News Ethiopian 737 crashed on way to Kenya, 157 people on-board

[Urwumpe]

Indeed, the word seems misapplied. We generally use it to describe politics focused on compromise rather than populism. Taking an option that does not live up to your ideals because in reality, it's the best you're going to get.
It is often applied with a negative conotation, though. Like for example "we really should do something about global warming quickly, but Realpolitik is making it impossible" or somesuch.

Especially when Germans use the term Realpolitik, you should be absolutely scared - Historic German Realpolitik involves forming an alliance with your political enemy (Italy) for attacking a country politically closer (Austria).

But in the Chinese case, the word should be rather "protectionist"

---------- Post added at 17:10 ---------- Previous post was at 16:36 ----------

Can somebody confirm my calculation, that the ETH302 did never exceed 800 ft altitude AGL,correcting for higher pressure at the airport than the ADS-B uses for its altitude calculations?

 

[Wolf]

Can't they just switch the autopilot off and take manual control? Why should you keep fighting a system if you can disable it?

It’s not thet simple. The system is designed to kick in even if the autopilot is disconnected. Basically when it senses that the airplane’s airspeed is too low it generates a pushdown force on the yoke to lower the nose and avoid potential stall. In order to disable the system you need to manually force the controls (similar to the jammed stabilizer recovery procedure).
Problem is apparently Boeing has implemented this new safety feature without properly inform operators and pilots. It is quite likely they will come up soon with a new Emergency Checklist for this.

 

[Urwumpe]

Wrong about the pushdown on the yoke - it acts on the electric trim system, not the yoke, the yoke actually has absolutely no effect on it. Manually forcing the controls does not help much there, it reactivates in 5 seconds. You can disable it by disabling the motors for the electronic pitch trim system, so you can only trim by the hand wheels. This then also effects the speed trim function of the autopilot.

 

[Wolf]

Wrong about the pushdown on the yoke - it acts on the electric trim system, not the yoke, the yoke actually has absolutely no effect on it. Manually forcing the controls does not help much there, it reactivates in 5 seconds. You can disable it by disabling the motors for the electronic pitch trim system, so you can only trim by the hand wheels. This then also effects the speed trim function of the autopilot.

Pardon me, you are absolutely right; it is a trim intervention. The big issue here IMO is the lack of crew awarness in regards to this new feature (despite there is actually a chrcklist for a runaway stabilizer condition)

 

[Urwumpe]

Pardon me, you are absolutely right; it is a trim intervention.

Yeah, and it has even less limits as the pilot using manual trim. That is pretty scary - its Boeing. Not Airbus, which would happily declare that the plane knows best how to fly.

 

[Wolf]

Yeah, and it has even less limits as the pilot using manual trim. That is pretty scary - its Boeing. Not Airbus, which would happily declare that the plane knows best how to fly.

Automation is a double edge weapon. The more you have the less the chances to get task saturated and make mistakes. On the other hand complacency and confirmation bias are around the corner as well as a decrease in awarness.
Some of the incidents and accidents on Airbus machines clearly show the hidden threats of modern aircraft systems

 

[dbeachy1]

And it's even worse than that: pulling back on the control yoke only disengages the MCAS autopilot for five seconds: after that, the system re-engages and will again point the nose down if it thinks the aircraft is stalling (including if it's not actually stalling but just getting bad data from a faulty sensor). Quoting from The Seattle Times regarding last October's 737 MAX Lion Air crash (emphasis added):

Scrutiny of Lion Air crash turns to automated systems that command Boeing 737 pitch

...

FAA mandates action

The FAA said its directive addresses the potential effects of false information coming from the sensor on the plane’s exterior that reports the plane’s “angle of attack” (AOA), which is the angle between the wing and the flow of air the jet is moving through.

This key data point is fed into the flight computer along with the temperature and air speed. These three metrics affect one another and are used by various systems that control the airplane’s flight.

The FAA said false AOA readings “can potentially make the horizontal (tail) repeatedly pitch the nose of the airplane downward, making the aircraft difficult to control.”

The danger, the FAA warns, is that this could “lead to excessive nose-down attitude, significant altitude loss, and possible impact with terrain.”

The Boeing service bulletin to airlines notes that though pilots may pull back on the yoke and adjust the horizontal tail to get the nose pointed back up,the condition pulling the nose down may then restart five seconds later.

The flight data of the Lion Air jet in the 12 minutes before it crashed shows a pattern of the plane repeatedly losing altitude and regaining it before it finally dived steeply into the sea.

Full article is here: https://www.seattletimes.com/busine...737-safety-alert-with-an-emergency-directive/

Although it's possible to disable the MCAS manually, it requires manually cranking the trim wheel or pressing the MCAS cutout switch on the trim wheel, and 737 pilots are not trained on that because the MAX was certified to not require retraining for existing 737 pilots (!!). Regarding the MCAS system on the MAX:

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.

Boeing has since added information about the MCAS system to the manual, but few 737 MAX simulators exist for pilots to actually train on it. More information on the MCAS is here: https://leehamnews.com/2018/11/14/b...-the-737-max-was-not-disclosed-to-the-pilots/

And on a side note, when the aircraft starts nosing-down when it shouldn't, it's inherently a stressful situation for the pilots, particularly at low altitudes: their 737 training kicks in and they pull back on the stick to disengage the autopilot and level the plane -- except in the case of the 737 MAX with a faulty AoA or mach speed sensor, when the MCAS kicks in again five seconds later and again points the nose down. The only way to disengage the MCAS is to remember to crank the trim wheel manually or press the MCAS cutout switch on the trim wheel -- and 737 pilots haven't trained for that since "the MCAS system is supposed to be fully automatic and not disengage".

The root of all this MCAS behavior is that it's a hack that Boeing did to fit the larger engines on the MAX and so had to move the engines forward to still have enough clearance, thus changing the aircraft's center-of-gravity as compared to normal 737s:

Until the MAX, there was no need for artificial aids in pitch. Once the aircraft entered a stall, there were several actions described last week which assisted the pilot to exit the stall. But not in normal flight.

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.

https://leehamnews.com/2018/11/14/b...-the-737-max-was-not-disclosed-to-the-pilots/

So yes, people can argue that "the pilots should know to disengage the MCAS", but 737 pilots aren't trained to interact with the MCAS at all -- the MAX was marketed as not requiring retraining for existing 737 pilots, and retraining is not (currently) required.

 

[Marijn]

It’s not that simple.

The job of an airline pilot is to take over manual control in case systems do fail. Any system which complicates that is a dangerous system imho. It violates the aviate, navigate communicate principle.

 

[Wolf]

The job of an airline pilot is to take over manual control in case systems do fail. Any system which complicates that is a dangerous system imho. It violates the aviate, navigate communicate principle.

Again, it is not that simple

 

[Urwumpe]

The job of an airline pilot is to take over manual control in case systems do fail. Any system which complicates that is a dangerous system imho. It violates the aviate, navigate communicate principle.

Still, remember: No aircraft is made to fly. Any system onboard an airliner can complicate this. There are even aircraft that CAN'T fly at all without computers in the loop, there is no manual control possible.



Even the Concorde would have been uncontrollable when the rather primitive FBW failed....

 

[Marijn]

I would be astonished if it turns out that the pilots were struggling to take manual control to pull the plane, a 737 which can be flown manually very easily, out of a descending situation and failed to do so in time. If pilots can't take manual control, why have pilots aboard at all? That's unheard of. So I think some other events must have caused this crash. We'll have to wait.

 

[Urwumpe]

I would be astonished if it turns out that the pilots were struggling to take manual control to pull the plane, a 737 which can be flown manually very easily, out of a descending situation and failed to do so in time. If pilots can't take manual control, why have pilots aboard at all? That's unheard of. So I think some other events must have caused this crash. We'll have to wait.

Would not be too unlikely. How would you feel, when the aircraft suddenly stops climbing in just about 100m altitude above ground? How would you react? The pilots just got theoretical training for the 737 MAX, there are no simulators for it.



They would very likely react like they had been trained in a simulator. For a normal 737.

 

[Marijn]

How would you feel, when the aircraft suddenly stops climbing in just about 100m altitude above ground? How would you react?

I haven't read much information about this crash. I didn't know trouble struck at only 100 meters above the groud. That's obviously very, very low. A winch-launch failure at 100 meters in a glider is already a situation in which there is little time to think. Are you sure that this plane never got above 100 meters before it's descend into the terrain?

But planes do not suddenly stop climbing. Something else must preceed that event. A change of AoA, less thrust, extension of speed-brakes, icing, whatever. Something must cause the climb to have halted and I think it's the job of pilots to notice these events in time and be ready for them.

How would you react?

Regardless of altitude, the first priority should be to bring the nose just under the horizon. From a diving situation, that would mean a firm but gentle pull on the controls to establish a normal glide. Everything else comes after that.

So I would probably crash the plane, because the autopilot needs to be shut off first. And if I understand you correctly, that's a complicated set of actions. I think the autopilot should disable immediately when any manual input is registered and give full control to the pilot. I doubt whether certificates of airworthiness are issued to planes which fight pilots.

 

[Notebook]

I think you can be very sure that something unusual happened here. They have good visibility with a horizon? two working engines? and it hits the ground in an unusual attitude.

N.

 

[Urwumpe]

Are you sure that this plane never got above 100 meters before it's descend into the terrain?

It did get higher - but checking the flight path with the terrain below means that it already stopped climbing the first time in about 100m AGL altitude and barely changed this pressure altitude while the crew attempted to recover.



https://www.flightradar24.com/blog/...g-the-crash-of-ethiopian-airlines-flight-302/



The terrain went into a depression after the airport until a group of low hills ended the flight and the aircraft was lost CLIMBING according to the ADS-B data.



Pressure was 1029 instead of 1013, as standard, soo the aircraft was about 500 ft/152 m higher as indicated by ADS-B.



Peak altitude above ground should have been about 280 meters (8150 ft -> 8600 ft / 2621m) at 8.99762°N 38.87167°E (2350m topo). Last signal was here:


https://opentopomap.org/#marker=12/9.01602/38.98415

 

[Marijn]

Local witnesses reported to Reuters that they saw smoke and sparks behind the aircraft before impact. https://www.reuters.com/article/us-...ations-ground-boeing-737-max-8s-idUSKBN1QS15F

---------- Post added at 09:49 PM ---------- Previous post was at 09:40 PM ----------

...
Peak altitude above ground should have been about 280 meters (8150 ft -> 8600 ft / 2621m) at 8.99762°N 38.87167°E (2350m topo).

Impressive analysis with the little data available. 280 meters is very low for an airliner. Whatever happened, the pilots had very little time.

 

[Urwumpe]

Local witnesses reported to Reuters that they saw smoke and sparks behind the aircraft before impact. https://www.reuters.com/article/us-...ations-ground-boeing-737-max-8s-idUSKBN1QS15F

That sounds rather unlike the MCAS caused the issues. But the article also says little about how much of the flight was observed.



Also, the airspeed constantly increased. If you remember how close to the ground it was, ground speed and airspeed should have been very close as well. Which means it was accelerating to 383 knots TAS in 8600 ft pressure altitude. That is at or above VMO, when converted into IAS. Maybe the witnesses observed structural damage or engine damage because of the excessive speed before crashing.

 

[Marijn]

They reported pieces of 'clothing' leaving the plane as well, which is hard to imagine. Perhaps they saw pieces of plating. But correctly remembering the details of such an event is hard, so if there was really a problem with the engines remains a question at this time.

 

[Linguofreak]

Is this a fake Chinese accent I am hearing there? :huh:

Nope, think more am American kid teasing a friend who's afraid if the dark: "Look at me. I'm Billy I'm so scaaaared, there might be ghooooosts".

An interesting use of the word "realpolitik", by the way. I think I heard it first in the 80s in connection with the German Green party when a rift appeared between the more fundamentalist wing trying to preserve the party ideology (the "Fundis") and the "Realpolitiker" (the "Realos") trying to compromise to make the program more mainstream and improve the electability and the chance of powersharing.

A quick search for "realpolitik" comes up with "a system of politics or principles based on practical rather than moral or ideological considerations", which sounds about right but seems almost exactly the opposite of your use of the word.

The current leaders of the three superpowers don't really strike me as ideologues so much as cynical opportunists out for power. And what I'm saying is that China's actions may be directed by political leaders based on what is politically useful (use a disaster to spread FUD about a rival) rather than by experts within their aviation authority based on actual safety concerns. Meanwhile, I think there's a good likelihood that the FAA's decision not to ground the aircraft has been unduly influenced by the desire to save face for a domestic manufacturer, once again, a consideration of practicality in achieving political goals rather than of the smooth and safe functioning of the airline industry.

 

[Urwumpe]

Meanwhile, I think there's a good likelihood that the FAA's decision not to ground the aircraft has been unduly influenced by the desire to save face for a domestic manufacturer, once again, a consideration of practicality in achieving political goals rather than of the smooth and safe functioning of the airline industry.

Or it could be because the software patch by Boeing is about to be released for the MCAS issue and its too early to tell what really caused the crash of ETH302.

---------- Post added at 09:25 ---------- Previous post was at 08:59 ----------

They reported pieces of 'clothing' leaving the plane as well, which is hard to imagine. Perhaps they saw pieces of plating. But correctly remembering the details of such an event is hard, so if there was really a problem with the engines remains a question at this time.

Possible - but pieces of clothing leaving the plane did happen in a previous crash that had a lasting impact in the region, so it could also be a mix of real observations and previous lore.

https://en.wikipedia.org/wiki/Nigeria_Airways_Flight_2120

Eye witnesses are no cameras, they maybe see about 30% of the crash and fill the gaps that did not see with memories.