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    Another crash...Boeing 737-800 MAX technical compromised?

    Aristide
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    Post  Aristide on Sun Mar 10, 2019 3:24 pm

    Today crashed a brand new Boeing 737 MAX from Ethiopian Airlines. After take off it lost dramatical on altitude and crashed. The entire scenario is almost identical to the LionAir crash 4 months ago, where another brand new 737-800 MAX crashed.

    It will be interesting to see how security is handeled now. I think there is a real danger that the 737-800 mMAX gets grounded. The design of the aircraft if flawed.

    The main problem is, that the basic hull design is from the early 60th, when the 737 was designed. The new engines are much bigger than engines were in the 60th.

    When you see the 737-100 you see what i mean:

    Another crash...Boeing 737-800 MAX technical compromised? 45977_1523912396

    Now look at the new 737-800 max

    Another crash...Boeing 737-800 MAX technical compromised? 27278122274_62e625ed49_b

    The old hull design leaves not enough space for the new advanced fuel saving full mantle engines under the wings. Boeing solved this problem with new engine pylons, which move the engines further forward.

    This solvs the space problem but creates many new problems. The entire weight distribution is changed. The aircraft gets top heavy and reacts very stocky towards flight movements.

    Boeing installed a new and advanced MCAS system to solve that problem. Which means, the computer stabilized the aircraft in flight. The Lion Air crash happened because MCAS failed and produced so many error messegaes, that the pilots got overwhelmed. It looks like the same happened here.

    If this is right, it will be interesting to see what happenes now. The 737-800 MAX is Boeings best selling aircraft with 5.500 orders.

    Air France has none and also no intention to buy.
    JohninMK
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    Post  JohninMK on Mon Mar 11, 2019 5:41 pm

    Bit more on this. Great design feature it seems, counter intuitive and counter other 737s. Brilliant stuff for pilots flying 737s all days of the week, in an emergency having to think which version he took off in that day.

    From Reu Ben on Facebook:

    Boeing’s automatic trim for the 737 MAX was not disclosed to the Pilots

    November 14, 2018,

    The automatic trim Boeing introduced on the 737 MAX, called MCAS, was news to us last week. Graver, it was news to the Pilots flying the MAX since 18 months as well.
    Boeing and its oversight, the FAA, decided the Airlines and their Pilots had no need to know. The Lion Air accident can prove otherwise.
    By placing the nacelle further forward of the wing, it could be placed higher. Combined with a higher nose landing gear, which raises the nacelle further, the same ground clearance could be achieved for the nacelle as for the 737NG.

    The drawback of a larger nacelle, placed further forward, is it destabilizes the aircraft in pitch. All objects on an aircraft placed ahead of the Center of Gravity (the line in Figure 2, around which the aircraft moves in pitch) will contribute to destabilize the aircraft in pitch.

    The 737 is a classical flight control aircraft. It relies on a naturally stable base aircraft for its flight control design, augmented in selected areas. Once such area is the artificial yaw damping, present on virtually all larger aircraft (to stop passengers getting sick from the aircraft’s natural tendency to Dutch Roll = Wagging its tail).

    Until the MAX, there was no need for artificial aids in pitch. Once the aircraft entered a stall, there were several actions described last week which assisted the pilot to exit the stall. But not in normal flight. The larger nacelles, called for by the higher bypass LEAP-1B engines, changed this. When flying at normal angles of attack (3° at cruise and say 5° in a turn) the destabilizing effect of the larger engines are not felt. The nacelles are designed to not generate lift in normal flight. It would generate unnecessary drag as the aspect ratio of an engine nacelle is lousy. The aircraft designer focuses the lift to the high aspect ratio wings.

    But if the pilot for whatever reason manoeuvres the aircraft hard, generating an angle of attack close to the stall angle of around 14°, the previously neutral engine nacelle generates lift. A lift which is felt by the aircraft as a pitch up moment (as its ahead of the CG line), now stronger than on the 737NG. This destabilizes the MAX in pitch at higher Angles Of Attack (AOA). The most difficult situation is when the manoeuvre has a high pitch ratio. The aircraft’s inertia can then provoke an over-swing into stall AOA.

    To counter the MAX’s lower stability margins at high AOA, Boeing introduced MCAS. Dependent on AOA value and rate, altitude (air density) and Mach (changed flow conditions) the MCAS, which is a software loop in the Flight Control computer, initiates a nose down trim above a threshold AOA.

    It can be stopped by the Pilot counter-trimming on the Yoke or by him hitting the CUTOUT switches on the center pedestal. It’s not stopped by the Pilot pulling the Yoke, which for normal trim from the autopilot or runaway manual trim triggers trim hold sensors. This would negate why MCAS was implemented, the Pilot pulling so hard on the Yoke that the aircraft is flying close to stall.

    It’s probably this counterintuitive characteristic, which goes against what has been trained many times in the simulator for unwanted autopilot trim or manual trim runaway, which has confused the pilots of JT610. They learned that holding against the trim stopped the nose down, and then they could take action, like counter-trimming or outright CUTOUT the trim servo. But it didn’t. After a 10 second trim to a 2.5° nose down stabilizer position, the trimming started again despite the Pilots pulling against it. The faulty high AOA signal was still present.

    How should they know that pulling on the Yoke didn’t stop the trim? It was described nowhere; neither in the aircraft’s manual, the AFM, nor in the Pilot’s manual, the FCOM. This has created strong reactions from airlines with the 737 MAX on the flight line and their Pilots. They have learned the NG and the MAX flies the same. They fly them interchangeably during the week.

    They do fly the same as long as no fault appears. Then there are differences, and the Pilots should have been informed about the differences.

    Aristide
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    Post  Aristide on Wed Mar 13, 2019 5:05 pm

    So entire EU, Australia, China plus various other countries banned the 737 Max. This can prrove fatal for Boeing. Lion Air plans to cancel 120 orders and switch to Airbus.
    JohninMK
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    Post  JohninMK on Wed Mar 13, 2019 7:26 pm

    Aristide wrote:So entire EU, Australia, China plus various other countries banned the 737 Max. This can prrove fatal for Boeing. Lion Air plans to cancel 120 orders and switch to Airbus.

    Not sure of your use of the word "fatal" as this will definitely not be death for Boeing. They will suffer short term problems but they will sort this issue and it will become a blip in their history.

    Note that whilst some US airlines have apparently 'parked' their 737Max (maybe by soft instructions from on high) the FAA has not grounded them. If they did there would be turmoil for Boeing which the US Government would not allow.

    With a backlog of orders stretching out years any that are cancelled will be gratefully accepted by others. I don't know what delivery dates are on the Lion orders but they will probably have a problem getting Airbus to match them.
    Aristide
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    Post  Aristide on Wed Mar 13, 2019 7:59 pm

    JohninMK wrote:
    Aristide wrote:So entire EU, Australia, China plus various other countries banned the 737 Max. This can prrove fatal for Boeing. Lion Air plans to cancel 120 orders and switch to Airbus.

    Not sure of your use of the word "fatal" as this will definitely not be death for Boeing. They will suffer short term problems but they will sort this issue and it will become a blip in their history.

    Note that whilst some US airlines have apparently 'parked' their 737Max (maybe by soft instructions from on high) the FAA has not grounded them. If they did there would be turmoil for Boeing which the US Government would not allow.

    With a backlog of orders stretching out years any that are cancelled will be gratefully accepted by others. I don't know what delivery dates are on the Lion orders but they will probably have a problem getting Airbus to match them.

    It is fatal. The 737 Max is 2/3 of their orders.

    Boeings problem is a systematic one. The 737 Max has a flawed design and now a horrible renomee, passengers actibely avoid to fly with her. Thats poison for airlines, last time an aircraft had such low renomee was the DC10.
    JohninMK
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    Post  JohninMK on Wed Mar 13, 2019 9:53 pm

    FAA now grounded all 737 Max.
    Aristide
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    Post  Aristide on Sun Mar 17, 2019 7:24 pm

    JohninMK wrote:FAA now grounded all 737 Max.

    Not just that. Today it was announced the flight recorder show the pattern is same as the LionAir crash from octobre. Boeing faces a massive problem with that.

    The 737-8Max is a flawed aircraft and its doubtful the problems can be solved at all.

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