737 Max 8


Ethiopian airliner down in Africa

The autopilot disengaging with a out of trim condition will cause a more violent pitching moment…

The aircraft can be routinely flown closer to a stall in order to save money. It all works fine, until something goes wrong and it doesn’t…

In the case of MCAS it looks to me to be a victim of the success of the 737’s longevity. It’s probably the most versatile airframe ever built having survived 50+ years of power-plant evolution, geometrical stretching, role revision and load growth (GTWO has not-far-off doubled I think since the 100).

Then along comes the straw that breaks the camel’s back – a couple of engines that really required a new airframe design to get properly certified with comfortable aerodynamic margins. But such is the versatility of software these days that any shortfall in aerodynamic completeness can be handily compensated for…

To counteract the MCAS trim forwards you need to pull with some 60 kg of force, using both control columns, to stop the aircraft nosing into the ground…

The plane “digs in” with neutral controls, and further, it “pitches up” even with forward stick…

sims have very little fidelity in reproducing a actual fully stalled condition…

how do you tell in a limited timeframe whether MCAS is trying to save your life or trying to kill you…?

The only reason to put this software system in the plane is because of the bigger engines (that had to be placed in a different area of the wings), which can cause the aircraft to stall…

The new MAX aircraft have been stretched to have over 200 seats. This means the engines go further back causing propensity to stall…

Nowhere else in the original manual were there details on what the MCAS does, bad indications and how to turn it off were included…

I thought the issue was that the engines were relatively speaking, further forward and higher which leads to the stall?

It seems flicking the switches is the only real option, easier said than done when you’re hauling back 50Kgs amidst the disco and wondering WTF?..

Boeing are explicit about overuse of stabiliser trim
during the approach to stall recovery. Positioning the stabiliser in such a sense can severely reduce elevator authority – was this not the contributing factor in the FlyDubai 738 crash in Rostov?..

Big well done to Southwest Airlines Safety Department for retrofitting their Max’s with the optional head down AoA display after the Lion Air accident!..

One cannot overide manually, the system stays in and you have to motor the trim fwd electronically using the system.

Happened with Lion Air…

Have you read what FAA says? They can’t draw any conclusions…

Is there no definitive visual or auditory signal that MCAS is active?..

Every 737 has 2 Angle Of Attack indicators, and an OPTIONAL warning light for a difference in value between the two. SW have paid extra to display the actual AOA value displayed on the respective pilots instruments…

Correct, except the AOA disagree warning light is an optional extra on the 737 MAX, so not every 737 has it…

Common sense and basic principles of human engineering dictate that a system or application that creates this much uncertainty and confusion, even among experts in a discipline, is begging for redesign…

The Lion Air crash happened presumably because of a faulty AOA indicator…

It is a computer controlled solution to aerodynamic instability inherent in the design.

While computerized aerodynamic stabilization of inherently unstable new designs may be the trajectory of future, to apply it as a fix as we push 50 year old designs to new limits may prove to be a mistake…

737 MAX stabilizer cutout switches are guarded. With the guards in their normal, closed positions the switches are forced into the position that provides normal operation of the stabilizer. To cutout the stabilizer motor (i.e., disable electric trim from any source) the guards must be raised and the switches moved to the position that is only possible with the guards raised. Guarded switches of this sort provide two very strong levels of safety. First they make it very difficult/impossible to toggle the switch inadvertently as the guard must be raised before the switch can be toggled. Second they make the polarity of the switch very clear as normal operation position is the only one possible with the guard closed…


MCAS is implemented within the two Flight Control Computers (FCCs). The Left FCC uses the Left AOA sensor for MCAS and the Right FCC uses the Right AOA sensor for MCAS. Only one FCC operates at a time to provide MCAS commands. With electrical power to the FCCs maintained, the unit that provides MCAS changes between flights. In this manner, the AOA sensor that is used for MCAS changes with each flight…

10 seconds, or 2 degrees forward, for each operation of MCAS. And after 5 seconds, you get another 2 degrees of trim, until you end up with full forward trim. It was designed for slow speed, but if it happens inadvertently at high speed, you could be in the sh1t…

The report said that the Fly Dubai pilots trimmed forward for 10 seconds…

If the f/o was flying, he only had 200 hours. After flaps up, the stick shaker goes off, which is mighty disconcerning, and MCAS bungs in a load of trim. The captain cannot see why the trim is trimming, and the low-hours f/o has no clue (seen that many times). The captian thinks he has an airspeed problem and is stalling, and tells the f/o to lower the nose – which the f/o does rather easily, because he is holding a load of back pressure. MCAS then bungs in another load of trim, and the f/o is now really struggling with the controls – never having felt an aircraft behave like this (at this stage, you need about 30 kg of force to hold the aircraft level).

The captain is still convinced the airspeed is wrong and they may be stalling (stick shaker still going), and shouts “I have control”, but does not realise so much pitch force is necessary, so the aircraft instantly pitches forward into a steep dive. Captain is mighty startled by this – is this pitch down the result of a stall? He has forgotten all about the previous trim episodes, and just hauls back on the stick. But MCAS now gives another load of forward trim, which makes the aircraft completely unflyable (60 kg of force necessary on the stick). And here comes terra firma….

Probably the MCAS subsystem will enter the course books of engineering schools, as a textbook example of AS, artificial stupidity, a system designed to be stupid, when you actually need a smart system…

Which engineering workgroup at Boeing could in their sane minds design such a system, that is supposed to save you from a stall but instead decisively flies you into the ground?..

The 737 is an old aircraft with bits bolted on over the decades…

Two professional airline crews have been unable to prevent their aircraft from flying them into the ground/sea…

Aerodynamic forces increase with the square of airspeed…

The Lion crew kept the aircraft reasonably steady for 6 minutes after MCAS issues presented, continuously and manually counteracting the MCAS nose down events that occurred during that whole time. The crew knew they had a stabilizer runaway b/c they kept using the electric trim to correct it. They kept the aircraft basically level at 5000 feet for that 6 minute duration, until, for the last four MCAS nose down commands

The system was obiously never designed to recognise that the aircraft was not stalled…

Why was there not a line of code that says: if ASI greater than 210 kts, deactivate system?..

It’s a systemic issue based on the ever increasing demand for air travel globally and the real cost involved in properly training pilots. The current reality is that the focus is on increasingly complex automation instead of pilot training…

“As a precautionary measure, EASA has published today an Airworthiness Directive, effective as of 19:00 UTC, suspending all flight operations of all Boeing Model 737-8 MAX and 737-9 MAX aeroplanes in Europe…”

If Normal-law drops out because of input errors, the aircraft defaults to Alternate-law, which is a basic control system running on attitude and power…

Boeing effectively using the trimmer as a primary flight control – deliberately placing the aircraft out of trim.

Advertisements
This entry was posted in Technology Disasters and tagged , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s