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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 29th Oct 2018, 16:12
  #121 (permalink)  
 
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My initial impression after reviewing the flight track last night was that the aircraft was experiencing roll control problems and finally rolled left at high speed into the water.
Although the maintenance history of Captain side pitot problems may be relevant, and there is always the possibility of maintenance action causing new problems, an airspeed indication problem of itself should not cause loss of the aircraft.
Those of you speculating on the possibility of stall warnings being triggered should remember that these warnings normally are generated from the angle of attack data which is not derived from airspeed but instead from the vanes on the sides of the cockpit.
The impact of defective air data on the aircraft feel systems needs to be discussed by someone with more 737 aircraft familiarity than myself but could potentially be a significant factor. Aircraft control appeared to be degraded early in the flight.
Speculation: Could both of the cockpit crew have been applying force to the control column and not have had a free hand for setting the power? The continued acceleration of the aircraft doesn't make good sense from a piloting perspective. They needed to set a reasonable power setting and investigate if they could not continue the climb or did not wish to continue the climb.
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Old 29th Oct 2018, 16:42
  #122 (permalink)  
 
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Aircraft mechanic here. And yes i am a Little bit disturbed that a leak like this happened. Shouldn’t be because there are names of flight crew and mechanics. Apart from that there are more than one copy of the report. As you can read on the bottom of said report. The pink we got is meant to stay with the technical Departement
I'm also disturbed that this document is in the public domain, but having lived and worked in Jakarta, I am not in the least bit surprised.
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Old 29th Oct 2018, 16:53
  #123 (permalink)  

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Pitot cover?

Could be static vents, blocked by insects. Loads of nesting bugs in Indonesian Islands. Or pitot covers. Do these people, inc ground engineers, do methodical walk-rounds. I saw little evidence of that during 5 long Hajj stints for Garuda. Laziness was endemic in the nation. And in the region, except for Singapore.
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Old 29th Oct 2018, 16:56
  #124 (permalink)  
 
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Originally Posted by HolyMoley
surely the chance of an aircraft having an unreliable speed issue one day and being lost the next due to a completely unrelated reason that also affects the airspeed (not removing pitot covers) must be vanishly small.
The probability of forgetting to remove the pitot covers on a day after there was a write up for Unreliable Airspeed is identical to the probability of forgetting to remove the pitot covers on a day after there was no write-up for UAS.

Not that I'm trying to claim that pitot covers are the cause here, but neither is it a given that the crash is due to an unreliable airspeed indication. That is just one of the few pieces of information that we have, that there was a UAS write-up on the previous flight, and there is speculation how that might have caused the crash, if it were to have reoccurred, whcih isn't a given.
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Old 29th Oct 2018, 16:56
  #125 (permalink)  
 
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Originally Posted by Icarus2001 View Post
I am not for one minute suggesting that in this case just pointing out to the "it did not stall" brigade that, yes it could have and also that FR data is fraught with errors. i have watched it plot an aircraft landing as I saw the aircraft turn during a missed approach, it has predictive algorithms so the speed and direction you see is not always what the aircraft is doing.
No, the data that is available for download from FlightAware and FR24, while it certainly requires care in interpreting, is what the aircraft was sending (with a couple of caveats that aren't relevant here) and is independent of any prediction algorithms.

One thing that sticks out from the plot is that, aside from the vertical excursions, the last five minutes or so before the plot stops consist of two minutes of dead straight flight followed by two and a half minutes of continuous small track changes. I'll leave it to other to speculate on the significance of that.
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Old 29th Oct 2018, 16:59
  #126 (permalink)  
 
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Originally Posted by Pontius Navigator View Post
There was earlier talk of pitot covers not being removed. Then a suggestion that they would not have been fitted overnight. Then that the system may have been maintained over night.

But there are other possible problems are there not? Could there be water in the system? Has there been significant rainfall around these two flights?
I'm currently in Jakarta and can confirm there was a very large storm last night from about 9pm-12am with considerable rainfall
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Old 29th Oct 2018, 17:10
  #127 (permalink)  
 
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Originally Posted by Localiser Green View Post
The same aircraft apparently had an unreliable speed issue on the previous flight from Bali to Jakarta last night. This was reported by the pilots according to Bloomberg.

FR24 data from that flight shows the aircraft enters a descent after takeoff, with increasing speed, similar to the event which happened on this flight at approximately 2,000ft. However on the DPS-CGK flight it happened at around 5,500ft.

14:25:21 - 5,500ft - 282kt
14:25:48 - 4,625ft - 324kt
14:26:13 - 5,400ft - 303kt
14:26:25 - 6,300ft - 276kt
14:26:37 - 6,600ft - 265kt
14:26:49 - 7,400ft - 247kt



Suggests around 2,000fpm descent rate with 42kt speed gain, followed by 3,000fpm climb losing 77kt. That's not a normal climb profile so something went wrong here, assuming the ADS data is accurate.
An aircraft can stall at any speed! It is the angle of attack which determines when stall (pitch angel) if they had flew at 350kt they would stall anyway if the nose was 40 degress nose up. A passenger airplane is is not designed nor have the trust required to do that, a rocket is a different thing.

i can’t remember exactly how it is but if your static or pitot ports are blocked (either one) your airspeed will increase with altitude. So if they put on the autopilot after take off the plane will pitch up and up to contain the airspeed increase and rather quickly put the aircraft in an unusal attitude, nose high low airspeed (actual airspeed). Autopilot will disconnect and stall warning alarms etc. If the pilots don’t react quicly and correct the airplane will stall. There might be a startle factor for the crew as well, which delay their reaction time. This only speculations from my side anyway. Tragic to see another fatal accident in Indonesia.
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Old 29th Oct 2018, 17:12
  #128 (permalink)  
 
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Originally Posted by Icarus2001 View Post
I am not for one minute suggesting that in this case just pointing out to the "it did not stall" brigade that, yes it could have and also that FR data is fraught with errors
So the prediction you are mentioning is only implemented for displaying live flights, but it is used because quite a few people will look up and want the planes on map to match up.
Also i would not trust the timestamping on the data, the outliers in the following plot are very likely because of one of the receivers clocks being off.

Apart from that FR24 on their blog released the raw data for the flight in much better granularity than available on their website flight history.
It's unlikely that these data, probably received by multiple receivers differ significantly from what was sent by the ADS-B sender of the aircraft in question.

Because the plots of the data on the blog website are somewhat lacking, i plotted the data below in case anyone is interested:



ADS-B Data Plot
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Old 29th Oct 2018, 17:44
  #129 (permalink)  
 
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Originally Posted by India Four Two View Post
I'm also disturbed that this document is in the public domain, but having lived and worked in Jakarta, I am not in the least bit surprised.
Likewise. I live in Jakarta and by 11am local time a member of a wholly unrelated Indonesian whatsapp group I’m in had forwarded unsolicited photos of the full passenger manifest. 3 hours later I received an unverified video purporting to have been filmed from inside the doomed flight by one of the passengers and sent to family just prior to the crash. Cultural values around accidents and death are VERY different in Asia compared to the West. To put this in perspective many years ago I attended the funeral of someone who’d been killed in a crash. Lo and behold the patents produced photos of the accident. Likewise at the funeral of someone who died in the fire at a disco in Bangkok everyone was encouraged to see pay respects to whar little remained of her body. Attitudes to privacy are wholly different which might help explain to many Westerners reading this why so much of what we consider should remain reapectfully private, is actually shared:with whar appears like glee. Just humans trying to comprehend tragedy in very different ways.
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Old 29th Oct 2018, 17:45
  #130 (permalink)  
 
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Air France A330
AirAsia A320
Lion Air 737

WHEN can we finally expect an AOA indicator in the flight deck? We need them. MAYDAY.
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Old 29th Oct 2018, 18:06
  #131 (permalink)  
 
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Thank you for the expanded plot wiedehopf. The final descent appears to be almost vertical with approx 2500' lost in 3 sec.
Condolences to all involved.

OAP
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Old 29th Oct 2018, 18:10
  #132 (permalink)  
 
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Originally Posted by Machinbird View Post
My initial impression after reviewing the flight track last night was that the aircraft was experiencing roll control problems and finally rolled left at high speed into the water.
Although the maintenance history of Captain side pitot problems may be relevant, and there is always the possibility of maintenance action causing new problems, an airspeed indication problem of itself should not cause loss of the aircraft.
Those of you speculating on the possibility of stall warnings being triggered should remember that these warnings normally are generated from the angle of attack data which is not derived from airspeed but instead from the vanes on the sides of the cockpit.
The impact of defective air data on the aircraft feel systems needs to be discussed by someone with more 737 aircraft familiarity than myself but could potentially be a significant factor. Aircraft control appeared to be degraded early in the flight.
Speculation: Could both of the cockpit crew have been applying force to the control column and not have had a free hand for setting the power? The continued acceleration of the aircraft doesn't make good sense from a piloting perspective. They needed to set a reasonable power setting and investigate if they could not continue the climb or did not wish to continue the climb.
If you leave the A/T engaged it will retard the thrust to try to maintain speed in a false overspeed condition, I have demonstrated this many times in the sim to illustrate the importance of memory actions on first indications of unreliable airspeed, sit there picking your nose and depending on vertical mode you’ll end up with high NUA and thrust decreasing which will quickly become a stall, no problem ( at least in the sim!!) but you need to think what the stab and trim has been doing whilst this has been going.

Looking at the tech log and assuming this is real ( which is incredulous) the test equipment would require certain ports to be sealed, lets see what the FDR comes up with, shouldn’t be difficult to find in 30m of water.
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Old 29th Oct 2018, 18:33
  #133 (permalink)  
 
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Equal and opposite reactions

Originally Posted by wiedehopf View Post
So the prediction you are mentioning is only implemented for displaying live flights, but it is used because quite a few people will look up and want the planes on map to match up.
Also i would not trust the timestamping on the data, the outliers in the following plot are very likely because of one of the receivers clocks being off.

Apart from that FR24 on their blog released the raw data for the flight in much better granularity than available on their website flight history.
It's unlikely that these data, probably received by multiple receivers differ significantly from what was sent by the ADS-B sender of the aircraft in question.

Because the plots of the data on the blog website are somewhat lacking, i plotted the data below in case anyone is interested:



ADS-B Data Plot
Fascinating thread, yet deeply tragic.
It seems from the graph that everything has an equal or opposite reaction!
One crumb of comfort would be that the debris field is fairly limited in shallow water and that the CVR and FDR should be recovered promptly and resolved, so that everyone can understand what happened here.
At times like this I can only think of Sir Arthur Conan Doyles' quote
"Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."
RIP
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Old 29th Oct 2018, 18:42
  #134 (permalink)  
 
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Surely the Tech Log would have been on the aircraft?
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Old 29th Oct 2018, 18:46
  #135 (permalink)  
 
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Originally Posted by Smithy02 View Post
Surely the Tech Log would have been on the aircraft?
Presumably. However, it is within the realm of possibility that someone would have photographed the relevant page at some point between blocking in on the previous flight, and blocking out on the accident flight.
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Old 29th Oct 2018, 18:49
  #136 (permalink)  
 
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Originally Posted by Onceapilot View Post
Thank you for the expanded plot wiedehopf. The final descent appears to be almost vertical with approx 2500' lost in 3 sec.
Condolences to all involved.

OAP
Please keep in mind that this is altitude plotted against time so you can't really tell the flight path from it.

If you believe the data the aircraft had a descent rate of 31000 ft per minute during the last recorded transmission.
That is around 300 knots vertical speed. Horizontal speed at that last data point is 360 knots.
That is a total speed of around 470 knots with the flight path angle being around 40 degrees downwards.

So this calculation is kind of gruesome but as the question came up i'll post it anyway.
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Old 29th Oct 2018, 19:08
  #137 (permalink)  
 
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Salute!

Besides the air data problems on previous flight, and possibly on the accident flight, I would like to re-visit the stabilizer. Just a fast mover guy here, but the sad story is worth understanding. Never know when a pilot here might see something early enough to take action, jez saying.....

Looking at thelfight path plot we have from a previous post, the end seems to happen very quickly, and not a "gradual" loss of control due to PIO chasing the altitude, attitude and speed.

So for you Boeing folks, is there a jackscrew stab trim as we had on the Alaska crash? A squak previously described unusual stab trim. If the stab "came loose" suddenly, I do not see any recovery possible. As Bach said, all crashes are the result of "loss of control". Plane comes apart, big part fails, new FBW laws act up, crew screws up, etc.

Gums asks....
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Old 29th Oct 2018, 19:09
  #138 (permalink)  
 
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Originally Posted by Wizofoz View Post
You can't stall a 737 at 300kts- it would break up first.
Va= 260 kias at sea level
and 306 kias at 31,000 feet

So, yes you could.
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Old 29th Oct 2018, 19:14
  #139 (permalink)  
 
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As someone with very limited single engine experience long long ago I'd love to get some thoughts from those in the pointy end. Just looking at the track between 23:25 and 23:29 I'm slightly confused. My understanding is that if the correct memory items where followed you would have established pitch and power as constants...normally in a gentle climb while troubleshooting. During those 4 minutes it appears that both speed and altitude remain "relatively" stable but with clear oscillations that appear to indicate an inverse speed to altitude shift so there is clearly an issue maintaining level flight. I've always thought that at higher altitudes hand flying a swept wing plane was significantly harder than at lower levels. Under an emergency would the aircraft commander normally take the controls and rely on the FO to trouble shoot or would he be more likely to allow the FO to maintain level flight while he looked at the issues?

It would appear that there was an upset and recovery at roughly 23:29:30 and then again roughly 2 minutes later that proved unrecoverable. In both instances it appears to be a roughly 800 ft drop over roughly 20 seconds...that seems awful "ham handed" for purely pitch induced control input to me without some sort of rolling oscillation involved??? What type of flight path variation would be "normal" for an experienced airline pilot with minimal hand flying currency? Hard to imagine losing the plane at 5000 ft. in benign VFR conditions without some other issue in play???
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Old 29th Oct 2018, 19:17
  #140 (permalink)  
 
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The tech log seems factual, not sure why it is such a bother that it is available online. At least it guards against fake news.
So far as I can understand from the photo the resolutions read as:
REF IFIM 34-20-00-810-801 REV 15/07/2018 PERFORMED FLUSHING LH PITOT ADM AND STATIC ADM (AIR DATA MODULE) OPS TEST ON GROUND FOUND SATISFIED
REF IFIM 28-34-00-810-803 REV 15/07/2018 PERFORMED CLEANED ELECTRIC. C???. PLUG OF ELEVATOR FEEL COMPUT?R C/O TEST ON GROUND FOUND OK
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