Indonesian aircraft missing off Jakarta
Your speaking with the benefit of hindsight. Put yourself in their shoes: 25nm MSA to the north is 2300'. Grid MORA's to the north are 3100'. Their intention was to return to Jakarta. Assuming they were working through the Unreliable Airspeed checklist, 5000 would have been a logical height. It's one of the standard heights published in the QRH for unreliable airspeed, it's above safety heights, but not too high for a return to Jakarta given their distance from the airfield. I think it's safe to assume they weren't expecting to have a flight control issue. Of course the CVR will confirm or invalidate these assumptions.
The curious thing is that there is only data for VREF40+70 at 5,000 feet and they were faster than that. Coincidentally or otherwise, they seem to have targeted 280 KIAS and that is the Climb, Cruise and Descent UAS target speed.
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Will all due respect some posters who are not in the industry, this is a technical discussion for knowledgable individuals who operate at a level substantially beyond layman "conjecture", just shooting the breeze about a subject they have no specialized knowledge of. It takes years of training and experience to understand the nuances of accidents. There are many on this forum who have been involved in aviation at the highest levels of piloting, accident investigation, training human factors and maintenance, some with experience of 60+ years.
We study and discuss accidents so we don't become the subject of a thread on PPRuNE. If you cannot help this process, then you are probably a hinderance contributing. Certain contributors indicate that they don't even the first level of understanding of what they don't even know. We are happy to answer questions*, although almost everything that has come up on this thread with the exception of the MCAS is extensively documented, just a google search away.
Questioning the prudence of certain causes of action? We do not know what happened, we do not know what the crew faced on the day, we cannot yet even begin to decide what a prudent course of action would be. Even with the magnificent view of hindsight, many months to consider all options, we still may not know.
Pilots do not go to work to try and kill themselves and their passenger. We are ACUTELY aware of the responsibility for the precious lives that fly with us. They are not our "customers", they are us.
May I politely suggest that you follow the thread, read up on the Dunning–Kruger effect, then use that awareness to *Ask Questions The Smart Way. Then if you have something that can add value, improve our collective knowledge and enhance safety without clogging up the board and wasting bandwidth please contribute. The introduction in the second link will give you more insight into the learning process happening here, albeit from a different knowledge field.
We study and discuss accidents so we don't become the subject of a thread on PPRuNE. If you cannot help this process, then you are probably a hinderance contributing. Certain contributors indicate that they don't even the first level of understanding of what they don't even know. We are happy to answer questions*, although almost everything that has come up on this thread with the exception of the MCAS is extensively documented, just a google search away.
Questioning the prudence of certain causes of action? We do not know what happened, we do not know what the crew faced on the day, we cannot yet even begin to decide what a prudent course of action would be. Even with the magnificent view of hindsight, many months to consider all options, we still may not know.
Pilots do not go to work to try and kill themselves and their passenger. We are ACUTELY aware of the responsibility for the precious lives that fly with us. They are not our "customers", they are us.
May I politely suggest that you follow the thread, read up on the Dunning–Kruger effect, then use that awareness to *Ask Questions The Smart Way. Then if you have something that can add value, improve our collective knowledge and enhance safety without clogging up the board and wasting bandwidth please contribute. The introduction in the second link will give you more insight into the learning process happening here, albeit from a different knowledge field.
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Do the cutout switches disable MCAS?
I'm still confused about the Boeing reiteration of the runaway trim abnormal as an existing procedure that will address a MCAS false activation. If the trim does not stop by using the cutoff switches they say to hold the trim wheel. Does this mean it may not be disabled by the cutout switches? It would make sense that the FAA would not want the MCAS system to be disabled since it's there for an aircraft handling issue. If MCAS can be disabled by the cutout switches then why did Boeing just reiterate the use of the runaway trim abnormal? You now are flying an aircraft where you should take more care to not get slow or load it up in a turn and you only have the your trim wheel if your elevator input cannot unload the aircraft. Why didn't that advice get included with the AD? Does anybody have access to the MEL and whether you can dispatch with MCAS inop?
jimtx, good questions. We don't yet know if the MCAS was required for certification of the Max or if it was accepted as an "add-on" due changes in engine size, weight & pylon mount, and as you ask, what the MEL limitations are, if any.
AW&ST highlights an article today entitled, "Lion Air Probe Expands to 737 MAX Design, Pilot Training" by (Sean Broderick and Guy Norris), states in part:
AW&ST highlights an article today entitled, "Lion Air Probe Expands to 737 MAX Design, Pilot Training" by (Sean Broderick and Guy Norris), states in part:
The directive points operators to existing runaway-trim procedures in the FCOM and quick reference handbook (QRH). If the runaway continues when the autopilot is disengaged—which would be the case if the MCAS is moving the stabilizers—pilots are to flip “cutout switches,” just as on the 737 Next-Generation (NG). As a last resort, pilots are told to “grasp and hold” the stabilizer trim wheel. The FAA has not ordered any changes to how pilots are trained or how the MCAS operates.
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jimtx, good questions. We don't yet know if the MCAS was required for certification of the Max or if it was accepted as an "add-on" due changes in engine size, weight & pylon mount, and as you ask, what the MEL limitations are, if any.
AW&ST highlights an article today entitled, "Lion Air Probe Expands to 737 MAX Design, Pilot Training" by (Sean Broderick and Guy Norris), states in part:
AW&ST highlights an article today entitled, "Lion Air Probe Expands to 737 MAX Design, Pilot Training" by (Sean Broderick and Guy Norris), states in part:
What keeps the trim from slipping once you have it where you want it? A brake?
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People are talking about an uncontrolled pitch down manoeuvre or ’bunt’ to bring about the final dramatic loss of altitude.
Another scenario could be that, during the attempted turn to return to the departure airfield, the aircraft suffered some sort of uncontrolled rolling and pitching manoeuvre. This would be especially likely if the ‘assistance’ of the MCAS was disabled via the Stab Trim in CUTOUT and the aerodynamic moments at high alpha, that the designers predicted, were in play during a ‘steep’ turn. An increase in the pitch up moment due to a simultaneous increase in power may also have contributed.
A real AoA increase during a hasty hand-flown turn regardless of any incorrectly sensed, and now managed, systems failures may have resulted in a loss of control.
The aircraft designers seemed to have anticipated that this aircraft would vulnerable to pitch excursions at high alpha and installed the MCAS to assist in this case. With it disabled, and flight crew muscle memory anticipating different performance from a legacy 737, they may have inadvertently and tragically placed the aircraft in a non-recoverable unusual attitude.
(I’m not a 737 driver although I have experience in a similar weight category and a reasonable knowledge of aerodynamics. I have read the whole thread.)
Another scenario could be that, during the attempted turn to return to the departure airfield, the aircraft suffered some sort of uncontrolled rolling and pitching manoeuvre. This would be especially likely if the ‘assistance’ of the MCAS was disabled via the Stab Trim in CUTOUT and the aerodynamic moments at high alpha, that the designers predicted, were in play during a ‘steep’ turn. An increase in the pitch up moment due to a simultaneous increase in power may also have contributed.
A real AoA increase during a hasty hand-flown turn regardless of any incorrectly sensed, and now managed, systems failures may have resulted in a loss of control.
The aircraft designers seemed to have anticipated that this aircraft would vulnerable to pitch excursions at high alpha and installed the MCAS to assist in this case. With it disabled, and flight crew muscle memory anticipating different performance from a legacy 737, they may have inadvertently and tragically placed the aircraft in a non-recoverable unusual attitude.
(I’m not a 737 driver although I have experience in a similar weight category and a reasonable knowledge of aerodynamics. I have read the whole thread.)
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Pushing on the ' nut ' will not move the stabilizer over a few thousands of an inch up or down- there is little to NO slack absent extreme wear >
NOTE added - technically, Boeing uses a BALLscrew on the 767/747/and SOME 737 - the difference being the " nut " contains a path for recirculating ball bearings -
see https://www.google.com/search?q=767+ball+screw+details&client=firefox-b-1-ab&tbm=isch&source=iu&ictx=1&fir=8R_i7jhyn421DM%253A%252C5Mq 2-dsu2Z5RgM%252C_&usg=AI4_-kS87Ir4HB0qg4Sz928mdwMREx_8eg&sa=X&ved=2ahUKEwiX9J2ihufeAhWG HXwKHXRqDigQ9QEwAXoECAQQBg#imgrc=8R_i7jhyn421DM:
http://www.beaver-online.com/documen...Stabilizer.pdf
https://www.aerospaceonline.com/doc/...actuators-0001
Unless the screw turns, nothing moves unless a major part breaks. Note the same concept has been used in automobile steering for decades - although newer models use electric motors to assist turning ( power steering )
And FWIW - in my earlier days at Boeing ( 1980's ) as an engineer in tooling/manufacturing area, I had to rig up a simple way to check the jackscrew install and horiz stab movement of the first 767 - long before the installation of the electrical ' drivers '. The spline drive connection for the electric motor would not fit any standard nut driver- so I made a polyurethane mold of the spline in a larger socket, and then used a simple low power ( air motor ) low speed nutrunner to turn the jackscrew and move the stabilizer over the full travel and adjustments.
Given that - I'm guessing that the cockpit trim wheel probably drives by cable a ' pulley ' attached to the jackscrew - which of course requires multiple turns to get a relatively small movement- and vice versa.
Last edited by CONSO; 22nd Nov 2018 at 02:56. Reason: Added a part of my background + " ballscrew"
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If the trim does not stop by using the cutoff switches they say to hold the trim wheel. Does this mean it may not be disabled by the cutout switches? It would make sense that the FAA would not want the MCAS system to be disabled since it's there for an aircraft handling issue. If MCAS can be disabled by the cutout switches then why did Boeing just reiterate the use of the runaway trim abnormal?
Here is what the author of the 737Max Review in Business and Commercial Aviation said in June 2017 Edition about the stall characteristics:
. We also flew an approach to stall in the clean configuration, a maneuver we had practiced with Otsuka in the Max 8 engi- neering simulator at Boeing’s Seattle campus. When the stall warning stick shaker was triggered, we consciously pushed forward on the control wheel to reduce pitch attitude and advanced the thrust levers to near maximum. As the engines accelerated, the resulting thrust caused a pronounced nose-up pitching moment. We countered the effect with ample push on the wheel and plenty of nose-down pitch trim on the stabilizer.
Tail Volume
As the fuselage has lengthened from the -100, I suspect the tail surfaces have remained the same. Of course the lever arm has increased.
Is it possible that the final dive was a product of an elevator stall, that larger surfaces could have prevented?
Is it possible that the final dive was a product of an elevator stall, that larger surfaces could have prevented?
Ironic.......
Last edited by T28B; 23rd Nov 2018 at 18:57. Reason: to assist those in need of understanding
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WSJ on 21 NOV
Goes on but NOTE NOTE NOTE
Regulators Push for Clarity on Boeing 737 Safety Systems After Lion Air Crash
U.S. airlines’ manuals for new 737 models offer inconsistent or confusing details of a second automated antistall feature, critics say
U.S. airlines’ manuals for new 737 models offer inconsistent or confusing details of a second automated antistall feature, critics say
By
Nov. 21, 2018 9:49 p.m. ET U.S. regulators are pressing for clarity on automated flight-control systems in Boeing Co.’s BA -0.12% latest 737 models in the wake of last month’s Lion Air crash, according to people familiar with matter, as they seek to address inconsistencies in how airlines have informed pilots about one of the features.The Indonesian-led probe of the Lion Air crash, which killed 189 people after plunging into the Java Sea at a steep angle and high speed, has revealed that the U.S. airlines describe certain features differently in their pilot manuals for Boeing’s family of 737 MAX aircraft. A number of veteran aviators, government safety officials and independent experts said the differences have sparked confusion within the aviation community.Andy Pasztor andAndrew Tangel
Some of the questions regulators, safety experts and pilots have addressed to Boeing and the airlines relate to a system that has been a focus of investigators since early in the probe. That system automatically pushes down the nose of an aircraft that is approaching an aerodynamic stall, a condition that occurs when a plane is flying dangerously slow with its nose too high, threatening a loss of lift.
Indonesian investigators are expected to release a preliminary report in coming days. Boeing is expected to announce a software fix to the MCAS system before the end of the year, according to government and industry officials.
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Fdr report from today legislators with knkt
MCAS is still trimming down automatic even though pilot push it with trimming up
Presentation KNKT at DPR regarding lion crash
tinyurl.com/Jt610-DPR
sorry newbie here cant post direct url
MCAS is still trimming down automatic even though pilot push it with trimming up
Presentation KNKT at DPR regarding lion crash
tinyurl.com/Jt610-DPR
sorry newbie here cant post direct url
Last edited by Realbabilu; 23rd Nov 2018 at 05:35.
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There are 2 FCC software versions regarding STS with following fundamental differences:
1. (POST SB 737-27-1220 issued in Feb 1999 and installed by now on most NGs and all MAXes) The stall detection circuit monitors the flap position and the angle of airflow. Near stall, the speed trim function trims the stabilizer to a nose down condition to allow for trim above the stickshaker AOA and idle thrust. The trim continues until the stabilizer gets to its limits or the aft column cutout position is exceeded.
1. (POST SB 737-27-1220 issued in Feb 1999 and installed by now on most NGs and all MAXes) The stall detection circuit monitors the flap position and the angle of airflow. Near stall, the speed trim function trims the stabilizer to a nose down condition to allow for trim above the stickshaker AOA and idle thrust. The trim continues until the stabilizer gets to its limits or the aft column cutout position is exceeded.
As airspeed decreases towards stall speed, the speed trim system trims the stabilizer nose down and enables trim above stickshaker AOA.
The MAX appears to be different - unless Boeing bulletin and the E-AD are wrong and a common issue has appeared on the MAX first when it has two (or maybe three) orders of magnitude fewer flight hours than the NG. There is much internet commentary stating that the larger engines set further forward mean the MAX has different pitch stability to the NG at high AOA, leading to the MCAS requirement.
We also know (see further up this thread) that there are hardware changes to the stab trim cut out switches on the MAX (labelling and function), and hence probably to physical wiring. We don't know if this is related to MCAS or not, but it seems likely and I highly doubt the change was made for fun or because someone said "no one ever uses these switches separately so lets make them do the same thing".
I think it is very likely that MCAS is an FCC software function evolved from the previous STS mod on the NG. The FCC does have both set of ADIRU data available (there is a cross link between the two FCCs) whether and how MCAS uses both AOA inputs, we don't know. This is based on info from various sites including: https://www.satcom.guru/2018/11/737-...n-command.html
You mentioned the Elevator Feel Computer having separate pitot-static sources, which it does, however it also takes an input from EFSM (Elevator Feel Shift Module) which is triggered by either SMYD (Stall Management Yaw Damper) which in turn take inputs from the on-side ADIRU, so a single AOA error would trip SMYD on that side (and hence stick shaker motor on that side, and the EFSM...
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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
http://www.anac.gov.br/assuntos/seto...evoriginal.pdf
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What keeps the trim from slipping once you have it where you want it? A brake?
Pushing on the ' nut ' will not move the stabilizer over a few thousands of an inch up or down- there is little to NO slack absent extreme wear >
NOTE added - technically, Boeing uses a BALLscrew on the 767/747/and SOME 737 - the difference being the " nut " contains a path for recirculating ball bearings -
Unless the screw turns, nothing moves unless a major part breaks. Note the same concept has been used in automobile steering for decades - although newer models use electric motors to assist turning ( power steering )
NOTE added - technically, Boeing uses a BALLscrew on the 767/747/and SOME 737 - the difference being the " nut " contains a path for recirculating ball bearings -
Unless the screw turns, nothing moves unless a major part breaks. Note the same concept has been used in automobile steering for decades - although newer models use electric motors to assist turning ( power steering )
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Not a 737 systems expert, but I'm not sure the answer is quite so simple as is being made out here. In fact, jackscrew driven mechanisms *can* move if the actuating nut is loaded and there's not enough resistance to the jackscrew turning. The landing gear on the airplane I fly is actuated by a jackscrew and recirculating ball nut. There is a braking device on the jackscrew to keep the landing gear retracted. without it, the weight of the landing gear on the ball-nut would be enough to turn the screw and the gear would descend. In fact that is the emergency gear extension procedure, to unlock the screw and the gear extends by it's own weight. On the other end of the cycle, there is a friction washer assembly whcih keels it from turning when extended and the aircraft weight is on the wheels. Also, Cessna 180's have a trimmable stabilizer actuated by a jackscrew and on the early models, the air loads at high airspeed would cause the trim system to move. I happen to know this because I own one. So there are two examples of aircraft systems in whcih "Pushing on the nut" does indeed "rotate the Rod" So what does keep the jackscrew on the 737 from turning under air loads? Is there a braking device? Does the gear train of the drive motor provide enough resistance?
BALL screws can be back driven, depending on design parameters. SDo just how much ' braking' is needed to prevent rotation is a design factor. Thus we have the problems/questions that arise when a simplified explanation in a blog is used instead of a multifactor detailed design analysis. Does BA use a brake ? probably- what friction factors are used for braking torque and backup operation really are are unknown by this SLF, and no doubt over 90 percent of the posters. One can assume that horiz stabs are NOT designed for ' free fall' like a landing gear !
Note in my prior comments above that I did carefully say " UNLESS THE SCREW TURNS " which I admit was an over simplification
No attempt at a good deed goes unpunished !
https://www.linearmotiontips.com/how...ll-back-drive/ may provide some clues
Last edited by CONSO; 22nd Nov 2018 at 14:26. Reason: clarification
