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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 16th Mar 2019, 21:53
  #1661 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
Have you ever flown a 737?

The trim wheel moves by itself all the time. When is it supposed to and when isn't it?
It's supposed to when the autopilot is on and after takeoff when the autopilot is off and the flaps are not up.
When you are reading erratic indications on your instruments and it is consistantly trimming down, switch it off, you might save some lives.
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Old 16th Mar 2019, 21:55
  #1662 (permalink)  
 
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Thought Experiment

Originally Posted by reamer View Post
Every pilot of the 737 has known since the Lionair crash that the first thing to do in this situation is simply switch off the mcas by cutting off the stab trim switches.
Constant Stall Horn
Air noise as the airspeed increases
Adrenaline is pumping
Your blood is coursing through your veins... into your eardrums

CA directs FO “Stab Trim Cutout Switches to Cutout”
PM says “What! I can’t here you. Say again!”

That F**king Horn

CA “I SAID, STAB TRIM SWITCHES TO CUTOUT”
FO “STAB TRIM SWITCHES CONFIRM”
CA “YES, AFFIRMATIVE!”
FO “BOTH?”
CA “YES! DO IT!”

You struggle as you pull
You need both Hands
Airspeed is increasingly and so is the forces on the stabilizer

OMG the throttles are still at firewall
CA “Pull the Theottle back!”
FO “WHAT! I can’t hear you.”
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Old 16th Mar 2019, 21:55
  #1663 (permalink)  
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Originally Posted by reamer View Post
It's supposed to when the autopilot is on and after takeoff when the autopilot is off and the flaps are not up.
When you are reading erratic indications on your instruments and it is cosistantly trimming down, switch it off, you might save some lives.
MCAS does not trim constantly and with everything else that might be going on...well it's already been pointed out above.

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Old 16th Mar 2019, 21:57
  #1664 (permalink)  
 
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Originally Posted by reamer View Post
HAL won't trim you down if he is switched off. Have you read the notice?
Question- who knows whether or not the artificial feel system drops to zero or stays at full force when HALs minions are disconnected ?

Do you ? Please cite source ...

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Old 16th Mar 2019, 21:59
  #1665 (permalink)  
 
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The F/O should know what to do too?
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Old 16th Mar 2019, 22:04
  #1666 (permalink)  
 
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Originally Posted by CONSO View Post
Question- who knows whether or not the artificial feel system drops to zero or stays at full force when HALs minions are disconnected ?

Do you ? Please cite source ...
It doesn' t. My source is experience. When I cut them off it felt the same,
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Old 16th Mar 2019, 22:07
  #1667 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
MCAS does not trim constantly and with everything else that might be going on...well it's already been pointed out above.
Okay, maybe not constantly, but often enough to make the plane uncontrollable.
Is your point that the pilots are blameless if they didn't cut off the trim switches?
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Old 16th Mar 2019, 22:07
  #1668 (permalink)  
 
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Thought Experiment

Originally Posted by Cloud Cutter View Post
No, the mindset of jumping to a conclusion that disparages a deceased flight crew who aren't here to defend themselves, without seeking to understand the full picture. We clearly disagree, your points noted with thanks, back to topic!
Its always the same.... Pilots eat their dead
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Old 16th Mar 2019, 22:09
  #1669 (permalink)  
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Originally Posted by reamer View Post
Okay, maybe not constantly, but often enough to make the plane uncontrollable.
Is your point that the pilots are blameless if they didn't cut off the trim switches?
No, my point was that the trim wheel moves by itself all the time. It's not unexpected, then throw in up to 9 different cautions/indications and it's easy to disregard.
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Old 16th Mar 2019, 22:16
  #1670 (permalink)  
 
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Next time I'm SLF . . .

. . . I wanna fly with reamer, not one of those ordinary pilots who are affected by work overload, startle factor, baffling PFD readings and alarming acft behavior, at high speed and low altitude. I mean, who wouldn't want to?
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Old 16th Mar 2019, 22:24
  #1671 (permalink)  
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Originally Posted by OldnGrounded View Post
. . . I wanna fly with reamer, not one of those ordinary pilots who are affected by work overload, startle factor, baffling PFD readings and alarming acft behavior, at high speed and low altitude. I mean, who wouldn't want to?
Simply writing a few words saying do it this way does not make anyone a better or worse pilot than anyone else.

Trying to understand every implication, cause and problem of a particular accident does make you better. As does trying to see this from the point of view of those dead pilots.
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Old 16th Mar 2019, 22:27
  #1672 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
Simply writing a few words saying do it this way does not make anyone a better or worse pilot than anyone else.

Trying to understand every implication, cause and problem of a particular accident does make you better. As does trying to see this from the point of view of those dead pilots.
irony alert! Don't take what he wrote literally.
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Old 16th Mar 2019, 22:35
  #1673 (permalink)  
 
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Originally Posted by RickNRoll View Post
irony alert! Don't take what he wrote literally.
Uh, right. That said, Chesty's contributions are polite and level-headed; he may expect the same from the rest of us -- which shouldn't be an unreasonable expectation.
I apologize. The "any good pilot [engineer/physician/whatever] would have . . ." attitude just really annoys me. And I'm pretty sure it doesn't contribute to safer operations in any discipline.
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Old 16th Mar 2019, 22:36
  #1674 (permalink)  
 
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Originally Posted by DaveReidUK View Post
You're probably right.

But what's really needed is an in-depth look at the (changed) relationship between the regulators and the industry (by no means confined to the USA).
Maybe. But so much of the certification work is done by designees (Boeing employed) and the truth is that the FAA executives who put that system in place are mostly retired, some employed in the private sector.
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Old 16th Mar 2019, 22:38
  #1675 (permalink)  
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Sorry OldnGrounded I misunderstood.

Still fuming about the Calcutta Cup, that's my excuse and I'm sticking to it.
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Old 16th Mar 2019, 22:40
  #1676 (permalink)  
 
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My thoughts about MCAS as a hardware designer:

1. Aircraft are nonlinear/unstable systems that can only be stabilized by control laws in a small (linear perturbations) part of the parameter space. A deep stall is an example of non-linearity.
2. Complexity explodes exponentially with state (autopilot mode, AOA vane failure detected etc.), an important design goal is to reduce state. State includes any if... then... in software.
When software initiates a state change on its own (autopilot switches off, systems disabled because of a broken sensor, stall recovery deployed) this should be announced to the pilot by aural warning. A pilot should always know exactly what the control state of the aircraft is, 'what is it doing now?' is not a good thing to wonder about up in the air.
3. There is unavoidable state that relates to the physics of flying: flaps, trim, gear = configuration. If automation is allowed to mess with configuration there must be cutouts and self-checks (cross checks against other sensors, stick position, whether data is consistent) to prevent instability.
4. MCAS has a very specific control function in a specific part of the flight envelope. It is easy to cross check with other sensors whether this part of the flight envelope is entered and how large a control input is required.

It puzzles me that, at complete odds with this, MCAS was given an integrating control function without bounds on a crucial flight control surface. Without data validity check. Without aural deployment warning. Without aural and visual AoA disagree warning. Without control input cross check. Without adiru cross check.

With safety critical subsystems there should always be at least 2 barriers before handing things over to a human as the last line of defense to prevent an incident.
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Old 16th Mar 2019, 22:50
  #1677 (permalink)  
 
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Originally Posted by dingy737 View Post
Thanks. Therefore and for argument sake, if these incidents were in fact “runaway stabilizers” we could expect the same tragic result. MCAS should have been interpreted as a “ RUNAWAY STAB. “ for which pilots are repeatedly drilled in the simulator.
MCAS: parameters for operation.
1. Autopilot OFF
2. Steep Bank/ Turn. ( what angle ?)
3. Flaps retracted.
4. High AOA
If the above 4 are correct, how many of those parameters were NOT met in Ethiopia. Nevertheless, prolonged trimming with the AP off instinctively requires stab switches OFF. I believe with the flaps NOT retracted, the Trim rate is increased as compared to flaps retracted. A runaway trim with flaps extended will very quickly overpower the pilot, the time frame allowed to identify and react appropriately, by selecting both switches OFF is extremely short if this occurs just after lift off. Once the pilot starts fighting the Yoke with both hands I suspect his mind will become focused on the physical deminishing the ability to keep thinking.
While MCAS was required to address column force characteristics in a turning flaps up stall maneuver, its logic does not include any consideration of bank angle or any other detection of turning conditions.
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Old 16th Mar 2019, 23:27
  #1678 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
Dear Mods, any chance you could give the altimetry geeks their own thread? It's been done to death and we don't need to see reams of calculations cluttering up the technical stuff.
As one such 'geek' (if what happens in modern cockpits doesn't actually need much human mathematical verification?), I don't entirely disagree. I do well appreciate most PP readers here do want to try to understand the foibles of AOA sensors and stab trim runaway with MCAS, and also to be able to scope the data inputs to MCAS so they have some idea of "what's it doing now". PPs will want particularly to be able to answer the related big questions about how MCAS really behaves armed with dodgy AOA and other data, and how to disarm it.

But the reason perhaps why some of us are questioning altimetry may well be because we see very low altitude reports from the outset, and wonder if this accident began with something else entirely e.g. an error during the take-off roll.

Fact is, unless we toss in the benefit of a couple of hundred fictitious feet for doubt, there otherwise seems precious little evidence from the tele-altimetry - which looks very consistent and accurate in so many respects all the way up to rotation - that the aircraft then left the ground at all normally.

If there was a static pressure increase at rotation (if that is a known feature of the aerodynamics at high AOA leading to the "below ground" 05:38:47.714 altitude of 7075') it would affect cockpit IAS, and VS indications too, would it not? And if that is evidence of an aerodynamic anomaly, and it is not a spurious measurement, then might other static pressure anomalies exist at the static port positions at high AOA with this airframe?

That said, the first ADS-B altitude report that has to be a truly airborne report - because it may be the first that can be truly validated as being above aerodrome level - is timed at 05:39:04.028. Yet that one is well over the dirt which has sloped some 150ft down from the runway by that point. Putting full credence in ADS-B 1013 altitude data, and taking Luc Lion's reminder of 420' differential from QNH, a quick look at that particular datapoint using the "Viewshed" tool in Google Earth, raises a question as to whether a spectator standing behind the other end of the runway could even still see the aircraft. Was it indeed so low that it disappeared off the end of the runway to such a spectator at the 07R threshold end? The previous datapoint is 5 secs earlier at 05:38:59.102, also over dirt not tarmac, and located 1542 feet further back. There is nothing in any of the datapoints along the centreline of the runway to suggest that they are anything other than spot-on location-wise. The two data points indicate an average ground speed of 1542 feet (0.2538nm) in the 4.74 secs between them, or 0.2538 * 3600/4.74 kts = 193kts. The actual reported speeds transmitted as those two datapoints are 200 kts and 207 kts (not sure how they are computed onboard the aircraft before transmission - sourced from onboard GPS or from INS?).

And at that 05:38:59.102 datapoint - the first just beyond the runway - ET302 may have been 100ft (+ or - 25ft) above the by then already downward sloping dirt. The VS between the two points assuming static pressure was then lapsing in book expected linear fashion should have indicated (7300'-7225' + or - 25') * 60/4.74 ft/min = (100' or 50') * 60/4.74 ft/min = between 633ft/min and 1266 ft/min. The lower would seem to reflect what was given in ADS-B reports and that in turn may suggest the aircraft was indeed still fighting for altitude down in the weeds.

IF it was, why was it in the weeds in the first place? It was still only 12-14 secs after initial signs of a rotation. MCAS doesn't explain weeds so soon on its own, does it? Did something happen first on the runway, which has not been much discussed (if something did happen), and did it line up a couple of holes in the cheese? And then did MCAS offer the third or fourth bad thing and the eventual gotcha? Or was the take-off normal and only afterward went pear-shaped?
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Old 16th Mar 2019, 23:46
  #1679 (permalink)  
 
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Originally Posted by reamer View Post
It's supposed to when the autopilot is on and after takeoff when the autopilot is off and the flaps are not up.
When you are reading erratic indications on your instruments and it is consistantly trimming down, switch it off, you might save some lives.
And in cruise as you burn off fuel and your cg changed , and when the Mach transducer says so. It’s constantly moving.
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Old 17th Mar 2019, 00:07
  #1680 (permalink)  
 
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Originally Posted by reamer View Post
Every pilot of the 737 has known since the Lionair crash that the first thing to do in this situation is simply switch off the mcas by cutting off the stab trim switches.
Wouldn't you get the aircraft back in trim with the yoke switches first?

Easy to say what you should do sitting at a keyboard.
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