Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

[MurphyWasRight]

Originally Posted by Smythe

Actually, yes, you can, and the 767 tanker does compare the AoA vane with the gyros. Most unmanned ac do not have AoA vanes, and rely on the inertial system.

Interesting paper showing the results of using different algorithms to estimate AoA

http://www.tc.faa.gov/its/worldpac/techrpt/tc16-52.pdf

Always amused by the CAT designations...from the draft FSB
Aircraft Category
B-737 C
B-737-CL C
B-737-600/700 C (even a 700 at CAT C is a struggle)
B-737-800/900/900ER C or D (CAT C?)
B-737-MAX C or D (CAT C?)

Thanks for the link, very helpful since it provides descriptions and resuls for of a number of approaches, although the classic vane sensor is not included. Have not read in depth yet but did notice this:

AOA DERIVED FROM INERTIAL MEASUREMENTS A third method of estimating AoA was briefly investigated. This consisted of determining the angular separation between aircraft body X-axis pointing angle and flight-path angle, resolved into the aircraft’s plane of symmetry (in level flight, the difference between pitch attitude and vertical flight-path angle). This estimate is shown on some of the AoA comparison plots but compared poorly to the sensed, derived, and calibrated AoA, primarily due to not having a good estimate of vertical flight-path angle.

The other algorithms include a number of other parameters in the mix, seems that inertial sensors (gyros and accelerometers) alone can't provide needed data.

Keep thinking the best thing is to have as many different sensor technologies as possible with intelligent integration and cross checking of them all.
This would (at first at least) not require critical level software if it was done as a separate advisory/diagnostic function.

[Loose rivets]

slacktide: #740

Utterly different? Disagree. On the 737 NG, there is also a piece of software also has control of the most powerful flying control surface. That piece of software is called STS. In fact based on statements in the most recent draft FAA FSB report on the MAX, MCAS is a sub-functionalty of STS.

Fair comment.

Not part of the 'argument', but thoughts going back to the STS seemingly working in reverse.

[slacktide]

Originally Posted by Smythe

Actually, yes, you can, and the 767 tanker does compare the AoA vane with the gyros.

No, it does not. If you believe that it does, please provide a published reference.

Although you can use the indicated airspeed, groundspeed, pitch angle, and rate of climb to try to estimate AoA, the results are subject to the cumulative errors associated with each individual measurement. Additionally, as described in the article, the computed AoA diverges from the actual AoA as you approach stall, which is exactly where you need accurate AoA the most. The linked article chalks this up to unmodeled forces and moments in their algorithm, meaning their method can only ever be an estimation.

One of the most critical problems with an AoA computation algorithm is that it can only tell you what your AoA WAS, based on previous airdata measurements. Additionally, an unchanging atmosphere is assumed. They cannot tell if the aircraft is encountering an updraft or a downdraft, or is descending through a shear between air masses with two different wind directions, both of which will change the actual AoA. The derived AoA systems are extremely laggy compared to direct measuring devices. I have flown behind the Aspen "derived AoA" described in the article, and I do not plan on spending the extra $2000 on that option when I do my own Aspen installation later this year. I am considering the Alpha Systems pressure-based direct measure AOA probe and heads-up display. I've flown behind that in a friend's plane, and found it to be responsive, and the HUD was actually useful compared the Aspen indicator that is way outside of your VMC scan. Lots of good videos of that Alpha Systems AoA in action if you search YouTube for "Backcountry 182"

[Smythe]

No, it does not. If you believe that it does, please provide a published reference.

Boeing spokesmen declined to elaborate on which sensor inputs are used to provide the data in the tanker design. The options include using data from the angle of attack vanes on both sides of the cockpit, or an angle of attack vane and inertial gyroscope.

https://www.mro-network.com/airframe...d-pitch-system

The other algorithms include a number of other parameters in the mix, seems that inertial sensors (gyros and accelerometers) alone can't provide needed data.

Concur, I think, with all of this, that additional sensors are needed to augment the algorithms. (just as AB has done with the A350) Far too many issues with shielding, pitch, sideslip, and turns, not to mention vertical winds which the fixed pitot flat lines

[slacktide]

Originally Posted by Smythe

Boeing spokesmen declined to elaborate on which sensor inputs are used to provide the data in the tanker design. The options include using data from the angle of attack vanes on both sides of the cockpit, or an angle of attack vane and inertial gyroscope.

https://www.mro-network.com/airframe...d-pitch-system

That is not a published reference. It's speculation by the author of the article, not a part of the statement by Boeing. Heck, he doesn't even claim it uses one method or another, just speculates that either might be possible.

Also, you misquoted the author by editing his grammar. You might have fixed his typo correctly, but he also might have been intending to type something totally different. Let your source's words stand for themselves.

[737 Driver]

Originally Posted by slacktide

On the NG, it is possible for the STS to fail in a way that causes undesired intermittent runaway trim, just like it is possible for MCAS to fail in a way that causes undesired intermittent runaway trim. Clearly, due to the reliance on a single unchecked AOA value, the demonstrated failure rate has been orders of magnitude greater on the MAX. But the scenario of intermittent runaway trim is still possible on NG.

I have been searching high and low for any actual cases of this happening on the 737NG, particularly as a result of a bad AOA or airspeed input in much the same way as occurred in the MAX accidents. If anyone has an actual case history of this malfunction, please post it here or send me a PM.

[fizz57]

Originally Posted by 737 Driver

I have been searching high and low for any actual cases of this happening on the 737NG, particularly as a result of a bad AOA or airspeed input in much the same way as occurred in the MAX accidents. If anyone has an actual case history of this malfunction, please post it here or send me a PM.

I don't believe you'll find any. Firstly because sts trim inputs are relatively small and secondly because the primary driver for sts - airspeed - is cross-compared between the two sides.

Sort of like mcas should have been, and shortly will be.

[737 Driver]

Originally Posted by fizz57

I don't believe you'll find any. Firstly because sts trim inputs are relatively small and secondly because the primary driver for sts - airspeed - is cross-compared between the two sides.

Sort of like mcas should have been, and shortly will be.

Do you have a reference? Looking at our FCOM and Maintenance Manual, I see no reference to a speed comparison. The STS seems to work primarily through the active FCC which should only be using the airspeed on the selected side. As a side note, in one Boeing-produced document that I have seen, MCAS is described as a sub-function of the Speed Trim System which leads me to think that the Stall ID function (flaps down) could have the same issue, except of course that it is inhibited by the control column cutout switches.

[GordonR_Cape]

Originally Posted by 737 Driver

Do you have a reference? Looking at our FCOM and Maintenance Manual, I see no reference to a speed comparison. The STS seems to work primarily through the active FCC which should only be using the airspeed on the selected side. As a side note, in one Boeing-produced document that I have seen, MCAS is described as a sub-function of the Speed Trim System which leads me to think that the Stall ID function (flaps down) could have the same issue, except of course that it is inhibited by the control column cutout switches.

Not a pilot, but a programmer, and I have no details on the above systems. However, the key difference is that Speed Trim takes a large airspeed input, and turns out a small control movement, while MCAS takes a small AOA input and turns out a large control movement. The ratio between input error and output error is many times larger, between the two systems. From a control system theory viewpoint, that is a terrible design.

Edit: The jargon "error" is the difference between the measured value of a parameter, and the "desired" value (according to various rules). In this discussion it also has another meaning: Boeing's proposed fix allows a difference of 5.5 degrees between left/right AOA as acceptable for MCAS activation. AOA is a value that can easily be measured with the same degree of accuracy as something like airspeed (even if reliability is very high).

Edit: IMO such a disconnection tells you more than you need to know about the usefulness (or lack) of such a system.

[flysmiless]

Authorities from different countries willing to review Boeing 737 MAX

FAA and EASA and few more authorities from different part of the world will be conducting a joint examination of the B 737 Max probably by 29th April.

So B737s (MAX) will grounded or what?

[Bend alot]

I can not see how the MCAS "fix" can still keep the 737 MAX within the limits required for certification.

It simply does not pass the Pub Test.

[compressor stall]

How many authorities? A camel is a horse designed by a committee.

[GordonR_Cape]

A source, and the name JATR should be a starting point: https://af.reuters.com/article/worldNews/idAFKCN1RV1A1

China, the European Aviation Safety Agency, Canada, Brazil, Australia, Japan, Indonesia, Singapore and the United Arab Emirates will all take part, the FAA said, in the Joint Authorities Technical Review (JATR) that is set to last 90 days, the FAA said. Most of the countries previously confirmed they would take part.

[Bend alot]

A noticeable exception - The Ethiopian Civil Aviation Authority.

[DaveReidUK]

Originally Posted by Bend alot

A noticeable exception - The Ethiopian Civil Aviation Authority.

Based on numbers on aircraft in operation, India and Turkey are more surprising omissions.

[Bend alot]

Come to think of it all countries that either grounded the 737 MAX or banned it from it's airspace prior to the FAA grounding should have an input in JATR.

[Smythe]

From Boeing investor guidance..

Boeing Co has told some 737 MAX owners it is targeting U.S. Federal Aviation Administration approval of its software fix as early as the third week of May and the ungrounding of the aircraft around mid-July, two sources told Reuters.

The dates are part of a provisional timeline that Boeing has shared in meetings with airline customers as it explains an upgrade to software that played a role in two fatal crashes and led to the worldwide grounding of its MAX 737 jetliner in March.

However, Boeing has not yet submitted its completed software package to the FAA for approval, two other sources said.

https://www.yahoo.com/finance/news/b...225009529.html

[flysmiless]

Now boeing has estimated the cost of MAX grounding at $1 billion. And probably this will be added upto production cost as an increase.

[Dee Vee]

Originally Posted by flysmiless

Now boeing has estimated the cost of MAX grounding at $1 billion. And probably this will be added upto production cost as an increase.

haha, somehow I doubt too many customers will be lining up to pay more for a B737 MAX....

Its got to come out of company profit, and the shareholders won't be happy.

[SMT Member]

Originally Posted by flysmiless

Now boeing has estimated the cost of MAX grounding at $1 billion. And probably this will be added upto production cost as an increase.

Not quite correct. They've estimated a loss of 1BN due to reduced deliveries of 737 frames only. And that's just the losses 'so far', they may well escalate if the grounding is extended. Then comes all the recertification costs, as well as the court cases they are facing from families of survivors, and investors.

It's also worth noticing that Boeing hasn't logged a single order for any aircraft type since the 737 Max was grounded.