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Boeing 737 Max Recertification Testing - Finally.

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Boeing 737 Max Recertification Testing - Finally.

Old 29th Nov 2020, 09:46
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Icelandair operates one 737 Max sim in Iceland. They are planning on 6 frames to be in operation in for Summer 2021 so there might be some sim slots available other airlines
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Old 29th Nov 2020, 12:48
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One wonders about the fidelity of the Max sims to replicate, accurately, the different aircraft dynamics compared to the NG that we are now doing the "additional training" on, such as the different pitch-up from the repositioned engines, especially with the recently agreed extra mods. Presumably if Boeing concealed the technical detail of some Max features from the aircraft purchasers they did the same with the sim builders.
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Old 29th Nov 2020, 16:46
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Outstanding points, WHBM !

I speak from several decades of flying the beasts, instructing in the suckers, and associating with those that flew the ones I did not.

Contrary to one or more contributors here, training can compensate for design deficiencies that resulted in undesireable aerodynamic characterstics. In other words, some planes worked better over most of the envelope than others, but one corner might have its problems. Other planes had great performance overall only if flown with a few things in mind.

So WHBM raises one of the best issues for discussion amongst we "professionals", huh?

The "no training required, but a 15 minute iPad check box session" for the Max was damned near criminal, in my not so humble opinion. If the MCAS was a cert requirement due to inherent and new aero characteristics of the plane I have to fly for the 0915 flight to Topeka, what was it and do I need to do something different and new ?? As good as I was, I was not a Chuck Yeager clone and only explored new aspects of the envelope a few times and they were not due to design or aero problems. One plane I flew had definite problems and the training was a key element that kept most pilots from departing the sucker ( F-101 Voodoo), Ask any Hun or Phantom driver how much aileron they used when at high AoA and the sucker was buffeting. Talk to a Mirage or Deuce or Six pilot about holding back stick and watching the rate of climb needle pegged going down while the plane seemed under control ( ditto for the crew of AF447). You can train to a great extent that compensate for the jet's aero characteristics when a blank sheet new design or harsh mod is not an option.

If they would let me do it right now, I would relish flying the real plane without MCAS enabled just to see "how it felt" if I pulled too hard in the pattern at holding speed/AoA. Would hope all 737 pilots could have that opportunity, wouldn't you? Can we demo this in the new, cosmic, realistic year 2020 sim for the Max? In other words, show me the difference that MCAS makes. Show me the trim wheel force requirements if I screw up and get going real fast with lottsa nose down trim. Show me how the normal yoke trim switches override the MCAS nose down commands. And the beat goes on. I wanna "feel" it, and I want my pilots to "feel" it. It is "touch" that separates "pilots" from mechanical technicians up there in the front of the plane.

Enuf rant, and now I have a second U.S. Thanksgiving dinner with the remains from Thursday, heh heh.
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Old 29th Nov 2020, 18:58
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You'll only feel what the elevator feel and centring unit wants you to feel
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Old 29th Nov 2020, 23:09
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“Contrary to one or more contributors here, training can compensate for design deficiencies that resulted in undesireable aerodynamic characterstics.”

Certainly, training can have a huge impact, but the use of training as compensation for unsafe design deficiencies is below the intended level of safety for Part 25 airplanes.
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Old 30th Nov 2020, 08:36
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GlobalNav

Are you implying it is OK for a Part 23 , or any other lower category ? I know a few aircraft in that category in which the manual says not to attempt things that would be perfectly normal in a standard aircraft.
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Old 30th Nov 2020, 18:00
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I was not implying anything about the Part 23 level of safety, I was being specific about what I have experience with.

To compare Pt 25 with Pt 23 is like having a discussion about presidential politics at the Thanksgiving table, and would accomplish about as much.
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Old 30th Nov 2020, 18:41
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That we can agree on ! But back to your initial sentence which still leaves me uncertain of what you meant :
the use of training as compensation for unsafe design deficiencies is below the intended level of safety for Part 25 airplanes.
Is that an opinion or a fact?,(I am not familiar with the TLS of part 35 a/c) and if it is a fact then what we are about to see now is definitively below the TLS, or are they going to move the standard to fit the exception? .
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Old 30th Nov 2020, 20:10
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I did not mean to create a debate about specific paragraphs of Part X versus Part Y of the codes/laws/rules etc.

I read the Part 25 stuff and other cert requirements way back when the MCAS debacle started. It seemed to me that the problem that MCAS addressed was due to reduced "back stick force" required as the AoA increased in certain parts of the envelope, but primarily related to AoA and not Q or gee, but maybe mach. So let's get the vocanulary standard, huh? Mods have not allowed us to move the technical and engineering stuff to the Tech Log, so guess we can duke it out here with all the political, legal and social stuff.

Due to my background, I use "stick force" referring to a control mechanism pilots use demanding nose up or nose down or roll commands. In some planes, the "stick" does not provide a lotta feedback if any, as in the Airbus or the Viper ( Concorde pilots here that actually flew the thing can contribute). In four planes I flew there was zero roll feedback, just springs!

So if we assert "the only feedback is due to x system", then that dog won't hunt. My concept of "feel" or feedback, is what the plane is telling you! Shake, rattle and roll. Maybe increased pressure or less pressure on your butt when in coordinated flight. I am not disputing basic instrument flying rule number one, and in the only seat that had flight controls for a coupla thousand hours in bad weather, I stand as a survivor.

So my beef with the rationale for MCAS implementation to meet Part 25 or whatever was not to satisfy "dangerous" or unsafe flight characteristics, but to stay on one side or the other of some curve depicted in the cert paragraph. I even found that on a technical web site blog and am too lazy now to find it and show. It was over at the Tech Log that the mods locked.

That being said, I stand by my feeling that training could have helped a lot versus an unknown system that:
1) The pilots didn't know about
2) Was poorly implemented for a host of reasons ( my systems engineering background with armament systems)

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Old 30th Nov 2020, 20:46
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From my 20yrs flying the previous iterations of this thing, I would say co-ordinating the power - pitch couple with engine response and control force v pitch response is not intuitive because, depending where you are with respect to airspeed, engine response and stick pressure, a given amount of stick force produces wildly differing pitch response depending what the thrust is doing.

All of these are benign when used in moderation, but recovering from a low speed, high nose situation with large thrust inputs will rapidly lead to a PIO if the stick pressure is not very carefully co-ordinated with engine response, since the thrust lags considerably behind the position of the thrust levers.
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Old 1st Dec 2020, 01:36
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Good grief, Hector.

If the jet had all those characteristics you allude, then at least a few hours of training musta been required, huh?


Last edited by gums; 1st Dec 2020 at 02:16. Reason: typo
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Old 1st Dec 2020, 15:43
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yo gums,
After your fortifying festive feasts, I wonder if recent posts in this thread have dented your 'training' armour.
Also there may be more room to manoeuvre now that the changes to 737 Max are known.

Moving from 'in principle' training should not replace a bad design (where the consequences of a MCAS event required extreme human performance), to 'in practice', training for systems with residual weaknesses after modification could be accepted

In principle the 737 Max should not have been designed as it was.
But,
In practice, after modification, training could provide sufficient safety even if not an ideal design.

The important aspect is not where the dividing line is (principle - practice), but who judges it; noting the current differences between regulators after MCAS mods.
These are judgement calls, influenced by underlying beliefs.
What safety credit can be assumed about trained crews in rare or surprising situations, noting that human performance demonstrated in training is unlikely to be what happens in real events - events which in some circumstances the industry cannot afford the experience of even one occurrence.

A distant overview is that not only did the FAA get MCAS wrong, their continuing differences with other regulators suggest their choices are not universally agreed, which in turn does little to restore their world standing.
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Old 1st Dec 2020, 20:58
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I agree with ya PEI. I am not advocating to train all the pilots to compensate for a really poor design. I also would have liked to have seen Boeing change a few things to satisfy the FAA cert requirements and avoid the nose up pitch characteristic I saw on the graphs.

Moving from 'in principle' training should not replace a bad design (where the consequences of a MCAS event required extreme human performance), to 'in practice', training for systems with residual weaknesses after modification could be accepted
In principle the 737 Max should not have been designed as it was.
But, In practice, after modification, training could provide sufficient safety even if not an ideal design.
I look at the data we have from the two fatal accidents and conclude that system knowledge and some training would have made a lotta difference. Folks that have flown deltas have been shown the high AoA characteristcs that they have. Concorde was the same as the F-102 or Mirage. Plane feels great, but you are going down at 10,000 feet per minute!! Folks flying the VooDoo were shown that the stick got "light" just before you departed. And so forth. Sure, make the planes foolproof and not as fuel efficient or maneuverable. Somehow I do not think that dog will hunt.

My understanding is the 727 and some British planes would never have been certified without a "pusher" or whatever to avoid the pitchup/deep stall condition. The 707 had some trim problems I recall, and was publisized by an accident with the U.S. skating team. Those planes were certified but seems that the pilots had some training to alert them of what would happen if the "systems" failed.

The MCAS and its failure modes were not part of any training or even discussion or reference material. So I maintain my position that even with a poor design that training would have made a difference.
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Old 1st Dec 2020, 23:48
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Originally Posted by PEI_3721 View Post
Moving from 'in principle' training should not replace a bad design (where the consequences of a MCAS event required extreme human performance), to 'in practice', training for systems with residual weaknesses after modification could be accepted

In principle the 737 Max should not have been designed as it was.
But, In practice, after modification, training could provide sufficient safety even if not an ideal design.
Even if we leave aside the "in principle" and the regs, the fundamental problem remains: "no new (sim) training" was part of the design.

Training could not have substituted for MCAS, could not ever compensate for changed / bad handling characteristics, because training was eliminated by design.
In fact, even the design of MCAS itself was limited because it had to work with "no new training" (no new warnings, no mention in the manual etc.), this is one reason why (according to e.g. this article) it all hung off only a single sensor. What was delivered wasn't just a bad design, it was a bad, bodged, design and no training by design.
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Old 2nd Dec 2020, 08:43
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Surely it's the other way round?

"No training" wasn't a design objective for MCAS.

"No training" was a commercial imperative.
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Old 2nd Dec 2020, 10:16
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"No training" was a commercial imperative

Indeed, one would need to be an insider to know how much time and money the manufacturers spend refining their commonality arguments.
Fly-by-wire with its ability to tweak the aircraft's behaviour has given Airbus such an advantage that Boeing has been running
behind for 30 years.
The Max was a challenge too far.

Last edited by oldchina; 2nd Dec 2020 at 12:00.
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Old 2nd Dec 2020, 13:08
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Please excuse a SLF.

But surely commercial imperatives didn't require MCAS to be such a dogs breakfast? After all it was "just" some sort of feel augmentation system, which required reasonably benign failure characteristics.

Feel augmentation could have been implemented in a straightforward manner with some sort of stick-pusher with limited authority. In which case the pilots instinctive reaction to simply apply more control column force would have saved the day.

... negative thought on what B has become ...

The chosen "aerodynamic" implementation mechanism which was found in practice not to have benign failure characteristics. With pilots failing to analyse the situation effectively (let alone intuitively). It also highlighted some skeletons in the closet: unreasonable force required for manual trim-wheel, over complex multi-warning situation to analyse, if pilots aren't told about MCAS they cannot include it in failure analysis -- and other checklists might require tweaking to compensate.

Last edited by Peter H; 2nd Dec 2020 at 13:09. Reason: politeness
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Old 2nd Dec 2020, 13:44
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oldchina

Boeing was fully caught up by 1995 with, arguably, a better FBW system having learned from Airbus's FBW launch. All they had to do was spread that 777 platform across the size range, as Airbus did, and gain all the same advantages plus having Airbus go first to mark all the potholes along the way. But they didn't, something else happened a couple of years later, turned it around and drove it off the cliff
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Old 2nd Dec 2020, 19:54
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American Airlines starts Boeing 737 Max flights to boost confidence in jets after fatal crashes American Airlines starts Boeing 737 Max flights to boost confidence in jets after fatal crashes (msn.com)
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Old 2nd Dec 2020, 23:00
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@ China and Peter an others......

One mo' time about FBW.

The MCAS moved the horzontal stab to keep the pitch moment of the beast within the FAA cert requirements. That is not a minor "tweak" of the plane's natural aero stability. A computer controlled movement of the elevator at the rear of the stab would have been "minor". Planes since the early 60's have had flight control "dampers" and "augmentation" to help we lowly pilots that get you there on time and maybe smooth things out a bit. The FBW Airbus and the military jets are not in the same arena with the 737 MAX.

The MAX problem was not "feel" from the longitudinal control system, it was the actual tendency of the plane to increase pitch at the same back stick or at least require less back stick when getting above a certain AoA. When I say back stick feel, what I mean is your plane wants to do something it normally does with "x" pound/ounces of pressure or movement, but now requires less or actually requires an opposite movement/pressure/force. The FAA requirement requires more "pull" as you try to get the nose up and increase the AoA. Dat's why the MCAS used the AoA probe and not body rates, Q, inertial gee, etc. Somewhere in there Boeing found that mach contributed to the pitch tendency and then increased the overall "gain" that MCAS exercised, then they had the damned thing keep pushing doen for "x" reps/seconds/whatever. Sheesh!

FBW systems vary as to the amount of "help" they can provide the "technicians" we now have flying the jets, but I cannot find any civilian commercial systems that depend upon the computers to correct for unconventional aero that we see in some military fighters requiring severe maneuverability. Those rascals have different operational requirements and most do not have 200 SLF's depending upon them to get to Detroit. The Airbus 330 aero design is so good that the crew of AF447 did not even realize they were deeply stalled ( not a "deep stall"). Go see the thousands of posts about that debacle and then you will conclude the system did exactly what it was designed to do given the air data provided to the computer and the pilot stick inputs.

FBW is not a magic bullet, and should not be used to compensate for poor aero design.

Last edited by gums; 3rd Dec 2020 at 03:34. Reason: typo; conclusion
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