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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 2nd Nov 2019, 04:05
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Originally Posted by Takwis
But the earlier 707-100s and -200s had no nudger/pusher, and yet it is a common type rating. I am certified to fly a 707-400, though I have never seen one. And also a 720 (which I have at least seen a few of), in the same type rating.
Interesting.
I too am rated on many Boeing Jets (737/747/757/767, all models) to name a few, but the numbers after a type signify incremental changes to the original aircraft such as seat capacity, engine thrust, ZFW,MTOW, fuselage length, wing span, EFIS.HUD.
Often, though, the higher number indicates a later version, and often-but-not-always, ... The number after the dash is basically just the variation of that aircraft type.

I believe that Boeing didn't want MCAS mentioned as an "anti-stall" device in the certification documentation, otherwise this would have meant the MAX would need a "new type certificate". If you have the time read (as I am sure you are fairly knowledgeable on this subject) part 25, then look at the JATR MAX report regarding MCAS et al. The original type cert on the 1967 B737 didn't have nudgers/stick push; Thus the MAX doesn't have this safety feature, which in hindsight would have been important in the outcome of both these accidents.

None of these 737 prior or new (NG/MAX) had stick pushers, only stick shakers.

Some interesting facts: (Source BCAG).
737 Family There are approximately 42 miles (67 kilometers) of wire on the Next-Generation 737-600/-700/-800/-900ER (Extended Range) models, four miles (6.4 kilometers) less than the 737-300/-400/-500 models.
• On average, there are approximately 600,000 total parts on a Next-Generation 737 airplane.

• Overall, the entire 737 family is the best-selling commercial jetliner in history, with orders for more than 11,550 airplanes through December 2013 from 266 customers. More than 7,700 737s have been delivered.
• The 737 accounts for approximately 56 percent of all Boeing commercial airplanes sold over the past 10 years (2004-2013).

• On Feb. 13, 2006, Boeing delivered the 5,000th 737 to Southwest Airlines. Guinness World Records acknowledged the 737 as "the most-produced large commercial jet" in aviation history.
• On Dec. 16, 2011, Boeing delivered the 7,000th 737 to flydubai.
• On Nov. 5, 2012, Boeing delivered the 7,370th 737 to Lion Air.
• On Mar. 20, 2013, Boeing delivered the 7,500th 737 to Malindo Air.
• Typically, about 50 gallons (189 liters) of paint are used to paint an average 737. Once the paint is dry, it will weigh approximately 250 pounds (113 kilograms) per airplane, depending on the paint scheme.
• With approximately 5,580 airplanes in service, the 737s (early 737s, Classic and Next-Generation) represent more than a quarter of the total worldwide fleet of large commercial jets flying today. **
• More than 342 airlines in 111 countries fly 737s.**
• On average, over 2,000 737 airplanes are in the air at any given time.*
• One 737 takes off or lands every 2.0 seconds.*
• For all 737 models, there are approximately 24,000 scheduled passenger flights per day. This means that 31 percent of all commercial flights are on 737s.***
• The 737 family has carried more than 16.8 billion passengers; that is equivalent to every single man, woman and child flying at least twice. (2013 world population was 7.1 billion).*
• The 737 has flown more than 119.0 billion miles; equivalent to approximately 640 round trips from the earth to the sun.*
• The 737 family has flown more than 184 million flights.*
• The 737 family has flown more than 264 million flight hours; the equivalent to one airplane flying more than 30,200 years nonstop.*

Last edited by 568; 2nd Nov 2019 at 04:15. Reason: text
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Old 2nd Nov 2019, 04:20
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The original type cert on the 1967 B737 didn't have nudgers/stick push; Thus the MAX doesn't have this safety feature, which in hindsight would have been important in the outcome of both these accidents.

None of these 737 prior or new (NG/MAX) had stick pushers, only stick shakers.
Exactly. The 707-100s (original type cert) did not have a stick pusher/nudger. Nor did the -200. But the -400 did. Same 'type'. Same type rating. So I don't see why the 737-100/200/300/400/500/600/700/800/900 not having a stick pusher would rule out a 737MAX having a stick pusher, and still be the same "type". It's got different engines, a hopped up nose gear, massive flat panel screens, and TWO (count them) TWO white position lights on the tailcone forgodsake.* If they can do all that to it, a little stick pusher lurking in the background shouldn't have made a difference.

And on another note, if installing a system like MCAS, far more powerful than a stick pusher, was sort of sneaked in, leaving it out of the pilot manuals, not disclosing to the FAA the full authority that it had, to keep it under the same type, don't you see that as horribly, in fact criminally dishonest?


*That was an important training topic. But MCAS was left out.
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Old 2nd Nov 2019, 04:40
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A couple of articles on the MAX saga.

https://aviationweek.com/commercial-...a1c3dd3c752677
https://aviationweek.com/commercial-...a1c3dd3c752677

I believe that Boeing didn't want MCAS mentioned as an "anti-stall" device in the certification documentation
It's not an anti stall device, though that's what a lot of articles claim, it's there to enable the longitudinal handling characteristics (control column forces) to comply with the relevant FAR.
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Old 2nd Nov 2019, 04:44
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Originally Posted by Takwis
Exactly. The 707-100s (original type cert) did not have a stick pusher/nudger. Nor did the -200. But the -400 did. Same 'type'. Same type rating. So I don't see why the 737-100/200/300/400/500/600/700/800/900 not having a stick pusher would rule out a 737MAX having a stick pusher, and still be the same "type". It's got different engines, a hopped up nose gear, massive flat panel screens, and TWO (count them) TWO white position lights on the tailcone forgodsake.* If they can do all that to it, a little stick pusher lurking in the background shouldn't have made a difference.

And on another note, if installing a system like MCAS, far more powerful than a stick pusher, was sort of sneaked in, leaving it out of the pilot manuals, not disclosing to the FAA the full authority that it had, to keep it under the same type, don't you see that as horribly, in fact criminally dishonest?


*That was an important training topic. But MCAS was left out.
Right on point.

If only Boeing had been "open" in all of the MAX certification, this thread and the loss of 346 lives wouldn't have occurred.
I have enjoyed reading your prior missives.
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Old 2nd Nov 2019, 05:29
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Originally Posted by megan
A couple of articles on the MAX saga.

https://aviationweek.com/commercial-...a1c3dd3c752677
https://aviationweek.com/commercial-aviation/2015-engineer-email-lack-mcas-redundancy-concern?utm_rid=CPEN1000000180327&utm_campaign=21954&utm_med ium=email&elq2=2d1b1f1a5f0e46a396a1c3dd3c752677

It's not an anti stall device, though that's what a lot of articles claim, it's there to enable the longitudinal handling characteristics (control column forces) to comply with the relevant FAR.
Please re-read my comments relating to that post.
MCAS was intended to replicate "stick force gradient" in the low speed stall flight envelope. I have stalled the real aircraft 737/747/757/767 MD-11etc (not simulators) and know the flight control force (column input) of many aircraft in both low and high speed situations.
Boeing didn't want MCAS to be an "anti-stall" aerodynamic function of the flight control system in the MAX for obvious reasons (new type cert).

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Old 2nd Nov 2019, 05:36
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Originally Posted by Takwis

*That was an important training topic. But MCAS was left out.
At some stage, we'll hopefully understand what Mr Forkner meant by "I'm doing a bunch of travelling… simulator validations, Jedi-mind tricking regulators into accepting the training that I got accepted by the FAA" and whether it had any relevance to the reported Southwest contract penalty clause.

As a matter of interest, was (the somewhat better) MCAS deemed worthy to be included in original KC 46 training?
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Old 2nd Nov 2019, 12:23
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Originally Posted by megan
It's not an anti stall device, though that's what a lot of articles claim, it's there to enable the longitudinal handling characteristics (control column forces) to comply with the relevant FAR.
Genuine question which I hope one of the design, test and certification experts on here can answer. What is the purpose of the regulation which mandates a progressive increase in control column force with increasing angle of attack, if not to protect against stalling?
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Old 2nd Nov 2019, 12:33
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Originally Posted by megan
It's not an anti stall device, though that's what a lot of articles claim, it's there (..) to comply with the relevant FAR.
Like many others here I don't care much for articles, except when composed by a select few writers. And even then ...

I do, however, place a somewhat higher level of trust in a competent authority, or even an expert panel composed of members from competent authorities. Such as the JATR who, in their report, made it clear MCAS is either a stall detection or stall prevention system, leaning as heavily as they could towards the latter.

What definition Boeing publicly chose to attach to it, and how they sold it to their regulator, is the subject matter of several investigations, none of which are looking particularly good from a BCA point of view.

Anyway, news on how the testing of the final package are doing with the FAA?
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Old 2nd Nov 2019, 12:56
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What is the purpose of the regulation which mandates a progressive increase in control column force with increasing angle of attack, if not to protect against stalling?
It has nothing to do with stalling per se. Relevant FAR's in my eyes.

§25.145 Longitudinal control.

(a) It must be possible, at any point between the trim speed prescribed in §25.103(b)(6) and stall identification (as defined in §25.201(d)), to pitch the nose downward so that the acceleration to this selected trim speed is prompt with(1) The airplane trimmed at the trim speed prescribed in §25.103(b)(6);

(2) The landing gear extended;

(3) The wing flaps (i) retracted and (ii) extended; and

(4) Power (i) off and (ii) at maximum continuous power on the engines. (b) With the landing gear extended, no change in trim control, or exertion of more than 50 pounds control force (representative of the maximum short term force that can be applied readily by one hand) may be required for the following maneuvers1) With power off, flaps retracted, and the airplane trimmed at 1.3 VSR1, extend the flaps as rapidly as possible while maintaining the airspeed at approximately 30 percent above the reference stall speed existing at each instant throughout the maneuver.(2) Repeat paragraph (b)(1) except initially extend the flaps and then retract them as rapidly as possible.

(3) Repeat paragraph (b)(2), except at the go-around power or thrust setting.

(4) With power off, flaps retracted, and the airplane trimmed at 1.3 VSR1, rapidly set go-around power or thrust while maintaining the same airspeed.

(5) Repeat paragraph (b)(4) except with flaps extended.

(6) With power off, flaps extended, and the airplane trimmed at 1.3 VSR1, obtain and maintain airspeeds between VSW and either 1.6 VSR1 or VFE, whichever is lower.(c) It must be possible, without exceptional piloting skill, to prevent loss of altitude when complete retraction of the high lift devices from any position is begun during steady, straight, level flight at 1.08 VSR1 for propeller powered airplanes, or 1.13 VSR1 for turbojet powered airplanes, with—(1) Simultaneous movement of the power or thrust controls to the go-around power or thrust setting;

(2) The landing gear extended; and

(3) The critical combinations of landing weights and altitudes. (d) If gated high-lift device control positions are provided, paragraph (c) of this section applies to retractions of the high-lift devices from any position from the maximum landing position to the first gated position, between gated positions, and from the last gated position to the fully retracted position. The requirements of paragraph (c) of this section also apply to retractions from each approved landing position to the control position(s) associated with the high-lift device configuration(s) used to establish the go-around procedure(s) from that landing position. In addition, the first gated control position from the maximum landing position must correspond with a configuration of the high-lift devices used to establish a go-around procedure from a landing configuration. Each gated control position must require a separate and distinct motion of the control to pass through the gated position and must have features to prevent inadvertent movement of the control through the gated position. It must only be possible to make this separate and distinct motion once the control has reached the gated position.

§25.175 Demonstration of static longitudinal stability.

Static longitudinal stability must be shown as follows:

(a) Climb. The stick force curve must have a stable slope at speeds between 85 and 115 percent of the speed at which the airplane—

(1) Is trimmed, with—

(i) Wing flaps retracted;

(ii) Landing gear retracted;

(iii) Maximum takeoff weight; and (iv) 75 percent of maximum continuous power for reciprocating engines or the maximum power or thrust selected by the applicant as an operating limitation for use during climb for turbine engines; and(2) Is trimmed at the speed for best rate-of-climb except that the speed need not be less than 1.3 VSR1.

(b) Cruise. Static longitudinal stability must be shown in the cruise condition as follows: (1) With the landing gear retracted at high speed, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15 percent of the trim speed plus the resulting free return speed range, or 50 knots plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1.3 VSR1, nor speeds greater than VFC/MFC, nor speeds that require a stick force of more than 50 pounds), with—(i) The wing flaps retracted;

(ii) The center of gravity in the most adverse position (see §25.27);

(iii) The most critical weight between the maximum takeoff and maximum landing weights; (iv) 75 percent of maximum continuous power for reciprocating engines or for turbine engines, the maximum cruising power selected by the applicant as an operating limitation (see §25.1521), except that the power need not exceed that required at VMO/MMO; and(v) The airplane trimmed for level flight with the power required in paragraph (b)(1)(iv) of this section. (2) With the landing gear retracted at low speed, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15 percent of the trim speed plus the resulting free return speed range, or 50 knots plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1.3 VSR1, nor speeds greater than the minimum speed of the applicable speed range prescribed in paragraph (b)(1), nor speeds that require a stick force of more than 50 pounds), with—(i) Wing flaps, center of gravity position, and weight as specified in paragraph (b)(1) of this section;

(ii) Power required for level flight at a speed equal to (VMO + 1.3 VSR1)/2; and

(iii) The airplane trimmed for level flight with the power required in paragraph (b)(2)(ii) of this section. (3) With the landing gear extended, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15 percent of the trim speed plus the resulting free return speed range, or 50 knots plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1.3 VSR1, nor speeds greater than VLE, nor speeds that require a stick force of more than 50 pounds), with—(i) Wing flap, center of gravity position, and weight as specified in paragraph (b)(1) of this section; (ii) 75 percent of maximum continuous power for reciprocating engines or, for turbine engines, the maximum cruising power selected by the applicant as an operating limitation, except that the power need not exceed that required for level flight at VLE; and(iii) The aircraft trimmed for level flight with the power required in paragraph (b)(3)(ii) of this section.

(c) Approach. The stick force curve must have a stable slope at speeds between VSW and 1.7 VSR1, with—

(1) Wing flaps in the approach position;

(2) Landing gear retracted;

(3) Maximum landing weight; and

(4) The airplane trimmed at 1.3 VSR1 with enough power to maintain level flight at this speed.

(d) Landing. The stick force curve must have a stable slope, and the stick force may not exceed 80 pounds, at speeds between VSW and 1.7 VSR0 with—

(1) Wing flaps in the landing position;

(2) Landing gear extended;

(3) Maximum landing weight;

(4) The airplane trimmed at 1.3 VSR0 with—

(i) Power or thrust off, and

(ii) Power or thrust for level flight.

(5) The airplane trimmed at 1.3 VSR0 with power or thrust off.

§25.255 Out-of-trim characteristics.

(a) From an initial condition with the airplane trimmed at cruise speeds up to VMO/MMO, the airplane must have satisfactory maneuvering stability and controllability with the degree of out-of-trim in both the airplane nose-up and nose-down directions, which results from the greater of—(1) A three-second movement of the longitudinal trim system at its normal rate for the particular flight condition with no aerodynamic load (or an equivalent degree of trim for airplanes that do not have a power-operated trim system), except as limited by stops in the trim system, including those required by §25.655(b) for adjustable stabilizers; or(2) The maximum mistrim that can be sustained by the autopilot while maintaining level flight in the high speed cruising condition.(b) In the out-of-trim condition specified in paragraph (a) of this section, when the normal acceleration is varied from + 1 g to the positive and negative values specified in paragraph (c) of this section—(1) The stick force vs. g curve must have a positive slope at any speed up to and including VFC/MFC; and

(2) At speeds between VFC/MFC and VDF/MDF the direction of the primary longitudinal control force may not reverse.

(c) Except as provided in paragraphs (d) and (e) of this section, compliance with the provisions of paragraph (a) of this section must be demonstrated in flight over the acceleration range—
(1) −1 g to + 2.5 g; or

(2) 0 g to 2.0 g, and extrapolating by an acceptable method to −1 g and + 2.5 g. (d) If the procedure set forth in paragraph (c)(2) of this section is used to demonstrate compliance and marginal conditions exist during flight test with regard to reversal of primary longitudinal control force, flight tests must be accomplished from the normal acceleration at which a marginal condition is found to exist to the applicable limit specified in paragraph (b)(1) of this section.(e) During flight tests required by paragraph (a) of this section, the limit maneuvering load factors prescribed in §§25.333(b) and 25.337, and the maneuvering load factors associated with probable inadvertent excursions beyond the boundaries of the buffet onset envelopes determined under §25.251(e), need not be exceeded. In addition, the entry speeds for flight test demonstrations at normal acceleration values less than 1 g must be limited to the extent necessary to accomplish a recovery without exceeding VDF/MDF.(f) In the out-of-trim condition specified in paragraph (a) of this section, it must be possible from an overspeed condition at VDF/MDF to produce at least 1.5 g for recovery by applying not more than 125 pounds of longitudinal control force using either the primary longitudinal control alone or the primary longitudinal control and the longitudinal trim system. If the longitudinal trim is used to assist in producing the required load factor, it must be shown at VDF/MDF that the longitudinal trim can be actuated in the airplane nose-up direction with the primary surface loaded to correspond to the least of the following airplane nose-up control forces1) The maximum control forces expected in service as specified in §§25.301 and 25.397.

(2) The control force required to produce 1.5 g. (3) The control force corresponding to buffeting or other phenomena of such intensity that it is a strong deterrent to further application of primary longitudinal control force.

Last edited by megan; 2nd Nov 2019 at 13:10.
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Old 2nd Nov 2019, 13:45
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Originally Posted by megan
It has nothing to do with stalling per se. Relevant FAR's in my eyes.
Those extracts tell us what characteristics need to be demonstrated; what I was hoping to get at was the reason for those regulations being in place. What is the hazard created by non-compliant stick force gradient, for instance?
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Old 2nd Nov 2019, 13:51
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ES, see if this answers any questions.

https://www.boeing.com/commercial/ae...y/fo01txt.html
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Old 2nd Nov 2019, 13:52
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Originally Posted by Easy Street
...What is the hazard created by non-compliant stick force gradient, for instance?
Pilot, relying on stick force feedback, inadvertently stalling the airplane?
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Old 2nd Nov 2019, 14:02
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Originally Posted by spornrad
Pilot, relying on stick force feedback, inadvertently stalling the airplane?
;-)
Thanks spornrad, was about to post this exact same answer...
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Old 2nd Nov 2019, 14:04
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Originally Posted by spornrad
Pilot, relying on stick force feedback, inadvertently stalling the airplane?
Bingo. It's so painfully obvious. All of the appeals to the arcane language of the certification regulations, as if they were handed down to Moses or something, are just smoke and mirrors, to distract us all from the fact that you don't want the stick to get lighter as you pull, because you might easily overshoot your target pitch, and stall the airplane.

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Old 2nd Nov 2019, 14:36
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Originally Posted by spornrad
Pilot, relying on stick force feedback, inadvertently stalling the airplane?
Originally Posted by Takwis
Bingo. It's so painfully obvious. All of the appeals to the arcane language of the certification regulations, as if they were handed down to Moses or something, are just smoke and mirrors, to distract us all from the fact that you don't want the stick to get lighter as you pull, because you might easily overshoot your target pitch, and stall the airplane.
Yes, Bingo, indeed. If it weren't for the risk of stalling, nobody would much care about reduced stick force as ANU increases.
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Old 2nd Nov 2019, 14:40
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Originally Posted by megan
ES, see if this answers any questions.

https://www.boeing.com/commercial/ae...y/fo01txt.html
Well, it explains how longitudinal stability is achieved but not why it’s important in the particular flight regimes covered by the regulations. It seems the posters who followed you share my judgement that Boeing is arguing about how many angels can dance on the head of a pin.

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Old 2nd Nov 2019, 14:53
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I believe the JATR report recommended that the 'bare airframe' (i.e.with no MCAS) should be air tested for longitudanal stability. This suggests to me that they are not wholly convinced by the reasons given by Boeing as to why MCAS was needed in the first place. Could it be that not only does the stick force become lighter at a high AoA but, even if the stick back force is reduced/released, aerodynamic forces on the forward positioned engine nacelles at high AoA continue to pitch the nose of the aircraft up into a stall?
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Old 2nd Nov 2019, 15:08
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Originally Posted by Avionista
I believe the JATR report recommended that the 'bare airframe' (i.e.with no MCAS) should be air tested for longitudanal stability. This suggests to me that they are not wholly convinced by the reasons given by Boeing as to why MCAS was needed in the first place. Could it be that not only does the stick force become lighter at a high AoA but, even if the stick back force is reduced/released, aerodynamic forces on the forward positioned engine nacelles at high AoA continue to pitch the nose of the aircraft up into a stall?
Here's the most directly-relevant recommendation from the JATR report:

Recommendation R3.4: The FAA should review the natural (bare airframe) stalling characteristics of the B737 MAX to determine if unsafe characteristics exist. If unsafe characteristics exist, the design of the speed trim system (STS)/MCAS/elevator feel shift (EFS) should be reviewed for acceptability.

Observation O3.4-A: The original implementation of MCAS was driven primarily by its ability to provide the B737 MAX with FAA-compliant flight characteristics at high speed. An unaugmented design would have been at risk of not meeting 14 CFR part 25 maneuvering characteristics requirements due to aerodynamics.

Observation O3.4-B: Extension of MCAS to the low-speed and 1g environment during the flight program was due to unacceptable stall characteristics with STS only. The possibility of a pitch-up tendency during approach to stall was identified for the flaps-up configuration prior to the implementation of MCAS.

Finding F3.4-A: The acceptability of the natural stalling characteristics of the aircraft should form the basis for the design and certification of augmentation functions such as EFS and STS (including MCAS) that are used in support of meeting 14 CFR part 25, subpart B requirements
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Old 2nd Nov 2019, 15:25
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There was a time when a "self-stalling tendency" was simply called by its name (talking about the 707-400).
In his book Davies stated that “The stick nudger introduces a small force into the elevator circuit which imposes positive stick free (! feel?) stability and removed the otherwise self-stalling tendency”. He goes onto to say that “as its input is so small all the runaway cases are completely innocuous.”
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Old 2nd Nov 2019, 15:40
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I think he means "stick free stability", as in you could let go of the stick, and the plane would be stable. I think.


and:
Extension of MCAS to the low-speed and 1g environment during the flight program was due to unacceptable stall characteristics with STS only. The possibility of a pitch-up tendency during approach to stall was identified for the flaps-up configuration prior to the implementation of MCAS.
That's a pretty clear confirmation of what we are talking about.
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