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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 24th Mar 2019, 00:54
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WSJ: Boeing Plans Fixes to Make 737 MAX Stall-Prevention Feature Easier for Pilots to

WSJ: Boeing Plans Fixes to Make 737 MAX Stall-Prevention Feature Easier for Pilots to Control
Subtitled: Federal Aviation Administration officials have tentatively approved sweeping software and pilot-training changes

Boeing Plans Fixes to Make 737 MAX Stall-Prevention Feature Easier for Pilots to Control

Federal Aviation Administration officials have tentatively approved sweeping software and pilot-training changes

By Andy Pasztor and Andrew Tangel

U.S. air-safety regulators have tentatively approved sweeping software and pilot-training changes for Boeing Co.’s BA -2.83% grounded 737 MAX jets, aimed at fixing problems with a suspect flight-control system, according to internal government documents and people familiar with the details.

The extensive revisions, these industry and government officials said, will make the automated stall-prevention feature, called MCAS, less aggressive and more controllable by pilots.

They also said the enhanced training, relying on self-guided interactive instruction on laptops, highlights information about when the system engages and how pilots can shut it off.

The changes amount to a reversal from major design and engineering principles Boeing relied on when it developed the stall-prevention system, which is suspected of causing the fatal dive that killed 189 people on board a Lion Air 737 MAX in Indonesia last October. A team of international crash investigators also is looking into whether a similar problem led to the crash of an Ethiopian Airlines plane less than five months later.

The Federal Aviation Administration has said it was working with Boeing to develop and install a revised MCAS system based on lessons learned from the Lion Air tragedy, but the extent of the changes goes beyond what some industry officials expected. An FAA spokesman declined to comment on specifics of the pending changes.

Accident investigators have said the Lion Air plane got erroneous information from one sensor that caused the stall-prevention system to misfire, repeatedly pushing the nose of the plane and ending at the maximum downward angle even though the pilots were resisting. Authorities have said they see clear similarities between that accident and the Ethiopian crash on March 10.

The modifications, officials said, create a gentler stall-prevention feature, redesigned so it won’t overpower other cockpit commands or misfire based on faulty readings from a single sensor. It is devised to automatically push the nose down only once—for no longer than 10 seconds—if the aircraft is in danger of stalling and losing lift.

The changes have been tentatively approved by FAA officials, the people familiar with the details said, subject to final ground-simulator checks and flight tests. They could be rolled out to airlines’ 737 MAX jets in the next few weeks.

A Boeing official said the new MAX software could still go through revisions, and the timing of formal approval from the FAA and foreign regulators remains fluid.

Even after the changes are fully implemented in the U.S., air-safety regulators in Canada and the EU are poised to conduct their own evaluation of the new software as well as how the FAA initially certified the plane to carry passengers. Those reviews could take months, according to safety experts.

Among other changes, the revised software would rely on two “angle of attack” sensors, rather than one, to measure the upward or downward angle of the wings and nose in flight. If two sensors send data differing by five degrees or more, MCAS wouldn’t activate at all, according to the officials briefed on the tentative changes.

The cockpit crew on the Lion Air flight struggled against MCAS—using manual nose-up commands some two dozen times—before losing control and plunging into the Java Sea at more than 500 miles an hour. The interim accident report revealed a constant 20-degree difference between signals from the sensor on the captain’s side and those from the co-pilot’s-side sensor.

On Saturday, Boeing said it has been “working diligently and in close cooperation with the FAA on the software update,” adding that the company is “taking a comprehensive and careful approach to design, develop and test the software that will ultimately lead to certification” by regulators.

During the investigations of the two crashes, Boeing and the FAA have faced criticism from pilot groups, airlines, politicians and airlines for alleged lapses in the original MCAS design—and for failing to adequately inform aviators.

About a dozen pilots from U.S. and international carriers are getting previews this weekend of the changes in the works, as well as related manuals and training, according to the Boeing official. "We want their feedback,” this official said. “It’s a dialogue.”

The group engaging in this weekend’s preview of the changes includes pilots from U.S. MAX operators: Southwest Airlines Co. , American Airlines Group Inc. and United Continental Holdings Inc., a person familiar with the matter said. On Wednesday, this person added, a larger group of more than 100 pilots from a broad cross section of MAX operators are due at Boeing’s 737 factory in Renton, Wash., for a similar session.

Investigators in the Lion Air crash said faulty data transmitted from a single sensor caused the MCAS system to assume the plane was in danger of stalling. The warnings began during takeoff and continued for much of the roughly 11-minute flight, apparently confusing the pilots and creating a cascade of related warning signals.

Under the new design, warning devices will alert crews if there is a problem with sensors before takeoff or in flight, people familiar with the redesign said.

They said automated commands to move a flight-control surface on the tail, called a horizontal stabilizer, can be counteracted by pilot commands.

The changes will be standard on all 737 MAX aircraft, for which Boeing has roughly 5,000 orders.

A draft FAA document spelling out the training revisions shows pilots now will be specifically informed about “MCAS activation thresholds,” “flight crew alerts” and how to turn off the system by flipping a single switch. Such details weren’t highlighted in earlier manuals or training materials circulated byBoeing.

FAA officials have determined the handing qualities of 737 MAX jets will be close enough to earlier 737 models that pilots won’t need additional training in ground-based simulators, which is expensive for airlines and disruptive to their schedules.
— Alison Sider and Robert Wall contributed to this article.

Write to Andy Pasztor at [email protected] and Andrew Tangel at [email protected]
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Old 24th Mar 2019, 01:55
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Originally Posted by jimjim1
I doubt very much it was a transmission/reception error on the BUS since that almost certainly has CRC error detection.
This is not correct. The error detection is a simple parity bit and so a bus error is not vanishingly unlikely.

ARINC 429 is pretty crude in the age of the interwebby
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Old 24th Mar 2019, 02:14
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Trim display and restricted sim availability

Two holes in the cheese:

​​​​Control surface position can be displayed on many ECAMs, along with flaps, spoilers, gear, etc. But where are trims shown besides on the wheel and knobs?

It may really help to show trim positions on the ECAM - and what is moving it when in motion: MAN, AP, STS, MCAS.

It might have helped the AF447 crew, especially if control stick/wheel disagree was displayed. But that would cost money and certification effort to develop.

A repeating theme in many posts is the expense, and consequential dearth, of sim sessions to explore the corners of the envelope. Crews are being trained to minimum standards because sims, and performance data in the corners of the envelope, cost money.

Now we see an imperative to develop new designs in a way that minimises, or even better eliminates, sim time.

The MBAs have succeeded at pinching carloads of pennies – but airframes are now outwitting the crews.
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Old 24th Mar 2019, 02:24
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Originally Posted by Loose rivets
I posted mentioning a previous link that stated that the rear (hidden) switch in each column had been removed from the MAX. If true, and it seems to be, it is a major change, inasmuch as a quick tug against a nose-down trim would not have remotely the same effect.

The changes to the two emergency cut out switches, mentioned again above, are extraordinarily misleading - if not covered in MAX conversion training.
The switches are still there & work as always, but do not stop MCAS.
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Old 24th Mar 2019, 02:42
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Originally Posted by BobM2
The switches are still there & work as always, but do not stop MCAS.
... and they can‘t because that would make the MCAS useless. MCAS is there to change the stick force at high AoA values. To maintain a high AoA at decreasing speed (w/o retrimming) you will need to pull pretty hard. That is exactly the situation where the trim inhibit switches are activated. If they would stop the MCAS it would never be activated in the desired part of the flight envelope.
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Old 24th Mar 2019, 02:48
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After Go!Go!Go! and bad process in design and certification, the rush now is to create a quickfix and use lobbying to push the planes back into the air without an extensive check and recertification.

This may not be smart: the losses during an extensive safety recheck would be painful but bearable. The effect of another "incident" might push Boeing heavily into the red.

It may be useful to blame "foreign pilot" error for every crash, but in the end mostly every plane flown outside the US is flown by a "foreign pilot", and foreign certification authorities might be more eager than the FAA to pursue the issue of certification of the Max after design changes from the previous 737 types.

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Old 24th Mar 2019, 03:18
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Originally Posted by mosquito88
Perfectly put.
Reliance on a single sensor driving a system that was not known to the crew and that could take over command of the aircraft is sheer madness (not to mention extreme negligence).
the last word of your post will be the crux of the coming legal battle. If found Negligent, there is no shield for a professional engineer (licensed).
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Old 24th Mar 2019, 05:39
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A key modification to limiting stabilizer commands is a revision that allows only one trim application for each new trigger of the MCAS system. Under the original design, the MCAS trims the aircraft nose down by moving the horizontal stabilizer up at 0.27 deg./sec. for 9.2 sec., stops for 5 sec., then trims nose down again for 9.2 sec., and continues to do so until the trim reaches the stabilizer travel limit or the crew intervenes. Boeing says that, as before, the crew will retain the capability to override the flight control law using either electric or manual trim, or by following the existing runaway stabilizer procedure and using the cutout switches as reinforced in the Operations Manual Bulletin issued on Nov. 6, 2018.

The enhanced software was demonstrated for the FAA on March 12, the day after the Civil Aviation Administration of China announced the first in a wave of 737 MAX groundings around the world; the FAA followed suit on March 13. Aviation Week was told that the software upgrade certification load, dubbed P12.1, was flown on the first 737-7 developmental aircraft, 1E001.

The greater part of the 1-hr. 20-min. test flight was flown at medium altitude between 13,500 and 17,350 ft. in a racetrack pattern over southwest Washington state. According to data from the flight-tracking website Flightradar24, the crew performed a series of high AOA maneuvers to validate the performance of the revised MCAS. These included at least six conducted during initial ascent, followed by descents from 17,000 to around 14,250 ft., during which speed dropped from more than 330 kt. to less than 180 kt.

The aircraft was then flown to 17,350 ft. and 265 kt. before pitching steeply nose down and recovering at around 15,900 ft. and 295 kt. The maneuver was repeated at a slower speed, before a further test point was conducted during which the 737 descended steeply from around 15,550 ft. to 13,500 while speed increased from 180 kt. to almost 270 kt. Two further steep descents and recoveries were then performed before the aircraft leveled off and returned to Seattle for landing.
Those were great test flights at higher altitudes. I read into the figures some steep descents of maybe 2000 ft even when the pilots presumably knew what to expect. I wonder if Boeing test pilots would like to do a test flight at about 1000ft or even 3000ft above ground (like ET302 or JT610 accidents) in the jump seat while some line pilots, who have not been told what the exercise is, are in the hot seats? Or is the new MCAS disabled until more than say 5000ft above ground? Also for what parameters will the repetitive trimming be restricted. And what will the authority limits of the trim units be and whether different at different speeds and altitudes. If MCAS disables itself for erroneous sensor input, if its moved trim then will it re-trim to a "neutral" or expect the pilots to break out the handles on the trim wheels?

It will be interesting to see the full details of the new MCAS.

Last edited by LandIT; 24th Mar 2019 at 09:43.
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Old 24th Mar 2019, 05:56
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Originally Posted by deltafox44
Airflow is horizontal only in level flight ! not in climb or descent
If by horizontal you mean at AoA ~ 0 degrees, that is very, very incorrect
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Old 24th Mar 2019, 06:20
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AoA vane question

Could someone familiar with the AoA vane and MCAS tell me what would happen if a bird strike jammed the vane in either an up or down condition?
Can the system detect a damaged sensor and if not, what would happen?
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Old 24th Mar 2019, 06:48
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Originally Posted by mosquito88
Could someone familiar with the AoA vane and MCAS tell me what would happen if a bird strike jammed the vane in either an up or down condition?
Can the system detect a damaged sensor and if not, what would happen?
In its certified form or yet to be released updated version? No one really knows, but I believe the PPRuNE brains trust would say something along the lines "it depends".

There would be many different failure scenario's, the AoA reported value could be frozen at its last known good position, it could detect the failure and report no value, and many other possibilities in between (erratic oscillations etc). The next question is the software side, and how much error checking and validation it does and how gracefully it handles anticipated failure modes.

Generally, the opinion (and Boeings own failure analysis) of the MCAS software is assumes the pilot will handle any system input error and disable the system via the stab trim via the cutout switches. This turned out to be a heroic assumption...

Seattle Times: Flawed analysis, failed oversight: How Boeing, FAA certified the suspect 737 MAX flight control system
System failed on a single sensor
The bottom line of Boeing’s System Safety Analysis with regard to MCAS was that, in normal flight, an activation of MCAS to the maximum assumed authority of 0.6 degrees was classified as only a “major failure,” meaning that it could cause physical distress to people on the plane, but not death.

In the case of an extreme maneuver, specifically when the plane is in a banked descending spiral, an activation of MCAS was classified as a “hazardous failure,meaning that it could cause serious or fatal injuries to a small number of passengers. That’s still one level below a “catastrophic failure,” which represents the loss of the plane with multiple fatalities.
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Old 24th Mar 2019, 08:26
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I just wonder why B737 (and B767 recently) nosedive into the ground every so often? Can't remember Airbuses nosediving recently.

B737 CL September 14, 2008 Perm - roll and nosedive just before approach
B737 CL November 17, 2013 Kazan - nosedive after GA
B737 NG March 19, 2016 Rostov - nosedive on final or after GA
B737 MAX October 29, 2018 Jakarta - nosedive after TO
B737 MAX March 10, 2019 Addis-Abeba - nosedive after TO

B767 23rd Feb 2019 Texas - nosedive just before approach
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Old 24th Mar 2019, 09:02
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Originally Posted by jimjim1
This is not correct. The error detection is a simple parity bit and so a bus error is not vanishingly unlikely.

ARINC 429 is pretty crude in the age of the interwebby
Can you verify this? This would be very crude early 1970th technology and with a Haming distance of 1 only protect against single bit failures. A two bit failure would create the next valid data. And there is no guarantee that any interference will only disturb 1 bit. Equaly likely is, that a sequence of bits are disturbed.
I still wonder where the 20 degrees constant offset in the Lion Air AOA sensor came from. See preliminary report. That’s not a stuck sensor.
If the Ethiopian will show a similar offset then there is another problem burried in their flight control system.


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Old 24th Mar 2019, 10:10
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That information is not hard to find https://en.wikipedia.org/wiki/ARINC_429

There is a lot of 1970s stuff in aviation, that should not be a surprise.
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Old 24th Mar 2019, 10:18
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I stopped reading this thread a long time ago, but can someone explain a point to an old, retired 737 driver? All 737s pitch up with the application of power; it's a consequence of the design. This one will pitch up more than most; again a consequence of the design. If the crew are made aware of this, is it really beyond the power of the human mind to be ready and correct the pitch? In other words, no need for this system at all.
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Old 24th Mar 2019, 10:43
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Originally Posted by Herod
I stopped reading this thread a long time ago, but can someone explain a point to an old, retired 737 driver? All 737s pitch up with the application of power; it's a consequence of the design. This one will pitch up more than most; again a consequence of the design. If the crew are made aware of this, is it really beyond the power of the human mind to be ready and correct the pitch? In other words, no need for this system at all.
To my understanding. There is a requirement of smth like 'linear pull': in the MAX, as the plane approaches stall, either pitch force on the stick, or force increment on the stick to pitch up, decreases and that's a big, uncertifiable drawback.
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Old 24th Mar 2019, 11:07
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WSJ:
U.S. air-safety regulators ... said the enhanced training, relying on self-guided interactive instruction on laptops, ...
Alright. The regulatory governmental body thinks, the cheapest possible means, ‘self-guided interactive instruction on laptops’ is actual training. Or better, even ENHANCED training. You can’t make this sh** up. No damn expensive instructors or simulators necessary. Is this still a safety minded world? Is everybody insane now? More catastrophies in the making. You can read it right there.
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Old 24th Mar 2019, 11:08
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Originally Posted by Herod
I stopped reading this thread a long time ago, but can someone explain a point to an old, retired 737 driver? All 737s pitch up with the application of power; it's a consequence of the design. This one will pitch up more than most; again a consequence of the design. If the crew are made aware of this, is it really beyond the power of the human mind to be ready and correct the pitch? In other words, no need for this system at all.
The reason for MCAS was stated by a previous poster. It is needed for purpose of certification. I reproduce the entire paragraph § 25.173, since I have not seen it in full in the thread.

AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

§ 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 V FC /M FC, 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.

The item that describes the specific details is § 25.175 Demonstration of static longitudinal stability.
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Old 24th Mar 2019, 11:22
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Originally Posted by jantar99
To my understanding. There is a requirement of smth like 'linear pull': in the MAX, as the plane approaches stall, either pitch force on the stick, or force increment on the stick to pitch up, decreases and that's a big, uncertifiable drawback.
I have read and understood all the certification requirements that led to MCAS. Can someone explain to a non-pilot: In what common circumstances would (edit badly worded question) the pilot of an aircraft actually want to raise the nose (end-edit) close to the stall angle, while flying with flaps up? High altitude turbulence avoidance or maneuvering? Tight turns at high bank angle?

Last edited by GordonR_Cape; 24th Mar 2019 at 12:36.
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Old 24th Mar 2019, 11:30
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Originally Posted by Euclideanplane
The reason for MCAS was stated by a previous poster. It is needed for purpose of certification. I reproduce the entire paragraph § 25.173, since I have not seen it in full in the thread.

AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

§ 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 V FC /M FC, 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.

The item that describes the specific details is § 25.175 Demonstration of static longitudinal stability.
It also allowed Boeing to claim that all that was need to transition to the Max was a short video presentation.
https://edition.cnn.com/2019/03/22/u...ntl/index.html
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