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737 max returning to service ?

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737 max returning to service ?

Old 1st May 2019, 18:35
  #101 (permalink)  
 
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Originally Posted by laxman View Post
Reading through these posts has been painful for this MAX qualified pilot but since this is a public board, and many non-fliers are making comments and contributions that defy reason and logic, that are coming from an emotional basis, and one not based upon any experience or knowledge, I should not be surprised.
Hi there Laxman
You are the man who should be taking on these outlandish comments!. Presumably you have the knowledge from having flown the Max to put things into a proper perspective. I have been surprised by the lack of comment from those who actually fly the Max but presumed they were keeping their heads down.
I flew 707s 737 200/400/800 NG and was airtest pilot on them in UK and at Boeing. Not 707 - only a boy then, but did 5000 hours on 707. And I would regard my comments as not unreasonable but yes, there are comments on this forum from persons who don't fly, and I actually find them helpful in that one can see what I don't see - the view of the general public.
In this case, or these two cases, it is apparent that the public as represented by the majority of postings have judged the Max as a death trap. I don't think so. But I could be wrong and it would be great to hear from someone who has been trained to fly them.
Happy flying
Y
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Old 1st May 2019, 19:29
  #102 (permalink)  
 
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f MCAS is creating more troubles than solving and if it is of no use for stall protection (Boeing's claim) why not just take out the entire MCAS? If authorities require heavier stick feel close to the stall for certification why not modify the feel system instead of violently interfering with the steering and using the trim to brute force the nose down?
Its not for feel.

At certain AoA conditions, between the engines moved forward and up (moving the CG forward), coupled with the engine nacelles provide a sudden jump in lift, the nose pitches up.
MCAS sole purpose is to bring the nose back down when this happens.
Nothing other than to counter the nose kicking up.

why not just take out the entire MCAS?
the MAX does not meet cert requirements without MCAS.

Looking at the TOD greenband, the forward CG is likely why on the 738, it is 1.5 to 6.5 and the MAX it is 3 to 8....(and also why at conditions, there is more of a tendency for the nose to kick up)

Last edited by Smythe; 1st May 2019 at 19:59.
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Old 1st May 2019, 19:53
  #103 (permalink)  
 
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If the future MCAS 2.0 runs only one time per flight -and less excessive- afterwards pilots have to fly "MCAS unprotected" in manual flight with flaps up conditions.
So all MAX pilots have to learn flying with no MCAS close to a stall anyway. Why is MCAS still required for certification? Obviously without MCAS a MAX is safe to fly as well if that system will be switched off after one use per flight. (I am aware of the stick feel close to a stall requirement)
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Old 1st May 2019, 20:01
  #104 (permalink)  
 
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The LEAP engines are both larger and relocated slightly up and forward from the previous NG CFM56-7 engines to accommodate their larger fan diameter.
This new location and size of the nacelle cause the vortex flow off the nacelle body to produce lift at high AoA; as the nacelle is ahead of the CofG this lift causes a slight pitch-up effect (ie a reducing stick force) which could lead the pilot to further increase the back pressure on the yoke and send the aircraft closer towards the stall.

This non-linear/reducing stick force is not allowable under FAR 25.173 "Static longitudinal stability".

Several aerodynamic solutions were introduced such as revising the leading edge stall strip and modifying the leading edge vortilons but they were insufficient to pass regulation. MCAS was therefore introduced to give an automatic nose down stabilizer input during elevated AoA when flaps are up.​​​​​​​"
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Old 1st May 2019, 20:05
  #105 (permalink)  
 
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14 CFR 25.173 - Static longitudinal stability.

25.173 Static longitudinal stability.Under the conditions specified in 25.175, the characteristics of the elevator control forces (including friction) must be as follows:

(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC/MFC, whichever is appropriate, or lower than the minimum speed for steady unstalled flight.

(b) The airspeed must return to within 10 percent of the original trim speed for the climb, approach, and landing conditions specified in 25.175 (a), (c), and (d), and must return to within 7.5 percent of the original trim speed for the cruising condition specified in 25.175(b), when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.

(c) The average gradient of the stable slope of the stick force versus speed curve may not be less than 1 pound for each 6 knots.

(d) Within the free return speed range specified in paragraph (b) of this section, it is permissible for the airplane, without control forces, to stabilize on speeds above or below the desired trim speeds if exceptional attention on the part of the pilot is not required to return to and maintain the desired trim speed and altitude.

[Amdt. 25-7, 30 FR 13117, Oct. 15, 1965]
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Old 1st May 2019, 20:06
  #106 (permalink)  
 
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Originally Posted by Kerosene Kraut View Post
If the future MCAS 2.0 runs only one time per flight -and less excessive- afterwards pilots have to fly "MCAS unprotected" in manual flight with flaps up conditions.
So all MAX pilots have to learn flying with no MCAS close to a stall anyway. Why is MCAS still required for certification? Obviously without MCAS a MAX is safe to fly as well if that system will be switched off after one use per flight. (I am aware of the stick feel close to a stall requirement)
The statements from Boeing have not been entirely clear, but my understanding is that there is one MCAS activation per event, not per flight. The ambiguity in the definition of an event is the sticking point IMO.
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Old 1st May 2019, 20:43
  #107 (permalink)  
 
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Originally Posted by Smythe View Post
The LEAP engines are both larger and relocated slightly up and forward from the previous NG CFM56-7 engines to accommodate their larger fan diameter.
This new location and size of the nacelle cause the vortex flow off the nacelle body to produce lift at high AoA; as the nacelle is ahead of the CofG this lift causes a slight pitch-up effect (ie a reducing stick force) which could lead the pilot to further increase the back pressure on the yoke and send the aircraft closer towards the stall.

This non-linear/reducing stick force is not allowable under FAR 25.173 "Static longitudinal stability".
Do you realize that you have just contradicted your previous post, which claimed that MCAS was not added to manipulate stick feel? 25.173(c) is ALL ABOUT stick feel.

(c) The average gradient of the stable slope of the stick force versus speed curve may not be less than 1 pound for each 6 knots.
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Old 1st May 2019, 20:54
  #108 (permalink)  
 
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I suppose, stick force/feel, but then again, doesnt seem like it matters, push it/pull it, MCAS simply pushes the nose down 2.5 degrees with stab trim.

Last edited by Smythe; 1st May 2019 at 21:22.
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Old 1st May 2019, 23:24
  #109 (permalink)  
 
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Which is why I am so sceptical about the massive number of posts here that seek to blame a single cause - MCAS.
There is usually a chain of factors involved in a accident and it only takes one of the links to be broken for the accident to be avoided. The Lion Air aircraft would have crashed on a previous flight had it not been for another pilot on the jump seat who correctly diagnosed what was going wrong. Had the defect been rectified after that flight it wouldn't have occurred either.

Post #103 is an excellent example of an accident chain and shows the importance of a safety culture and crew discipline.
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Old 1st May 2019, 23:54
  #110 (permalink)  
 
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Originally Posted by krismiler View Post
There is usually a chain of factors involved in a accident and it only takes one of the links to be broken for the accident to be avoided.
It has been noted in the various posts and threads on Lion Air and Ethiopia that the MCAS can be argued to have been doing what it was supposed to do, given the signal it was receiving.
That signal - be it a bad probe or a bad signal due to something in the signal's path - is the first hole in the cheese to open. But there were others. The larger questions on system design and redundancy have been done to death already, since the Lion Air crash, so I'll not comment on them but Boeing has to. The piece that has me scratching my head is the info regarding the AoA disagree, alerts, and why it is or isn't an option, etc. I have a number of friends who fly for SWA, and in time I'll get a chance to visit with them in person on this thing.

In order for those flying these aircraft to return to them to their intended service, a variety of aviation authorities need to be content that this system (overall) will either "break the links in the chain" (link in safety chain model) or "prevent a few of the holes lining up" (Reason's model) in future passenger carrying flights.
I agree with the poster who observed that the attempt to focus on a single factor (the smoking gun) is a fundamentally wrong way to look at both the accident and the systemic remedy/mitigation. Mr Reasons likely would weep at some of the assertions being made.
Regardless, the flight deck crews need to be aware of how their systems work, their known failure modes, and the mitigation for same.
That trifecta seems to me to be getting lost in some of the discussion . (I hope to hear from laxman if he's still interested in commenting).
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Old 2nd May 2019, 03:58
  #111 (permalink)  
 
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Originally Posted by slacktide View Post
Do you realize that you have just contradicted your previous post, which claimed that MCAS was not added to manipulate stick feel? 25.173(c) is ALL ABOUT stick feel.

(c) The average gradient of the stable slope of the stick force versus speed curve may not be less than 1 pound for each 6 knots.
The rule that the Max could not meet without MCAS is 14 CFR 25.203(a).
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Old 3rd May 2019, 22:37
  #112 (permalink)  
 
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Originally Posted by Dave Therhino View Post
The rule that the Max could not meet without MCAS is 14 CFR 25.203(a).
Is that fact, or is it your opinion, or is it someone else's opinion? Do you have any documentation of this that you can share?
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Old 4th May 2019, 09:52
  #113 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
The statements from Boeing have not been entirely clear, but my understanding is that there is one MCAS activation per event, not per flight. The ambiguity in the definition of an event is the sticking point IMO.
I agree, I believe if AOA is too high, Mcas will activate once then wait that the AOA is back normal, if AOA is back normal and it goes up again, mcas will activate again.
The MCAS 2.0, will only activate is the 2 AOA show high angle (like for a stick pusher in the planes I used to fly)

i believe this one activation only, is for the case of the 2 AOA failed showing high AOA, you will have only one Mcas then no more for the full flight.


​​​​​
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Old 4th May 2019, 10:23
  #114 (permalink)  
 
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Originally Posted by Lonewolf_50 View Post
In order for those flying these aircraft to return to them to their intended service, a variety of aviation authorities need to be content that this system (overall) will either "break the links in the chain" (link in safety chain model) or "prevent a few of the holes lining up" (Reason's model) in future passenger carrying flights.
Seems to me there's no getting away from Boeing having "broken" the 737 by overtweaking it into a stall-happy monster, which then needed to have that proclivity Fixed.

The original Fix wasn't good enough and got a lot of people killed when the links held / holes lined up twice in five months.

The new Fix had better be flawless 100% of the time, because Boeing is now helplessly wedded to this monster, and any further crash may well have dire consequences for a company whose reputation is teetering badly.
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Old 4th May 2019, 12:32
  #115 (permalink)  
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The new Fix had better be flawless 100% of the time, because Boeing is now helplessly wedded to this monster, and any further crash may well have dire consequences for a company whose reputation is teetering badly.
And I think you should have put ANY in capital before "further crash" , Because the next Max that goes down for ANY reason will cause a huge steer up and the Boeing situation will become unattainable, even if a year after an NTSB report establish that the cause had nothing to do with the aircraft itself. The period between the crash and the report will be too long for people to wait to regain confidence.. We unfortunately live today in instant news and requiring immediate answers.
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Old 4th May 2019, 15:34
  #116 (permalink)  
 
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Originally Posted by ATC Watcher View Post
And I think you should have put ANY in capital before "further crash" , Because the next Max that goes down for ANY reason will cause a huge steer up and the Boeing situation will become unattainable, even if a year after an NTSB report establish that the cause had nothing to do with the aircraft itself. The period between the crash and the report will be too long for people to wait to regain confidence.. We unfortunately live today in instant news and requiring immediate answers.
Fully agree. All commercial interests are eager (though nervous in their heart of hearts) to get the thing back in the air. (If you fly from Winnipeg to Saskatoon these days, you might find yourself on a wet-leased Oman Air machine.) But what makes them think the travelling Public is going to take kindly to flying the Max? And if, as you say, one crashes for Any reason, all their fears will come roaring back. Boeing faces a long and exceedingly tricky path leading out of the doghouse. Interesting times.
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Old 5th May 2019, 20:39
  #117 (permalink)  
 
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latest Seattle Time article is especially damning. AR engineers and process.
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Old 6th May 2019, 05:58
  #118 (permalink)  

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A link to said article in the Seattle Times: Engineers say Boeing pushed to limit safety testing in race to certify planes, including 737 MAX
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Old 6th May 2019, 06:11
  #119 (permalink)  
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Originally Posted by Smythe View Post
I suppose, stick force/feel, but then again, doesnt seem like it matters, push it/pull it, MCAS simply pushes the nose down 2.5 degrees with stab trim.
J
er, nope, it doesn't do that. It may be semantics but the 2.5 degrees is not an attitude value, it is the shift of the trimmable horizontal stabiliser, THS by a maximum value of 2.5 degrees Aircraft Nose Down, AND, which is stabiliser leading edge up. [corrected for error]which will give whatever to the aircraft attitude, dependent on what the driver does on the control column. MCAS is an input for control force, it is not a pitch attitude adjusting system, of course left unchecked it apparently is good for about 40 degrees nose down...

Last edited by fdr; 6th May 2019 at 16:37. Reason: corrected THS sense for error...
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Old 6th May 2019, 06:30
  #120 (permalink)  
 
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Originally Posted by fdr View Post
Aircraft Nose Down, AND, which is also stabiliser leading edge down..
are you sure?
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