Lionair 610 crash

[AviatorInsight]

As in not enough aerodynamic capability to rescue the pitch attitude in the time /altitude remaining. Or the correction would break the aircraft?

I don’t think there would be enough authority. The elevators are tiny compared to the massive stabiliser.

 

[jb747]

As in not enough aerodynamic capability to rescue the pitch attitude in the time /altitude remaining. Or the correction would break the aircraft?

The trim would be overriding the elevator. So, full nose down trim, and full nose up elevator....the nose would go down.

Do pilots ever tell management to not buy certain electronics enhancements in new purchases?

Do management ever listen? The line pilots are expected to simply take whatever they are given.

 

[Quickstatus]

What is supposed to happen to the stabiliser trim during the 5 sec period?.

 

[jb747]

What is supposed to happen to the stabiliser trim during the 5 sec period?.

From what I can gather, it should do nothing by itself in that period, but it could be moved by the normal trim switches. The 5 seconds also appears to restart each time a manual trim input happens.

 

[fairbasa]

Some more info from Boeing explaining the background for the MCAS on the MAX:

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Last week the FAA issued Emergency Airworthiness Directive 2018-23-51 that is applicable to the MAX-8 and MAX-9 aircraft only. This AD is not applicable to the NG. The AD addresses a possible failure mode on the MAX where erroneous Angle of Attack (AoA) signals can cause the stabiliser to drive towards a nose down position. During certification stall testing it was found that due to the larger engine nacelles the MAX tended to pitch up during the stall exasperating the stalled condition. To address this issue Boeing introduced the Manoeuvre Control Augmentation System (MCAS). The MCAS system commands the stabiliser nose down to improve longitudinal stability during manual flight with flaps up at high angles of attack approaching the stall, or during steep turns with high load factors.

The MCAS function becomes active when the airplane Angle of Attack exceeds a threshold based on airspeed and altitude. Stabilizer incremental commands are limited to 2.5 degrees and are provided at a rate of 0.27 degrees per second. The magnitude of the stabilizer input is lower at high Mach number and greater at low Mach numbers. The function is reset once angle of attack falls below the Angle of Attack threshold or if manual stabilizer commands are provided by the flight crew. The AD addresses the case where an erroneous AoA signal on the on-side FCC causes the stabiliser trim to drive nose down during the normal flight regime when in manual flight.

It is of course possible for the NG AoA probes to fail or provide erroneous signals. This may result in continuous or intermittent stick shaker on the affected side only, minimum speed bar (red and black) on the affected side only, inability to engage the autopilot, automatic disengagement of the autopilot, IAS DISAGREE, ALT DISAGREE and illumination of the FEEL DIFF PRESS light. However as the NG does not have MCAS installed the stabiliser will not drive nose down and there should be no increase in nose down control forces
-----

So Boeing introduced a system designed to stop a stall induced by the pitch-up moment caused by the MAX's larger more powerful engines, but instead when fed erroneous data it actually pitched down without a high AoA and crashed the plane...

 

[coriander]

Exasperating is not the right word..........

 

[fairbasa]

Exasperating is not the right word..........

Yes, I think they were looking for exascerbating

 

[coriander]

Or even exacerbating.....

Nevertheless, the PR spinners should have a basic command of English.

 

[Phil888]

The trim would be overriding the elevator. So, full nose down trim, and full nose up elevator....the nose would go down.



Do management ever listen? The line pilots are expected to simply take whatever they are given.

Good Morning JB first post on here so very much a posting boggy - reading this thread A sense of deja vu arrises comparing to early Airbus automation, and the lack of intuitive understanding (“what’s it doing?”) which featured in so many of their early accidents.. Turning now to the MAX8 differences -What will be interesting will be to see if the 737MAX simulators replicate this high AOA trimming during stall training.

I also am curious to see the FAAs input regarding this. Were they aware of the change ?

Interesting that the crew were hand flying through 5000ft. Maybe this problem had been evident on other flights but the autopilot (being engaged) masked it. Sources said Boeing risk assessment team felt the chances of the MCAS going off in flight were so remote, they felt an explanation of the system was unnecessary.

Really? Denying flight crew system knowledge? If True this is dreadful.Aviation has come a long way, but it seems some (manufacturers, risk assessment teams and lawyers) have forgotten some of the lessons learned and recorded in blood

 

[Deleted member 29185]

Welcome to AFF @Phil888

 

[AviatorInsight]

Interesting that the crew were hand flying through 5000ft. Maybe this problem had been evident on other flights but the autopilot (being engaged) masked it.

Why is that interesting? I regularly hand fly until above 10,000ft, especially when the departure has a few turns in it. Why let the A/P have all the fun on a complete CAVOK day? In any case, if they had an airspeed unreliable situation to deal with first, then the memory items are to disengage the A/P and A/T and even turn the FDs off. You then set an attitude and power setting according to your flap state. Flaps up is 4º and 75% N1. This will give you a slight climb at low altitudes until you can get to the checklist and then in the back of the QRH is all the power settings and attitudes for the segment of flight that you want.

The MCAS is only designed to work when the A/P is off, so it couldn't have been masked by the A/P on earlier flights. There needs to be certain parameters for it to work, most likely with an airspeed/altitude disagree, or AoA disagree. If these conditions are present, the book says to revert to manual flight.

Sources said Boeing risk assessment team felt the chances of the MCAS going off in flight were so remote, they felt an explanation of the system was unnecessary.

I suspect this will be implemented in the next update into all the manuals and more than likely into our cyclics once we get he MAX sim. Our manuals made no mention of it, nor in our differences package that we received from the company.

 

[jb747]

Even on the 380, the guys regularly hand fly it....

Whilst everyone has locked in to the MCAS system, remember that nothing is really known, and all of this is conjecture.

 

[AviatorInsight]

Some more info from Boeing explaining the background for the MCAS on the MAX:

So Boeing introduced a system designed to stop a stall induced by the pitch-up moment caused by the MAX's larger more powerful engines, but instead when fed erroneous data it actually pitched down without a high AoA and crashed the plane...

My understanding of that statement is that they tried to make the MCAS behave like a stick pusher (without it actually being installed on the yoke). So they got the stick shaker (caused by the airspeed unreliable?) then an AoA disagree in which case the MCAS kicked in and trimmed nose down.

 

[jb747]

I just can't help but wonder, 'what on earth were Boeing thinking'. Basic students are told never to fly with trim. You move the controls, and then trim out the residual force...not the other way around.

 

[Phil888]

Whilst everyone has locked in to the MCAS system, remember that nothing is really known, and all of this is conjecture.

Agree , fingers and toes cossed in hope of the CVR being found and usefull to the investigators

 

[fairbasa]

I just can't help but wonder, 'what on earth were Boeing thinking'. Basic students are told never to fly with trim. You move the controls, and then trim out the residual force...not the other way around.

But what if that was the only way of getting it certified?

Throw in a band-aid patch for a situation that is pretty unlikely to occur anyway, or back to the drawing board for some fairly significant design changes?

 

[jb747]

But what if that was the only way of getting it certified?

Well, perhaps in that case it did not deserve to be certified.

Throw in a band-aid patch for a situation that is pretty unlikely to occur anyway, or back to the drawing board for some fairly significant design changes?

I'm not terribly big on 'unlikely situations'. Eventually some poor sod gets stuck with having to deal with them.

 

[Deleted member 29185]

Throw in a band-aid patch for a situation that is pretty unlikely to occur anyway, or back to the drawing board for some fairly significant design changes?

It's far easier to deal with solutions in design phase than investigation stage. From what I've read here, there appears to be some quite simple solutions like triplicate sensors (with basic programming could likely resolve the issue of a faulty sensor without much ado). I can't see where that involves 'significant design changes" as 99% of the logic preexists.

 

[fairbasa]

It's far easier to deal with solutions in design phase than investigation stage. From what I've read here, there appears to be some quite simple solutions like triplicate sensors (with basic programming could likely resolve the issue of a faulty sensor without much ado). I can't see where that involves 'significant design changes" as 99% of the logic preexists.

Sorry if I was unclear, I was referring to JB's comments about the philosophy behind the MCAS system and why it exists at all, rather than just the inputs it's fed by.

The 737 was originally designed with turbojets in mind and is quite low to the ground. When the much larger turbofans came along they had to shift the engines up and forward on the wing to provide sufficient ground clearance. Now with the MAX they've thrown even bigger more powerful turbofans on so they've had to lengthen the landing gear and again move the engines up and further forward on the wings. This seems to have created undesirable handling characteristics in certain scenarios which Boeing are trying to overcome with bandaid electronic fixes which run counter to how pilots are taught to fly the plane and use trim (as JB stated).

Triplicating sensors is another control you can add to help ensure the MCAS acts only when it's intended to, but it won't resolve the actual hazard (the undesirable handling characteristics). Only a fundamental re-design could achieve that.

 

[Deleted member 29185]

but it won't resolve the actual hazard (the undesirable handling characteristics). Only a fundamental re-design could achieve that.

Many thanks for the explanation. I find it perturbing I guess, that even base level tradespeople are taught the hierarchy of controls which places elimination of the hazard as the highest and most desired control measure. I guess the almighty dollar is playing more than a small part in all this.