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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 14th Mar 2019, 13:16
  #1321 (permalink)  
 
Join Date: Sep 2011
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Choose : You just got airborne and cleaned up in IMC;

2 Warnings come up, screaming and flashing, ringing and tinkling.
- Overspeed
- STALL

Choose what you will do because : Some failing sensors, or some twisted code lines, are giving you and your co-pilot conflicting information and warnings.

Then, like in most modern airframes where ( willing or not) some parts of the flight control management system are ALWAYS ON, the airplane itself starts trimming itself.

But to what information IS the airplane trimming itself? ? ? ? ?
Do you know?
Does it know?


Food for thought.
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Old 14th Mar 2019, 13:17
  #1322 (permalink)  
 
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Originally Posted by Sailvi767 View Post


I am going to assume you don’t fly for a living. There is no way you would not recognize a stab out of trim condition while hand flying the aircraft. In addition the aircraft would only accelerate like you portray if the pilot failed to adjust power to maintain the desired airspeed.
Sure about that? Someone new to the aircraft, captain average, and a bit tired.

At 3,000 ft, the stick shaker starts going like mad, causing a hell of a racket, and you think you have an airspeed problem and might be stalling. Sure, the controls are getting heavier and heavier, and you trim a bit for that, but this is caused by the aircraft stalling - isn’t it? (You cannot hear the trimmer, over the din of the stick-shaker.) So you have to let the nose drop, untill you are sure you have enough airspeed.

Ok, you are getting a bit low now, time to pull back. Ahh, but the aircraft will not respond - pull as hard as you like, but the stick feels jammed (you need 60 kg of force to counter full stab-trim). You shout to the f/o to help pull, but the ground is coming up fast.... End of short story...

Silver
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Old 14th Mar 2019, 13:22
  #1323 (permalink)  
 
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Originally Posted by jimtx View Post
The handling differences due to thrust line may have been tuned out but it wasn't by MCAS. Windup turns are done with set thrust.
I think that deserves some clarification. I don't fully agree.

I'm a 30-year flight test engineer and am currently helping to rewrite the handling qualities flight test manual for the US Navy Test Pilot School. We focus more on military than transport aircraft, but we do test and fly 737-derivative airplanes (P-8A Poseidon and the C-40 Clipper) and the test methods are universally applicable.

Windup turns are done with set thrust, yes. Power is set as required to maintain the specified airspeed. What is being compared is the response of the airframe to increasing AOA or g at a fixed airspeed, and throttles are fixed during the maneuver to avoid contaminating the results with another independent variable. Several things can be learned from WUTs, including control force or deflection as a function of load factor or AOA, buffet characteristics as a function of AOA, and structural characteristics as a function of g.

While each test point is conducted at a specific power setting, the tests are typically conducted at a range of power settings. This provides a chance to assess the effect of power setting on the various aforementioned characteristics.

MCAS is (at the core) merely a trim application system, designed to reduce the control forces which develop at higher AOA and g with the new-and-repositioned engines. As such, it is a handling qualities difference that is definitely related to thrust line changes. Those differences would typically be revealed by a series of WUT test points. In this case, a WUT at high thrust would be worse, because of the increased pitch-with-power tendencies.
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Old 14th Mar 2019, 13:32
  #1324 (permalink)  
 
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Originally Posted by Brandon
MCAS is (at the core) merely a trim application system, designed to reduce the control forces which develop at higher AOA and g with the new-and-repositioned engines.
I thought the MCAS increases the (lightening) stick force required to keep pulling back as AOA increases (so pilots have less tendency to pull thru into a stall), the more pronounced nose-up pitch occurring because of the aerodynamic lift generated by the bigger, more forward-positioned engine cowls.

In any case, the mention of wind up turns in the context of pax 737s is a bit of a furphy, IMO. The main issue is high AOA and reducing stick force, however you arrive at the high AOA.
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Old 14th Mar 2019, 13:33
  #1325 (permalink)  
 
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Originally Posted by BrandonSoMD View Post
I think that deserves some clarification. I don't fully agree.

I'm a 30-year flight test engineer and am currently helping to rewrite the handling qualities flight test manual for the US Navy Test Pilot School. We focus more on military than transport aircraft, but we do test and fly 737-derivative airplanes (P-8A Poseidon and the C-40 Clipper) and the test methods are universally applicable.

Windup turns are done with set thrust, yes. Power is set as required to maintain the specified airspeed. What is being compared is the response of the airframe to increasing AOA or g at a fixed airspeed, and throttles are fixed during the maneuver to avoid contaminating the results with another independent variable. Several things can be learned from WUTs, including control force or deflection as a function of load factor or AOA, buffet characteristics as a function of AOA, and structural characteristics as a function of g.

While each test point is conducted at a specific power setting, the tests are typically conducted at a range of power settings. This provides a chance to assess the effect of power setting on the various aforementioned characteristics.

MCAS is (at the core) merely a trim application system, designed to reduce the control forces which develop at higher AOA and g with the new-and-repositioned engines. As such, it is a handling qualities difference that is definitely related to thrust line changes. Those differences would typically be revealed by a series of WUT test points. In this case, a WUT at high thrust would be worse, because of the increased pitch-with-power tendencies.
That is all good and well, and always works when all sensors are giving you and the systems the correct information.

AF447 => An iced over AOA probe gives false info, and it does not matter what happened the next minutes, they never figured out in time what the actual problem was.
The B-2 crash => See? With failing sensors there simply is NO TIME.
The X-31 crash => (Where pitot anti-ice was not connected) => The plane goes out of control SO FAST, the only way out is to eject.

When given false information from failing sensors, (and not knowing it) or the failure codes redraw so fast on screen that you simply can not keep track of all of them => It is game over.

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Old 14th Mar 2019, 13:37
  #1326 (permalink)  
 
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Originally Posted by silverstrata View Post
Sure about that? Someone new to the aircraft, captain average, and a bit tired.

At 3,000 ft, the stick shaker starts going like mad, causing a hell of a racket, and you think you have an airspeed problem and might be stalling. Sure, the controls are getting heavier and heavier, and you trim a bit for that, but this is caused by the aircraft stalling - isn’t it? (You cannot hear the trimmer, over the din of the stick-shaker.) So you have to let the nose drop, untill you are sure you have enough airspeed.

Ok, you are getting a bit low now, time to pull back. Ahh, but the aircraft will not respond - pull as hard as you like, but the stick feels jammed (you need 60 kg of force to counter full stab-trim). You shout to the f/o to help pull, but the ground is coming up fast.... End of short story...


This is one of the better comments in this discussion. As a long-time flight test engineer with personal experience flying jumpseat aboard Boeing commercial-class airplanes during many test flights, and many hundreds of hours in the related simulators both testing and flying the simulators, I have personally witnessed aircrew in simulated emergency situations with all four feet standing on the bottom of the forward display panel to gain enough leverage to pull with >100 lb on the yoke to control the airplane (and specifically in runaway stab trim and hyd-fail situations). Nobody had a hand free to fiddle with manual trim or deal with the stab trim cutout switch and its guard (at least on the aircraft types I've tested).

Yes, these things are addressed in pilot training. But I've also watched extremely-intelligent and supremely-trained flight test pilots miss very obvious things due to the confusion surrounding automation (I helped test a major glass-cockpit upgrade to a Boeing 707-derived military jet, which included adding modern-day Honeywell autopilot systems). I've personally sat behind them in the jump seat and watched them completely miss what was going on outside the window, as two pilots and a flight engineer got wrapped up trying to figure out some stupid aspect of VNAV operation, to the point where a safety "knock it off" call had to be made to get them to break their "target fixation" on the troubleshooting.

Watch the video of the recreation of the cockpit troubleshooting in the AeroPeru crash due to tape covering the Pitot-static ports... two well-trained pilots so confounded by an airplane acting differently than they expected, that some very basic hand-flying principles and alternate information sources were missed for nearly an hour.

It's easy to armchair-quarterback a situation after the fact - but I've seen it all happen enough times to recognize the reality of the man-machine interfaces.
Ultimately, if a design is such that a pilot can get confused enough to lose all situational awareness, the problem fundamentally is a poor design, not just pilot training or problem-fixation.
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Old 14th Mar 2019, 13:38
  #1327 (permalink)  
 
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Originally Posted by Vilters View Post
That is all good and well, and always works when all sensors are giving you and the systems the correct information.

AF447 => An iced over AOA probe gives false info, and it does not matter what happened the next minutes, they never figured out in time what the actual problem was.
The B-2 crash => See? With failing sensors there simply is NO TIME.
The X-31 crash => (Where pitot anti-ice was not connected) => The plane goes out of control SO FAST, the only way out is to eject.

When given false information from failing sensors, (and not knowing it) or the failure codes redraw so fast on screen that you simply can not keep track of all of them => It is game over.
You will probably find a lot of things to learn and appreciate in this video of the AeroPeru crash due to Pitot-static port blockage.
https://www.dailymotion.com/video/x6m3uwb
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Old 14th Mar 2019, 13:42
  #1328 (permalink)  
 
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Originally Posted by bill fly View Post


Sure, but I bet there is plenty of motivation now we know how it works/fails.

See the teacup a few posts further up “If you think safety is expensive... etc”

I agree the decision making process that got to the current system and its certification will come under a lot of scrutiny in the next few weeks.
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Old 14th Mar 2019, 13:47
  #1329 (permalink)  
 
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Originally Posted by Less Hair View Post
How much longer could Boeing build new NGs?
If it had customers it could build them almost for ever.

The bigger question is how long would it take to spin up the production of NG engines and other parts. I suspect that getting back to building 100 plus NG engines per month would take 6 plus months to fully achieve.
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Old 14th Mar 2019, 13:49
  #1330 (permalink)  
 
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Originally Posted by boxmover View Post


If it had customers it could build them almost for ever.

The bigger question is how long would it take to spin up the production of NG engines and other parts. I suspect that getting back to building 100 plus NG engines per month would take 6 plus months to fully achieve.
They will almost certainly be able to divert resources budgeted to the MAX towards other airframes
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Old 14th Mar 2019, 13:56
  #1331 (permalink)  
 
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Originally Posted by WHBM View Post
Perfectly possible. Train the training captains first, let them have some real, non-sim experience of it on test flights, all to a plan, start revenue flights with two captains, then progressively have them train the FO's, starting with the experienced ones. It's not hard to come up with that. Isn't devising this sort of transition what the role of Chief Pilot is all about ?
These days the roll of the Chief Pilot is to get the program flown at minimum cost. The will design a program that meets the minimum legal standards and if they think it necessary a bit above that. Training Captains off line flying non revenue flights is way beyond what’s going to happen unless it’s legally mandated.
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Old 14th Mar 2019, 13:59
  #1332 (permalink)  
 
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Originally Posted by El Bunto View Post
The FAA language is "a pilot of average skill".

However the first time such a pilot now gets behind the yoke is after the aircraft has been certificated, sold to an airline, built, delivered... Maybe they should involve FO Joe Average a bit earlier in the lifecycle.
This seems a poor FAA perspective. By definition, 50% of pilots will be below that average skill level.

Particularly when they only have 200 hours total.

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Old 14th Mar 2019, 14:09
  #1333 (permalink)  
 
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Originally Posted by Luc Lion View Post
ManaAdaSystem,
look at the diagram below ; the "control column stab trim cutout switches" only operate on the electric path of the electric trim buttons.
The STS is on the other electric path, the path of the autopilot system.
So this means the STS system will trim even if the column cut out switches are in the cut out position?
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Old 14th Mar 2019, 14:12
  #1334 (permalink)  
 
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Originally Posted by Rated De View Post
Does anybody find it odd, that Boeing's public statement is attempting to suggest they the company 'ordered' the grounding?
Isn't that Cart before the Horse?
Or is it evidence of regulatory capture??
No, it's not odd, although the wording is slightly misleading.

My understanding is that, while regulators like the FAA, EASA, etc have imposed territorial bans on the Max flying through the airspace that they have jurisdiction over, Boeing has sought the grounding of the worldwide fleet (I don't know if that has actually happened yet).

The FAA, as well as being responsible for what is and isn't allowed in US airspace, is also the continuing airworthiness authority for the 737. It has the power to grant a request by Boeing to temporarily suspend the aircraft's Type Certificate (in respect of only the Max, obviously). If it did so, other airworthiness authorities (EASA, ANAC, etc) would have no option but to follow suit and the Max would be effectively grounded worldwide.
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Old 14th Mar 2019, 14:23
  #1335 (permalink)  
 
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Average

Originally Posted by WHBM View Post
This seems a poor FAA perspective. By definition, 50% of pilots will be below that average skill level.

Particularly when they only have 200 hours total.
The use of average here is sloppy. Leaving out of account the numerical quantification of skill, and its distribution among pilots, it is quite possible that a majority of them are below average. However, what I want is the aeroplanes I travel in to be manageable safely by pilots of minimum allowable skill. Not every flight deck will be occupied by superhero pilots. If the first officer has just got his licence I want the captain to be a senior trainer, and if the captain has just been promoted then please may his co-pilot be of considerable experience on the type.
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Old 14th Mar 2019, 14:36
  #1336 (permalink)  
 
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Originally Posted by dead_pan View Post
Another SLFie who may be stating the obvious, but surely the goal of any airframer is to produce an aircraft that even the minimum standard of pilot can fly and have a decent chance of successfully troubleshooting in the event of something going awry? Not prejudging anything BTW
Therein lies the problem. What would be your minimum standard? Aviation authorities have different standards. Do you happen to know what the FO had for total flight time? And what was the Captain's total time in airframe? If you take the time to discover these significant facts, then that should scare you.

I'm not letting Boeing off the hook for such a poor design, but there's a reason that several other crews have documented this very issue and landed safely.
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Old 14th Mar 2019, 14:42
  #1337 (permalink)  
 
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NTSB to France

NTSB Sends Additional Investigators to Assist in Ethiopian Investigation
3/14/2019​

WASHINGTON (March 14, 2019) —The U.S. National Transportation Safety Board is dispatching three investigators to France Thursday to assist with the downloading and analysis of flight recorders from the Boeing 737 MAX 8 that crashed Sunday near Addis Ababa, Ethiopia.

The NTSB investigators have expertise in recorders, flight crew operations and human factors. The French Bureau d'Enquêtes et d'Analyses (BEA) will be downloading the flight data recorder and cockpit voice recorder in support of the Ethiopian investigation.

The investigation is being led by the Ethiopian Aircraft Accident Investigations Bureau in accordance with the standards defined in International Civil Aviation Organization Annex 13. The NTSB appointed an accredited representative to the investigation under the ICAO standards because the airplane was manufactured in the United States. All investigative data regarding the investigation will be released by Ethiopian authorities.

For more information on NTSB participation in foreign investigations go to: https://go.usa.gov/xEswV.

The NTSB investigators dispatched to France will work in coordination with investigators on the ground in Addis Ababa. Those investigators were sent immediately after the accident and have been integral to the efforts underway in Ethiopia. They are being assisted by technical advisers from the Federal Aviation Administration, Boeing and GE/Safran, the manufacturer of the engines.

The NTSB is an independent U.S. federal agency charged with investigating transportation accidents and issuing recommendations to improve safety.
###
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Old 14th Mar 2019, 14:45
  #1338 (permalink)  
 
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Originally Posted by CRayner View Post
If the first officer has just got his licence I want the captain to be a senior trainer, and if the captain has just been promoted then please may his co-pilot be of considerable experience on the type.
Amazingly enough in many realities in EASA as well as a few others jurisdictions worldwide, You will find that a newly promoted Captain with 100 hours (yes one hundred) PIC time is considered "experienced" and can hence fly with any newly 250 hours released FO. Forget Senior Trainers flying with released FOs, hence non training flights, that's "not efficient" or having experienced (and skilled, which is not always the same) FOs to fly with newly promoted Capts as well. Let's enjoy the deregulation.
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Old 14th Mar 2019, 14:54
  #1339 (permalink)  
 
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If the airframe/sensors are feeding the pilots/systems with wrong information, it does not matter if they have 20.000 or 200 hrs PIC.
If at high speed and low altitude as in this case, there is NO time.
If error codes refresh so fast on screen that you can not follow them visually? You have no time to fall back on experience and evaluate and have mere minutes/seconds till impact.
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Old 14th Mar 2019, 14:56
  #1340 (permalink)  
 
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For those who want to understand how we came to this amateur job:

It’s unique to the MAX because the 737 MAX no longer has the docile pitch characteristics of the 737NG at high Angles Of Attack (AOA). This is caused by the larger engine nacelles covering the higher bypass LEAP-1B engines. The nacelles for the MAX are larger and placed higher and further forward of the wing,

By placing the nacelle further forward of the wing, it could be placed higher. Combined with a higher nose landing gear, which raises the nacelle further, the same ground clearance could be achieved for the nacelle as for the 737NG.

The drawback of a larger nacelle, placed further forward, is it destabilizes the aircraft in pitch. All objects on an aircraft placed ahead of the Center of Gravity will contribute to destabilize the aircraft in pitch.

The 737 is a classical flight control aircraft. It relies on a naturally stable base aircraft for its flight control design, augmented in selected areas. Once such area is the artificial yaw damping, present on virtually all larger aircraft (to stop passengers getting sick from the aircraft’s natural tendency to Dutch Roll = Wagging its tail).

Until the MAX, there was no need for artificial aids in pitch. Once the aircraft entered a stall, there were several actions described l which assisted the pilot to exit the stall.

The larger nacelles, called for by the higher bypass LEAP-1B engines, changed this. When flying at normal angles of attack (3° at cruise and say 5° in a turn) the destabilizing effect of the larger engines are not felt.

The nacelles are designed to not generate lift in normal flight. It would generate unnecessary drag as the aspect ratio of an engine nacelle is lousy. The aircraft designer focuses the lift to the high aspect ratio wings.

But if the pilot for whatever reason manoeuvres the aircraft hard, generating an angle of attack close to the stall angle of around 14°, the previously neutral engine nacelle generates lift. A lift which is felt by the aircraft as a pitch up moment (as its ahead of the CG line), now stronger than on the 737NG. This destabilizes the MAX in pitch at higher Angles Of Attack (AOA). The most difficult situation is when the manoeuvre has a high pitch ratio. The aircraft’s inertia can then provoke an over-swing into stall AOA.

To counter the MAX’s lower stability margins at high AOA, Boeing introduced MCAS. Dependent on AOA value and rate, altitude (air density) and Mach (changed flow conditions) the MCAS, which is a software loop in the Flight Control computer, initiates a nose down trim above a threshold AOA.

It can be stopped by the Pilot counter-trimming on the Yoke or by him hitting the CUTOUT switches on the center pedestal. It’s not stopped by the Pilot pulling the Yoke, which for normal trim from the autopilot or runaway manual trim triggers trim hold sensors. This would negate why MCAS was implemented, the Pilot pulling so hard on the Yoke that the aircraft is flying close to stall.

It’s probably this counterintuitive characteristic, which goes against what has been trained many times in the simulator for unwanted autopilot trim or manual trim runaway, which has confused the pilots of JT610. They learned that holding against the trim stopped the nose down, and then they could take action, like counter-trimming or outright CUTOUT the trim servo. But it didn’t. After a 10 second trim to a 2.5° nose down stabilizer position, the trimming started again despite the Pilots pulling against it. The faulty high AOA signal was still present.

How should they know that pulling on the Yoke didn’t stop the trim? It was described nowhere; neither in the aircraft’s manual, the AFM, nor in the Pilot’s manual, the FCOM. This has created strong reactions from airlines with the 737 MAX on the flight line and their Pilots. They have learned the NG and the MAX flies the same. They fly them interchangeably during the week.

They do fly the same as long as no fault appears. Then there are differences, and the Pilots should have been informed about the differences.

Source: https://leehamnews.com/2018/11/14/bo...to-the-pilots/

Unfortunately the lion and Ethiopian's pilots have not had this chance

Last edited by cervo77; 14th Mar 2019 at 15:27.
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