MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
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"Joe, the guys in the engineering cab are having a problem with a pitch up during wind up turns. It's now too late for any hardware modifications, we need to fix it in software. You remember that MCAS gizmo we did for the tankers. We need that in the Max to counter it.
"But boss, that's an entirely different code base. We can't just copy and paste that into the Max. Systems engineering must do a hazard and risk analysis for that, is it already in progress? They haven't come to see me yet."
"Well Joe, we do have the STS, we do also hava a hazard and risk analysis for that. Just do a reimplentation in there. Maybe we'll need to add a line or two to the analysis. After all, at worst case, it's just a runaway trim, as it always has been. The guys in the engineering cab are waiting for a prototype by the end of the week."
"Boss, the KC46 uses both AOA sensors but we are having only the one hardwired to us available in the STS subsystem. We need to request a new basline from R***C***, making the remote one available to us. That takes three months. We also need to fix synchronisation issues due to transport delay . Then systems engineering has to define behaviour in case of AOA disagree. Has the display and alerting concept been revised yet? Will we have the same kill switch, we have on the KC46 for it? When can we expect a spec for that? By the way, our task run time of the STS on that 'ol FCCs are already boarderline. I can't guarantee that we can actually fit it in there."
"Joe, flight testing is already on the way. The project must not be delayed. It is crucial for the companies future in the single aisle market. We have a problem, we have solution from the KC-46 project. We will follow a "do min" approach. No hardware modifications. Just make it work with one AOA sensor. Systems engineering will take care of the remainder. You make a prototype available to the engineering cab by end of week."
...
What would you do?
"But boss, that's an entirely different code base. We can't just copy and paste that into the Max. Systems engineering must do a hazard and risk analysis for that, is it already in progress? They haven't come to see me yet."
"Well Joe, we do have the STS, we do also hava a hazard and risk analysis for that. Just do a reimplentation in there. Maybe we'll need to add a line or two to the analysis. After all, at worst case, it's just a runaway trim, as it always has been. The guys in the engineering cab are waiting for a prototype by the end of the week."
"Boss, the KC46 uses both AOA sensors but we are having only the one hardwired to us available in the STS subsystem. We need to request a new basline from R***C***, making the remote one available to us. That takes three months. We also need to fix synchronisation issues due to transport delay . Then systems engineering has to define behaviour in case of AOA disagree. Has the display and alerting concept been revised yet? Will we have the same kill switch, we have on the KC46 for it? When can we expect a spec for that? By the way, our task run time of the STS on that 'ol FCCs are already boarderline. I can't guarantee that we can actually fit it in there."
"Joe, flight testing is already on the way. The project must not be delayed. It is crucial for the companies future in the single aisle market. We have a problem, we have solution from the KC-46 project. We will follow a "do min" approach. No hardware modifications. Just make it work with one AOA sensor. Systems engineering will take care of the remainder. You make a prototype available to the engineering cab by end of week."
...
What would you do?
I wouldnt design a single sensor control loop in an aero control application THAT ISNT SANITY CHECKED because it would possibly be considered criminal negligence. Just look at a computer mouse to see the possible failures, starting with connector disconnection, connector corrosion, wire failure, contamination and mechanical failures of the actual sensor, boards growing solder whiskers, component failure on the sensor board etc.
Sensor failures are just a question of when rather than if. However the INS data on the 737, and probably other data, can be used to sanity check the AoA sensor.
Look at what happens when a pitot or static port gets blocked - will that be safe if it is a single sensor?
Edmund
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If management tells you to take off with an unfixed tech issue which you consider potentially hazardous, do you do it?
I wouldnt design a single sensor control loop in an aero control application THAT ISNT SANITY CHECKED because it would possibly be considered criminal negligence. Just look at a computer mouse to see the possible failures, starting with connector disconnection, connector corrosion, wire failure, contamination and mechanical failures of the actual sensor, boards growing solder whiskers, component failure on the sensor board etc.
Sensor failures are just a question of when rather than if. However the INS data on the 737, and probably other data, can be used to sanity check the AoA sensor.
Look at what happens when a pitot or static port gets blocked - will that be safe if it is a single sensor?
Edmund
As an engineer I will always raise my concerns and make sure that they are documented somewhere. And this is probably one reason why I am more "Joe" than "boss".
However when told to go ahead with a certain design by superiors I have to and will do - although I might disagree. Just imagine I'd do something on my own account and something would go wrong either economy or safety related. Now I'd be really in trouble.
Changing job's is always a cheap recommendation. Easier said than executed when you have a family and a life - it took me several years to leave such toxic venture.
BA and FAA had appropriate processes in place to prevent these things happening. They were ravished. Willfully. For commercial reasons. This does not happen on engineering level.
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https://www.wsj.com/articles/boeing-...ry-11576532032
Their supplier's base will erode in no time. It will become very expensive to restart production after only a few weeks.
Failures will begin with smaller businesses and cascade upwards.
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According to multiple news sources, Boeing is suspending production of the Max in January. So where do they go from here?
https://www.wsj.com/articles/boeing-...ry-11576532032
https://www.wsj.com/articles/boeing-...ry-11576532032
The MAX is dead, commercially. If it ever gets certified, they'll have to sell it off for peanuts, exactly what Mr. O'Leary in Ireland is waiting for.
And with the high profile media coverage, it has raised a lot more concern in the flying public than the 787 battery events did, so I am not so sure that the MAX debacle will be forgotten that easily.
People do realize that this is more than just a tech screwup. They understand the muddy FAA/Boeing relationships, and the business considerations, and know that safety was last, despite all the contrary statements and advertising blurb.
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Company was ignoring safety and business threats, allowing agreed testing milestones to pass unnoticed. Took me 6 months of squawking and losing sleep to finally go find another job. New job is not as interesting, on paper, but no one will burn down in their sleep.
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Claims of the Max program death are I suggest greatly exaggerated. Those on PPRUNE need to remember that the Max problems are a lot more salient to those in the industry and on here than those outside of it, or those who fly a few times a year. If the airlines are willing to trust it, and are thus willing to commit to it, then most passengers will be fine with it after 6 months.
It is not that the public is ignorant, it is just that other things are more pressing. Many on here would be horrified if they knew what a doctor knows about the medical system or a professor knows about higher education - again not ignorance or bad, just that the more we know of an industry, the more the issues are salient.
I suggest the real threat to the Max is if airlines or insurance companies do not trust it.
TME
It is not that the public is ignorant, it is just that other things are more pressing. Many on here would be horrified if they knew what a doctor knows about the medical system or a professor knows about higher education - again not ignorance or bad, just that the more we know of an industry, the more the issues are salient.
I suggest the real threat to the Max is if airlines or insurance companies do not trust it.
TME
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From Business Insider, today:
Here's the gruesome truth of how much Boeing's 737 Max debacle is expected to hurt the US economy
Boeing's recent decision to pause 737 Max production will cut 0.5 percentage points from gross domestic product growth in the first quarter of 2020, JPMorgan said Tuesday.
The model is Boeing's best-selling product, and the production cut will have a material effect on GDP by pulling inventory growth lower, chief economist Michael Feroli said in a note.
More
Boeing's recent decision to pause 737 Max production will cut 0.5 percentage points from gross domestic product growth in the first quarter of 2020, JPMorgan said Tuesday.
The model is Boeing's best-selling product, and the production cut will have a material effect on GDP by pulling inventory growth lower, chief economist Michael Feroli said in a note.
More
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I just have a wild (and scary) thought. If with this new fancy engines a 737 might has a deeper nose-up tendency in some corners of the flight envelope. Can it has a deeper nose-down tendency in some corners of the flight envelope as well?
They are installed much further forward than usual.
Maybe in in both crashes it was a moment when after reaching the certain angle the planes were suddenly pushed nose down because of that?
They are installed much further forward than usual.
Maybe in in both crashes it was a moment when after reaching the certain angle the planes were suddenly pushed nose down because of that?
The position of the engines cause increased drag at high AoA, which in turn causes a pitching moment around the CG. The reason for this is that the protruding engines cause the projected frontal area (Ap) to increase with pitch, and drag is proportional to Ap. The effect should be symmetric, since this is drag and not lift, but I guess it is unusual to see high values of negative AoA. It would be interesting to see how strong this effect is at a few degrees negative AoA.
Psychophysiological entity
568 in answer to my suggestion that some aircraft could be delivered to their intended purchasers.
MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
Indeed, the problems would be mind-bending, but perhaps not as horrific as the spectre of these beautiful hulls in say, red hot Arizona dust. It is just one possible plan for minimising a situation that must be beyond Boeing's worst nightmare.
Icarus
Yes, I am aware and agree that you had to read between my lines to see that I inferred the need to cruise normally. If the movement of one lever can cut it out, surely there must be a way of temporarily fooling the system.
Acceptance flights? Well, since they won't be flown for a while, is it conceivable the flight tests could be flown in the future at destination. I suppose the spectre of factory fixes have to be taken into account. Also, I am assuming the software fixes will be akin to an ordinary on-board download. Maybe black boxes will be changed as well. I wonder just what the fix entails.
Whatever, my notion of kind-of half-delivering some aircraft, really is not a very cunning plan but my heart bleeds for Boeing. I can feel anger but the thought of this company going down fills me with dismay. The aged design concept that is the 737 has carried a lot of people since 1967. And just as an aside, I recall a Boeing salesman in Texas telling me that Britannia were the highest utilisation airline in the world. >19 hours per 24. Just one of the little memories that stick in the mind.
MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
There may also be a problem with the insurance underwriters until "the fix" is in place.
Customer acceptance flights probably haven't taken place on the parked jets.
Customer acceptance flights probably haven't taken place on the parked jets.
Icarus
Quote:So how to get them there.
Flap extended, crew only ferry flights have already happened.
Acceptance flights? Well, since they won't be flown for a while, is it conceivable the flight tests could be flown in the future at destination. I suppose the spectre of factory fixes have to be taken into account. Also, I am assuming the software fixes will be akin to an ordinary on-board download. Maybe black boxes will be changed as well. I wonder just what the fix entails.
Whatever, my notion of kind-of half-delivering some aircraft, really is not a very cunning plan but my heart bleeds for Boeing. I can feel anger but the thought of this company going down fills me with dismay. The aged design concept that is the 737 has carried a lot of people since 1967. And just as an aside, I recall a Boeing salesman in Texas telling me that Britannia were the highest utilisation airline in the world. >19 hours per 24. Just one of the little memories that stick in the mind.
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From fundamental aerodynamics, the answer is definitely yes.
The position of the engines cause increased drag at high AoA, which in turn causes a pitching moment around the CG. The reason for this is that the protruding engines cause the projected frontal area (Ap) to increase with pitch, and drag is proportional to Ap. The effect should be symmetric, since this is drag and not lift, but I guess it is unusual to see high values of negative AoA. It would be interesting to see how strong this effect is at a few degrees negative AoA.
The position of the engines cause increased drag at high AoA, which in turn causes a pitching moment around the CG. The reason for this is that the protruding engines cause the projected frontal area (Ap) to increase with pitch, and drag is proportional to Ap. The effect should be symmetric, since this is drag and not lift, but I guess it is unusual to see high values of negative AoA. It would be interesting to see how strong this effect is at a few degrees negative AoA.
Rivets ,on the C130 ,it has increased hydraulic pressure to the rudder when you select flaps (below limit speed) .it is a well known `cheat` if you need to `vigorously manoeuvre` the aircraft above f/limit(speed or `g`) by popping a couple of c/bs,and then put the flap selector to 20*,and obtain full hyd. pressure to the rudder...so I was told...!
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Can it has a deeper nose-down tendency in some corners of the flight envelope as well? They are installed much further forward than usual.
From fundamental aerodynamics, the answer is definitely yes.
Probably not a concern of note.
I have no inside information re the specific flight test activities for this aircraft but the usual reason for pitch stability problems with engines pushed out in front at low speed with high thrust and high alpha relate to the normal lift force up front of the engine. In this case, the force is at the nacelle lip as the flow turns into the engine. The force is directed up so we see a nose up pitching moment which is destabilising. Same sort of thing occurs with a number of piston to turboprop conversions where the new engine installation sees the prop pushed well forward for basic CG reasons. Again, the flow changes direction going through the prop disc and there is a significant destabilising nose up pitching moment, especially during the missed approach situation.
On the piston switch to turboprop, the usual fix is to incorporate a SAS facility - typically a variable downspring in the circuit. As far as I can deduce from what one can read in the public domain, the MAX original fix was a cheap way to gain a similar effect utilising stuff which was already in the aircraft's configuration.
Unfortunately the game plan was brought unstuck by later mods in the program as indicated in much earlier posts in this, and other, threads on the subject.
I see PEI_3721 is following the present discussion. His background is quite pertinent so we may get further commentary from him or other specialist folks in due course.
From fundamental aerodynamics, the answer is definitely yes.
Probably not a concern of note.
I have no inside information re the specific flight test activities for this aircraft but the usual reason for pitch stability problems with engines pushed out in front at low speed with high thrust and high alpha relate to the normal lift force up front of the engine. In this case, the force is at the nacelle lip as the flow turns into the engine. The force is directed up so we see a nose up pitching moment which is destabilising. Same sort of thing occurs with a number of piston to turboprop conversions where the new engine installation sees the prop pushed well forward for basic CG reasons. Again, the flow changes direction going through the prop disc and there is a significant destabilising nose up pitching moment, especially during the missed approach situation.
On the piston switch to turboprop, the usual fix is to incorporate a SAS facility - typically a variable downspring in the circuit. As far as I can deduce from what one can read in the public domain, the MAX original fix was a cheap way to gain a similar effect utilising stuff which was already in the aircraft's configuration.
Unfortunately the game plan was brought unstuck by later mods in the program as indicated in much earlier posts in this, and other, threads on the subject.
I see PEI_3721 is following the present discussion. His background is quite pertinent so we may get further commentary from him or other specialist folks in due course.
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Claims of the Max program death are I suggest greatly exaggerated. Those on PPRUNE need to remember that the Max problems are a lot more salient to those in the industry and on here than those outside of it, or those who fly a few times a year. If the airlines are willing to trust it, and are thus willing to commit to it, then most passengers will be fine with it after 6 months.
It is not that the public is ignorant, it is just that other things are more pressing. Many on here would be horrified if they knew what a doctor knows about the medical system or a professor knows about higher education - again not ignorance or bad, just that the more we know of an industry, the more the issues are salient.
I suggest the real threat to the Max is if airlines or insurance companies do not trust it.
TME
It is not that the public is ignorant, it is just that other things are more pressing. Many on here would be horrified if they knew what a doctor knows about the medical system or a professor knows about higher education - again not ignorance or bad, just that the more we know of an industry, the more the issues are salient.
I suggest the real threat to the Max is if airlines or insurance companies do not trust it.
TME
Psychophysiological entity
sycamore. Luxury! On the HP Herald 60% of the weight of my flight bag was hand tools.
From that Market Insider article. (that is some 'note'.)
And there was me saying that stored aircraft were not 'money in the bank'.
It's not a, 'At least, they're an asset' kind of scenario. They might be worth 30 billion dollars one moment, and be a bewildering liability the next. It's hard to imagine a middle road when the product has cost so much to build. In particular, I'm not sure who'd buy 800 almost new engines that don't quite fit.
From that Market Insider article. (that is some 'note'.)
The model is Boeing's bestselling product, and the production cut will have a material effect on GDP by pulling inventory growth lower, JPMorgan's chief US economist, Michael Feroli, said in a note . . .
. . . Since the production adjustment, the 737 Max hasn't hit GDP growth - the decline in deliveries to airlines was offset by an inventory buildup, the economist said. The company already has 400 undelivered planes in storage. "Accordingly, the expected drag on 1Q GDP growth should be concentrated in reduced inventory accumulation," Feroli wrote.
. . . Since the production adjustment, the 737 Max hasn't hit GDP growth - the decline in deliveries to airlines was offset by an inventory buildup, the economist said. The company already has 400 undelivered planes in storage. "Accordingly, the expected drag on 1Q GDP growth should be concentrated in reduced inventory accumulation," Feroli wrote.
It's not a, 'At least, they're an asset' kind of scenario. They might be worth 30 billion dollars one moment, and be a bewildering liability the next. It's hard to imagine a middle road when the product has cost so much to build. In particular, I'm not sure who'd buy 800 almost new engines that don't quite fit.
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I predict the 737 MAX inventory will be written off. The Chinese or Europeans or Canadians will get blamed. The company is preparing a new design for market, and as soon as they have the project ready they will file for Chapter 11, and a lot of the stock will be acquired on the cheap by a rescue team and then they launch the new design sales, with government incentives as the dastardly communist Chinese and socialist Europeans and health insured Canadians and .. and ... and insert your favorite country here ... killed the MAX ... see above. And yes, Muilenburg will come out of this with ... lots of moolah, and current shareholders will get raped.
Edmund
Edmund
They might be worth 30 billion dollars one moment, and be a bewildering liability the next. It's hard to imagine a middle road when the product has cost so much to build. In particular, I'm not sure who'd buy 800 almost new engines that don't quite fit.
Last edited by edmundronald; 18th Dec 2019 at 04:08.
