N1/ EPR, (and PFD of course), on any aircraft, because they tell us the result of our inputs. The moving thrust levers and yoke movements are the inputs, not the outputs. But you don't need to be glued to them - just part of your normal scan which includes looking out of the window. I have never had to watch Airbus FBW "like a hawk" - it works very well and reliably. I've certainly never felt the need to hand-fly every departure up to cruising level before putting the automatics in, as someone suggested.

But we are getting off piste here.

Last edited by Uplinker; 11th Feb 2021 at 16:40.
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Old 11th Feb 2021, 16:37
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I mentioned before on this thread about the possibility of a single thrust lever reducing/not advancing and that is now confirmed by the preliminary report. It's actually unbelievable that it went unnoticed for over a minute, but still very possible knowing the training/standards in indo.
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Old 11th Feb 2021, 16:38
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Originally Posted by Capn Bloggs View Post
Uplinker, I normally find your posts quite good and balanced, That one though is ridiculous. What are the pilots doing through all of this, may I ask?
I think we would all like to know that.

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Old 11th Feb 2021, 17:22
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Derjodel in his #552 post clearly states the issue of the era. This is a time of transition in the airline industry, as too much of the work required to maintain good flying skills has been automated. Unlike earlier days, the pilot’s essential tactile and cognitive connection with the airplane when several things are happening at once is nowhere near what it needs to be when things go wrong. No amount of training or improved simulation can make up for this, and further automation can only make it worse. You cannot make better pilots in airplanes designed to increasingly diminish the need for them.
Another issue also mentioned before is the covid crisis that does not end with the last of the pandemic. A complex but smoothly functioning airline industry has been completely derailed and the problem confronting the flight crews now afflicts the entire industry. Benched for too long, the need for rusty but essential skills will be greatest when they are anything but sharp.

Last edited by ferry pilot; 11th Feb 2021 at 17:34.
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Old 11th Feb 2021, 17:29
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This can and does happen anywhere in the world, as standards are incredibly low for manual flying on instruments, let alone upset recovery training which - if it exists at your company - is probably a joke. Having it beaten into their heads to use automation as much as possible or giving into that habit by themselves, crews tend to respond to abnormal situations by trying to diagnose the problem with the automation instead of disconnecting AP & AT and flying out of it.

At this point, I'm afraid the CVR won't have much to reveal. The crew was so caught up with figuring out what was happening with the autothrottle that they allowed the situation to progress to the point where the AP couldn't hold off the roll anymore and it left them in a steep dive to the left, as the malfunctioning autothrottle increased the thrust asymmetry for a few more seconds before disconnecting.

To their credit, I think they were pulling out of the dive when they hit the water, they just weren't aggressive enough on the recovery. fdr was putting up some scenarios earlier on what might have happened. 10900' should be enough for any 737 to recover from a 1-2 turn spin or rolling inverted. In this case, I think the roll at AP disconnect just rolled them to 80-90 degrees of bank and the nose sliced on down as they were wondering what the hell was happening. Perhaps they didn't trust their instruments at first, but they would have felt the initial acceleration downhill, and as the aircraft picked up speed they would have heard it too. If they were pulling up straight at the end, they probably addressed the thrust asymmetry, but I don't see any of those details in the last 20 seconds of FDR recording.

To the incredulous, this is definitely not the first time this happens. This is basically a copycat of the TAROM A310 at Otopeni in the 90s, where the First Officer allowed the malfunctioning AT to retard one lever to idle and push the other one to TO thrust, resulting in a wingover in IMC (also to the left, if I'm remembering it right) and a basically vertical dive into the ground. In a sinister coincidence, the Captain was having a heart attack or seizure while this was happening.

The industry are treating these horrendous accidents as statistical blips, but the reality is that some sort of IMC mess-up resulting in a steep dive into the ground happens every year or two, sometimes more than one in the same year. It usually involves a 737, as there is a lot of them out there, there are much more short & medium range flights than long haul, and the automation is pretty crude compared to something like the A320. One would think that this would trigger some alarm bells and that someone would recognize that there is a need for crews who can confidently handfly these aircraft in IMC and recover from severe upsets on instruments.

Btw, handling-related question: for those who got the chance to do the rudder hardover on the 737 sim, did unloading & reducing angle of attack give you enough aileron authority to arrest the roll? How did you fly afterwards? Did you need to offset the thrust to compensate for the yaw from the stuck rudder?
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Old 11th Feb 2021, 17:46
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Originally Posted by Stuka Child View Post
To their credit, I think they were pulling out of the dive when they hit the water, they just weren't aggressive enough on the recovery.
See posts #89 and #147.

If they were pulling up straight at the end, they probably addressed the thrust asymmetry, but I don't see any of those details in the last 20 seconds of FDR recording.
The Preliminary Report is silent regarding the final 20 seconds of the flight.
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Old 11th Feb 2021, 17:51
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The industry are treating these horrendous accidents as statistical blips, but the reality is that some sort of IMC mess-up resulting in a steep dive into the ground happens every year or two, sometimes more than one in the same year. It usually involves a 737, as there is a lot of them out there
there you have it. more aircraft flights of aging technology = more cock ups
so do we need to scrap out old fleets or below avg pilots?

I used the descriptor of below avg pilots because of what I read on here most seemed to know what to do
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Old 11th Feb 2021, 18:29
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Originally Posted by Teddy Robinson View Post
From Report..
1. Auto Throttle broken. Repaired twice.
2. During take off AT pulls back left engine.
Incorrect summary posted again and again and again... This thread is moderated and so many posts are being deleted. Why aren't posts like these deleted, which simply copy & paste false information all over again? Don't just copy stuff from the internet - read the actual report, guys! The report does not report any A/T failure during takeoff. It reports a normal takeoff.
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Old 11th Feb 2021, 22:14
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Spurious activation of Reverse ThrustIt looks like a spurious signal from the EEC drove the left Thrust Lever to idle to allow for an inadvertent deployment of Reverse Thrust (ala Lauda Air over Thailand). As Auto Thrust was engaged, the right engine will drive forward or remain in position to compensate for the loss of thrust from the left engine. It is this this assymetric condition that brought about the uncommanded bank resulting in the Auto Pilot tripping.
Thrust reverser is a mechanical mechanism, if the translation sleeve moves the warning light illuminates and crew action would be to shut the engine down. The auto throttle system will only command the climb power selected by LVL Change or VNAV, if the crew had selected VS mode in the last 1000 feet, the thrust adjusts according to the MCP speed.

Last edited by Kirks gusset; 11th Feb 2021 at 22:39.
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Old 11th Feb 2021, 23:02
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Spurious activation of Reverse Thrust

Originally Posted by Yipoyan View Post
It looks like a spurious signal from the EEC drove the left Thrust Lever to idle to allow for an inadvertent deployment of Reverse Thrust
Well the spurious part is right.

EEC ? 737-500 ? Hmmmm.

It looks like an entirely evidence-free proposition.

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Old 11th Feb 2021, 23:54
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There is no EEC on the 737 Classic, it has a hydromechanical fuel control system.

The thrust reduction on the left engine appears to be very gradual. Should reverser deploy in-flight on the classic 737, the thrust lever is rapidly pulled back to idle by the restow mechanism to prevent thrust in excess of idle. This would have definitely been noticed by the crew.
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Old 12th Feb 2021, 01:26
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DaveReidUK

No EEC, purely mechanical T/R thrust pullback, not to mention the EEC on Lauda had zilch to do with the T/R deployment.

So, great post aside from everything in the post being wrong
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Old 12th Feb 2021, 01:32
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Originally Posted by Stuka Child View Post
At this point, I'm afraid the CVR won't have much to reveal. The crew was so caught up with figuring out what was happening with the autothrottle that they allowed the situation to progress to the point where the AP couldn't hold off the roll anymore and it left them in a steep dive to the left, as the malfunctioning autothrottle increased the thrust asymmetry for a few more seconds before disconnecting.
Quite the contrary - the crew failed to address a straight forward problem - one that had reportedly occurred on previous flight. ALL they needed to do was take manual control of the thrust levers to save the situation. The question is why they didn't take the relatively simple steps necessary to save themselves (along with the aircraft and passengers).
Only the CVR can possibly reveal that answer.
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Old 12th Feb 2021, 01:34
  #575 (permalink)  
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FlyingStone

That is my recollection of the FCU on the -3 engine as well. There is mechanical feedback to the throttle to ensure the lever is and remains at idle as the FCU schedules into reverse. That would suggest that a TR problem will give a rapid and complete closure of the thrust lever to idle. If it is working anywhere near correctly.. If the cable itself has a failure (other types I fly have repetitive inspections of the TR follow-up cables due to failures), a failure in the cable itself could be an issue. Cannot recall if the TR cable acts under tension to close or not, which could discount that as a failure mode. The other issue that can cause both thrust levers to reduce is a TAT probe failure, which signals for limit cases to the AT system calculation, or of the PT2 on an engine going bad, as that has a limiter input to the FCU, but that should not move the thrust lever. The main memory of the FCU was it was quite expensive to buy the replacement.

The FCU was properly known as a MEC and had the PMC as a trimming system which was a form of limited EEC/DEEC. The MEC took the PS12 and T2 for the governing system input along with PLA. The only other items that it did was to give flight idle, variable bleed valves, VBV and the variable stator valves, VSVs. The latter was IIRC fluidic control system but with mechanical feedback to the MEC. Expensive when they went bad. The PMC trimmed fuel electrically and didn't drive the PLA. Hazy.

TD Racer On the CVR, I'm not sure it will reveal anything of great note in this case. That the crew didn't correct the TL split is indicated in the FDR data reportedly. There are not too many logical reasons why a crew member on seeing a split would not remove the split, yet that appears not to have happened. The highest likelihood is the crew were not aware of the split through distraction with other tasks, and that can be assessed in a simulator with a cohort of drivers as to the likelihood of detection. To get in before the objections, there is a history of extended time to detect a condition or a complete failure to detect in our sorry past. Take a B747 that has a gear red light for 2 minutes and lands with no nosewheel... and that was a "top-of-the-line" IP. Expectations of immediate and correct crew responses is akin to "they said artificial sweeteners were safe, and WMD's were in Iraq, and Anna Nicole married for love!". If it's recovered, great, but the event shows that the crew likely never recognized the condition, otherwise they would have got to Ponkianak for their Kopi Luwak.

Last edited by fdr; 12th Feb 2021 at 02:11.
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Old 12th Feb 2021, 02:03
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I have quoted what is claimed to be a translation of the report. Nothing more, nothing less.
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Old 12th Feb 2021, 02:10
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I think it has more to do with the degradation of piloting skills all over the world. This has been the result of airlines, manufacturers and regulators facilitating a rapid increase in world wide airline travel without the impediment of ensuring a high standard of training. You can blame it on the nationality and culture of the individual pilots but how do you explain the Turkish Airlines accident in Amsterdam and AF447? Certainly Indonesia seems to have more of the headlines but I think it is a symptom of the world wide problem not just because it was a B team crew at the controls.
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Old 12th Feb 2021, 02:22
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Not aware of the TL split...not aware of increasing yaw to the left? Assuming inputs to requested heading change accounted for the yaw? We need that CVR to try to determine what human conditions may have led to such a very early lack of attention (or inability to respond) by PF to clear warning signals. I’d also be interested to have been a fly on the wall during the previous 12|24 hours to know if anything about the preflight period may have impacted on crew, especially PF. These are things that can never be discovered in a report unfortunately, but they do fan the flames of “more automation” calls.
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Old 12th Feb 2021, 02:28
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I forgot to mention that on the TAROM accident flight, the FO kept trying to re-engage the autopilot as the aircraft rolled over on its side. Forget about disconnecting the autothrottle, forget about flying manually.
If people are wary to handfly on a normal day, how can they be expected to suddenly become confident in a crisis? In weird situations, many people revert to instinct. If the instincts are wrong (automatics are going to save the day), because the training was all wrong (automatics do it so much better than you, don't even try), accidents will happen. I'm only bringing up the TAROM flight, because it was exactly the same type of upset caused by the exact same thing. But there are many examples where crews have allowed automation to kill them, because they either lacked the confidence to disconnect or because they didn't even notice what was happening.

So I wouldn't find it so surprising if this particular crew was actually aware of the autothrottle problem and kept trying to figure it out, instead of disconnecting it, until they found themselves rolled over and in a dive. In the context of what's been happening over the years, it's really not that strange a scenario. There are people who would literally rather die than take manual control of their aircraft outside of takeoff and landing.
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Old 12th Feb 2021, 02:30
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fdr, if the mechanical T/R thrust reduction comes into play, it rapidly moves the throttle to idle (less than a second - known as a 'throttle snatcher'). It's rapid enough that you don't want your hand in the way. It also makes a very audible noise when the lever hits the stop. Oh, and it would also have been obvious on the FDR. All in all, the T/R is a non-sequitur in this discussion.

I maintain it's going to very difficult to understand why the crew failed to notice or react to the throttle split without the CVR. For example, the key to the similar TAROM crash was the the left seat pilot suffered some sort of medical emergency just as the uncommanded throttle movement occurred. It was the distraction of whatever happened to the left seat pilot that distracted the PF enough that he let the situation get out of hand. A simulator will never give that sort of insight into the why...
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