jaysona

I'm not quite sure why you're referencing an 18-year old document and fail to see its relation to an airplane with an EIS of one year ago.
The Rockwell Collins IMA for the 7M8 has the AOA indicator.

Previous models did not have an AOA indicator, as BPs (Block Points) were release to address bugs, fixers, features etc, the AOA indicator was added, as of 2016 (iirc) the AOA is part of the display for the glass cockpits (previous models have no IMA) and is available as a retrofit option for operators that want to have it.

There is no point in comparing the 7M8 cockpit displays/avionics to previous models, as that is like comparing potatoes and oranges.

Stranger

More on the stealth differences in behavior between the NG and the Max... Relevant to the Lionair crash and presumably the AC fleet.

https://www.flightglobal.com/news/ar...in-737-453602/

RangerNS

Dons mirrored aviator glasses

WildcatYXU

The article doesn't mention the biggest problem - the reason why MCAS is there and why pulling back on the column doesn't stop the nose down trim. It is the shift of CG forward caused by having larger and heavier engines moved forward compared to 737 NG. That had negative impact on flight characteristics of the MAX. To fix that more horizontal stab authority would be necessary. That apparently didn't happen, hence the electronic band aid. Too bad it may turn the aircraft into a dive bomber.
https://www.seattletimes.com/busines...ticle_left_1.1

Stranger

Starting to look like Boeing may be in trouble with that mess. Press picking the thing up left and right. And in s way that does not inspire too much confidence.

Band aid indeed. Plus, the thing blew up in their face in the worst possible way. Largely of their own doing. First by solving their problem that way, which by itself is not reassuring, then by keeping the thing as discrete as they could. Then the crash.

Does not look good for the Max...

Stranger

Rereading this, it seems to me that you have it upside down, no? You move the mass center up front, the increased torque due to the negative lift on the horizontal stabilizer actually leads to an increase in the angle of attack. So to avoid stalling (as the aoa gets larger) they add this gimmick which is supposed to reduce the angle of attack.

Which is not quite as scary BTW. Not quite that the plane is inherently unstable and needs computer assistnce to make it safe.

canopus27

There's plenty of pilot related discussion about this issue over on pprune: https://www.pprune.org/rumours-news/...akarta-61.html

WildcatYXU

I know too little about aerodynamics to carry on a meaningful discussion, so only one remark: To maintain the same AOA with your CG shifted forward you need more negative lift from the horizontal stabilizer. To have that at the same speed and trim you need a larger stabilizer. That didn't happen. As a result the handling of the aircraft changed enough for Boeing to introduce an automated augmentation system.

Stranger

Actually this is not an issue of aerodynamics but stability. The two orques, of wing lift, and of stabilizer vertical lift, should balance each other. And if the mass center (CG) is ahead of the wings, you are right. But then the tendency will be for the aoa to get too low, and the protection would push up, not down?

The Lev

Actually from Boeing's perspective this blew up in the least worst possible way. Imagine for a moment that the same thing happened on an American Airlines flight. There's a good chance that the outcome would have been the same, but I have to believe that the FAA would have grounded the Max and the class action lawsuits would be piling up like crazy. 189 people dying in far-off Indonesia is not the same as 189 Americans. (Cynic's glasses removed).

From what I've read, the issue is not really the weight being further forward but the engine nacelles being larger and placed further forward. In normal flight this isn't a problem because the air is hitting the engines straight on, but as the angle of attack increases, the force of air against the bottom of the engines place more upward force on the wing than was the case with the NG. That upward pressure could cause the plane's nose to keep pushing higher until the aircraft stalls.


Bottom line is that Boeing didn't think it important to tell pilots about this even though the natural pilot's reaction of pulling up on the yoke would not work due to the new system they installed. It was all about getting the same type rating and being able to tell airlines that minimal cross-training would be required for experienced NG pilots. Anyone who had flown a 7M* could have been pushing up daisies right now thanks to the boys in Seattle.

WildcatYXU

As I wrote, I'm really out of my depth here and I didn't describe the problem properly. Here's Bjorn Fehrm's explanation:

https://leehamnews.com/2018/11/14/bo...to-the-pilots/

Stranger

So it seems the issue is actually due to extra lift from the engines... And a clean solution would have entailed redesigning the stabilizers. Instead of having a potentially/occasionally naturally unstable configuration, that depends upon computers to counterbalance the instability.

Stranger

Not just "not telling the pilots," but not telling customers who bought the plane, including AC. Marketing overriding serious safety-related technical issues. Once again the spin doctors won the day it seems.

24left

And many thought the half-lavs with sinks that spray water back at you, and the poorly designed galleys were the worst issues with these aircraft.

canopus27

I think those are the reasons why Boeing introduced the new system (MCAS), and then didn't tell anyone about it.

But it sounds like the primary reason the plane crashed is that the system is actually dependent on a single AoA detector. The speculation is that the AoA detector failed in the incident plane, and so MCAS system then decided to trim the nose down into the ground. If the pilots had known about the system (and now this includes the AC pilots who are continuing to fly the planes), then they may have been able to compensate and recover .... but even if they could, that's not an ideal state to be in. For a plane to drive significant aerodynamic changes based on a single non-redundant indicator, strikes me as a complete failure of engineering.

Not telling the pilots about it only compounds the problem.