The system is designed to help bring the nose down in a stall. The stickshaker should in theory keep you from ever getting into that situation.

I don't think that was what the system was designed for. It was designed to prevent you from getting to stickshaker. At clean high AOA the aero effect of the nacelles adds nose up input and if you are hand flying your stick force will lesson while the nose continues up. MCAS adds that stick force artificially with downtrim.

Also remember this was designed to be same type as most of the other 73s operated by SW. if you don’t install a stickshaker you would have had to tell them about MCAS.

From below is what I understand, from what I have read:
Boeing wanted to make the MAX more fuel efficient. The more efficient engines are bigger, and don't fit under the 737 wing. They had to move the engines somewhat further towards the nose, to provide enough clearance. This new engine position disrupts the CG of the aircraft.

The engineers decided that the new CG could make it difficult to recover from a stall, so they added this system to automatically pitch the plane down when it sensed a stall...unfortunately the system is only connected to one of the AOA sensors, instead of both. And the pilots cannot override the software with the flight controls...their only choice is to cut off the power, and if they do it too late, the stabilizer could be moved too far for the pilots to recover.

Cliff,

Two points:
1: it's not a CofG thing. It's as 1W2A said: higher AoAs lead to a forward shift in the center of pressure, due to the position of the nacelles.
2: Once power to the pitch trim is cutoff using the pedestal switches, one merely reverts to manual trim using the big-ass trim wheel. In theory, that's the end of the problem.

See the attached link, which I found to be informative:
737 MAX - MCAS

Matt

Moving the engines forward moves the CG forward and would make stall recovery easier. The problem is they moved the thrust asis forward which causes a nose pitch up tendency with power application. This happens to most airframes with underslung engines to some degree. MCAS was designed to make the aircraft fly line earlier versions of the 737 to preserve the common type rating.

Seems like a bigger horizontal stabilizer with a bigger elevator or maybe replace both with a stabilator would be the definitive fix. The first would be expensive, the second really expensive, but either solution would be cheaper than what is going to be spent resolving these two accidents. Saying you are going to fix the problem by wiring in another AOA indicator and adding some more software just seems unacceptable.

When Beech was developing the King Air series throughout the years the FAA required three separate Type Certificates as the models grew and became more complex. Maybe the MAX needs to start from scratch.

Would it be logical to have the 737 max series jets flown as a separate type? Another words, pilots perhaps shouldn't cross-pollenate across the various series of B-737 aircraft. Fly the standard Guppies, or Fly the Max Guppies, but not both.

I have never been a big fan of 757 and 767 being flown as a common type. Not enough stuff in common....

I wonder why only one probe is tied to MCAS? That might be a single point of failure to a fairly critical system.

Now Ethiopian Airlines have the downloads from both the CVR and the
FDR. They are looking into it and may publish the “results”: Either put the blame on Boeing and their MAX 8, or admit their pilots and or mechanics screwed up. (Or a combo)
Not sure if Boeing, the FAA and the NTSB have the data yet.
(Boeing would probably be happy to publish their innocence if indeed pilot error or bad mx caused the crash)
Something completely surprising could of course also be the cause, a bomb, a fire or a highjacking, whatever:(
Standing by..

Where did you see / confirm this?




What is full nose down trim (how many degrees) on a 737 Max?

Read this and understand all.

https://www.seattletimes.com/busines...ajEOa2CxroB-x0

Still looking for factual confirmation that the jackscrew was found in full nose down position....

Check the hyperlink saying Ethiopian jackscrew found nose down embedded about a third of the way into the article. Or try about 50 other articles with google.

Nope, not there....

Second hit on google for Ethiopian airline jackscrew.

https://www.washingtonpost.com/world...=.3f67f66e4575

Nope, not there either...

This all your going to get from official sources.
You will have to wait for the pictures of the jackscrew if that's what your after.
https://www.faa.gov/news/updates/?newsId=93206

Dear NFnsquared,

We were going to wait until the report was finished but as you are not a trusting soul I feel I must reassure you. The jackscrew was discovered in nose down trim.

Love,

Minister Mgwell Mgwell DaDa
Air Minister for Ethiopia

Again, just asking Trip where he got his info about the jackscrew being found in the full nose down position...or was that a misstatement?

What would of happened if they left the flaps down longer, 1-3000’+ AGL, and done much of the climbout without the autopilot? Of course we’ll naturally keep that nose parked up to control airspeed.


Those 2 things and we wouldn’t be talking about this.

I know, hindsite is easy.

MCAS doesn’t work with the autopilot on. The whole point is to avoid pitching nose up at high AoA when hand flying. Also, if this is the same thing as the Lion Air incident autopilot was probably not an option.

The flight the night before the Lion Ait crash had stick shaker start at rotation, with associated stall warnings which leads one to believe the airspeed is unreliable. Once they climbed away and raised the flaps, MCAS started trimming nose down. The crew the night before used the stab trim cutout switches and landed.

Software update to the MCAS is like a band-aid solution for a band-aid solution. The 737 has grown too much to fit in the original type, IMO. The elevator should be redesigned to be able to overpower the full nose down stab trim as well as full nose up stab trim in a stall. Then there is no need for MCAS.

Yes it is, and it's been in several other media reports (which admittedly probably came from the same wire report).

That would take a long time and cost a vast amount of money, to develop, certify, and then retrofit. Even more money due to grounding losses from all the airlines that have the MAX. Would stall and possibly break the MAX program.

Dollars to donuts they come up with a better bandaid.

Reading comprehension fails one of us. Where does it say in that link (or any other link) that the jackscrew was found in FULL nose down trim?

Ah, semantics. I don't see where it says that, but what it says is...

"All we can say definitely is that the trim was in a position similar to the position found on the Lion Air airplane"

So if not full down, seriously out of trim in the nose down direction, of a magnitude known to have caused the plane to crash once before.

At one time Boeing was looking at developing a lighter weight 757. Think the number of passengers was to be about the same as the MAX is now. Not sure the MAX is really fixable without major airframe design changes. By the time you made those changes you would have.......a lighter weight 757.

The MAX will most likely be “fixed” with a software update and zero airframe modification.

But hey maybe you’re right and they’ll test and then retrofit new wings, landing gear, tail, and cockpit onto hundreds of planes to make “a lighter weight 757”.

My guess:

1. Comparator logic, so that MCAS uses data from BOTH AoA vanes. In the event of disagreement, it would either be inhibited, or an alert. Possibly a disable-switch added.

2. Mandatory sim-training where the MCAS runs away.

3. I think it will happen in phases. AoA mod will happen quickly...I believe it’s there, just needs to be modded in the software.

A disable switch would take a year to get delivered airplanes modded. New would include it.

Sim training: they’ll give them six months to train everyone.

Flying again by May 15.

Just a guess.

They are seriously looking at doing that right now. But a bigger plane, it would overlap perhaps the top end of the 737 range in pax but will have much longer range. Different plane for a different market niche. But they can't just cancel the MAX and tell everyone to buy a larger, more expensive plane which they haven't even designed yet... everyone would just buy NEOs instead. From a pilot and pax perspective, that would be great. From an American perspective, that would constitute a massive loss in US export dollars.

Still not clear if the NMA will even be launched, but it's looking highly possible in the next year.

Or just reopen the 757 line. The odds of Boeing ever delivering 5,000 of the MAX airplanes, or whatever the back-order number is, are not high. With the 757 you have adequate landing gear for the airframe, no preflattened nacelles, and no Rube Goldberg nose-down system wired in to the stabilizer trim mechanism. They won't do it of course. Makes too much sense. Boeing could call it the 757neo

It would take years to re-open and begin production... assuming they have the right documents and people to even be certifiable to do that.

Without a "NEO" update, it would fail miserably in fuel burn compared to the various A321NEO versions. That would take even more years and $.

Nobody would buy it, they'd just get on the airbus waiting list for NEOs.

Agreed.



1. Yes, something like that. I assume all sensors feed to a data bus of some sort? As I understand it, each of the 2 FCCs gets data from a single AOA sensor, not both. Wondering if the fix is for the active FCC to read from both AOAs or for the active FCC interact with the non-active FCC to compare AOA inputs?


2. Already done, but I know what you mean...


3. I would assume it could be done fairly quickly, assuming a central data bus or an easy interconnect between data busses which would make the fix purely a programming fix? That may be the fix that Boeing was about to push?



I assume a disable switch would just be a logic input to tell the active FCC to quit the MCAS routine?

They won’t do that because it’s ludicrous and makes zero sense. Like most of your posts on accident threads.

A very popular rumor is in 2005 or so Boeing offered a prominent purple cargo carrier brand new 757s for a very reasonable price in order to keep the line open. The airline said no thank you and the line closed. When that happens they destroy all the tools and dies and it is no longer possible to reopen the line. Several years later the same purple cargo carrier purchased about 120 worn out 757s and ended spending about the same amount per jet to update, standardize, and turn them into freighters.

Boeing may have destroyed the tooling, but I’d bet they still have all the engineering documents for them...

Can they do that, given that the plane will not pass Part 25 standards without MCAS?
Would FAA really approve a single AoA failure as "extremely improbable" (as required by P25).

I believe in the Seattle Times they already said that is what was in the works after lion air and before Ethiopia. Presumably that is the current software fix along with a fix to MCAS that only allows one two degree trim change instead of the continual two degree changes every ten seconds.

What happens with the system when the flap lockout mechanism doesn't work and the system actuates at lift-off with take-off flaps extended or on approach with the flaps extended? Those are high angle-of-attack situations.

What happens if the system doesn't work at all when the aircraft approaches a stall, especially at a high altitude?

Those obviously are not issues with other models of the 737 that don't have the system. There was an aircraft designer who famously said: "The parts you leave out never fail".

Thus the fix. The problem wasn’t the system is bad. The problem was a singled failed AOA indicator could activate it. The fix is it will take two to activate it. If both AOA indicators say you are stalled, you are probably stalled.