Ethiopian airliner down in Africa
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Excellent posts Aloha.
Having personally survived an "Airspeed disagree" event on a dark and stormy night I can confirm that the cacophony of warnings etc. (including simultaneous stick shaker and over-speed !) are startling to say the least.
And you dont have much time to catch it either.
Three things saved me that night:
1) Attitude and thrust, its all you've got, but it works.
2) The good fortune of working for a carrier that spent a lot of sim. time working on the non-normal checklist when it changed a few years back.
3) A ten thousand hour F/O who was priceless on the night.
Not sure that either crew in incidents were so lucky.
Having personally survived an "Airspeed disagree" event on a dark and stormy night I can confirm that the cacophony of warnings etc. (including simultaneous stick shaker and over-speed !) are startling to say the least.
And you dont have much time to catch it either.
Three things saved me that night:
1) Attitude and thrust, its all you've got, but it works.
2) The good fortune of working for a carrier that spent a lot of sim. time working on the non-normal checklist when it changed a few years back.
3) A ten thousand hour F/O who was priceless on the night.
Not sure that either crew in incidents were so lucky.
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FCeng84,
Given your familiarity with 737 systems I wanted to address a question to you:
As far as I understand, FCC-enabled MCAS receives single channel sensory data from the ADIRU, mainly AoA (so as to trigger MCAS in the first place) and speed (so as to regulate just how much trim input is required based on Mach number schedule).
My question is about the total control column forces with both SMYD stall protection features ANDhaving MCAS in its maximum setting. Allow me to explain further:
1. MCAS: assuming an AoA sensor failure where the data is relayed as equal or higher than the activation threshold of MCAS, then MCAS kicks in. Assuming a low speed readout by MCAS, it is then set to its maximum throughput (10 seconds of trim and 2.5 degrees nose down, since it works on a speed schedule based on Mach).
2. SMYD/EFS: As I understand, the SMYD computer enables the EFS (Elevator Feel Shift) and STS (Speed Trim System) to do the following during low airspeed conditions - EFS on one hand doubles Hyd A pressure to control column in its AFT axis, and STS trims the stab Nose Down (though respecting the column cutout switches, something MCAS ignores altogether).
The conclusion is the STS trimming you down (so as long as you don't pull aft), the EFS doubling aft forces, and MCAS also trimming at up to 2.5 degs nose down within 10 seconds (if uninterrupted). Essentially, you can end up in full Nose Down stab trim with doubled elevator control forces, thus severely affecting your authority.
Do you agree with my reasoning that SMYD/EFS interaction with MCAS (when low speed is relayed) can be additive in terms of struggling to keep the nose up and having limited authority?
Makes you wonder just how much attention Boeing engineering gave to both these systems' interaction at the design stage.
Given your familiarity with 737 systems I wanted to address a question to you:
As far as I understand, FCC-enabled MCAS receives single channel sensory data from the ADIRU, mainly AoA (so as to trigger MCAS in the first place) and speed (so as to regulate just how much trim input is required based on Mach number schedule).
My question is about the total control column forces with both SMYD stall protection features ANDhaving MCAS in its maximum setting. Allow me to explain further:
1. MCAS: assuming an AoA sensor failure where the data is relayed as equal or higher than the activation threshold of MCAS, then MCAS kicks in. Assuming a low speed readout by MCAS, it is then set to its maximum throughput (10 seconds of trim and 2.5 degrees nose down, since it works on a speed schedule based on Mach).
2. SMYD/EFS: As I understand, the SMYD computer enables the EFS (Elevator Feel Shift) and STS (Speed Trim System) to do the following during low airspeed conditions - EFS on one hand doubles Hyd A pressure to control column in its AFT axis, and STS trims the stab Nose Down (though respecting the column cutout switches, something MCAS ignores altogether).
The conclusion is the STS trimming you down (so as long as you don't pull aft), the EFS doubling aft forces, and MCAS also trimming at up to 2.5 degs nose down within 10 seconds (if uninterrupted). Essentially, you can end up in full Nose Down stab trim with doubled elevator control forces, thus severely affecting your authority.
Do you agree with my reasoning that SMYD/EFS interaction with MCAS (when low speed is relayed) can be additive in terms of struggling to keep the nose up and having limited authority?
Makes you wonder just how much attention Boeing engineering gave to both these systems' interaction at the design stage.
In order to work out your scenario let's be specific about a few aspects of the proposed sequence:
1. Are we starting from takeoff with indicated AOA failed high?
2. What is the speed time history following liftoff and through this sequence?
3. Are there any thrust changes or is that left at takeoff setting throughout?
4. What flap setting are we starting with and when are the retractions including when do we go Flaps Up?
5. What is the pilot doing with respect to pitch trim?
- No trim inputs at all
- Trimming as needed to keep column forces less than 5 lbs
- Allowing column forces to build up to a higher level and then trimming off force (What level before applying trim?)
6. I suggest having the pilot add column as needed along the way to keep pitch rate at about zero after having complete the takeoff rotation.
I'd be glad to walk through the sequence once the scenario specifics per above are defined. If you want to define more than one variation go ahead.
FCeng84
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I notice that in endlessly repeating your point of view you never mention the fact that the pilots were contending with unreliable airspeed and the distraction of a stick shaker. Care to illuminate us on why?
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Excellent posts Aloha.
Having personally survived an "Airspeed disagree" event on a dark and stormy night I can confirm that the cacophony of warnings etc. (including simultaneous stick shaker and over-speed !) are startling to say the least.
And you dont have much time to catch it either.
Three things saved me that night:
1) Attitude and thrust, its all you've got, but it works.
2) The good fortune of working for a carrier that spent a lot of sim. time working on the non-normal checklist when it changed a few years back.
3) A ten thousand hour F/O who was priceless on the night.
Not sure that either crew in incidents were so lucky.
Having personally survived an "Airspeed disagree" event on a dark and stormy night I can confirm that the cacophony of warnings etc. (including simultaneous stick shaker and over-speed !) are startling to say the least.
And you dont have much time to catch it either.
Three things saved me that night:
1) Attitude and thrust, its all you've got, but it works.
2) The good fortune of working for a carrier that spent a lot of sim. time working on the non-normal checklist when it changed a few years back.
3) A ten thousand hour F/O who was priceless on the night.
Not sure that either crew in incidents were so lucky.
With stick shaker going was there an AOA fault?
What was found to be the source of the event you describe?
What model was that?
How did that experience compare with applicable training?
Thanks in advance,
FCeng84
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Yes, clearly different than a runway and yes, the column cutout doesn't work with MCAS. Yes the trim wheel moving, even in manual flight, even when not trimming with the yoke switch is normal in a 737. That said you would think in 7-12 minutes of watching the nose get heavier and heavier and the trim moving downward on occasion on its own you would kill the trim with the stab cutout switches. I totally get the anger at Boeing but experienced 737 pilots should be able to figure this out, in particular with a bit of time, and after the Lion Air accident and the required reading of the MCAS system and its failure mode you would think any 737 MAX pilot would be able to figure this out very, very quickly let alone with time. Lots of blame to go around here in these accidents, starts with Boeing but as usual it ends in the point end of the jet.
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Hi guys
A few points being missed here I think so far. Now some of these are of course just opinion but here goes.....
1 the 737 can fly with everything turned off. It’s a mechanical plane. That is it’s great virtue. So to crash one you have to forget that it’s actually a real ordinary plane and you are meant to be in total control! Always.
2 that being so, if STAB moves unexpectedly, turn off STAB SWITCHES as generations of pilots have done ,and fly straight and level. Why not take control of the plane? You can.
3 MACS only works with autopilot out at high AoA slow speed
4 the fact MACS malfunctions or maybe is not we’ll designed which we don’t know yet, is not the cause of the crash. although it would be desirable if it worked in a sensible manner. Eg two AoA inputs, doesn’t repeatedly incrementally trim nose down and a limit on the number of trim wheel turns etc etc as postulated here.
5 this nose down trim goes back to the 707 which had a stick pusher- it’s not really a new idea at all
6 the cause here? Looks to me like we’re forgetting the basics and the accumulated knowledge of 50 years of operating the 737.
as someone said, the MAX is like a cart (or perhaps a 707)with a couple of computers and glass screens, but underneath it’s a very simple uncomplicated plane. Fly it 6/60 and it will fly. 6 deg nose up. 60% power. Like any other plane.
7 the stabilizer trim switches on the yoke-the ones you use all the time, cannot apparently override (apply automatic brake) against MACS. Now- That’s something very different from the previous models and if true an important issue. But not the cause.
Thats my ten pence worth for today
i would fly a Max in a heartbeat. Provided the pilots
A few points being missed here I think so far. Now some of these are of course just opinion but here goes.....
1 the 737 can fly with everything turned off. It’s a mechanical plane. That is it’s great virtue. So to crash one you have to forget that it’s actually a real ordinary plane and you are meant to be in total control! Always.
2 that being so, if STAB moves unexpectedly, turn off STAB SWITCHES as generations of pilots have done ,and fly straight and level. Why not take control of the plane? You can.
3 MACS only works with autopilot out at high AoA slow speed
4 the fact MACS malfunctions or maybe is not we’ll designed which we don’t know yet, is not the cause of the crash. although it would be desirable if it worked in a sensible manner. Eg two AoA inputs, doesn’t repeatedly incrementally trim nose down and a limit on the number of trim wheel turns etc etc as postulated here.
5 this nose down trim goes back to the 707 which had a stick pusher- it’s not really a new idea at all
6 the cause here? Looks to me like we’re forgetting the basics and the accumulated knowledge of 50 years of operating the 737.
as someone said, the MAX is like a cart (or perhaps a 707)with a couple of computers and glass screens, but underneath it’s a very simple uncomplicated plane. Fly it 6/60 and it will fly. 6 deg nose up. 60% power. Like any other plane.
7 the stabilizer trim switches on the yoke-the ones you use all the time, cannot apparently override (apply automatic brake) against MACS. Now- That’s something very different from the previous models and if true an important issue. But not the cause.
Thats my ten pence worth for today
i would fly a Max in a heartbeat. Provided the pilots
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It is very easy to make suggestions as to how each crew should/ could have handled the situation and I suspect the CVR/FDR readout will be disturbing.
Its 10+ years since I last flew the 737 but IIRC the memory items for a stall warning just after takeoff were to select Flap 1.
This was probably to safeguard a scenario where Flaps were selected UP and not the Gear.
Woukd the crews workload have reduced and a diagnosis been easier if Flap 1 had been selected even if speed well in excess of 250 kt?
This would also have disabled MCAS.
Its 10+ years since I last flew the 737 but IIRC the memory items for a stall warning just after takeoff were to select Flap 1.
This was probably to safeguard a scenario where Flaps were selected UP and not the Gear.
Woukd the crews workload have reduced and a diagnosis been easier if Flap 1 had been selected even if speed well in excess of 250 kt?
This would also have disabled MCAS.
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The problem with the above is that at least in the Lion Air accident it did not happen that way. The MCAS commanded 2.5 units of nosedown trim which was countered by the CA retrimming the aircraft. 5 seconds later MCAS again commanded 2.5 units nose down trim and again it was electrically countered by the Captain. This cycle repeated itself 21 times. That’s a lot of time to diagnose the problem. MCAS does not drive the stab full nose down and cause a instant plunge into the ground. It moves in 2.5 degree increments and electrical trim is available to counter it. Not that difficult to retrim electrically and then disable the trim motors. Your now in trim and have manual trim available.
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AI, AS, PG ... who needs computers if you have such humans
So, under your criteria, the Captain was competent and the first officer not. But what about the MCAS ? After 21 times MCAS actions were countered by the Captain, MCAS wasn't able to "understand" it was doing something wrong ? Idem when the first officer was pulling desperately the column aft ??? No need for complex AI here, just a few lines of code...
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Originally Posted by FCeng84
While the MCAS software update developed after the Lion Air accident that is almost ready to go to the fleet will likely remove reliance on the three MCAS design assumptions listed above and thus would have greatly improved the likelihood of a safe outcome for the Ethiopian event we are left with a huge elephant in the room. After making the planned update we still must address the following:
A. How many other key points in the 737MAX safety story are based on pilot response assumptions that may not be valid?
B. How about other airplane models? Are they deemed safe based on faulting assumptions regarding pilot action?
- For instance, how may current 737 crews (all models) would not respond quickly enough to a classic stabilizer runaway that was not arrested by column cutout (i.e., pulling the call far enough)? I know this is covered in simulator sessions for 737 pilots, but is that enough?
C. Moving forward with the current status and future of commercial aviation have we gotten to the point where basic flying skills and system awareness are so low that we are at risk throughout the whole industry?
D. Can current and future pilot reaction short falls be addressed through training? If so, what kind, how much, and how often?
E. How will we know that we have achieved a sufficient industry wide level of safety?
A. How many other key points in the 737MAX safety story are based on pilot response assumptions that may not be valid?
B. How about other airplane models? Are they deemed safe based on faulting assumptions regarding pilot action?
- For instance, how may current 737 crews (all models) would not respond quickly enough to a classic stabilizer runaway that was not arrested by column cutout (i.e., pulling the call far enough)? I know this is covered in simulator sessions for 737 pilots, but is that enough?
C. Moving forward with the current status and future of commercial aviation have we gotten to the point where basic flying skills and system awareness are so low that we are at risk throughout the whole industry?
D. Can current and future pilot reaction short falls be addressed through training? If so, what kind, how much, and how often?
E. How will we know that we have achieved a sufficient industry wide level of safety?
My view is that Boeing, FAA and probably a whole pile of other people engaged in aircraft manufacture (including my side of the Atlantic) may want to take a very close look at how their entire design, manufacture, training, introduction to passenger flying and oversight systems have evolved over the decades. This sort of thing simply should not happen on 21st century aircraft; we should have enough layers of safety such that the hole in the final, pilot's, slice of cheese is acceptably small. If the Ethiopian crash has the same flavour as Lion Air, some pretty big and incorrect assumptions have been made.
The posts from FCeng84, #2018, Ethiopian airliner down in Africa
and Aloha KSA, #2022, Ethiopian airliner down in Africa
… … essential reading for everyone before considering posting to this or related threads - ‘sticky link’ mods?
FCeng adequately identifies the problems associated with ‘assumption’, but less so it’s association with, and the effects of hindsight.
The outcome of an event (success) does not change the risk of the decision before the event.
Similarly, outcome and assumption in piloting ability. Regulations might imply that there is ‘an average pilot’ (as I recall the wording - ‘without exceptional skill or force’), the danger is if the industry judges or classifies people in a mathematical or mechanical manner; we are not machines, computers, but variable and fallible individuals.
Aloha, et al,
An increasing difficulty in modern aviation is how experience is to be gained, communicated, and heeded by everyone. What might have been true for earlier versions of the aircraft and operational environment in the widest sense, is no longer so.
Differences training is only forward looking; design and regulation must look over back and consider the history, if not then history will ‘find all of us out’.
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FAA missed certification issues
Last edited by offa; 19th Mar 2019 at 09:06. Reason: Typo
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As a long-time 737 driver I'll just chime-in a few points. Regarding the trim wheel ability to move the stab at high speed from full deflection: I seriously doubt that there would ever be too much force on the elevator that the trim wheel could not move it. There is a lot of leverage in the jack screw, and the turns of the trim wheel make very minute changes to the angle of the stab.
But know that moving from full deflection to neutral would take a painfully long time. On the -200 we used to wind the trim full fore and aft as part of the preflight checks. (We stopped doing that on the NG.) . Using the motor-driven trim this took about a minute to go full forward, full aft, then back to about 4 units. It is not physically possible to wind the trim wheel that fast for that long manually, especially when your aircraft is lurching about like a rodeo bull. Also note that it doesn't take much movement to change the aircraft's attitude significantly, and the aircraft is very controllable using manual trim. Back in the cargo days I once did a 20 minute flight using only the rudder and stab trim and manual power (on the -200) from after flaps up to 10000' on descent. That's right - I didn't touch the yoke, autopilot-off from climb-out to descent. It was very controllable and stable. (That was a good training exercise, too.)
My First Point: If we don't catch this mis-trim early, un-doing it manually will take a very long time and maybe more time than is available when your aircraft is only 1000' AGL. AND to use the trim wheel for more than small changes, one has to fold the handle out. A handle that has injured many a knee in simulator sessions because combined with the trim motor's speedy rotation of the wheel, it can leave one with a permanent limp.
Second: For all the arm-chair Monday morning QB's who are saying: "Oh, they should have recognized it immediately and disconnected the trim:"
(1) Just after takeoff there is a lot going on with trim, power, configuration changes, and as noted above, the darn speed trim is always moving that trim wheel in seemingly random directions to the point that experienced NG pilots would treat its movement as background noise and normal ops. Movement of the trim wheel in awkward amounts and directions would not immediately trigger a memory item response of disconnecting the servos. No way.
(2) The pilots could very reasonably not have noticed the stab trim movement. Movement of the stab trim on the 737 is indicated by very loud clacking as the wheel rotates. On the -200 it was almost shockingly loud. On the NG, much less so. HOWEVER, the 737 cockpit is NOISY. It's one reason I am happy to not be flying it any more. The ergonomics are ridiculous. Especially at high speeds at low altitudes. With the wind noise, they may not have heard the trim wheel moving. The only other way to know it was moving would be yoke feel and to actually look at the trim setting on the center pedestal, which requires looking down and away from the windows and the instruments in a 'leans'-inducing head move. On the 717, for example, Ms. Douglas chimes in with an audible "Stablizer Motion" warning. There is no such indication on the 737.
(3) The fact that they were at high power and high speed tells me the stick shaker was activated. With that massive vibrator between your legs, alternating blue sky and brown out the window, your eye balls bouncing up and down in their sockets as the plane lurches up and down in positive and negative G's, it would have been a miracle if one of the pilots calmly reached down, flicked off the stab servo cutout switches, folded out the trim handle, and started grinding the wheel in the direction of normalcy. These pilots said over the radio that they had "unreliable airspeed". So they did not even know which instruments to rest their eyes on for reliable info. Their eyes were all over the cockpit looking for reliable info, the plane is all over the place like a wild boar in a blanket not behaving in any rational way. And the flying pilot may have been using the tiny standby IFDS for airspeed and attitude. Ouch.
Finally, runaway stab trim is a very, very rare occurence up until now. We trained it about once every other year in the sim because it is so rare. And when we did it was obvious. The nose was getting steadily heavier or steadily lighter with continuous movement of the trim wheel. That is a VERY different scenario than what these pilots faced.
We also trained for jammed stabilizer, the remedy for which is overcoming it with force. The information they were faced with could very reasonably have been interpreted that way, too.
An URGENT AD from the FAA/ Boeing after Lion Air would have helped get it back to the front of the pilot's minds for sure. Extra training by the airline or an urgent pilot memo would have helped. Maybe one was issued, we don't know yet.
A better question might be: given this nose down attitude, high speed, and fully nose down or almost fully nose down stab, how much altitude would they have had to have to be able to recover. I'm thinking at least 10000 feet to recognize the problem, disconnect the switches, fold out the handle and start frantically winding the stab back to normalcy while the flying pilot tries to gain control via the elevator. It's entirely possible that this scenario, if not recognized early on, is unrecoverable at any altitude.
But know that moving from full deflection to neutral would take a painfully long time. On the -200 we used to wind the trim full fore and aft as part of the preflight checks. (We stopped doing that on the NG.) . Using the motor-driven trim this took about a minute to go full forward, full aft, then back to about 4 units. It is not physically possible to wind the trim wheel that fast for that long manually, especially when your aircraft is lurching about like a rodeo bull. Also note that it doesn't take much movement to change the aircraft's attitude significantly, and the aircraft is very controllable using manual trim. Back in the cargo days I once did a 20 minute flight using only the rudder and stab trim and manual power (on the -200) from after flaps up to 10000' on descent. That's right - I didn't touch the yoke, autopilot-off from climb-out to descent. It was very controllable and stable. (That was a good training exercise, too.)
My First Point: If we don't catch this mis-trim early, un-doing it manually will take a very long time and maybe more time than is available when your aircraft is only 1000' AGL. AND to use the trim wheel for more than small changes, one has to fold the handle out. A handle that has injured many a knee in simulator sessions because combined with the trim motor's speedy rotation of the wheel, it can leave one with a permanent limp.
Second: For all the arm-chair Monday morning QB's who are saying: "Oh, they should have recognized it immediately and disconnected the trim:"
(1) Just after takeoff there is a lot going on with trim, power, configuration changes, and as noted above, the darn speed trim is always moving that trim wheel in seemingly random directions to the point that experienced NG pilots would treat its movement as background noise and normal ops. Movement of the trim wheel in awkward amounts and directions would not immediately trigger a memory item response of disconnecting the servos. No way.
(2) The pilots could very reasonably not have noticed the stab trim movement. Movement of the stab trim on the 737 is indicated by very loud clacking as the wheel rotates. On the -200 it was almost shockingly loud. On the NG, much less so. HOWEVER, the 737 cockpit is NOISY. It's one reason I am happy to not be flying it any more. The ergonomics are ridiculous. Especially at high speeds at low altitudes. With the wind noise, they may not have heard the trim wheel moving. The only other way to know it was moving would be yoke feel and to actually look at the trim setting on the center pedestal, which requires looking down and away from the windows and the instruments in a 'leans'-inducing head move. On the 717, for example, Ms. Douglas chimes in with an audible "Stablizer Motion" warning. There is no such indication on the 737.
(3) The fact that they were at high power and high speed tells me the stick shaker was activated. With that massive vibrator between your legs, alternating blue sky and brown out the window, your eye balls bouncing up and down in their sockets as the plane lurches up and down in positive and negative G's, it would have been a miracle if one of the pilots calmly reached down, flicked off the stab servo cutout switches, folded out the trim handle, and started grinding the wheel in the direction of normalcy. These pilots said over the radio that they had "unreliable airspeed". So they did not even know which instruments to rest their eyes on for reliable info. Their eyes were all over the cockpit looking for reliable info, the plane is all over the place like a wild boar in a blanket not behaving in any rational way. And the flying pilot may have been using the tiny standby IFDS for airspeed and attitude. Ouch.
Finally, runaway stab trim is a very, very rare occurence up until now. We trained it about once every other year in the sim because it is so rare. And when we did it was obvious. The nose was getting steadily heavier or steadily lighter with continuous movement of the trim wheel. That is a VERY different scenario than what these pilots faced.
We also trained for jammed stabilizer, the remedy for which is overcoming it with force. The information they were faced with could very reasonably have been interpreted that way, too.
An URGENT AD from the FAA/ Boeing after Lion Air would have helped get it back to the front of the pilot's minds for sure. Extra training by the airline or an urgent pilot memo would have helped. Maybe one was issued, we don't know yet.
A better question might be: given this nose down attitude, high speed, and fully nose down or almost fully nose down stab, how much altitude would they have had to have to be able to recover. I'm thinking at least 10000 feet to recognize the problem, disconnect the switches, fold out the handle and start frantically winding the stab back to normalcy while the flying pilot tries to gain control via the elevator. It's entirely possible that this scenario, if not recognized early on, is unrecoverable at any altitude.
Ask the expert.com - could you explain TCMA and it’s functionality on the MAX8?
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Similarly, outcome and assumption in piloting ability. Regulations might imply that there is ‘an average pilot’ (as I recall the wording - ‘without exceptional skill or force’), the danger is if the industry judges or classifies people in a mathematical or mechanical manner; we are not machines, computers, but variable and fallible individuals.
This is relevant. At some point a subtle shift occurs; moving ever so slightly away the assumption changes, more specifically the definition shifts.
It is not noticed and to the casual observer the base assumption is unchanged. Over time, the foundation upon which the assumption was founded bears little resemblance to the original.
Subtle language shifts will give a clue, but the regulator must be looking for them.
Self regulation, regulatory capture.
The safety analysis Boeing sent to the FAA reported that the MCAS could only move the plane’s horizontal tail 0.6 degrees (out of a physical maximum of a little less than five degrees). But during later flight tests, Boeing discovered that 0.6 degrees of movement wasn’t enough to avert a high-speed stall, the Seattle Times reported. Boeing eventually increased the limit to 2.5 degrees.Despite quadrupling the amount that the MCAS could move the plane’s tail, Boeing never updated the documents it sent to the FAA. FAA engineers only found out about the change after the Lion Air crash, when Boeing sent a notice to airlines explaining how the system worked.
This encapsulates organisational deviance from normal.
Although this change is more substantial, it is often missed, so the outcome isn't adjusted either.
It is an incremental tweak here, a subtle shift there.
None of it is really nefarious, over time it isn't questioned. Call it 'assumption precession'. Small changes unnoticed do not alter the course of the event however over time the outcome will be nothing like what was envisaged. They can deliver a big shock when they are finally noticed.
“The FAA believed the airplane was designed to the 0.6 limit , and that’s what the foreign regulatory authorities thought, too,” an FAA engineer told the Times. “It makes a difference in your assessment of the hazard involved.”
Economic models are built on assumptions, like rational expectations and reasonable man.
Does Bill Gates perceive a change in say interest rates and act the same as a minimum wage worker in Chicago? Of course not but these assumptions are what underpin modern economic theory and they are in part the reason why the model fails: Bad assumptions.
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Now that we're down to two global manufacturers the pace can slacken whilst they chip away at their 12,000 aircraft backlogs. That's not healthy competition. Neither is the careful dovetailing of widebodies so that one is not directly competing with the rival's.
It doesn't look like the Russians are gaining much traction as a competitor but if the Chinese can use their African and Asian influence to sell the C919 then perhaps we'll get back to a more innovative playing field. How will B and A compete with C when they're all using the same engines? They'll need to raise their airframe game.
* Interestingly in both cases the innovator was competing against TWO active rivals, not one.
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A question not asked on this thread yet..
For a safety system it makes no sense to have a 'single point of failure' this is a sine qua non of any safety related engineering. MCAS is obviously a safety system and (despite disparaging comments here) Boeing engineers will not have deliberately chosen to make it unreliable. So this begs a question.
First there are a LOT of 737's flying; from Wikipedia:
A large number of those 737 (if not all) will have the same AoA feeding similar ADIRU and will get an Unreliable Airspeed alert plus stick shaker if AoA disagree. Out of 50 or so Max 8 they have already had two errors only months apart. If that was the rate in the whole fleet there would be continual unreliable airspeed reports and no engineer in their right mind would hang a safety system onto a single AoA if they were that unreliable. From that one can only assume that AoA is normally very reliable to the extent that failures are very rare on previous 737 models.
So the question is - why are the AoA systems on 737Max8 failing at a rate higher than acceptable? Is this just a sad coincidence that when a safety related system is designed to use the AoA output - two failures arise in 6 months -or- is there something different about the Max that is leading to AoA problems?
Even 'ramp rash' could be affected by the different position of the engines when push crews and catering used to NG have to work with the Max.
Any thoughts?
First there are a LOT of 737's flying; from Wikipedia:
" As of 2006, there were an average of 1,250 Boeing 737s airborne at any given time, with two either departing or landing somewhere every five seconds"
So the question is - why are the AoA systems on 737Max8 failing at a rate higher than acceptable? Is this just a sad coincidence that when a safety related system is designed to use the AoA output - two failures arise in 6 months -or- is there something different about the Max that is leading to AoA problems?
Even 'ramp rash' could be affected by the different position of the engines when push crews and catering used to NG have to work with the Max.
Any thoughts?
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Literally, we seem to have a black and white mandatory certification requirement, ignored or overlooked by the project engineers who postulated moving these large engines up and forwards, developing into a mad rush for an affordable workaround... to a situation that would RARELY be met; would be UNDERSTANDABLE to a crew if it was; and could be ANSWERED COMPREHENSIBLY by a pre-existing and time-honoured stick shaker (or re-engineered shaker/ pusher pair)
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Yeh. Think I made that point earlier based on such a blatantly naive solution to an Alpha ~ Stick force condition, messing so brutally with stab trim.
Literally, we seem to have a black and white mandatory certification requirement, ignored or overlooked by the project engineers who postulated moving these large engines up and forwards, developing into a mad rush for an affordable workaround... to a situation that would RARELY be met; would be UNDERSTANDABLE to a crew if it was; and could be ANSWERED COMPREHENSIBLY by a pre-existing and time-honoured stick shaker (or re-engineered shaker/ pusher pair)
Literally, we seem to have a black and white mandatory certification requirement, ignored or overlooked by the project engineers who postulated moving these large engines up and forwards, developing into a mad rush for an affordable workaround... to a situation that would RARELY be met; would be UNDERSTANDABLE to a crew if it was; and could be ANSWERED COMPREHENSIBLY by a pre-existing and time-honoured stick shaker (or re-engineered shaker/ pusher pair)
Also, as far as we know, MCAS itself might have worked as intended, had the single AoA sensor it depends on not acted up. The problem apparently is, that against fundamental state of the art aerospace engineering principles, it was designed without redundant sensor data input, thus making it irregularly vulnerable as a system, that in case of malfunction potentially leads to outcomes in the "catastrophic" category.
Anyway, the jackscrew was found in the HST full nose down position, and it's highly unlikely the pilots put it there. Pilots and passengers are dead, but Boeing's order book is still full.
Insurances rationally calculate a fatality in aircraft accidents somewhere between 2 to 4 million US $ per victim.
So we stay at about 1 billion US $ for lost lives. Plus another 1-2 billion payments to customers for lost revenue due to the grounding.
Versus 600 billion US $ for Boeing's backlog for the 737 MAX?
Of course there are also highly unpredictable non tangible risks in that equation, image related, fear of traveling public etc.
Probably manageable though, and overall, the cost analysis is still in favour of the hasty design and pseudo-certification procedure. And looking at the numbers, Boeing management still deserves their yearly bonus, no?
(if you find cynicism, you can keep it.)
Last edited by Interflug; 19th Mar 2019 at 13:42.