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Thread: Countries Restricting 737 MAX Flights After Second Crash

  1. #171
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    https://www.reuters.com/article/us-e...-idUSKCN1RF0B6

    Here is the full Reuter’s article describing what the Ethiopian pilot’s did in response to the MCAS event. They followed the recommended procedure, tried the manual trim wheel, and decided to try enabling the electric trim again.

    I am anxious to see more details on the FDR/CVR.

  2. #172
    https://www.wsj.com/articles/an-airc...503385?mod=mhp

    Snippet:

    They argue that a pilot could have disabled an errant software system in Boeing ’s 737 MAX and still not have been able to recover if the aircraft’s speed and configuration were imposing more force on the tail surfaces than could be overcome by hand-cranking the trim wheel.

    If this account is accurate, it explains why an experienced Ethiopian Airlines pilot, who had been briefed on how to handle a failure of Boeing’s MCAS software after last year’s Lion Air crash, could not save his plane. In fact, he may have been reduced to turning the defective MCAS back on in hopes of freeing up the trim wheel.
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  3. #173
    GJM posted while I was working this on a tablet...

    I read a article earlier with a lot more details and I can't find it now. This wasn't it, but has some of the points I want to discuss.
    https://www.reuters.com/article/us-e...-idUSKCN1RH0FJ

    - 1 stick shaker fired, not both (makes sense if you understand how these aircraft are setup)
    - the throttle levers were never reduced from takeoff thrust, for the entire event
    - they hit 500 knots at some point

    Like mentioned earlier in the thread, MCAS was not enabled until they cleaned up on climbout. One side AOA showed +73 degrees or something (can't remember from earlier article). SS fires on one side only. Can someone talk to when MCAS hits?

    Regardless, the nose pitches down and the airspeed increases. So they fought the jet for some time, stab trim cutout, but were still unable to manually trim. They turned stab trim back ON, but I read they did NOT use the electric trim on the yoke.

    So after reading this I immediately thought of Aeroperu 603. That aircraft crashed when maintenance left tape over the static ports and the crew was left with unreliable airspeed and altitude. They got the overspeed clacker and tried to slow down. I wonder if the Ethiopia crew thought they were stalling and left the throttles pinned?

    I get it in both these incidents (Peru included), the smart plane tells you something is wrong and you believe it.

    As the airspeed built up, the ability the manual trim was reduced, per the article. This was something I was unaware of. I imagine the Q they were at was pretty high as the nose kept trimming down.

    340 is Vmo. Can't remember what dive speed is, but we go faster in test and for certification so that there is not a cliff there. As the energy builds up your ability to bend things gets easier, over control etc. There is another speed beyond V dive at which you go ballistic. It would be safe to say these guys hit that speed at some point and nothing could be done to recover, sadly.

    Like most accidents, it's multiple things that happen that get you dead. The swiss cheese lined up for these guys and the outcome was terrible.

    I wonder how many US carriers had the same thing happen and reported it in the NASA database? Was Boeing working a fix ala Sig drop safety and just hoped nothing bad would happen in the interim?

  4. #174
    I am on a computer now. To be clear, I am not pointing fingers. It would be nice to get all the information as each article seems to leave out pertinent information. The first article I read said a possible bird strike damaged the AoA vane. Regardless of the cause, I wonder if in each of these cases, before MCAS, they were already dealing with a caution. I stated earlier, and hopefully the 737 drivers know, the AoA vane contributes to the ADIRU and thus the airspeed for each side. If you hook up a druck for air data and move the vane, the airspeed will be affected for that side, maybe not a huge number, but it changes the look-up tables.

    My guess like earlier in this thread was that the AoA failure would have driven an Airspeed Disagree. Regardless, the crew is now going WTF? They make the right call to continue to climb and clean up... then bang, MCAS starts spinning the trim nose down. Its bad and needs to be addressed. The focus on not having an "AoA Disagree" light is a non-issue in my mind, my bet is they had indications of a problem as soon as the bird hit or for Lion Air during the roll.

    OK, just found these flight data recorder data traces for Lion Air. It answers some of my questions above.

    Interesting things from the Lion Air data:
    - Looks like SS activated on the takeoff roll, after rotation, and right before WOW. Was that ever in the news? Crew must have been like WTF is going on?

    - Crew put the flaps back down after the initial MCAS hits x2. Problem is solved and you see no more MCAS activation. Looks like SS stops, and then continues again. So then they put the flaps back up, MCAS is back on, and the rest is history. Crap man, they had it saved! Also note the split in airspeed, L vs R (red vs green trace on the bottom graph), that happened during the takeoff roll. Curious if the airspeed disagree caution hit on takeoff roll and I am not inferring they should have rejected for that, or the SS.


    https://www.seattletimes.com/busines...ontrol-system/

  5. #175
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    The only good thing about the above is that it looks like MCAS is working as advertised. I had been concerned that it might not have been.

  6. #176
    Glock Collective Assimile Suvorov's Avatar
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    Probably a no-no due to internet protocol, but I'll post this whole article from Aviation Week. It requires a (free) subscription which I know most here do not have. Finally a pretty good picture into what actually happened......

    Here is the link -https://aviationweek.com/commercial-aviation/ethiopian-crash-data-analysis-points-vane-detachment?fbclid=IwAR3y2_vxWRcwb2vcmiSNFtoyETN6ss hzbz31Evpm_s7w81IzE14Fb0XEy9U

    Here is the article

    LOS ANGELES—As the investigation continues into the causes of the Mar. 10 Ethiopian Airlines Boeing 737 MAX accident, sources close to the probe say flight data recorder (FDR) data firmly supports the supposition that the aircraft’s left angle-of-attack (AOA) sensor vane detached seconds after take-off and that, contrary to statements from the airline, suggests the crew did not follow all the steps for the correct procedure for a runaway stabilizer.

    Detailed analysis of the FDR trace data shows that approximately six seconds after liftoff was signaled by the weight-on-wheels switch data, the data indicate the divergence in angle-of-attack (AOA) and the onset of the captain’s stick-shaker, or stall warning. Almost simultaneously, data shows the AOA sensor vane pivoted to an extreme nose-high position.

    This, says one source, is a clear indication that the AOA’s external vane was sheared off—most likely by a bird impact. The vane is counter-balanced by a weight located inside the AOA sensor mounting unit, and without aerodynamic forces acting on the vane, the counterweight drops down. The AOA sensor, however, interpreted the position of the alpha vane balance as being at an extreme nose-high angle-of-attack.

    With the stick shaker active, the trace indicates the crew pushed forward on the column to counteract what they believed were indications of potential approach to stall. The aircraft, now in level flight, also accelerated rapidly as its power setting remained at 94% N1 thrust used for take-off. This was followed by some manual trim inputs using the thumb switches on the control column.

    Seconds after speed advisories were heard, the crew raised the flaps. With the autopilot turned off, flaps up and erroneous AOA data being fed to the flight control computer (FCC), the stage was set for the MAX’s maneuvering characteristics augmentation system (MCAS) to activate. This is indicated by approximately 8-sec of nose-down stabilizer movement, which was followed by the use of manual trim on the control column. However, with the MCAS having moved the stabilizer trim by 2.5 units, the amount of manual nose-up trim applied to counteract the movement was around 0.5 units, or roughly only 20% of the amount required to correctly re-trim the aircraft.

    Because of the way the aircraft’s flight control computer P11.1 software worked, the use of manual trim also reset the MCAS timer, and 5 sec. later, its logic having not sensed any correction to an appropriate AOA, the MCAS activated again. The second input was enough to put in the full nose-down trim amount. The crew again manually counteracted with nose-up trim, this time offsetting the full amount of mis-trim applied by the latest MCAS activation.

    By then, some 80% of the initial MCAS-applied nose down trim was still in place, leaving the aircraft incorrectly trimmed. The crew then activated the stabilizer trim cutoff switches, a fact the flight data recorder indicates by showing that, despite the MCAS issuing a further command, there was no corresponding stabilizer motion. The aircraft was flying at about 2,000 ft. above ground level, and climbing.

    The crew apparently attempted to manually trim the aircraft, using the center-console mounted control trim wheels, but could not. The cut-out switches were then turned back on, and manual trim briefly applied twice in quick succession. This reset the MCAS and resulted in the triggering of a third nose-down trim activation lasting around 6 sec.

    The source says the residual forces from the mis-trim would be locked into the control system when the stabilizer cut-off switches were thrown. This would have resulted in column forces of up to around 50 lb. when the system was switched back on.

    Although this could have been reduced by manually trimming the aircraft, this did not occur, and the third MCAS activation placed the aircraft in a steep nose-down attitude. This occurred with the aircraft near its peak altitude on the flight—about 6,000 ft. The engines remained at full take-off power throughout the flight, imposing high aerodynamic loads on the elevators as the crew attempted to pull back on the columns.

    Vertical acceleration data also indicates momentary negative g during which the AOA sensor on the left side unwinds. This is seen as further validation of the theory that the external part of the alpha vane was detached as the apparent change in angle indication could only be explained by the effect of negative g on the counterbalance weight, forcing it to float up inside the sensor housing. In addition, the captain’s stick shaker also comes off twice in this final phase, further reinforcing the severed vane notion.

    The source indicates the crew appeared to be overwhelmed and, in a high workload environment, may not have followed the recommended procedures for re-trimming. Boeing’s stabilizer runaway checklist’s second step directs pilots to “control aircraft pitch attitude manually with control column and main electric trim as needed,” according to one U.S. airline’s manual reviewed by Aviation Week. If the runaway condition persists, the cut-out switches should be toggled, the checklist says

  7. #177
    Site Supporter entropy's Avatar
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    Damn birds.

  8. #178
    Concise video about why MCAS is on the plane.


  9. #179
    Site Supporter entropy's Avatar
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    Never trust a man who over annunciates.

  10. #180
    https://www.wsj.com/articles/boeing-...d=hp_lead_pos1

    Boeing Signals Additional Software Problem Affecting 737 MAX Airliners
    Company reveals glitch can render a type of safety alert inoperable on the now-grounded plane

    By Andy Pasztor and Andrew Tangel Updated April 30, 2019 12:28 a.m. ET

    Boeing’s statement came a day after The Wall Street Journal reported the company hadn’t told airlines flying 737 MAX jets that certain safety alerts wouldn’t function as expected. The issue of nonfunctioning alerts came to light after the crash of a Lion Air jet in October in Indonesia, but there were no indications since then that it stemmed from a mistake on the part of the plane maker.

    The alerts offer an extra safeguard for pilots in the event a separate stall-prevention system called MCAS, suspected in the deadly Lion Air crash and the crash of an Ethiopian Airlines 737 MAX in March, may be on the verge of misfiring. The two crashes took a total of 346 lives, leading regulators around the world to ground the 737 MAX fleet.
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