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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 7th Nov 2018, 06:55
  #701 (permalink)  
 
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Originally Posted by Capn Bloggs View Post
The QF A330 that took the plunge, twice, didn't result in grounding the fleet, despite the authorities NEVER working out what happened. Airbus came up with a procedure where crews push-button-disabled a particular system.


If you're comfortable handflying and the aeroplane starts doing something in pitch you don't like with, say, full back stick, you trim against it. Or you grab the trim wheel and stop it. Or you engage the AP! My point is, you have to be happy with hand-flying to be able to have spare brain space to try something.

So, is the STS the culprit when the speeds/AoA go haywire?
Yes the QF A330 didn't result in a grounding, nor was the erroneous ADIRU issue resolved. The 'incident' wasn't fatal. One can imagine the pressure bought to bear by both operators and manufacturers on the regulator was substantial.
In this case, 189 souls were lost.
In a different era perhaps prudence would prevail.
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Old 7th Nov 2018, 06:56
  #702 (permalink)  
 
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Originally Posted by spongenotbob View Post
Ostrower's piece appears to be an embroidered rehash of the Bloomberg article.

Based on his previous abysmal reporting of the tech log issue ("the perilous unreliability of Lion Air documents"), I think that waiting for independent confirmation of his "additional reporting" might be prudent.
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Old 7th Nov 2018, 07:00
  #703 (permalink)  
 
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Originally Posted by Capn Bloggs View Post
The QF A330 that took the plunge, twice, didn't result in grounding the fleet, despite the authorities NEVER working out what happened. Airbus came up with a procedure where crews push-button-disabled a particular system.


If you're comfortable handflying and the aeroplane starts doing something in pitch you don't like with, say, full back stick, you trim against it. Or you grab the trim wheel and stop it. Or you engage the AP! My point is, you have to be happy with hand-flying to be able to have spare brain space to try something.

So, is the STS the culprit when the speeds/AoA go haywire?

No, it is not the speed trim system. It is the regular autopilot trim system that commands the nose down trim in case of approaching stall AOA.

Probably the previous crew encountered the same problem and mistakenly wrote it up as a STS fault.
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Old 7th Nov 2018, 07:22
  #704 (permalink)  
 
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That’s interesting, I’m pretty sure the NG does no such thing. Can anyone post how this works on the Max?
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Old 7th Nov 2018, 07:24
  #705 (permalink)  
 
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Now that it's shaping up to include a stab trim issue, there is a parallel discussion going on
on the tech forum which may interest some on the STS issues.
B-737 Speed Trim System

I've never seen a 737 MAX, does it still have the stab trim wheels?
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Old 7th Nov 2018, 07:34
  #706 (permalink)  
 
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Originally Posted by Derfred View Post
That’s interesting, I’m pretty sure the NG does no such thing. Can anyone post how this works on the Max?
Actually, the NG does:

The EFS module increases hydraulic system A pressure to the elevator feel and
centering unit during a stall. This increases forward control column force to
approximately four times normal feel pressure. The EFS module is armed
whenever an inhibit condition is not present. Inhibit conditions are: on the ground,
radio altitude less than 100 feet and autopilot engaged. However, if EFS is active
when descending through 100 feet RA, it remains active until AOA is reduced
below approximately stickshaker threshold. There are no flight deck indications
that the system is properly armed or activated.
As airspeed decreases towards stall speed, the speed trim system trims the
stabilizer nose down and enables trim above stickshaker AOA. With this trim
schedule the pilot must pull more aft column to stall the airplane. With the column
aft, the amount of column force increase with the onset of EFS module is more
pronounced.
That is from a by now pretty old NG FCOM, i haven't been typed for the last three years on the 737.

That said, we had a few AoA malfunction on our 737 fleet, thank god the only serious thing that happened was a runway overrun without injuries due to different speed indications during take off (abort close to indicated V1, but probably way above V1). In flight the problems caused by the AoA were actually quite severe, indications for IAS, Altitude, VS, flight path vector, wind indication and ground speed all became unreliable on the affected side. Comparator warnings were not always generated, so it was usually detected by pilots saying "this doesn't look right" and then comparing indications across the flight deck. Most problems happened in mid to high altitudes though, so there was plenty of space to recover. And it might or might not have any relevance to the current case.
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Old 7th Nov 2018, 07:53
  #707 (permalink)  
 
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Boeing known issue

Gizmodo and Bloomberg reporting that fatal nose dive issue is known with the new 737 and what pilots should do at high speed stall.
(can’t post link)
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Old 7th Nov 2018, 08:02
  #708 (permalink)  
 
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Thanks Denti. I was aware of the elevator feel input in a stall, and have experienced it in the Sim. Pull the aircraft into a stall and try to hold it in the stall, the back pressure becomes VERY heavy. That’s the elevator feel “anti-stall” in action.

But I wasn’t aware of any “anti-stall” stab trim operations, other than the STS simply doing it’s normal STS thing.

Is the Max different?
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Old 7th Nov 2018, 08:36
  #709 (permalink)  
 
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Originally Posted by Derfred View Post
Thanks Denti. I was aware of the elevator feel input in a stall, and have experienced it in the Sim. Pull the aircraft into a stall and try to hold it in the stall, the back pressure becomes VERY heavy. That’s the elevator feel “anti-stall” in action.

But I wasn’t aware of any “anti-stall” stab trim operations, other than the STS simply doing it’s normal STS thing.

Is the Max different?

No, the max trims down just as the 737NG trims down. The post you quote is from a 737NG FCOM and clearly states it trims down.
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Old 7th Nov 2018, 09:13
  #710 (permalink)  
 
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From the Seattle Times article:
And the air-speed indicators on both sides of the flight deck disagree.
Now i do understand a malfunctioning AoA sensor sensing high AoA would make the red/black band come up on the speed tape (and activate the stick shaker)

But the IAS being displayed should still be correct? Which would technically not be UAS or IAS disagree at all?

Anyone have a guess if this is a compound issue or the UAS issue was not an UAS at all just interpreted that way?
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Old 7th Nov 2018, 09:18
  #711 (permalink)  
 
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Who can share a copy of the Bulletin?

737 Max angle-of-attack sensor subject of Boeing bulletin

  • 07 Nov 2018 19:29 GMT+10:00
  • Flight Global
Boeing has issued an operations manual bulletin to 737 Max operators, covering air data sensors, following investigations into the crash of Lion Airflight JT610.

The manufacturer says it issued the bulletin on 6 November, directing operators to “existing flight crew procedures" to address circumstances involving erroneous angle-of-attack sensor information.

Angle-of-attack information is critical to avoiding the onset of stall conditions.

Indonesia's National Transportation Safety Committee has indicated that the ill-fated flight “experienced erroneous input" from such a sensor, says Boeing.

It stresses that issuing bulletins or recommendations, when appropriate, regarding the operation of its aircraft is a "usual process".

“The investigation into Lion Air flight 610 is ongoing and Boeing continues to co-operate fully and provide technical assistance at the request and under the direction of government authorities investigating the accident,” the manufacturer adds.

Media reports had earlier surfaced saying that Boeing was preparing to issue a service bulletin to Max operators.

The NTSC has said that it believes the crashed aircraft had been operating with airspeed indicator faults during its last four flights. It also called on Boeing and the US National Transportation Safety Board to take necessary action to prevent future cases of faulty flight system readings.

Flight JT610 had been operating from Jakarta's Soekarno-Hatta International airport to Pangkal Pinang when it crashed into the sea near the town of Karawang, claiming the lives of all 189 occupants.
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Old 7th Nov 2018, 10:02
  #712 (permalink)  
 
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It also called on Boeing and the US National Transportation Safety Board to take necessary action to prevent future cases of faulty flight system readings.
Seriously? Make an aircraft which defies the laws of physics and never breaks down? 3 independent pitot-static systems isn't enough?
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Old 7th Nov 2018, 10:07
  #713 (permalink)  
 
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.

IF this is a software/coding problem, does that mean that the whole flight control system will need to be re-certified as if the checks missed one (huge) error what else might have been missed ?

Well, at least the lawyers will make lots of money out of this tragedy.

.
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Old 7th Nov 2018, 10:45
  #714 (permalink)  
 
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Originally Posted by NSEU View Post
Seriously? Make an aircraft which defies the laws of physics and never breaks down? 3 independent pitot-static systems isn't enough?
Enough for the National Team of Scaredy Cats? Are you kidding? These are the people that make the FAA look sensible, rational, even daring.
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Old 7th Nov 2018, 10:48
  #715 (permalink)  
 
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IF this is a software/coding problem, does that mean that the whole flight control system will need to be re-certified as if the checks missed one (huge) error what else might have been missed ?
If it was all fly by wire then maybe. My understanding is that it's only the spoilers that are electrically signalled. The rest of the system is cables, pulleys and hydraulics.

Last edited by TURIN; 7th Nov 2018 at 11:32. Reason: Crossed post
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Old 7th Nov 2018, 11:19
  #716 (permalink)  
 
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Boeing warns that the stabilizer system can reach its full downward position if not counteracted by pilot trimming the aircraft and disconnecting the stabilizer trim system.
So is it time to re-introduce all the deleted posts regarding stabilizer trim and elevator efficiency and early jet aircraft design (which the 737 still is over wide areas) ?

Otherwise I am still confused about the different messeges you receive....
- "UAS", which mainly means a pitot issue
- "Faulty speed and altitude indications", which more points to a static pressure issue
and now finally
- "angle of attack sensor subject", which is a totally different system altogether

If we are confused, the pilots probably have been as well...

Now i do understand a malfunctioning AoA sensor sensing high AoA would make the red/black band come up on the speed tape (and activate the stick shaker)
But the IAS being displayed should still be correct? Which would technically not be UAS or IAS disagree at all?
Well, whether the red/black band comes up on the speed tape or the speed goes down (due to UAS), both would reduce the margin between indicated airspeed and calculated stall speed, which may then trigger the stick shaker and the nose-down auto-trim, if the algorithm is made this way...
.
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Old 7th Nov 2018, 11:41
  #717 (permalink)  
 
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This issue existed on this specific plane for multiple flights prior to the accident flight. The previous flight was hand flown by the FO (my understanding) so it was a manual approach and landing which would have required multiple power settings and configurations as well as a continual ongoing trimming of the aircraft. So what would make this flight different?
I keep coming back to the combination of level flight (vs. the normal climb out) and the presence of an engineer (in cockpit?). My understanding is that SOP would be for power and pitch to be set such that a stabilized climb rate would be maintained while the non memory items on the checklist were performed...since this didn't happen and a mayday/pan wasn't called
I'm speculating that the decision to maintain (or try to) 5000 ft. was tied somehow to the engineer. Multiple oscillations and variable flight path....got to believe that the interaction of the engineer and crew will be a critical component of what happened and that the breach of the sterile cockpit doctrine will be central to how events unfolded.
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Old 7th Nov 2018, 11:45
  #718 (permalink)  
 
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Now that we have AOA in the spotlight, and reports of indicators issue on other Lion 737 Maxx, what could be the cause? The sensor itself, the computer monitoring and converting its readings, or the software converting those readings for interpretation by the STS, among other things??

Can the FDR parameters disclose this? Also, AOA gauge on the PFD was an option on the NG. Is it still an option on the Max, and does Lion have it?
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Old 7th Nov 2018, 11:56
  #719 (permalink)  
 
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Originally Posted by phil gollin View Post
.

Just before the flood of information and supposition starts, may I just note that the confidentiality held regarding this crash and investigation has been very good. Normally on here there is endless discussion regarding leaks and voluminous criticism of the leaks (especially when it concerns certain parts of the world). Thankfully, this time things have proceeded properly, I can only hope it continues whilst the first (and then second, hopefully) recorders are examined.

.
Professionalism through experience unfortunately
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Old 7th Nov 2018, 11:58
  #720 (permalink)  
 
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Also, AOA gauge on the PFD was an option on the NG. Is it still an option on the Max, and does Lion have it?
What use would it be if, as it appears, the AoA system was putting out duff gen? A dud AoA gauge would just confuse the crew even more.
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