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Maintenance Lapse Identified as Initial Problem Leading to Lion Air Crash

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Maintenance Lapse Identified as Initial Problem Leading to Lion Air Crash

Old 4th Jan 2019, 16:53
  #101 (permalink)  
 
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okay, got it! Thanks!

on a similar note, what is that crazy airspeed sensor mounted on a window port??
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Old 4th Jan 2019, 17:44
  #102 (permalink)  
 
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Maybe similar to the combo AoA probe/ Pitot tube combinations that's on the A350?
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Old 4th Jan 2019, 18:27
  #103 (permalink)  
 
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Originally Posted by underfire View Post
on a similar note, what is that crazy airspeed sensor mounted on a window port??
Looks like the 737 MAX 9 prototype.

Given that it's going to an airline eventually (ironically to Lion Air, albeit their Thai offshoot), it makes sense to mount a test probe on a window blank rather than cutting holes in the fuselage skin.
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Old 4th Jan 2019, 18:55
  #104 (permalink)  
 
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My problem with this entire accident is bad AOA or not, the airplane should not have nosed into the ocean. This was not a fatal discrepancy. If the horizontal stab is continuing to trim nose down disconnect it and manually trim the stab.
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Old 4th Jan 2019, 19:09
  #105 (permalink)  
 
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Looks like maybe an OAT probe, maybe not
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Old 4th Jan 2019, 19:21
  #106 (permalink)  
 
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Originally Posted by Wodrick View Post
Looks like maybe an OAT probe, maybe not
Certainly looks to me to be a Total Air Temperature (TAT) probe - obviously fitted for flight test proposes. Airspeed probes nearly always have a round or oval inlet, for some reason the rectangular inlet is preferred for temp.
Just speculating - perhaps a different design probe, using flight test to verify it's performance vs. the normal TAT probe. Or maybe unheated, so that they can measure the effect of probe heat on the normal probe when not in icing or similar conditions.
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Old 4th Jan 2019, 19:21
  #107 (permalink)  
 
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It's a flight test airplane... Its used to verify the "real" systems during the flight test program.
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Old 4th Jan 2019, 23:16
  #108 (permalink)  
 
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Salute tjernagel!

The crash was not a simple loss of AoA that the crew was using to fly or a vital input to a fly-by-wire system such as the Airbus 320 and following versions. As much as it is touted, the 777, the early F-18 and such were nowhere near FBW than the Airbus, shuttle, or the Viper I flew long ago.

It's a flight test airplane... Its used to verify the "real" systems during the flight test program.
Correct, but who did the crew verification of the "real" MCAS during the flight test and have one test point where the AoA was off the wall and the plane kept commanding nose down? Not "runaway trim", because you could beep the trim and the system stops commanding nose down for 5 or 6 seconds, then whaaahoo.

I will try to return to my cave for awhile, but a point or two.
- I cannot imagine a new system in a new mod of an old plane that has the potential to make the plane go nose down without pilot consent and without some kinda warning light that the new system is active. Stick shaker? Yes. Some kinda restricttion on commanding further nose up? Sure. But commanding nose down over and over without some kinda signal that something was awry? I don't wanna fly that beast as a pilot or SLF.
- I cannot imagine the system above not being made very public to all pilots and carriers using the plane. GASP!! Without the AoA aspect as a contributing cause to this crash, how come all pilots flying the type did not know a new system was installed and what its purpose was and how it worked. Sheesh.

Gums sends...

Last edited by gums; 5th Jan 2019 at 02:27. Reason: grammar?
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Old 4th Jan 2019, 23:49
  #109 (permalink)  
 
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Originally Posted by gums View Post
Salute tjernagel!

The crash was not a simple loss of AoA that the crew was using to fly or a vital input to a fly-by-wire system such as the Airbus 320 and following versions. As much as it is touted, the 777, the early F-18 and such were nowhere near FBW than the Airbus, shuttle, or the Viper I flew long ago.



Correct, but who did the crew verification of the "real" MCAS during the flight test and have one test point where the AoA was off the wall and the plane kept commanding nose down? Not "runaway trim", because you could beep the trim and the system stops commanding nose down for 5 or 6 seconds, then whaaahoo.

I will try to return to my cave for awhile, but a point or two.
- I cannot imagine a new system in a new mod of an old plane that has the potential to make the plane go nose down without pilot consent and some kinda warning light that the new system is active. Stick shaker? Yes. Some kinda restricttion on commanding further nose up? Sure. But commanding nose down over and over without some kinda signal that something was awry? I don't wanna fly that beast as a pilot or SLF.
- I cannot imagine the system above not being made very public to all pilots and carriers using the plane. GASP!! Without the AoA aspect as a contributing cause to this crash, how come all pilots flying the type did not know a new system was installed and what its purpose was and how it worked. Sheesh.

Gums sends...
Newer 737 NG's already has a stall protection system that nosed the plane down during a stall.
The difference between the MAX and NG is that the NG will cut out all nose down stab trim if the control column was pulled back far enough. The MAX mcas fcc output locks out the column cutout switch so this can't be done unless the control stand switches are flipped.
So would it make sense that someone who lacked the mcas training but had sufficient NG training should have believed something is wrong with the stab trim when it continues to nose down with the control column pulled back? Just because you can bump it back with manual trim means nothing, you are effectively in a tug of war with the fcc.
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Old 4th Jan 2019, 23:56
  #110 (permalink)  
 
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Originally Posted by MickG0105 View Post
What the hell does that mean? Could that have anything to do with the apparent ineffectiveness of the ANU trim commands after control was handed over to the FO?
Only the FO column cutout module interfaces with the fccs. The mcas engage coil is contained within it.
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Old 4th Jan 2019, 23:59
  #111 (permalink)  
 
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Gums - I for one appreciate your well reasoned and clearly presented thoughts. I hope you don't spend too much time in that cave or that if it does it includes a means to connect to PPRuNe often to share your insights.

Your last post included a reference that has long been a touchy one for me. FWB literally means Fly-By-Wire. We most often presume that to be an electrical wire, but if you extend "wire" to also include mechanical cable then our commercial fleets have been FBW for a long time! My real point, however, is that FBW and Augmented are not one and the same. If I take a mechanical linkage from pilot stick to elevator and replace it with an electrical sensor that measures stick position, a wire that transmits that stick position to an elevator actuator, and an elevator actuator that responds to electrical inputs I have FBW, but I do not have an augmented control system. The augmentation part is where the system uses other inputs besides pilot stick position to determine where to put the elevator.

The 777 is a good example of both simple FBW and complex control augmentation. For it's pitch axis the 777 in its full-up Normal Mode provides considerable augmentation to increase stability, compensate for configuration and thrust changes, and include envelope protection to aid the pilot in keeping angle-of-attack and speed within normal ranges. In the lateral axis the 777 essentially provides proportional gearing from the pilot's wheel to the various wing surfaces used to command roll. 777 also has Bank Angle Protection that works by directly moving the pilot's wheel, but the linkage from wheel to wing surface does not involve any augmentation. In its back up (Secondary/Direct) modes the 777 essentially provides direct pilot controller to surface gearing in all axes.

Those of you who strapped themselves into birds like the Viper were the real pioneers of fully augmented flight with lots of trust in the systems and hopefully an ejection seat that you never had to call upon. Building on that foundation we now see more and more augmentation being used in commercial transport control systems. There is certainly room and need for sound judgement as to how those systems are designed, validated, verified, trained, and maintained. One of the biggest challenges is determining what the limits should be as to how much we are willing to employ augmentation to make up for less than desirable open loop handling characteristics.

Back down off my soap box for now,

FCeng84
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Old 5th Jan 2019, 03:45
  #112 (permalink)  
 
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Salute FCeng!
Taking a rest now, but I have to clarify my definition of FBW for you and others to ponder. I take a harsh position concerning "augmentation" versus pure FBW. The Airbus inplementation is the closest system to what I flew, and even it has a control cable or two for one control surface. It also is a gee command, albeit biased by pitch and roll attitude. Still the closest system to the F-16 and shuttle.

Well before the Viper prototype we had the A-7D "control aug" component of our flight control system that used transducers in the stick control grip to talk to the autopilot. It did this when we did not have autopilot engaged, so-called "manual", but used the autopilot connections to move ailerons and elevator. On my FCF flights I would hold the stick between by legs and simply twist/tilt the grip to bank and pitch. It was functionally FBW, but not really.... heh he. What it did was allow very small, sensitive inputs to the pitch and roll control surfaces using minimal actual movement of the stick. It also used "inertial" sensors that I never bothered to locate, and assumed were in the autopilot hardware. The result was control surface movement when you had your hand completely off the stick! You could tell if the guy in front had "control aug" on because the ailerons and elevator would be twitching on every bump in the taxiway. This characteristic was very evident in the Viper, and you can even see it in the AB 320series. For we "light" types, it made for super close formation flying and very nice ILS approaches following the HUD and/or ADI steering bars. From what I have learned the past two months about the 737 is that even tho the pilots call it flying "manual" the plane still has Hal "helping", as in the STS system. And now the MCAS.

Other than some "x" planes and the captured saucer at Groom Lake, we had the first true FBW in the YF-16, although I beleive at the time the X-15 was pure FBW, and the shuttle was being developed with pure FBW. I cannot emphasize enuf, and have repeated over and over, there were zero mechanical connections to any control surface, period. Constant hydraulic pressure was supplied to the integrated servo actuators and electrical commands moved the small valves in the ISA's. If the electrical connections were gone, then we only had the nylon letdown. A few years later we saw the Enterprise glide down to the strip at Edwards, and it had zero mechanical connections of any kind to the control surfaces. We also saw a few test articles that did away with the hydraulic connection to the ISA's, and had pure electric jets. I dunno what they did with that saucer over near Wendover.

With respect to the point about "augmentation", it looks like we are defining terms and design features. My community used the term FBW meaning no mechanical connections., only electrical signals to the actuators regardless of them being electrically powered or using hydraulic pistons. The only FBW mode I have seen in any plane that has negligible "augmentation" is the "direct" law found in the ;bus, where stick position is turned into control surface position with minimal or little regard for dynamic pressure ('q") or other variables. It is entirely possible to have a functional FBW system with a surface movement corresponding to a stick position or pressure using a fixed "gain" - e.g. 30 degrees of deflection moves the aileron 10 degrees. No problem, and you see this every day with home hobby drones and high perforemance RC planes. However, that implementation is relatively coarse and can easily be "augmented" by bringing into play body rates, dynamic pressure, Aoa, gee and attitude. As with the 'bus, you can get a plane to feel really good and easy to put where you want it to go. The Viper was like that, and the interaction of all those variables came into play. For example, left/right pressure ( mainly pressure, but stick moves less than a eight of an inch) commands roll rate, not aileron deflection. Hal looks at dynamic pressure and AoA and ......, then commands the ailerons, rudder and the independent horizontal stabs to move at "x" rate to "y" degrees in order to result in commanded roll rate. The damned thing is like a video game except for the 9 gees and bouncing your head off the canopy when rolling too sharply.

I personally liked the "augmentation" in the Sluf, and I cannot imagine what a nightmare the Viper would have been without variable gains and rate functions, not to mention AoA inputs.

Thanks for all the tech stuff, FCeng, and we'll see each other later for sure..

Gums sends..

Last edited by gums; 5th Jan 2019 at 03:46. Reason: forum text protocol
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Old 5th Jan 2019, 09:02
  #113 (permalink)  
 
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Originally Posted by tjernagel View Post
My problem with this entire accident is bad AOA or not, the airplane should not have nosed into the ocean. This was not a fatal discrepancy. If the horizontal stab is continuing to trim nose down disconnect it and manually trim the stab.
Nailed it IMHO tjernagel.

The fundamental question must be, did the crew fail to disconnect the trim and operate it manually? If not, then why not?
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Old 5th Jan 2019, 09:24
  #114 (permalink)  
 
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Originally Posted by KRUSTY 34 View Post
The fundamental question must be, did the crew fail to disconnect the trim and operate it manually? If not, then why not?
Yet another reason why it's essential that the CVR is found.
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Old 5th Jan 2019, 22:10
  #115 (permalink)  
 
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Originally Posted by k3k3 View Post
When the first NATO E-3A aircraft were delivered a couple of them had recurring AOA problems, left and right indicators consistently had the same disparity. After much head scratching it was found that during manufacture, the template for drilling the holes for securing the mounting rings for the interchangeable transducers had not be turned over when going from the left to the right of the nose, with the results we found. The men from Boeing came with their template, drilled the holes in the right place and all was good.

But this was 35 years ago.
corporate memory and all that jazz..
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