MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
If they are going for the aero fix, which I still doubt, then the easiest solution is to
1. reduce the efficiency of the vane on the nacelle, which will give a nose down trim at high AOA, but a commensurate degradation of the Vs1g.... it is a pretty fix, but not optimal, just doable.
2. add VGs to the outer wing area, probably outboard of the ailerons, which would tip load slightly, and changes the total bending moment on the wing slightly. It would potentially alter the CG envelope slightly, but it would be improved for aft CG's, and slightly more restrictive for the fwd case.
3. add a wedge to the aft underside of the outer wing, outboard of the aileron. An elegant solution. same effects, just without the barbed wire on the wing.
4. adding additional fences etc (vortilons are the reduction of a fence to the minimum profile) would also achieve a similar outcome, but have a drag count and are ugly.
5. another odd vortex device located behind the slat could be set to alter lift rather than only drag,
lots of choices...
The trim wheel is another issue to be dealt with if the industry considers it important to sort out. Sorting MCAS reduces the issue to manageable levels, but it is still something that needs training to cover the ANU case.
however, the fastest way forward is likely to be to sort out the MCAS architecture. Doing the aero mods would require a fair bit of validation flight testing, most of that would not come from CFD modelling.
1. reduce the efficiency of the vane on the nacelle, which will give a nose down trim at high AOA, but a commensurate degradation of the Vs1g.... it is a pretty fix, but not optimal, just doable.
2. add VGs to the outer wing area, probably outboard of the ailerons, which would tip load slightly, and changes the total bending moment on the wing slightly. It would potentially alter the CG envelope slightly, but it would be improved for aft CG's, and slightly more restrictive for the fwd case.
3. add a wedge to the aft underside of the outer wing, outboard of the aileron. An elegant solution. same effects, just without the barbed wire on the wing.
4. adding additional fences etc (vortilons are the reduction of a fence to the minimum profile) would also achieve a similar outcome, but have a drag count and are ugly.
5. another odd vortex device located behind the slat could be set to alter lift rather than only drag,
lots of choices...
The trim wheel is another issue to be dealt with if the industry considers it important to sort out. Sorting MCAS reduces the issue to manageable levels, but it is still something that needs training to cover the ANU case.
however, the fastest way forward is likely to be to sort out the MCAS architecture. Doing the aero mods would require a fair bit of validation flight testing, most of that would not come from CFD modelling.
One of the linked Seattle Times articles stated that they initially tried to solve the force problem with aerodynamic tricks - vortex generators, etc. Nothing did much good. Then someone came up with the basic MCAS idea and it immediately solved the force problem.
If they couldn't figure out how to fix it aerodynamically before, I wouldn't be optimistic they can fix it aerodynamically now.
If they couldn't figure out how to fix it aerodynamically before, I wouldn't be optimistic they can fix it aerodynamically now.
In reply to Jim A at #1377 evolution of ODA is explained in Notice of Proposed Rule Making at https://www.federalregister.gov/docu...ion-procedures
NPRM leaves no doubt that purpose of ODA is to reduce FAA’s involvement in certification. FAA strenuously denies that ODA amounts to self-certification, notwithstanding that NPRM states
ODA was deficient when 787 battery debacle happened - see my post at #1216. It still wasn’t working effectively when DoT Office of Inspector General reported in October 2015 that “FAA LACKS AN EFFECTIVE STAFFING MODEL AND RISK-BASED OVERSIGHT PROCESS FOR ORGANIZATION DESIGNATION AUTHORIZATION”. https://www.oig.dot.gov/sites/defaul...5E10-15-15.pdf. So who knows what other hazards are lurking.
Only meaningful way to restore trust in 737 Max is a Special Certification Review for which FAA has explicit statutory power. Read about examples such as MD-11 at https://scholar.smu.edu/cgi/viewcont...3&context=jalc.
NPRM leaves no doubt that purpose of ODA is to reduce FAA’s involvement in certification. FAA strenuously denies that ODA amounts to self-certification, notwithstanding that NPRM states
“The proposal requires the ODA Holder to perform self-audits and ensure that no one interferes with individuals performing functions for the FAA. ....”
And
“The ODA Holder is ultimately responsible for the functions performed by the ODA Unit....”
And
“The ODA Holder is ultimately responsible for the functions performed by the ODA Unit....”
ODA was deficient when 787 battery debacle happened - see my post at #1216. It still wasn’t working effectively when DoT Office of Inspector General reported in October 2015 that “FAA LACKS AN EFFECTIVE STAFFING MODEL AND RISK-BASED OVERSIGHT PROCESS FOR ORGANIZATION DESIGNATION AUTHORIZATION”. https://www.oig.dot.gov/sites/defaul...5E10-15-15.pdf. So who knows what other hazards are lurking.
Only meaningful way to restore trust in 737 Max is a Special Certification Review for which FAA has explicit statutory power. Read about examples such as MD-11 at https://scholar.smu.edu/cgi/viewcont...3&context=jalc.
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So I would be astonished, disappointed and angry if the mechanical trim forces problem would not be fixed.
This might have been borderline in the 60ies but it is not something acceptable worsened by wheel and sabilizer size 2010ish, even if grandfathered. Can anyone see an all female cockpit crew beeing prohibited? Is it acceptable to have two pilots having to crank that wheel at the same time while having to manage an emergency situation? Pilots having to prove their ability to trim manually each 6/12/24 months? This is ridiculous.
The "rollercoaster" procedure is also not acceptable today which has been admitted by themselfes by removal from the manuals.
I guess, the climax is approaching with BA having to shut down the assembly line. Whether the root cause is parking space or the negative cash flow - I don't believe they can keep this up until October leave alone 2020.
In my industry something like the latest FCC problems would take at least 8 months if it is a task scheduling fix, 1 1/2 years plus if a new hardware step is required. I would expect that taking significantly longer going from automotive to aeronautical. You can also interpolate from the MCAS fix. This was high level software only. Messing around with task scheduling and you are on a completly different boat, also with testing and validation.
This might have been borderline in the 60ies but it is not something acceptable worsened by wheel and sabilizer size 2010ish, even if grandfathered. Can anyone see an all female cockpit crew beeing prohibited? Is it acceptable to have two pilots having to crank that wheel at the same time while having to manage an emergency situation? Pilots having to prove their ability to trim manually each 6/12/24 months? This is ridiculous.
The "rollercoaster" procedure is also not acceptable today which has been admitted by themselfes by removal from the manuals.
I guess, the climax is approaching with BA having to shut down the assembly line. Whether the root cause is parking space or the negative cash flow - I don't believe they can keep this up until October leave alone 2020.
In my industry something like the latest FCC problems would take at least 8 months if it is a task scheduling fix, 1 1/2 years plus if a new hardware step is required. I would expect that taking significantly longer going from automotive to aeronautical. You can also interpolate from the MCAS fix. This was high level software only. Messing around with task scheduling and you are on a completly different boat, also with testing and validation.
Seems to me that Boeing were originally hoping for the cheapest, simplest fix being:
Software modification AND acceptance that existing training regimes are (should be) adequate - hence the repeated statements that "properly trained and skilled crews" should have been able to recover the accident aircraft
But every passing week has made this less accessible as a solution as it has become apparent that MCAS operation does not resemble any "normal" trim runaway training and that stalled trim procedures have been consigned to the dustbin of history(Probably rightly).
So the Boeing desired outcome now becomes accepted software mod WITH additional training (for which, one imagines, Boeing may wish to make a contribution)
OR
if this proves too difficult and/or expensive owing to complications arising from processor lag or who knows what else, then there is the option of an aero solution, though hard to see how this can be effected in any short time frame on existing airframes
BUT BUT BUT
The manual trim wheel thing strikes me as a showstopper in either case above
If the wheel is required as a risk control then it MUST be usable in the case where the risk has crystallised and the control is required. At present it appears that pilots should use electric trim to control pitch and only use manual trim if that fails. But if this has failed then, by definition, the aircraft will be significantly out of trim and.....
And then, well, if that has to be redesigned, engineered, and potentially cockpit layout changed how is this implemented across the NG fleet??
Nasty questions for everyone methinks
Software modification AND acceptance that existing training regimes are (should be) adequate - hence the repeated statements that "properly trained and skilled crews" should have been able to recover the accident aircraft
But every passing week has made this less accessible as a solution as it has become apparent that MCAS operation does not resemble any "normal" trim runaway training and that stalled trim procedures have been consigned to the dustbin of history(Probably rightly).
So the Boeing desired outcome now becomes accepted software mod WITH additional training (for which, one imagines, Boeing may wish to make a contribution)
OR
if this proves too difficult and/or expensive owing to complications arising from processor lag or who knows what else, then there is the option of an aero solution, though hard to see how this can be effected in any short time frame on existing airframes
BUT BUT BUT
The manual trim wheel thing strikes me as a showstopper in either case above
If the wheel is required as a risk control then it MUST be usable in the case where the risk has crystallised and the control is required. At present it appears that pilots should use electric trim to control pitch and only use manual trim if that fails. But if this has failed then, by definition, the aircraft will be significantly out of trim and.....
And then, well, if that has to be redesigned, engineered, and potentially cockpit layout changed how is this implemented across the NG fleet??
Nasty questions for everyone methinks
I wonder how the cash flow is going. Airlines do not pay all the money at delivery, they make (commonly financed) progress payments as production goes along. Are they still expected to make these payments to the manufacturer when the product cannot be delivered ? What if they refuse ? I wonder what provision there is in the contracts for this situation.
I can only guess that contracts on grounded or the airworthiness of aircraft are addressed - certainly on new "types".
I doubt Boeing are currently putting much effort in chasing overdue payments on the MAX aircraft, but then this is Boeing!
One of the linked Seattle Times articles stated that they initially tried to solve the force problem with aerodynamic tricks - vortex generators, etc. Nothing did much good. Then someone came up with the basic MCAS idea and it immediately solved the force problem.
If they couldn't figure out how to fix it aerodynamically before, I wouldn't be optimistic they can fix it aerodynamically now.
If they couldn't figure out how to fix it aerodynamically before, I wouldn't be optimistic they can fix it aerodynamically now.
maybe... but the basic pitch issue is relatively quantifiable, at least a limit case can be made for it. We know the problem is a clean config issue, that strongly suggests that the Cm of the flaps is sufficient to remove the problem from the board. It is also an aft CG case issue...
Adding a tab or wedge outboard of the aileron will increase the section CLmax of that area by about 40% (its a size thing... ) It does bring down the AOA slightly where CLmax occurs, but at the same point where the normal stall would occur, there is a greater CL than would otherwise be the case. Adding VGs at the front of the wing, (and these are for high AOA so they would be between 3-5%c from the LE) increases the AOA slope, and much higher CLmax, as well as higher AOA before the break can occur. VG's for the issue if used need to be on the slat TE itself. The local Cm from a tab or wedge is considerable, but the overall effect due to the sweep effect and increased loading of the wing tips is much greater, about a 3%MAC shift, which is about what you get with the flaps... more or less. Boeings usual VG stands proud at about 20mm, and that is too large for a VG at the TE of the slat, for effectiveness and drag, they need to be around 6-8mm in height if located around the 3-5%C location, which makes them effective at high AOA and less so at any other time.
Adding a reflex to the B737 has been done by STC previously. Was also done to other aircraft. That can be accomplished with a piece of foam rubber along the upper edge of the main flap aft element, which constitutes the wing TE of the yehudi section. That would give a modest local CL and Cm reduction in that area, but shifts Cp outboard and aft, and give an overall increase in Cm. Its handy to have swept wings. It is possible that can result in some buffet at very low AOAs at high Mach, but it would otherwise reduce buffet at high AOA.
Removal of the strakes is viable, but comes with a TO performance penalty, the other options aerodynamically all alter the span wise lift distribution, but that can be tailored to occur at only high AOA which equates to low speeds, and is otherwise straightforward to apply.
MCAS was a simple and relatively easy fix with no expected downside, whereas all aero fixes alter loading, including torsion and bending, and some are adverse to parts of the performance envelope, but some are beneficial at all points within the envelope. Altering span wise loading is not for the faint hearted structurally, but having looked at that area previously, there is not a big impact from doing that for this problem.
The manual trim, get a bigger wheel, or add another stby trim motor, there should have been one from day one, the design has always been less than stellar. The real problem for this was the unknown unknowns that came to light with MCAS. Pitch up issues can be dealt with, but absolutely need training to be safe, pitch down is just nasty. Get rid of the MCAS by aero mods, and train for the pitch up, and apologise for the missing link in the training of the crews from the 60's to 20's... what is old is new again.
The pitch issue is not that big a problem the fact that MCAS didn't function with flaps deployed quantifies that... and any of the aero mods achieves that level of Cp shift that will offset the Cm sufficient to normalise the control force.
A point of clarification, the aero issue is not that big a deal, there are a few phone numbers that TBC could call to get that sorted, but the MCAS was and is a major deal, and it introduced unintended consequences that are severe. The manual trim issue was a lousy design that was adequate in the past but thrust into prominence with MCAS. It is fixable or trainable, MCAS is fixable or replaceable. After the shock of the events, the confidence of the design system is in question, and that doesn't make it easier to get the work done that is necessary.
I hope TBC does get their act together soon. Their products are competent usually, but the corporation itself needs some self reflection.
Last edited by fdr; 15th Jul 2019 at 12:29.
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I wonder how the cash flow is going. Airlines do not pay all the money at delivery, they make (commonly financed) progress payments as production goes along. Are they still expected to make these payments to the manufacturer when the product cannot be delivered ? What if they refuse ? I wonder what provision there is in the contracts for this situation.
To be honest, I find the financial aspect of the crisis equally intresting than the technical one. I do wonder how things were going if BA was not a major asset to public finance in the western world. My personal impression is that there are a lot of entities betting on the "too big to fail"-scenario. The 737 MAX might be good for some more shockwaves through the industry. IMHO we have just seen the tip of the iceberg.
If a milestone is not met the next payment will be delayed. The delivery delay itself is not so much the problem but to cover for the planned capacity needed otherwise. Lease something else, switch fleets, delay fleet retirements, big overhauls and such. The delivery stop will affect production sooner than later and that trickles down through the supply chain. That might become some big issue and this seems to be the reason why they kept the rate up until now.
concerns about whether the average pilot has enough physical strength to manually crank a flight-control wheel in extreme emergencies.
This further shows how outdated the type is when most other manufacturers are using modern FBW control systems where pilot strength isn’t a requirement. A teenage girl could easily cope with the control force requirements on an A320.
#1399
“The delivery stop will affect production sooner than later and that trickles down through the supply chain. That might become some big issue and this seems to be the reason why they kept the rate up until now.”
“The delivery stop will affect production sooner than later and that trickles down through the supply chain. That might become some big issue and this seems to be the reason why they kept the rate up until now.”
As far as MCAS is concerned my gut feeling is that Boeing will stick with a software solution supplemented as necessary by training. However should they go down the route of aero changes I'm curious how much that might affect the claimed fuel savings for the MAX. Any ideas?
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As far as MCAS is concerned my gut feeling is that Boeing will stick with a software solution supplemented as necessary by training. However should they go down the route of aero changes I'm curious how much that might affect the claimed fuel savings for the MAX. Any ideas?
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Or to quote an old British saying: "you can't turn a pig's ear into a silk purse".
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One of the linked Seattle Times articles stated that they initially tried to solve the force problem with aerodynamic tricks - vortex generators, etc. Nothing did much good. Then someone came up with the basic MCAS idea and it immediately solved the force problem.
If they couldn't figure out how to fix it aerodynamically before, I wouldn't be optimistic they can fix it aerodynamically now.
If they couldn't figure out how to fix it aerodynamically before, I wouldn't be optimistic they can fix it aerodynamically now.
The problem maybe that thoses fixes involve airframe mods and so new certification while Boeing was intending to grandfather the new model and avoid retraining aircrews.
Had a discussion last week with the senior aerodynamicist of a very well known planemaker.
His opinion is that the MAX issue should be fixed with aerodynamic devices.
He mentioned that at some point they discovered that some rear fuselage strakes or "keels" worked well on a business jet, and to their surprise, did reduce drag in cruise, due to some modifications of the turbulent airflow on the rear portion of the fuselage.
Last edited by Fly Aiprt; 15th Jul 2019 at 18:21. Reason: Typo
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Alan Mulally and his 'working together' policy produced a very fine aircraft in the B777. It seems that every product following this was an utter cock-up. What on earth has gone wrong within Boeing.
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He mentioned that at some point they discovered that some rear fuselage strakes or "keels" worked well on a business jet, and to their surprise, did reduce drag in cruise, due to some modifications of the turbulent airflow on the rear portion of the fuselage.
As noted, the MAX extended the taper at the APU, and removed the vanes...(same old story, reduced drag to add fuel efficiency,of course!)