The MAX has larger engines than previous 737s, and they are in a slightly different position. As a result, the plane has a tendency to pitch its nose up. To keep that from getting out of control if pilots flying manually aren’t attentive, MCAS automatically pushes the nose down if the sensor says the nose is too high.
In other words, Boeing fixed a hardware flaw with software. I am no aeronautical engineer, but this seems wrong to me. The hardware needs to be correct in and of itself. The software layer should be for enhancing the capabilities of the hardware, not for fixing fundamental flaws in hardware.
Not a really a hardware flaw--a design choice/hardware compromise so that existing 737 infrastructure could be used. The low ground clearance of a 737 is one of its main selling points. It's customers have a large investment in infrastructure around this capability--Think of things like loading ramps, luggage carts, servicing vehicles, etc.
So in other words they designed it this way in order to make the 737 MAX is cheaper to operate, and therefore easier to sell. That's terrible. Boeing traded off safety for profits.
What's more, this software fix depends on 1 out of 1 sensor inputs. There's no redundancy or conflict detection, if the pilot is flying the plane it uses the sensor on the left, if the copilot is flying the plane it uses the sensor on the right. This is a safety-critical system with absolutely no redundancy at all.
(Boeing would sell you a third AoA sensor and the AoA Disagree readout as an optional upgrade though! So it's not like they didn't think about it, they just didn't care enough to include it in the base spec.)
Yes cost is a factor. The alternative might not be feasible economically. I don't think the failure here was reusing the 737 design, but the downstream due diligence of implying no significant changes. I also think airline training is a factor--both Boeing for the new systems and the airliners because runaway stabilizer trim has been in the aircraft emergency checklist for over 50 years and every pilot should know it. That same procedure would have saved these planes.
> I also think airline training is a factor--both Boeing for the new systems and the airliners because runaway stabilizer trim has been in the aircraft emergency checklist for over 50 years and every pilot should know it. That same procedure would have saved these planes.
While training is absolutely one (of many) factors in these crashes, it's worth noting that while the runaway stabilizer checklist response would save this plane, the symptoms of this runaway MCAS issue DO NOT MATCH those of a "normal" runaway stabilizer as pilots train on it in simulator.
Essentially, pilots are being called upon to recall a trained response based on input which is significantly different from any that they've seen in training. Other flight logs on Lion Air prior to the crash show that even when the pilots correctly hit upon flipping the stabilizer trim cut out, it took them minutes to realize that was the solution, and they only fully confirmed that when they tried turning it back on, experienced another pushover, and then cut it out for good.
Boeing's assertion that there was no need for additional simulator training for the Max series is clearly incorrect -- even in non-fatal incidents pilots have demonstrably and in multiple cases not been able to correctly recognize the MCAS runaway as a kind of Stabilizer Runaway without spending time searching for and running multiple checklists.
Sacrificing safety in order to reduce cost is unjustifiable. When you design a multi-layer system, the higher layers should be for enhanced functionalities, not for fixing flaws in lower layers. Boeing designed flawed hardware (yes, it was intentional but that doesn't mean it is not a flaw) and tried to fix the flaw in software.
Then Boeing supplied a flight manual that a pilot described as 'inadequate and almost criminally insufficient', in order to convince customers that moving from older 737s to the MAX does not require extensive retraining. All in all, there is ample evidence that Boeing put profits above safety.
The MAX has larger engines than previous 737s, and they are in a slightly different position. As a result, the plane has a tendency to pitch its nose up. To keep that from getting out of control if pilots flying manually aren’t attentive, MCAS automatically pushes the nose down if the sensor says the nose is too high.
See: https://www.wsj.com/articles/what-you-need-to-know-about-fly...
In other words, Boeing fixed a hardware flaw with software. I am no aeronautical engineer, but this seems wrong to me. The hardware needs to be correct in and of itself. The software layer should be for enhancing the capabilities of the hardware, not for fixing fundamental flaws in hardware.