zeroptzero

Sunwing Airlines in Canada has made a last minute change to ground their 737-8 max planes, great news for us, I never thought I'd be so happy to ride on an older plan, lol, yippee !

cosmomiller

Thanks. I have been boning up a little on the systems and discovered an easter egg that may be a factor in this investigation. The Boeing 737 is an older design that has endured through the years. Constant updates have made it a moneymaker. Think how long Ford kept the Crown Victoria around. Little updates and efforts to market it as a police cruiser made Ford a bunch of money. The R&D for that car were done a long time ago. Boeing has done the same. However, the devil is in the details.

Improvements in engines precipitated a necessary design change to mount the engines a little further out on the wings. The size difference also meant the thrust line was further down from the wing. That created a strong pitch up moment when the now more powerful engines spooled up. That created an environment for increased stalls. So Boeing came up with an automatic anti-stall system called the Maneuvering Characteristics Augmentation System or MCAS for short. This system is designed to automatically correct the flight path when it detects the aircraft approaching a critical flight envelope limit. As I mentioned, this system relies on an AOA or angle of attack (relative wind to the chord of the airfoil) of a SINGLE sensor. If that sensor reports erroneous data, the output from the computer will be erroneous. The big change Boeing has in its software is adding a variety of sensors. However, there is something else.

The MCAS system is designed to kick in automatically when the plane is flown manually. It does not have to "kick" in when the autopilot is on because the autopilot is supposed to take all of these input into account. (Autopilots will usually kick off if certain limits or aircraft upsets occur-the plane basically says "this is beyond my abilities, you Mr Pilot have it") If the plane is being flown manually, as is most likely for the Ethiopian flight (weather was perfect and the copilot needed time) the MCAS could have been activated from a faulty AOA sensor. The initial reaction from the pilot flying would be to depress the autopilot disconnect button/switches on the yoke but again, the autopilot was not on! This would have led to a "startle" factor. Now both pilots are fighting the plane trying to pull up or back on the yoke. The airplane is increasing in its nose down to the point beyond control. I do not know if the trim kill switches will prevent the MCAS system from working. If they do not, it is (was) a fatal flaw.

Another real world example. Airbus also has a system to make the aircraft "stall proof". I won't get into the details but the several FMS (Flight Management System) computers combined with lots of sensors and IRS (Inertial Reference Systems-laser ring gyros the size of quarters) all work in symphony to keep the plane working in the operating envelope designed for passenger transport. After all it is a transport plane and not a fighter. Each phase of flight has its own computer code. In this case the phase of flight that "captures" an altitude when programed, just happened NOT to have that Alpha protection inserted. (Alt *-called alt star which appears on your display during that phase of flight) That detail was missed by the engineers. During a demonstration in Toulouse France, an A330, flown by Airbus test pilots, was demonstrating the "stall proof" characteristics to a group of observers on the ground. They were simulating a single engine (engine out) profile. They were intentionally flying low and slow, the opposite of what professional pilots would do in an actual similar condition. Airbus was attempting to demonstrate that even if the pilots did the imprudent thing, the airplane would save them from their errors. The problem occurred during an Alt* level off at low altitude. The plane stalled and impacted the ground killing all aboard. They discovered the vaunted stall proof design was absent in that one small phase of flight. Physics took over. Back to the drawing boards to insert better code. It did not make the news, really, because it was not in passenger service.

Chuck S

Emergency Airworthiness Directive 2018-23-51 was issued last year for the 737-8 and -9 aircraft . Not sure why this was not acted on unless these are different aircraft. Looks like what happened here.

Don't you love kinder-gentler terms line "possible impact with terrain" rather than more honest brutal terms like "crash." -- Chuck

http://rgl.faa.gov/Regulatory_and_Gu..._Emergency.pdf

MAGGIEMAE

cosmomiller

[QUOTE=Chuck S;24577181]

Don't you love kinder-gentler terms line "possible impact with terrain" rather than more honest brutal terms like "crash."

-- Chuck
I suspect many professions have "sterile" acronyms. We have another called CFIT which stand for: Controlled flight into terrain. Translation: someone flew a perfectly good airplane into the ground without realizing it.

ralper

I didn't want to push this thread into the Politics forum so I just started a thread in politics about why the FAA hasn't grounded the plane. If you're a member go into politics and add your thoughts.

windhund116

Cosmo, is it CFIT or uncontrolled flight into terrain --- in the case of Lion Air?

Thanks!

ralper

I agree. An excellent writeup.

jukngene

An interested article that essentially amplifies what Cosmo posted: https://airfactsjournal.com/2019/03/...mAA-kBPtAZU8IM

dlq04

Financial Times: US bows to international pressure and grounds Boeing 737 Max