737 grounded???

Discussion in 'Hangar Flying' started by Aerowerx, Mar 13, 2019.

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  1. Apr 9, 2019 #81

    pictsidhe

    pictsidhe

    pictsidhe

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    The pilot of 447 was unaware that the co-pilot had been holding back on the stick for the entire descent. He knew what to do when he discovered that. But, that came too late.
     
  2. Apr 9, 2019 #82

    BJC

    BJC

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    It’s my contention that both pilots in the front of a commercial air carrier should know how to fly.


    BJC
     
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  3. Apr 9, 2019 #83

    Heliano

    Heliano

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    Opinions in several postings in this forum point to the right direction: Boeing has a more appropriate and more conservative approach to automation than Airbus; hand flying skill is still a must; Also situational awareness is critical: could have saved the Air France A330 over the Atlantic; etc.
    However two topics must be clarified:
    1 - The American Airlines A300 rudder failure: back then the airworthiness requirements in force (FAA, EASA, etc.) did NOT address rudder reversal, that is, full deflection to one side causing a pronounced sideslip angle then reversing the rudder deflection to the other side. What was required by then is full deflection to one side then back to neutral. This accident sent all the aircraft manufacturers scrambling to double check their designs for this weakness. The manufacturer I worked for by then was only producing regional jets with "T" tail ("T" tails require a stronger vertical tail anyhow, to withstand asymmetric vertical loads on the horizontal tail, and to be flutter-free) and found out their designs were OK.
    2 - The 737 MAX history is not complete, and more information is needed to fully understand these accidents: The MAX series have, larger, bulkier engines. To keep using the same landing gear system Boeing had to move the engines forward and upward. This new arrangement seems to have caused changes in the aerodynamic behavior at high angles of attack. I - as most of the public - do not know the extent of these changes, i.e., if they cause longitudinal controlability problems or stability problems. May be the MCAS was added to correct these aerodynamic shortcomings. A big engine may in theory produce flow detachment on the wing or wake on the tail. Remember the little plate on the GE CF6 installations? The MCAS changes the stabilizer incidence, and it seems to change it at a much faster rate than a normal manual retrimming (I do not know if the wheel at the central console moves along with the MCAS actuation). Therefore, depending on how fast it actuates, if it happens inadvertently it may create an out-of-control situation before the crew can do anything.
    I've read some comments comparing the MCAS to the MD11's LSAS but they are totally different, first because the LSAS actuates the elevator, not the stabilizer, and second because the LSAS, with limited authority, has nothing to do with controlability - its intent is to add longitudinal stability. I've flown the MD-11 for five years.
     
  4. Apr 9, 2019 #84

    Vigilant1

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    The (large, painted with stripes) manual trim wheels do spin as the MCAS-directed trimming occurs.
    The MCAS trimming can be stopped at any time by either turning off the electric trim or trimming in the opposite direction using the normal trim switches on the yoke. After approx 10 seconds, if excessively high AoA is still sensed by the active AoA vane, then the MCAS will again attempt to trim nose down (and it can again be countered with the trim switch). There's no limit to how often this cycle can be repeated.
    The rate at which the MCAS directs the stab trim to occur is (reportedly) up to 0.27 degrees per second. This is not faster than the trim speed when activated by the switches on the yoke.
     
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  5. Apr 9, 2019 #85

    pictsidhe

    pictsidhe

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    Yes. I think the Air France crash was partly due to the pilot assuming that the co-pilot knew what he was doing. It's well known what assumptions are the mother of...
     
  6. Apr 9, 2019 #86

    BJC

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    I’ve heard that it is possible to stop the trimming action by holding the manual trim wheel.

    BJC
     
  7. Apr 9, 2019 #87

    Tiger Tim

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    I was at a talk by a well seasoned test pilot instructor who spent a good deal of time talking about this accident. IIRC he said afterward he took one of his school's two-seat jets up with the vertical fin instrumented to measure strain and got some data for himself. In stable cruise he pushed one rudder pedal to the floor and let it stabilize for a second at that yaw angle, then centred the pedals briefly, then put in some small amount of opposite rudder well before the plane had straightened out. I forget the units used, but the forces on the tail during that initial rudder input were quite a bit higher than I expected, then were an equal amount in the opposite direction just by centering the rudder, then went off the charts when he put in opposite input. I don't think any pilot had expected that prior to the accident as it was common to teach 'below maneuvering speed you can put in full control input without damaging the aircraft' when it turns out they really only mean elevator input.

    Coincidentally, I used to employ the actor that played the First Officer who caused that accident in the episode of Mayday (or Air Crash Investigation depending on what country you're in). He's also a commercial pilot who now even flies for a national airline, possibly even on an Airbus by now.
     
  8. Apr 9, 2019 #88

    davidb

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    One well trained experienced pilot and one apprentice pilot works fine when everything is fine. History proves it is much better to have two trained and experienced pilots working together when unusual and critical things go wrong. Thankfully, the FAA has upped the minimum experience required in recent years and has mandated an emphasis on CRM.

    History has also shown CRM skills are just as important as two experienced pilots because it enables the synergy.
     
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  9. Apr 10, 2019 #89

    BJC

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    A senior check pilot for all 737’s just confirmed that the trim can be stopped by holding the manual trim wheel.


    BJC
     
  10. Apr 10, 2019 #90

    Vigilant1

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    Thanks. One thing that apparently >doesn't< work when the MCAS is working is to apply opposite yoke pressure when the trim is running. This is one way that pilots in the 737 have learned (by habit) to disengage the trim, but it (reportedly) doesn't work that way in the 737MAX when MCAS is doing its thing (as it would largely defeat the purpose of MCAS--to force the nose down if a pilot is pulling back on the yoke and forcing the plane into an extreme nose-high AoA). This is one factor that has been cited as a reason the mishap crews thought they couldn't stop the trim from running--the technique they usually used (push the yoke in the opposite direction) wasn't working. Again--the memory procedure for trim anomalies doesn't say "apply opposite yoke," it says to turn off the autopilot, then it says to flip both cutout switches to "off" and use the manual trim wheel. And it doesn't say you should turn the switches back on, either.
     
  11. Apr 10, 2019 #91

    Heliano

    Heliano

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    Thank you, Vigilant1. What you wrote is very good info. You've taught me a little more about the MAX. The thing I am still curious about is how much MCAS is crucial for stability/control at hi AOA's, and what the aerodynamic differences are between the MAX and the NG/Classic.
     
  12. Apr 10, 2019 #92

    TXFlyGuy

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    You might add this is not just 737 pilots that this applies to with regards of stopping a runaway trim with opposite yoke deflection, but ALL Boeing pilots.

    As far as reengaging the trim switches after a situation has been stabilized...the checklist is your friend.

    To follow up on a comment made by Heliano, about the landing gear / engines on the Max, Boeing wanted to modify the gear when they designed the 737-900, to give greater ground clearance for the engines. The argument was made as to why this was the proper course of action to the FAA. That idea was accepted by the Feds, however Boeing was advised that if they changed the landing gear a new type rating would be required for the -900.

    Thus Boeing slapped yet another Band-Aid on the aging Fluf, making all of their customers happy with the common type.

    Here is a post from an airline forum...
    Replies: 18 | Views: 1,837 Time for Boeing to Replace the 737

    The current "Max" version of the 737 is a 50+ year old design with a heavy slathering of lipstick. The 737 should have had a clean sheet replacement decades ago. Due to Boeing's continual laziness, lack of innovation and not enough competition, they have been content to keep re-heating a relic of the 60's.
     
  13. Apr 10, 2019 #93

    Vigilant1

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    The discussion at the link provides another in the chorus of "brilliant in hindsight" observations we are being treated to.
    "Pleasing customers" (by maintaining the same type rating) is an important factor in being successful as a company. Boeing has done that. As far as "lack of competition", it is easy to find 10 more jabbering heads that claim Boeing chose to make the compromises needed to maintain the type rating >because < of competition from Airbus. And how many glitches (as big or bgiger than MCAS has proven to be) might have been lurking in a new clean-sheet design? We'll never know, but in the design of commercial airliners there is much to be said for the safety of evolution over revolution.
    Boeing will make this plane better. I just hope the answer isn't some opaque
    hardware/software voting monstrosity that a competent crew can't readily understand and fly around when needed. Boeing has been successful in part by avoiding this trap.
     
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  14. Apr 10, 2019 #94

    BBerson

    BBerson

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    Was a new Type rating really needed for the more suitable gear? Or just arbitrary Rule-making?
     
  15. Apr 10, 2019 #95

    TXFlyGuy

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    I would be curious to know if Boeing's desire to modify the landing gear (make it a bit taller) on the -900 had been allowed by the FAA, and still maintaining the common type, would it have had a positive impact on the Max, making the obtuse MCAS program completely unneeded?
     
  16. Apr 10, 2019 #96

    TXFlyGuy

    TXFlyGuy

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    Only Boeing and the FAA can answer that.

    I became aware of this development as my employer was one of the early customers for the -900, and these arguments were being thrown all over the place.

    So Boeing made another compromise in the design, to keep the Fed's happy...and their customers.

    Safety is considered important, up until it starts costing too many $$$.
     
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  17. Apr 10, 2019 #97

    Tiger Tim

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    Any other free flight modelers sitting here thinking, "I'd have just made the stabilizer bigger," or is it just me?

    (Obviously there's a huge difference when looking at engineering and weight and certification versus some balsa wood sticks being in a slightly different place)
     
  18. Apr 10, 2019 #98

    davidb

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    The Max 10 has the new gear and it is the same type rating. I don’t think the new gear affects the type rating. The new gear isn’t really needed until you stretch the fuselage a bit more. The new gear is quite complex (read expensive) because they had to design something taller that still fits in the old space.
     
  19. Apr 10, 2019 #99

    BBerson

    BBerson

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    Yes, but the question was (see post 95) could Boeing have made a taller and a simpler modification than the MCAS, if the FAA had not threatened to impose the Type rating card?
     
  20. Apr 10, 2019 #100

    TXFlyGuy

    TXFlyGuy

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    Is the gear you reference taller than the previous landing gear? That was the main point of contention between Boeing and the FAA.
     

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