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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 18th Dec 2019, 18:47
  #4641 (permalink)  
 
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JT, #4634,

Re fitting “a variable downspring in the circuit”, this appears to be the underlying theory of MCAS - electronic ‘down spring’. However the implementation differs between aircraft with ‘conventional’ stick-trim relationships, and those with trimmable tailplanes (737).
Adding a downspring in a stick-elevator-trimtab system results in the force being applied directly to the stick - pilot feel, aircraft ‘stability’.
With the 737 trim configuration the ‘spring’ force is applied to the tail (HStab), which moves the aircraft, then requiring pilot input and change of feel. Although this can be described as backward action, aircraft with these trim systems appear normal to the pilot, they are controlled and fly like any other aircraft.

All is well until the trim system misbehaves, a powerful tail force pitches the aircraft which can overcome the elevator power generating high stick forces.
The trim differences/effects are considered in MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures see the link to the accident report
and https://www.skybrary.aero/bookshelf/books/2627.pdf

There are few examples of spring fixes in aircraft with a trimmable tail; those which have involve high integrity installations.

There may be options to fix the aerodynamics - with difficulty. I recall seeing a down tab on the trailing edge of the MD90 / B717 engine pylon; are these in service - probably related to stall recovery.
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Old 18th Dec 2019, 18:54
  #4642 (permalink)  
 
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Originally Posted by Takwis View Post
If they are, they lose altitude, each time they do it. (I think those are stalls, a sharp altitude loss, and a rapid speed increase, then speed and altitude return to entry conditions.)
Stalling? At 500knots? Seriously? That's going some!
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Old 18th Dec 2019, 19:02
  #4643 (permalink)  
 
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Okay, wind-up turns leading to accelerated stalls...the stated aerodynamic situation the MCAS was designed for, at 500knots groundspeed, at around 33,000 feet. We're guessing. Anyone got a better one?
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Old 18th Dec 2019, 19:08
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The original MCAS was said to be intended for high speed upsets. Low speed mode and more power were added later on.
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Old 18th Dec 2019, 19:56
  #4645 (permalink)  
 
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Originally Posted by Takwis View Post
"If nose up trim is required, RAISE THE NOSE WELL ABOVE THE HORIZON with elevator control. Then slowly relax the control column pressure and manually trim nose up. Allow the nose to drop TO THE HORIZON while trimming. Repeat...."

Done per the instructions, there should not be a loss of altitude.
The question is, will the nose consistently drop to horizon only, and not below ? Every such maneuver I taught/made/saw being made resulted in a loss of altitude.
Especially since when countering MCAS, the crew will have a hard time "raising the nose well above the horizon"...
But I admint never having done that in an airliner.
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Old 18th Dec 2019, 20:37
  #4646 (permalink)  
 
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Originally Posted by Takwis View Post
We need a good nickname for the first generation 737s. For that matter, the term "next-gen", or NG is pretty outdated, at this point.
Jurassic, Classic, NG and Max, seems to be the accepted convention.
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Old 18th Dec 2019, 20:45
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Originally Posted by Takwis We need a good nickname for the first generation 737s. For that matter, the term "next-gen", or NG is pretty outdated, at this point.
Jurassic, Classic, NG and Max, seems to be the accepted convention.
Wasn't it the FLUF?

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Old 18th Dec 2019, 20:55
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Originally Posted by pilotmike View Post
Stalling? At 500knots? Seriously? That's going some!
i seem to remember something like “you can stall at any speed at any attitude” from my training.
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Old 18th Dec 2019, 21:38
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Originally Posted by derjodel View Post


i seem to remember something like “you can stall at any speed at any attitude” from my training.
Granted the following is the extreme case not possible in a subsonic commercial transport- but the following description- regardless of reason - might be called a stall ( airplane not flying )

On December 12, 1953, Chuck Yeager flew the Bell X-1A 1,650 mph, becoming the first man to fly two and one-half times the speed of sound. At Mach 2.4 at 80,000 feet the aircraft spun out of control, spinning on all 3 axes. G-forces sent Yeager’s head into the canopy, cracking it and bending the control stick. The aircraft spun down 51,000 feet in 51 seconds before he regained control at 25,000 feet.
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Old 18th Dec 2019, 22:39
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Originally Posted by Grebe View Post
Granted the following is the extreme case not possible in a subsonic commercial transport- but the following description- regardless of reason - might be called a stall ( airplane not flying )
i guess it was just a stall! At high altitude, the stall AoA get’s much lower, specially at high speed: https://www.nasa.gov/centers/dryden/...ain_H-1731.pdf
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Old 19th Dec 2019, 02:08
  #4651 (permalink)  
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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures Mk II

NY Times, an hour or so ago:

President Trump called Boeing’s chief executive on Sunday to discuss the company’s plans to halt production of the 737 Max, according to three people with knowledge of the matter who spoke on the condition of anonymity to talk about a private call.

Mr. Trump told the executive, Dennis A. Muilenburg, that he had heard that Boeing was planning to permanently shut down the Max production line, according to two of the people. Mr. Muilenburg assured the president that any pause to production would be temporary, and that there would be no layoffs as a result of the move, they said.

A day later, Boeing announced it was temporarily halting production of the 737 Max, which has been grounded for nine months after two crashes that killed 346 people.

On the call, which lasted five to 10 minutes, Mr. Trump expressed concern about the health of the company more broadly, and asked whether Mr. Muilenburg was doing O.K., the two people said.Mr. Trump also asked about the status of the fix for software that Boeing developed for the Max and which was found to have played a role in both crashes.

Mr. Muilenburg said that the company had a fix ready, but that American and international regulators still had to test it and approve it.


More
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Old 19th Dec 2019, 02:15
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Then, two days after the second accident, in Ethiopia on March 10, Mr. Muilenburg called Mr. Trump and insisted the Max was safe. The United States grounded the plane the next day, however, after most other regulators around the world had already done so.
In a just world, Muilenburg would be considering his trial strategy rather than what to say to keep the stock afloat.
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Old 19th Dec 2019, 02:26
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Originally Posted by OldnGrounded View Post
NY Times, an hour or so ago:
President Trump called Boeing’s chief executive on Sunday to discuss the company’s plans to halt production of the 737 Max, according to three people with knowledge of the matter who spoke on the condition of anonymity to talk about a private cal
Translation - there are at least three members of Trumps staff who should be fired at the minimum if not jailed.

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Old 19th Dec 2019, 02:32
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Originally Posted by Water pilot View Post
In a just world, Muilenburg would be considering his trial strategy rather than what to say to keep the stock afloat.
I haven't wanted to flood the threads with articles, but there have been several in the past few days where analysts have asked why Muilenburg still has a job.

My best guess, honestly, is that they're waiting for the right time to cut him loose -- when they think he'll take much of the blame with him. Of course, they've probably promised to give him a huge golden parachute to convince him to stick around and take the licks. It'll take big bucks if he ends up having to defend himself in civil litigation.

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Old 19th Dec 2019, 02:49
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Sometimes I think that Americans have forgotten that we live in a democracy. There is certainly nothing illegal about leaking the contents of a non classified discussion that the President has with a business leader. In normal times there would be a White House readout on the conversation.
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Old 19th Dec 2019, 02:51
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Derjodel, I had a read of the linked document. Not every line. Can you point to the part that shows the critical angle (stalling angle) is much lower at high altitude?

My reading of Kermode and Davies suggests that angle is constant for an aerofoil section.

At high altitude, the stall AoA gets much lower, specially at high speed: https://www.nasa.gov/centers/dryden/...ain_H-1731.pdf
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Old 19th Dec 2019, 03:19
  #4657 (permalink)  
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Thread closed, further discussion here: MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures Mk II

Let's try to keep on topic please. Off topic posts have bogged down this thread which has grown to a size that stalls the IB server when moderation is needed eg deleting OT posts, which takes time out of the lives of the volunteer moderating team.
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