In computer engineering we call this a 'byzantine failure', which could be discussed until the cows come home without a resolution. Seems to me that the only protection is a pilot that has done a lot of flying without the automation and a strong 'feel' for the aeroplane.

sounds like it...

https://edition.cnn.com/world/live-n...ash/index.html

In respect of the MCAS/certification requirement.

Gums, the 101 had a particular issue related to the T tail configuration, which gave endless entertainment and some great movies. The Max's issue stems from the nacelles of the LEAP donks, and they are destabilising at higher AOA. The engine weight is beneficial to static stability, lift from the nacelle forward of the Cp (sans nacelle) is not.The nacelle lift is fairly non linear to AOA, a substantial portion is induced by the vortex flow off the nacelle body at higher (not high for a 16 or 18 etc...). I suspect that the MLA is also playing into the equation, but don't have info on the criteria for the triggering of that, however the MLA whenever active reduces the static stability of the aircraft.

The Max is not the first Boeing or 737 to have some quirks, the classic STS is understood, but the NG did as well but was cured with good revision. The B767 had its own variant of quirks with 25.173 compliance which was cured aerodynamically by add ons and then by refined design.

The unfortunate state of affairs is that the envelope area that is protected by 25.173 that resulted in MCAS which has the potential to cause more serious handling problems is as much a compliance/box ticking exercise as it has to do with acceptable safety of flight. Without direct knowledge on the PSCP that was undertaken, that being proprietary to TBC, one can assume from the information released that the issue arises during a wind up turn profile at aft CG, which doesn't happen as often as takeoffs and landings occur with a single AOA vane as a sensor in the current system architecture. Put the reg in perspective, a century after Sperry starting handing out instruments for IMC flight... a Pitts usually has a little trim requirement, not much and is nice to fly; it sits where you point it until disturbed, dynamic stability is not an issue, VFR is fine, IFR is not too bad. Another single engine jet I fly only has a trim change for the gear and flap change; from 100KCAS to 450KCAS there is no appreciable trim change, and that is a delight to fly, VFR or IFR, it is statically weakly positive, but has good dynamic stability. Static stability was important in the days of lousy instruments, and hand flying, as a cue to what the driver was doing.

In a perfect world the planes would have linear responses that are just so, meeting the regs. To do that needs assistance or FBW, and the latter comes with it's own set of benefits and attendant risks. The B777 and 787 FBW systems are nice to fly, but are more importantly simple to revert to Cessna 150 state, but then MAS had a wild ride with even that system once upon a time. The Airbus FBW is nice for a pilot to fly when it is working properly, when it is not, it can be pretty entertaining getting the right result. [A logical weirdness in the 777 and 787 is that the plane is hand flown with a speed (AOA) referenced through the trim switch, but with the autothrottle in SPD mode as well... and underneath it all the planes still have a phugoid that is not taken out by the control law. That is just curious and makes the A320/330/340 etc nice to fly in comparison, other than in a crosswind].

FC84, great input.

§25.173 Static longitudinal stability.

Under the conditions specified in §25.175, the characteristics of the elevator control forces (including friction) must be as follows:
(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC/MFC,whichever is appropriate, or lower than the minimum speed for steady unstalled flight.
(b) The airspeed must return to within 10 percent of the original trim speed for the climb, approach, and landing conditions specified in §25.175 (a), (c), and (d), and must return to within 7.5 percent of the original trim speed for the cruising condition specified in §25.175(b), when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.
(c) The average gradient of the stable slope of the stick force versus speed curve may not be less than 1 pound for each 6 knots.
(d) Within the free return speed range specified in paragraph (b) of this section, it is permissible for the airplane, without control forces, to stabilize on speeds above or below the desired trim speeds if exceptional attention on the part of the pilot is not required to return to and maintain the desired trim speed and altitude.
[Amdt. 25-7, 30 FR 13117, Oct. 15, 1965]

Boeing apparently issued this ;

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. If the original elevated AOA condition persists, the MCAS function commands another incremental stabilizer

With refence to BOLDed statement (emphasis mine) can someone tell me what that means? By MAGNITUDE do they mean rate of MCAS trim input ( I though fixed rate of .27ish per per second.)?
Does it mean a range where it begins and stops?
What would be the upper and lower MACH numbers they are refering to?

I assumed it just ran pending the other conditions and the rate of trim input did not change

Magnitude is Mathematics jargon meaning size irrespective of direction.

The magnitude of 2 is 2.

The magnitude of -4 is 4.

In this case it means an amount of trim applied either up OR down.

Longer undercarriage to hold more wheels/brakes and to give more tail clearance? Room for big round engine UNDER the wing? Call it the Boeing 757?

I am so grateful for all the data Lion Air and the Indonesian Aviation authorities have provided so far. The world is a better place with their assistance.

Cost money compared to what?

What value did they put on grounding a fleet of aircraft, losing public confidence, 300 something deaths, subsequent lawsuits etc etc?

I suspect the heart of this issue is short term thinking and noone thinking about the long term because they only get paid in the short term.

I'd bet right now that a cleansheet 737 with 2019 technology/system suite and aerodynamics is looking alot cheaper than the mess they find themselves in today.

Hardly an exception, it's still too often a rule. But sweeping under the carpet can prove expensive.

https://cimg1.ibsrv.net/gimg/pprune....b1db2043a5.jpg

Sorry, couldn't resist.

Not as simple as that. MAX total order book value is somewhere around $600 billion - that is the size of the opportunity at risk long term if they didn't do the MAX.

These accidents, the groundings the lawsuits, the fallout, whatever subsequent band-aid they patch the plane up with (make no mistake, there will be one, and probably a political price with the rest of the world's regulators along with it), might cost several billion, or maybe into the tens or even towards a hundred (with lost orders), but that is still cheaper than abandoning the market to Airbus.

Fact is that the timing was probably the biggest factor - the neo came along right when Boeing were putting everything into fixing their 787 screw up, if they had gone for a cleansheet 737 they faced a huge execution risk and concurrently failing at 787 and new737 would have been very very bad.

Considering that they opted for the quick-cheap-easy solution (compared to cleansheet design) and still seem to have managed to mess it up, avoiding the cleansheet may yet prove to have been a wise decision.

I don't want to be in the shoe's of the Boeing guy who is going to sign off on this.

If they think they can fix what is clearly a hardware/sensor issue with an MCAS software update must live in dreamland.

But , tja, we live in an IT is GOD period.

This is clearly a HARDWARE issue, the software is secondary.

Salute Salvi !!!

I would laugh, but this is a sad time for commercial flying, and I have a hard time not screaming and throwing things.

Only time I was ever surprised in peacetime flying when something happened was when one leading edge flap folcded up but I could keep going straight ahead and finally got the sucker around to land it. Well, I did have a reversed aileron-rudder interconnect wire connection in the VooDoo one day over a decade before , but the nose moving opposite the roll command is an easy one to detect.

Gums....

Regarding how to ' handle' faulty sensors re inertial/GPS systems

See pages 40 and 41 on 787 v 777 features. One wonders why such was not incorporated in MAX ?

http://www.ata-divisions.org/S_TD/pd...ngtheB-787.pdf

•Calculated from angle of attack and inertial data
-AOA –voted dual sensors plus inertial data
-Accurate Coefficient of Lift (CL)
-Airplane Mass from FMC -Validated after Takeoff
•Algorithm developed for enhanced stall protection
•Avoid displaying data known to be bad
-Loss of valid voted VCAS
= Display synthetic airspeed VSYN
-Loss of valid voted PSTATIC= Display GPS altitude

AOA from inertial data?
 

This keeps coming up... I don't understand how inertial data can tell you anything about AOA, unless you make the assumption that the air outside the aircraft is stationary with respect to the inertial frame of reference, which seems like a particularly bad assumption to make.

Click on the link in the post you quoted from. It doesn't say what you think it does.

Possibly using pitch rate information to smooth and/or interpolate the sensor readings? The IVSI does something like that.

everything below is about LION AIR:

1. i see no evidence you can't disable MCAS with stab trim cutout. this is the bottom line fix that works even when all else fails. i have yet to see it won't work or didn't work in any of these accidents, it just wasn't tried.
2. i see no evidence that MCAS didn't perform *as designed* in response to an inaccurate indication of a stall based on a flawed AOA sensor. that's a software response to a hardware failure.
3. Boeing has already stated the coming fix to the software will: 1) have MCAS compare both AOA sensors and require them to match prior to any application of trim 2) have a visual alert appear to the pilots showing the MCAS application and 3) disable the ability of MCAS to apply more than a certain amount of total trim, a value which can be overcome by pilots with yoke force. that seems comprehensive in terms of a fix that would have prevented the lion air accident from happening.

i see ZERO reason the MCAS issue wouldn't be resolved by the coming fix even for pilots who don't understand the proper use of the stab trim cutout switches but of course we have to wait and see what the evidence shows with this weeks tradgedy.

the point is that while what you say is correct, the loss of Lion's Max show that the real world is more complex than a simple switch flick, on the day it didn't happen. The crew there were missing information.

Wind forward 5 months, and with the new knowledge and AD etc, we see a likely repeat of the deal in Addis. A simple switch flick didn't happen, or didn't permit recovery in time.

Sitting in a simulator and doing a procedure is slightly different to confronting a sudden life threatening, time critical event even when the cure is known.

https://theaircurrent.com/aviation-s...n-the-737-max/

There is an optional module that will notify the pilots that the AoA sensors are out of agreement. It should be mandatory with MCAS but is optional so that it gets around grandfathering rules. Sheer bloody mindedness.

I respect both fdr and gums's opinions here and I am reluctant to criticize fellow pilots, in particular the Lion Air crew who at the time did not know of the existence of MCAS, none of us did. However there were fixes to the Lion Air disaster, fixes the previous crew did find but in the over ten minutes of MCAS engagement for Lion Air that accident crew did not. This latest crash, which has yet to be proven is related to MCAS, flew for last I saw at least six minutes. The MCAS system is flawed but I struggle to blame all responsibility on the jet alone *if* these were caused by MCAS, as we need to be honest and look at crew make-up closely. But for the grace of god go I. Hopefully governments, manufacturers and pilots all learn from this.

The issue is, was this a needless risk. Boeing aleady knows how to make use of redundant information from AoA sensors yet it didn't do so in this case.

CB737;

the debris field in Addis indicates that on the day, prior knowledge didn't alter the outcome effectively. The individual may be easily blamed post hoc, that is the way of the world, however, in this case one can assume that the flight crew had a vested interest in having a boring day and not making headlines, yet it didn't end up that way. The fault that occurs with the MCAS has defeated two crews to date. ET's FDR, CVR and debris evidence will show whether the crew got the stab cutout switches in the sequence. Centaurus' comments and the associated thread on aerodynamic load reduction on the stab is quite possibly the missing piece in both of these events.

The certification requirement doesn't provide a guarantee of elevator authority being able to always offset an incorrect stabiliser setting. 25.255 and 25.665 cover the trim case in general, however the setup for show compliance is not the type of event that occurred. 25.672 covers stability augmentation system requirements and is probably going to get an airing in court in the near future, each paragraph is going to be topical. Boeing, Airbus, Cessna and various other aircraft builders have come across events where the stab trim has compromised controllability. Boeing, FAA SEA ACO/TAD have competent people in their programs, finding latent failures before an event is hard, it is much easier afterwards, and ET's loss speaks loudly that more is to be learnt here in order to reliably defend operation.

Salute Canyon !

No problem, man. There's a lot more layers in this onion to peel back

There are human factors, fault analysis tree problems, crew training or lack thereof, actual implementation of the kludge to get certification, and then management decisions and then FAA procedures that gave the MAX a pass and then airline flight crew education/training, and then........

Gums sends...

The story is well known within Boeing - Boeing never wanted to do the MAX, work had been ongoing on a 737 replacement aircraft for years. If the 787 hadn't been botched so badly, there is a good chance the 737 replacement would have been launched prior to the A320 NEO. But resources (both manpower and money) were spread thin by the 787 and the 747-8 development. So Airbus beat Boeing to the punch with the NEO - which was selling like the proverbial hotcakes. A new aircraft would have taken at least two years longer than the MAX, and then figure at least two more years to get up to the 50-60 aircraft production rate. That's ~2000 NEO aircraft that Airbus would deliver before Boeing could effectively respond if they went the route of a new aircraft instead of the MAX. And that was simply untenable to Boeing.

What Boeing still has going for it is the NMA (and the MAX fiasco might encourage Boeing to launch the NMA sooner - especially if MAX orders start going away) - the plan for the NMA has been to cover the range from 180 - 250 seats. So potentially a viable alternative to the 737-8/9/10 MAX if they can keep the recurring costs and operating costs down.

thats why it takes more than a simple comparison a third ' party' is needed such as inertial, or position sensors.

You're not wrong.

But the optional "AOA DISAGREE" warning on the Max only alerts if the disparity between the two exceeds 10°. That would, of course, have trapped the 20° discrepancy on the Lion Air flight.

And now about Boeing wunnerful quality control from WSJ- off this topic but IMO does fit in with this mess. CEO and several PR and mid management types need "to spend more time with family" PR code for brass being FIRED !

CNN; "Air Force Roper emphasized to reporters that while the issue of the material and objects -- known as Foreign Object Debris, or FOD -- being left inside an aircraft as it comes off the production line is not a design or safety risk, it is a matter of great concern to the military"

lol, I remember, after a D check somewhere Far East, our techs found a flashlight in the stabilizer, 2 wooden planks in the #2 fuel tank which while floating around were bouncing off wiring and pumps etc(B744), guess isn't a safety issue in the US Air Force....

When did the USAF start operating B744s ?

I guess not pulling the pins on the ejection seats is not a safety risk either by that standard. :mad:

As Dave stated , you are not wrong.

That being said, take into account both the pitot and static ports...so much attention to the pitot, and none to the static...you cant have a pitot without a static...
As an example, if the port pitot is shielded due to crabbing, so is the port static. the starboard pitot and static are overexposed.

Think about the readings using the port pitot with the port and starboard static...in a crosswind situation.
While the pitot are mounted close to the nose, the static are further back, compounding the issue..

this is a very complex dance.


https://cimg0.ibsrv.net/gimg/pprune....b67906204a.png
https://cimg6.ibsrv.net/gimg/pprune....9615fb7eb5.jpg

she's sooo happy! Luv the AOA indicators..highspeed pushback or early indication of the nosedown problem :}

https://cimg6.ibsrv.net/gimg/pprune....08f89d405b.jpg

The flow over the nose area is dependent on alpha and beta angles. A disagreement trigger value between AOA vanes can be set from test information and estimated fairly accurately by RANS or preferably DES type CFD to model the upwash changes. The mapped values could be used to correct in all cases as well. Vanes do fail, I paid for 2 in a couple of years with just one B737CL. Alternative sensing can be achieved by static vents and mapping, it is more reliable than the vane, but still can be affected adversely by contamination. slickest variant of those got out of sorts in Guam and cost the USAF a bundle in one smoking hole. Sensors fail, (how many of our cars have CELs on right now?)

actually the B2 was rebuilt and put back in service ..:cool: