Indonesian aircraft missing off Jakarta

[dragon6172]

Originally Posted by gmx

The pilots on lion 610 were in regular contact with ATC and as late as 20 seconds before impact with the ocean they indicated their preferred flight level. This suggests they were not under duress in operating the aircraft until the very end. It is still very much unclear why their successful and consistent NU trim corrections are suddenly insufficient to counteract MCAS.

My understanding is there was a change in which pilot was flying near the end of the flight. The original pilot dealt with the ND trims with NU trims consistently. This can be seen pretty clear in the FDR traces. Each ~10 second ND trim is followed by ~10 seconds of NU trim. Then after the change of flying pilot, the NU trims are only a second or less at a time, and never really counter the ND trim at all.

The question is why the change in flying pilot? The CVR will go a long way in answering this, if it can be found.

[Lonewolf_50]

PJ

The stick shaker remained active throughout the flight.

It stands to reason that the maintenance crew won't go out and trouble shoot a problem that is not brought to their attention. Your point on "where's the write up?" will hopefully get answered in due course. It has me puzzled, given the detail provided in the A-SHOR report cited on page 21. (this refers to the previous flight)

PIC advised the controller that the altitude of the aircraft could not be determined due to all aircraft instruments indicating different altitudes and requested to the controller to block altitude 3,000 feet above and below for traffic avoidance.

One thing I found interesting on the timeline was what might have been some trouble shooting by the cockpit crew with the flaps, but that particular report points me toward a compound malfunction; you've got one problem making the pitch control a problem, and another problem presenting both pilots with confusing altitude information. (though if all that meant was "an ALT disagree alert" this might be a red herring).

[InfrequentFlier511]

And the crew of previous flight also recognized there was a trim problem, but in their case almost immediately disabled the automated trim and trimmed via the mechanical trim wheels.

That seemed quite logical to me, whether or not it was a classic presentation of runaway stabilizer, it must have at least appeared as an intermittent fault. From the memory items, auto trim isn't essential so, if it's making things worse instead of better, turn it off.

In hindsight, some mention of MCAS in the training material would have been a good idea, but... there's a lot of systems on a modern aircraft, it is unreasonable to expect pilots to have an intimate knowledge every single one of them and how a malfunction affects control. Would knowing of the existence of MCAS make a decisive difference over knowing that there are automated systems that alter trim and that can be turned off if they cause problems? Where Boeing really dropped the ball is in allowing MCAS to continue to mess with the trim when other systems knew that the AoA data it was using was unreliable.

[CONSO]

Originally Posted by Lonewolf_50

PJ
It stands to reason that the maintenance crew won't go out and trouble shoot a problem that is not brought to their attention. Your point on "where's the write up?" will hopefully get answered in due course. It has me puzzled, given the detail provided in the A-SHOR report cited on page 21. (this refers to the previous flight)
One thing I found interesting on the timeline was what might have been some trouble shooting by the cockpit crew with the flaps, but that particular report points me toward a compound malfunction; you've got one problem making the pitch control a problem, and another problem presenting both pilots with confusing altitude information. (though if all that meant was "an ALT disagree alert" this might be a red herring).

THIS REPORT ??
http://knkt.dephub.go.id/knkt/ntsc_aviation/baru/pre/2018/2018%20-%20035%20-%20PK-LQP%20Preliminary%20Report.pdf
PAGE 22

The engineer performed flushing the left Pitot Air Data Module (ADM) and static ADM to rectify the IAS and ALT disagree followed by operation test on ground and found satisfied. The Feel Differential Pressure was rectified by performed cleaned electrical connector plug of elevator feel computer. The test on ground found the problem had been solved.
At 2320 UTC, (29 October 2018, 0620 LT) the aircraft departed from Jakarta using runway 25L and intended destination Pangkal Pinang. The DFDR recorded a difference between left and right Angle of Attack (AoA) of about 20° and continued until the end of recording. During rotation the left control column stick shaker activated and continued for most of the flight.

[climber314]

He went to 5,000 ft per the Airspeed Unreliable Checklist (table below). The Alt Disagree Checklist is quick. (Looking at the 737NG-800 QRH) Fly pitch and power as per the QRH. Next figure out why the trim is being stupid and that dumb wheel keeps spinning the wrong way. Keep the wheel in the GREEN if you have to hold the D%#@ thing.

[tdracer]

Originally Posted by silverstrata

And the engines are much more powerful - up to 30 k lb of thrust. All that extra thrust, low down on the airframe, generates a large pitch up moment - especially if the aircraft is slow and the elevator is becoming less efficient. You can actually get to a situation where the aircraft simply goes vertical, or flips over backwards.

S

Ah, no they are not... The maximum engine ratings on the Max are very similar to the corresponding models of the NG. The larger models are allowed more thrust because the increased leverage of the tail (due to the longer fuselage) permits it. This is all governed via the rating plugs on the FADEC - and there is logic on the aircraft side that will put up a warning if the engine ratings are too high for the aircraft model.
This is nothing new - the 737 'Classic' -3/4/500 models had the same max thrust limitations - but it was done mechanically. The 737-3/4/500 models all used the same engine, one the shorter -300 and -500 models, there was a physical stop to how far the throttle could be advanced to prevent excessive power nose-up from becoming an issue.

[wiedehopf]

People looking for the report a quicker download is possible here:
Lion Air Boeing 737 MAX 8 crashed into Java Sea off Jakarta » JACDEC

I believe avherald.com also has it available.

[MickG0105]

Originally Posted by GarageYears

I understand the intent here, but as revealed by the FDR traces, the crew of the fated flight clearly understood there was a trim issue, they repeatedly applied trim opposite to that applied by the automation (MCAS) - true, they may not have understand 'what' was applying the trim, but clearly they knew it was happening. The question is why did they not hit the cut off switches?

And the crew of previous flight also recognized there was a trim problem, but in their case almost immediately disabled the automated trim and trimmed via the mechanical trim wheels.

- GY

The question as to why did JT610 not run the Runaway Stabilizer NNC all the way to 'STAB TRIM CUTOUT switches (both) ...... CUTOUT' just as JT43 did will remain largely open until the CVR is recovered (hopefully it will have enough of JT43 preserved to compare the two cockpits). Short of that I'd offer two observations:

1. The presentation of the problem on take-off goes IAS DISAGREE + L stick shaker first at a couple of hundred feet, MCAS commanded ND trim second on flap retraction. When the IAS DISAGREE + L stick shaker manifested itself on JT43 they would have ran the Airspeed Unreliable memory items and importantly they maintained pitch of 15° and the existing takeoff thrust. That attitude meant that when the MCAS commanded ND trim kicked in on flap retraction control column forces built rapidly (the CFFORCE_PITCHCWS forces on JT43 quickly spiked to levels not experienced by JT610 until the last 40 seconds or so of their flight). JT43 was presented with pressing imperative to do something about the ND trim, hence STAB TRIM CUTOUT switches to CUTOUT.
2. Through a confluence of factors (most likely a briefed plan for UAS and an impromptu reaction) JT610 were never presented with the same control column force 'imperative'. There's plenty of evidence to support the contention that JT610 had briefed for a UAS and the plan was to get to 5,000 and establish level flight flaps up at VREF40+70 (per the QRH Flight With Unreliable Airspeed table), stabilse and return to Jakarta. On take-off, lo and behold, the initial IAS DISAGREE + L stick shaker presents. Priming and confirmation bias will now shape the crew's perception of and decisions about everything that happens subsequently. When the MCAS commanded ND trim kicked in on flap retraction JT610's (I suspect impromptu) reaction is to re-extend flap. That action temporarily halts MCAS so they're not subjected to significant control column forces as they climb and because they are levelling off when MCAS bites them next they're not subjected to significant control column forces for most of the rest of the flight. The MCAS commanded ND trim is 'manageable' manually with control column and main electric trim up until the point when it isn't.

I suspect that this might be one of those cases where the guys with the plan (albeit for the emergency that they were expecting, not the one they got) faired much worse than the guys without a plan who just reacted instinctively. If indecision is the key to flexibility, a prepared plan is probably its enemy.

[safetypee]

td #1815
So if the thrust has not changed and the revised engine mount might not contribute a significant pitching moment, then why introduce MCAS. Perhaps higher engine wt and changed location - the cg effect messed with the long stab, particularly approaching the stall; thus ‘augmentation’ was required. If this is not the issue, then the MAX handling would be essentially the same as previous models.
Or did someone think that MCAS was a good idea given previous accident history.

MickG0105 ‘a prepared plan is probably the enemy’
… in lieu of the absence of manufacturer’s advice, drills, and fault finding - absence of any reference to MACS.

[underfire]

Four operators have reported instances of excessive stabilizer trim system coasting (stabilizer trim wheel continues to rotate) after the control wheel stabilizer trim switches have been activated and released. The reports indicate that when the pilot released the trim switches, the stabilizer trim wheel coasted up to 40 turns (four units of trim). In some instances the trim wheel stopped moving in the commanded direction and then rotated up to 40 turns in the opposite direction.

Not only a Lion Air problem.

[Loose rivets]

Ian W #1794

For some reason they didn't switch the auto stab trim off. I would really like to know where that flying spanner was, as this looks like a fault finding exercise gone wrong rather than set the systems safe and land.

What a fascinating thought. I've flown with people that launched into the most extraordinary series of flight testing - with a full load of SLF. I thought those days were history.


Mad (Flt) Scientist.

MCAS appears designed to give assistance to using the elevator to recover from a high AoA condition. Likely the scenario for which it is implemented also includes some combination of high thrust (causes nose-up moment) and stab trimmed to abnormally nose-up position. Both 737NG and, I think, at least one AB variant have had high pitch angle upsets in very similar conditions, and the concern for such a scenario has been the subject of more general discussions.

Sorry, lost poster.

It is still very much unclear why their successful and consistent NU trim corrections are suddenly insufficient to counteract MCAS.

Doesn't this shout about the high fuel flow during the last sharp climb?

[glad rag]

"The engineer performed flushing the left Pitot Air Data Module (ADM) and static
ADM to rectify the IAS and ALT disagree ..."

which is another bag of worms opened...perhaps a translation issue?

[Lonewolf_50]

Originally Posted by CONSO

THIS REPORT ??

I am referring to this from page 21 of the interim report from KNKT. (It had to do with the previous flight)

The PIC also reported the flight condition through the electronic reporting system of the company A-SHOR. The event was reported as follows:

Airspeed unreliable and ALT disagree shown after takeoff, STS* also running to the wrong direction, suspected because of speed difference, identified that CAPT instrument was unreliable and handover control to FO. Continue NNC of Airspeed Unreliable and ALT disagree. Decide to continue flying to CGK at FL280, landed safely runway 25L.
Note: STS = Speed Trim System

My other use of the term 'report' has to do with the voice report made shortly before they lost contact (page three of the interim report from KNKT):

At 23:31:09 UTC, the LNI610 PIC advised the ARR controller that the altitude of the aircraft could not be determined due to all aircraft instruments indicating different altitudes. The pilot used the call sign of LNI650 during the communication. The ARR controller acknowledged then stated “LNI610 no restriction”.

[climber314]

Originally Posted by underfire

Not only a Lion Air problem.

Flight Crew Operations Manual Bulletin
Number: FLR-6(FR)
Issue Date: August 10, 2012

[DaveReidUK]

Originally Posted by glad rag

"The engineer performed flushing the left Pitot Air Data Module (ADM) and static
ADM to rectify the IAS and ALT disagree ..."

which is another bag of worms opened...perhaps a translation issue?

No translation involved - it's a direct quote from the tech log (written in English).

[tdracer]

Originally Posted by safetypee

td #1815
So if the thrust has not changed and the revised engine mount might not contribute a significant pitching moment, then why introduce MCAS. Perhaps higher engine wt and changed location - the cg effect messed with the long stab, particularly approaching the stall; thus ‘augmentation’ was required. If this is not the issue, then the MAX handling would be essentially the same as previous models.
Or did someone think that MCAS was a good idea given previous accident history.

I only know that the max thrust didn't change significantly on the MAX (no pun intended) - others have postulated that the positioning and size (diameter)/weight of the engine made things worse but I'm not in a position to comment. I wasn't close enough to the MAX program to know what drove the requirement for MCAS - my involvement on the MAX was basically limited to participating in some propulsion design reviews.
All that being said, my educated guess is that your comment about it being 'a good idea given previous accident history' is probably pretty close to the mark.

[Roger_Murdock]

Originally Posted by tdracer

I only know that the max thrust didn't change significantly on the MAX (no pun intended) - others have postulated that the positioning and size (diameter)/weight of the engine made things worse but I'm not in a position to comment. I wasn't close enough to the MAX program to know what drove the requirement for MCAS - my involvement on the MAX was basically limited to participating in some propulsion design reviews.
All that being said, my educated guess is that your comment about it being 'a good idea given previous accident history' is probably pretty close to the mark.

Seattle Times reports: (in the article "U.S. pilots flying 737 MAX weren’t told about new automatic systems change linked to Lion Air crash")

A former Boeing executive, speaking on condition of anonymity because discussion of accident investigations is supposed to be closely held, said that Boeing engineers didn’t introduce the change to the flight-control system arbitrarily.

He said it was done primarily because the much bigger engines on the MAX changed the aerodynamics of the jet and shifted the conditions under which a stall could happen. That required further stall protection be implemented to certify the jet as safe.

[slacktide]

Originally Posted by safetypee

So if the thrust has not changed and the revised engine mount might not contribute a significant pitching moment, then why introduce MCAS.

This has been extensively discussed previously on this thread, and in several news articles. MCAS has nothing to do with thrust. MCAS has everything to do with lift. The nacelle on the 737 MAX is larger than the nacelle on the 737 NG. The center of pressure of the nacelle is also forward of the center of gravity, on both aircraft. At very high angles of attack, the nacelle begins to generate some amount of lift. Because the Cp(nacelle) is forward of Cg(aircraft), this causes a nose-up pitching moment. Because the nacelles are larger on the MAX than on the NG, and they are mounted further forward of the wing on the MAX, the nose-up moment is larger on the MAX than on the NG. The intent of MCAS is to feed in nose-down stab trim to counteract the nose-up moment caused by the lift from the larger nacelles.

Further explanation, with pretty graphics: https://leehamnews.com/2018/11/14/bo...to-the-pilots/

[gums]

Salute!

i don't know about you other pilots, but I would be very interested in a change to my plane that involved some aerodynamic characteristics and then a kludge mechanism that used an existing system ( that I also did not like) to 'help" me from staliing the plane and then fail to tell me about it! GASP!

This is gonna be a lawyer fest, and I can also see a flight crew concern that must be dealt with by Boeing.

Gums opines...

[Bleve]

Originally Posted by DaveReidUK

The Preliminary Report, although it reproduces Lion Air's Safety Instruction (Appendix 5.2) which explicitly refers to "one Engineer on board", also makes it clear that he/she was included in the 181 passenger count (which, added to the two pilots and six F/As, gives the published total of 189 fatalities).

That would seem to indicate deadheading/positioning and imply a seat in the cabin, though there's no evidence offered either way for that.

I have often ridden on a flightdeck jumpseat even though I was on the manifest as a passenger.