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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 22nd Nov 2018, 15:25
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New York Times exposé of Lion Air

‘Spend the Minimum’: After Crash, Lion Air’s Safety Record Is Back in Spotlight

JAKARTA, Indonesia — The government safety inspector had spent all night at the Makassar airport, in eastern Indonesia, several years ago, poring over a Lion Air jet that had suffered a hydraulic failure. Telling airline employees that the plane was to be grounded until the problem was fixed, the inspector went back to a hotel for a quick shower.

When the inspector returned, the plane was on the runway, about to take off.

Furious, the inspector demanded that the passengers disembark. But a supervisor with Lion Air explained how the airline had gone over the inspector’s head: Federal transportation officials in Jakarta, the Indonesian capital, had given permission for takeoff, the inspector said. The plane was in the air minutes later.
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Old 22nd Nov 2018, 16:00
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Originally Posted by Setpoint99 View Post
‘Spend the Minimum’: After Crash, Lion Air’s Safety Record Is Back in Spotlight

JAKARTA, Indonesia — The government safety inspector had spent all night at the Makassar airport, in eastern Indonesia, several years ago, poring over a Lion Air jet that had suffered a hydraulic failure. Telling airline employees that the plane was to be grounded until the problem was fixed, the inspector went back to a hotel for a quick shower.

When the inspector returned, the plane was on the runway, about to take off.

Furious, the inspector demanded that the passengers disembark. But a supervisor with Lion Air explained how the airline had gone over the inspector’s head: Federal transportation officials in Jakarta, the Indonesian capital, had given permission for takeoff, the inspector said. The plane was in the air minutes later.
I would require a lot more information and context before getting outraged. What precisely was the "hydraulic failure"? Was it something which could legally be deferred in accordance with a MEL, and the inspector was trying to force them to replace something that the aircraft could be legally dispatched without?
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Old 22nd Nov 2018, 16:03
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Originally Posted by CONSO View Post
Whether or not a 'jackscrew" can be back driven depends on the thread pitch and friction ( braking ) factors. . For a simple example - a course ( large) pitch ( few threads per inch ) is often used for jacking up buildings and heavy objects and are NOT likely to be back driven ..
Correct me if I'm wrong, but the coarser the thread pitch (all other things being equal), the more likely a jackscrew is to be back driveable (the spiral ratchet screwdriver principle). Is that what you're saying?

I can't see air loads on the stab being capable of overcoming the combined braking friction in the jackscrew, gearbox and actuator unless we're talking about a previously undisclosed failure in addition to the issues already discussed.
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Old 22nd Nov 2018, 16:16
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Originally Posted by DaveReidUK View Post
Correct me if I'm wrong, but the coarser the thread pitch (all other things being equal), the more likely a jackscrew is to be back driveable (the spiral ratchet screwdriver principle). Is that what you're saying?

I can't see air loads on the stab being capable of overcoming the combined braking friction in the jackscrew, gearbox and actuator unless we're talking about a previously undisclosed failure in addition to the issues already discussed.
I think that’s right. The mechanical advantage of the threads is sufficient to restrain the jackscrew. Add the friction of the drive motor, and even though the nut is carried in bearings, the HS stays put? Question: Is the drive always engaged?

As to programming versus mechanical upgrades, I found nothing about “software only” to establish the new MCAS system. I got thoroughly bogged down in “Onboard programmable modules”, “Line replaceable units” and its acronym LRUs.

Sistering STS with MCAS and only one trim drive? If Trim is flight critical, (the crash suggests so), where is drive redundancy? How is one drive isolated from the other(s) such that opposite inputs would (not) stall a (single) motor?

So, somebody please tell me the HS was not Stalled? Because that is just another word for “jammed”...Is there nothing worse than runaway Trim? Perhaps an HS that cannot reverse it?

STS: Speed too high, NU..... MCAS:: AoA Too High, ND.......

Question. Was the five second pause (MCAS) put in to allow “recompute”?

Did STS see the pause as a chance to NU? Hence a game of porpoise? What are the relative velocities of NU, ND? Same? NU faster?

Unknowledgeable wants to know.

Last edited by Concours77; 22nd Nov 2018 at 16:43. Reason: Keep coming up with stupid questions...
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Old 22nd Nov 2018, 16:18
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I cannot remember or find the details, but there were some incidents back in the early days of the 707 when airloads did backdrive the screw jack on the stabiliser. BOAC had one over Toronto shortly after take-off and the crew only just managed to retain control. Some posters on PPRuNe may be able to find or, perhaps, know the details.
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Old 22nd Nov 2018, 16:45
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Originally Posted by Bergerie1 View Post
I cannot remember or find the details, but there were some incidents back in the early days of the 707 when airloads did backdrive the screw jack on the stabiliser. BOAC had one over Toronto shortly after take-off and the crew only just managed to retain control. Some posters on PPRuNe may be able to find or, perhaps, know the details.
There have been a number of 707/720 accidents where the THS has been implicated, including a fractured jackscrew, a stalled actuator and a trim motor failure, but I'm not aware of any that involved a working stabilizer jackscrew being backdriven by airloads.
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Old 22nd Nov 2018, 17:01
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Originally Posted by b1lanc View Post
Apparently, not all airlines or administrative bodies were caught off guard. From the Jan 2018 ANAC ODR with Training requirements - note MCAS is identified as Class B on Page 18. The stab trim cutout switch nomenclature change is mentioned on pg 19 as Class A training.

http://www.anac.gov.br/assuntos/seto...evoriginal.pdf
Strangely, the latest FAA FSB report I could find does not have any reference to the MCAS and differs in the answer under "FLT CHAR" for a few of the Flight Controls listed. The FAA doc has "no" while the Brazilian Report has "minor". But the response for the MCAS in the Brazilian report is "no" . http://fsims.faa.gov/wdocs/fsb/b737_rev_16.pdf. It's possible rev 16 is not the latest report though.
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Old 22nd Nov 2018, 17:12
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Originally Posted by Realbabilu View Post
Fdr report from today legislators with knkt
MCAS is still trimming down automatic even though pilot push it with trimming up
tinyurl.com /Jt610-DPR
That Press Release - " Presentation of NTSC on PK-LQP Questions in the DPR - Submission of NTSC to the V Commission - 22 November 2018 " - seems only to be as yet in Indonesian. The meat of it appears to be that the NTSC will release a preliminary report of the FDR Data on 28th November. In the press release though are quite a few charts (in the slideshow, at the top of the page) that may (or may not...)be FDR-derived.

Don't see anything directly in it about MCAS behavior on the fatal flight - but, then, my Indonesian is all-but non-existent...

Last edited by Gary Brown; 22nd Nov 2018 at 17:25. Reason: Edited for layout and links
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Old 22nd Nov 2018, 17:54
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Originally Posted by DaveReidUK View Post
Correct me if I'm wrong, but the coarser the thread pitch (all other things being equal), the more likely a jackscrew is to be back driveable (the spiral ratchet screwdriver principle). Is that what you're saying?

I can't see air loads on the stab being capable of overcoming the combined braking friction in the jackscrew, gearbox and actuator unless we're talking about a previously undisclosed failure in addition to the issues already discussed.
Mr Reid, you are correct.

There is a point where a coarse pitch, usually on an Acme threaded bar, will become "non-reversible" as a function of reduction in pitch and concomitant increase of friction between the nut and the leadscrew. However, with recirculating ball systems where the leadscrew has a rounded threadform conforming to the radius of the balls, the frictional element substantially is reduced which, of course, is the purpose of having the ball race. Nevertheless, even with this system, there will be a point at which the mechanism becomes non-reversible. Hardly a definitive observation but looking at the video above, it would seem that the Boeing arrangement possibly might be sufficiently low-geared to prevent a reversed actuation.

Also, it is possible that in order to achieve optimal screwjack speed, the motor drive would be via a worm/wheel arrangement, thus making the system truly non-reversible.

Last edited by Gipsy Queen; 22nd Nov 2018 at 19:45.
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Old 22nd Nov 2018, 17:59
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looks like FDR data, typical "flightscape" plot format. One plot looks like it's the previous flight (since it shows flaps being deployed and then speed dropping off on landing as you'd expect)

there's a good 20 degree AOA split throughout that flight ...

There's a bunch of trim command looking data traces too; the resolution on the plots doesn't seem quite good enough to read the parameter names (perhaps not by error)

re https://www.pprune.org/rumours-news/614857-indonesian-aircraft-missing-off-jakarta-76.html#post10317513 (post 2 above)

Last edited by Mad (Flt) Scientist; 22nd Nov 2018 at 18:04. Reason: added link to post, properly - nope, wont allow a url
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Old 22nd Nov 2018, 18:01
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Originally Posted by AGBagb View Post
That Press Release - " Presentation of NTSC on PK-LQP Questions in the DPR - Submission of NTSC to the V Commission - 22 November 2018 " - seems only to be as yet in Indonesian. The meat of it appears to be that the NTSC will release a preliminary report of the FDR Data on 28th November. In the press release though are quite a few charts (in the slideshow, at the top of the page) that may (or may not...)be FDR-derived.

Don't see anything directly in it about MCAS behavior on the fatal flight - but, then, my Indonesian is all-but non-existent...
Google translate from the press report;
14. The next investigation process: This accident is the first time this has happened in the world for B 737-8 MAX aircraft, so it is necessary to do flight simulations using engineering simulators and algorithms, especially the MCAS system and others at the Boeing facility in Seattle accident and see the impact on the plane for the damage that occurred.
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Old 22nd Nov 2018, 18:12
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Originally Posted by DaveReidUK View Post
Correct me if I'm wrong, but the coarser the thread pitch (all other things being equal), the more likely a jackscrew is to be back driveable (the spiral ratchet screwdriver principle). Is that what you're saying?

I can't see air loads on the stab being capable of overcoming the combined braking friction in the jackscrew, gearbox and actuator unless we're talking about a previously undisclosed failure in addition to the issues already discussed.
Its MORE than just the pitch ( lead) please take the time to read this simplified explanation

https://www.linearmotiontips.com/how...ll-back-drive/

and for an approximation of loads

https://www.aerospaceonline.com/doc/...actuators-0001
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Old 22nd Nov 2018, 18:12
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Originally Posted by AGBagb View Post
That Press Release - " Presentation of NTSC on PK-LQP Questions in the DPR - Submission of NTSC to the V Commission - 22 November 2018 " - seems only to be as yet in Indonesian. The meat of it appears to be that the NTSC will release a preliminary report of the FDR Data on 28th November. In the press release though are quite a few charts (in the slideshow, at the top of the page) that may (or may not...)be FDR-derived.

Don't see anything directly in it about MCAS behavior on the fatal flight - but, then, my Indonesian is all-but non-existent...
Edit: NOT the accident flight! Thanks wiedehopf & Luc Lion.
Excellent translation below from Sam Asama as well.

Initial/TO/Climb Stab Trim Value shown is just under 7.5 followed by a period of flux with the value ultimately returning to 5.0 preceding leveling at 5,000 ft. This pre-nosedise value of 5.0 continues, increasing to approximately 6.75 with incremental stepping (upward) throughout the course of the descent to a maximum value of just over 7.5 and subsequently returning to a value of 5.0.

Last edited by climber314; 22nd Nov 2018 at 19:35.
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Old 22nd Nov 2018, 18:15
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xxxxxdeleted

Last edited by Rananim; 23rd Nov 2018 at 00:45.
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Old 22nd Nov 2018, 18:16
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My short summary of what I perceive to be the most salient points of the NTSC powerpoint presentation:

"The next steps in the investigation process will include continuing to collect information related to aircraft maintenance and flight crew training.

The AoA sensor component that was removed from the aircraft in Bali was received by the NTSC and will be inspected in the USA.
the NTSC is requesting (via the NTSB) to get more information about AOA sensors installed at DPS (Bali), which had been repaired (or perhaps supplied) by a Florida repair station.

The NTSC plans to issue a Preliminary Report on November 28, 2018, but will first share the report with the Ministry of Transportation (and/or other government agencies) and Lion Air, and the families of the victims.

Further investigation: This was the first accident in the world for a B737-8 MAX aircraft, so it will be necessary to do flight simulations using engineering simulators and algorithms, especially MCAS systems (my emphasis) and others at Boeing facilities, Seattle and reconstructing flights that have crashed (or perhaps reconstructing various crash scenarios) to see the impact damage on the aircraft.

INVESTIGATION CHALLENGES: NTSC does not have sufficient internal resources for such a large accident. (NTSC) is currently being assisted by various organisations, such as BASARNAS, BPPT, Ministry of Transportation, Pertamina, Ministry of Energy and Mineral Resources, Indonesian military, etc. The current number of NTSC investigators (10) is not enough to carry out all investigative activities for current investigations in Indonesia.

NTSC does not currently have storage facilities for some of the aircraft parts that have been designated for further evaluation. NTSC also doesn’t have adequate physical space for meeting rooms for the various teams.

Due to the amount and complexity of digital systems of B737 Max 8 aircraft (and other new aircraft types) it will take NTSC a lot of time to study and understand the aircraft systems (especially new systems) in order to analyze any problems that exist."

Sam
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Old 22nd Nov 2018, 18:18
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Originally Posted by DaveReidUK View Post
There have been a number of 707/720 accidents where the THS has been implicated, including a fractured jackscrew, a stalled actuator and a trim motor failure, but I'm not aware of any that involved a working stabilizer jackscrew being backdriven by airloads.
Not of course directly (or even necessarily) implicated, but can anyone explain Item 4 on the Runaway Stab memory item list quoted below. How is that the Stab could continue "uncommanded" movement after the two cutout switches are flipped? What is it that those switches do or don't do? Is the QRF allowing for some purely mechanical "uncommanded trim" that can only be mechanically countered with the wheel (assuming noting's catastrophically broken...)?

If the Runaway Continues
3 STAB TRIM CUTOUT SWITCHES (both) - CUTOUT


If the Runaway Continues
4 STABILIZER TRIM WHEEL - GRASP and HOLD
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Old 22nd Nov 2018, 18:24
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Originally Posted by climber314 View Post
Initial/TO/Climb Stab Trim Value shown is just under 7.5 followed by a period of flux with the value ultimately returning to 5.0 preceding leveling at 5,000 ft. This pre-nosedise value of 5.0 continues, increasing to approximately 6.75 with incremental stepping (upward) throughout the course of the descent to a maximum value of just over 7.5 and subsequently returning to a value of 5.0.
The picture you are describing seems to be from the previous flight.
(See on the x-axis written DPS and CGK would indicate a flight from Denpasar to Jakarta, the accident flight however departed Jakarta)

So you can see the constant up and down after selecting flaps up being produced by manual flight fighting the MCAS system so to speak.

Then they switched off the trim and a couple of minutes later maybe tried to switch it back on and obviously switched it back off with manual trim for the rest of the flight.

Traces as far as i can read from top to bottom are:
BLUE: TRIMUPMANUAL
YELLOW: TRIMDOWNMANUAL (yoke switches would be my guess)

BLUE: PITCHTRIMPOSITION

GREEN: TRIMUPA (A for automatic would be my guess)
VIOLET: TRIMDOWNA

RED: STICKSHAKERLEFT
GREEN: STICKSHAKERRIGHT

RED: CCFORCE_PITCHWSLOCAL
GREEN: CCFORCE_PITCHWSFOREIGN

RED: ANGELOFATTACKINDICATEDL
GREEN: ANGELOFATTACKINDICATEDR

LIGHT GREEN: FLAPS?????POSITION

RED: COMPUTEDAIRSPEEDL
GREEN: COMPUTEDAIRSPEEDR

BLUE: ALTITUDE_101325MB_L

Last edited by wiedehopf; 22nd Nov 2018 at 18:41.
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Old 22nd Nov 2018, 18:32
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Originally Posted by Rananim View Post
posted by Babilu

Explanation on MCAS

Note that MCAS overrides pilot stick input...first automatic override of a pilots input to a primary flight control in their commercial design history to my knowledge.Previously all anti-stall devices merely warned and aided the pilot to recognize and recover from a stall(eg,PLI,EFS,autoslats,shakers)

That leaves either a)counter-trimming or b)selecting BOTH trim switches to CUTOUT as a way for the pilots to override MCAS triggered by false ADIRU data.
Boeings AD mandates (b) as the approved procedure but hindsight is 20/20.If the pilots dont recognize it as runaway trim due i)startle factor ii)trim is not continuous but in 9 second stages iii)false stickshaker masks trim and degrades pilots alertness then they are left with (a)

Pilots have spoken about overriding STS with main electric trim.All B737 pilots have done this.But STS uses AP stab trim motor(presumably B/U in the MAX) whilst stick trim uses main electric(presumably PRI in MAX).A pilot flying manually cant trim down and pull on the stick at the same time...not unless the override switch is in override.What if MCAS is using the same trim motor as the one actuated by stick trim?MCAS description says it uses lower trim rate at higher mach and vice versa.So it may well be using PRI motor at low altitudes and B/U at higher altitudes.In which case there is a possibility that the simultaneous command of opposing trim in the same trim motor could lead to motor stall and burnout.MCAS is trimming down using PRI motor because a/c is at low altitude and low mach.Pilot pulls on stick to no effect.Pilot then trims up using stick trim(PRI) causing clutch engagement and motor stall.Who wins?MCAS or the pilot?How many reversals can this trim motor withstand before failure?Any engineers please comment.

The underlying concept of Boeings commercial design has always been that the pilot has the final say.The input to the stick by the pilot overrides any device or warning system controlled by HAL.For Boeing to have deviated from this principle means there were serious concerns about MAX's pitch characteristics.In shooting for glory and lower fuel burn they have sacrificed their soul at the altar of greed and complacency.When the pilot pulls the houses must get smaller.....always.

Above comments do not relieve a pilot from exercising airmanship and killing ALL HS trim when the pitch control of his/her aircraft is in doubt.
Rananim:

”....Sistering STS with MCAS and only one trim drive? If Trim is flight critical, (the crash suggests so), where is drive redundancy? How is one drive isolated from the other(s) such that opposite inputs would (not) stall a (single) motor?...”

post number 1514

just sayin.
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Old 22nd Nov 2018, 18:38
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Originally Posted by wiedehopf View Post
The picture you are describing seems to be from the previous flight.
(See on the x-axis written DPS and CGK would indicate a flight from Denpasar to Jakarta, the accident flight however departed Jakarta)

So you can see the constant up and down after selecting flaps up being produced by manual flight fighting the MCAS system so to speak.

Then they switched off the trim and a couple of minutes later maybe tried to switch it back on and obviously switched it back off with manual trim for the rest of the flight.
Oops... I had just switched from this slide.
Still interesting to note the AoA values vs. Stab Trim on the previous slide.

Edit: Slide/Graph removed and replaced with enlarged(?) image in post #1538

Last edited by climber314; 22nd Nov 2018 at 19:32.
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Old 22nd Nov 2018, 18:50
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Originally Posted by AGBagb View Post
Is the QRF allowing for some purely mechanical "uncommanded trim" that can only be mechanically countered with the wheel (assuming noting's catastrophically broken...)?
The manual pitch trim on the 737 is a 100% conventional cable-and-drum arrangement that Lindbergh would probably recognise. I'm struggling to think of any possible failure mode that would result in uncommanded movement.

The "grasp and hold" action item makes use of the fact that there is a clutch in the trim actuator gearbox which ensures that manual trim inputs override any electrical inputs to the actuator from either the trim switches or the autopilot.
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