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Another 737 MAX down.

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29 minutes ago, Kip Powick said:

Ethiopian Airlines Pilots Initially Followed Boeing’s Required Emergency Steps to Disable 737 MAX System

I find that a very misleading headline.....considering what they actually did (switches back on).

Seems like an accurate headline to me.  It also seems very puzzling why they wouldn't simply manually trim the airplane afterwards 

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What does one manual rotation of the trim equal on the stab? Perhaps it wasn’t correcting the nose down attitude quickly enough and they re-selected both stab trim switches? 

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 Extreme cases of mis-trim may require the efforts of both pilots on the trim wheel and/or aerodynamic unloading to trim manually. What puzzles me is after the switches were reselected "on" the trim should have responded to the pickle switches being selected to nose up as MCAS can be reversed with opposite trim.

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1 hour ago, rudder said:

The ratio of manual trim wheel rotations to actual stab trim movement is significant....

Umm, I've cranked the wheel full nose up to full nose down and lets just say it's not an insignificant number of turns. 2 or 3 turns of the wheel would most likely be unnoticeable considering all that was going on at that moment.

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13 minutes ago, Maverick said:

Umm, I've cranked the wheel full nose up to full nose down and lets just say it's not an insignificant number of turns. 2 or 3 turns of the wheel would most likely be unnoticeable considering all that was going on at that moment.

Yup.

”Significant” = big number of turns for small amount of stab movement

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1 hour ago, rudder said:

The ratio of manual trim wheel rotations to actual stab trim movement is significant....

Somewhere in the order of 10 rotations of the wheel to 1 unit of trim.

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5 hours ago, ng78 said:

Seems like an accurate headline to me.  It also seems very puzzling why they wouldn't simply manually trim the airplane afterwards 

How can it be accurate when it infers that the crew followed a checklist...but turned on the TRIM switches again?

 Here I am assuming they thought they were actioning a regular runaway trim situation.

In my opinion I think most drivers know that if there is a pitch issue, one turns off the trim switches and manually trims. The switches are NOT turned on again.

In other words they did not follow the Boeing checklist yet the non informed reader will certainly assume the complete and accurate checklist  was followed based on the headline.....but then again, it is the PRESS.....5153.gif

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2 hours ago, Kip Powick said:

How can it be accurate when it infers that the crew followed a checklist...but turned on the TRIM switches again?

 Here I am assuming they thought they were actioning a regular runaway trim situation.

In my opinion I think most drivers know that if there is a pitch issue, one turns off the trim switches and manually trims. The switches are NOT turned on again.

In other words they did not follow the Boeing checklist yet the non informed reader will certainly assume the complete and accurate checklist  was followed based on the headline.....but then again, it is the PRESS.....5153.gif

The headline said "initially" ... which is accurate.  They did in fact initially follow the procedure, but by turning the switches on again they then deviated from that procedure

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https://www.seattletimes.com/business/boeing-aerospace/boeings-emergency-procedure-for-737-max-may-have-failed-on-ethiopian-flight/

Quote

The elevator and stabilizer normally work together to minimize the loads on the jackscrew. But in certain conditions, the elevator and stabilizer loads combine to present high forces on the jackscrew and make it very difficult to turn manually.

In this scenario, the air flow pushing downward against the elevator would have created an equal and opposite load on the jackscrew, a force tending to hold the stabilizer in its upward displacement. This heavy force would resist the pilot’s manual effort to swivel the stabilizer back down.

This analysis suggests the stabilizer trim wheel at the Ethiopian captain’s right hand could have been difficult to budge. As a result, the pilots would have struggled to get the nose up and the plane to climb.

If after much physical exertion failed, the pilots gave up their manual strategy and switched the electric trim system back on, MCAS would have begun pushing the nose down again.

Further down:

Quote

The instructions in the old manual say that the pilot should repeatedly do this: Release the control column and crank the stabilizer wheel, release and crank, release and crank, until the stabilizer is swiveled back to where it should be.

The 1982 manual refers to this as “the ‘roller coaster’ technique” to trim the airplane, which means to get it back on the required flight path with no force pushing it away from that path.

“If nose-up trim is required, raise the nose well above the horizon with elevator control. Then slowly relax the control column pressure and manually trim nose-up. Allow the nose to drop below the horizon while trimming (manually). Repeat this sequence until the airplane is trim,” the manual states.

 

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That makes perfect sense since you are unloading the forces on the stab making it easier to trim.  The passengers might not like it but manually trimming can be an exhausting process.

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 This is what I've been trying to say. This statement is right out of the Max and NG flight crew training manuals

"Excessive air loads on the stabilizer may require effort by both pilots to correct the mis-trim. In extreme cases it may be necessary to aerodynamically relieve the air loads to allow manual trimming. Accelerate or decelerate towards the in-trim speed while attempting to trim manually."

Several years ago on the NG there was a requirement to trim the stabilizer full nose down prior to deicing to ensure the fluid was drained. In order to accomplish this the electric trim was used to its limit - which is not full nose down - the cutout switches were then moved to cutout and the remaining trim travel was done manually. From that experience I can tell you that holding a mis-trimmed elevator control back while trying to lean forward and operate a very stubborn crank would be no easy task!

It is possible they were not successful trimming manually and flipped the switches back on. According to what we've been reading opposite trim inputs with the thumb switches should revers the MCAS inputs. Perhaps they ran out of time?

MCAS, or any other runaway trim condition needs an immediate response or the possibility exists of it becoming unrecoverable IMHO

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Ethiopian Airlines crew followed Boeing rules, preliminary crash report says

 
‎Today, ‎April ‎4, ‎2019, ‏‎5 hours ago | The Associated Press
AFP_1EP9GQ

The crew of the Ethiopian Airlines jet that crashed six minutes after takeoff last month performed all procedures recommended by Boeing when the plane started to nosedive but could not save it, according to findings from a preliminary report released Thursday by Ethiopia's government.

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1 hour ago, Arctic Ace said:

MCAS, or any other runaway trim condition needs an immediate response or the possibility exists of it becoming unrecoverable IMHO

Absolutely!

My only B737 experience was a relatively short time period on the -200. I transitioned onto that airplane from the A320, which was much like giving up my car in favour of riding a horse and buggy to work. The only thing that disturbed me about the airplane was the trim runaway procedure. It felt like we were patching a severed jugular vein with a finger bandage. Admittedly the -200 is the only aircraft of that generation that I've flown and maybe it was quite common back in the day but I'm happy I never had to use the procedure in anger.

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From D.P. Davies, "Handling the Big Jets", (2nd ed., 1970):

Quote

 

On stuck stab, hold as long as possible to the trim speed, and be prepared for "very high", but predictable and manageable stick "loads" on approach and landing.

On runaway, "must be stopped as soon as possible.  .... it the runaway is not arrested, life is going to be very difficult. The fact that some aeroplanes can be flown under some conditions of configuration and speed is of academic interest only. If this should occur at high speed the aeroplane is bound to be in severe trouble; the only hope is to get the speed off. There is not much  point in taking this analysis any further. The design of aeroplanes is such that the possibility of this failure (that is, the failure to stop the runaway) occurring is extremely remote, so if the tail starts off on its own or does not stop moving when the input is removed, take the required emergency action immediately...."

 

Obviously he treated the trimmable stabiizer with great seriousness and extraordinary respect for it's capable (and lethal) power. I would like to have been able to hear what Davies would say regarding the present circumstances.

 

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Previously the Stab Cutout switches to cutout was not a memory action in the Runaway Stabilizer QRC. The only memory actions were Control Column - Hold Firmly and Autopilot (if engaged) - Disengage. I believe the logic behind this was that the control column actuated cutout switches which stop operation of the main electric and autopilot trim when the control column movement opposes trim direction would prevent further trimming until the checklist could be consulted. Unfortunately MCAS operation disables this function. Modern day training ingrains a sense of touch nothing without checklist guidance unless it is a defined memory action. This possibly resulted in delaying moving the trim cutout switches to the point of being unrecoverable - especially at lower altitudes. Opposite trim using the thumb switches should have worked though. This I don't understand.

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"From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units. During this time, aft force was applied to the control columns which remained aft of neutral position."

Just a WAG but possibly air loads from the nose up elevator position caused the stabilizer to creep nose down.

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I stand to be corrected but it appears that the thrust levers were never manually moved (?) and the engine speed remained at 94% N1 for the entire event flight. In level flight at low altitude the corresponding airspeed would have been well beyond the barber pole.

At the IAS outlined in the report the air loading on all of the control surfaces would have been extreme. No wonder stab trim could not be manually adjusted.

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From factual information pg 1:

”The takeoff roll appeared normal, including normal values of left and right angle-of-attack (AOA). During takeoff roll, the engines stabilized at about 94% N1, which matched the N1 Reference recorded on the DFDR. From this point for most of the flight, the N1 Reference remained about 94% and the throttles did not move. The N1 target indicated non data pattern 220 seconds before the end of recording. According to the CVR data and the control column forces recorded in DFDR, captain was the pilot flying.”

Pg 12.  

The left Indicated Airspeed increased, eventually reaching approximately 458 kts and the right Indicated Airspeed reached 500 kts at the end of the recording. The last recorded pressure altitude was 5,419 ft on the left and 8,399 ft on the right.

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Three weeks to delivery of prelim report on Ethiopian. Six weeks and still nothing from the NTSB on the Atlas 767 but lots of unofficial details are leaking out. 

Here’s the ET report. They selected both switches to cutoff but couldn’t move the stab trim manually.

http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+B737-800MAX+%2C(ET-AVJ).pdf/4c65422d-5e4f-4689-9c58-d7af1ee17f3e

 

Edited by blues deville

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Perhaps of interest:

Updated FAA Statement on Boeing 737 MAX4/4/19 8:30am Update

FAA Statement on Boeing 737 MAX

The investigation by Ethiopian authorities remains ongoing, with the participation of the FAA and the NTSB. We continue to work toward a full understanding of all aspects of this accident. As we learn more about the accident and findings become available, we will take appropriate action.


4/2/19 4:00pm Update

FAA Establishes Joint Authorities Technical Review (JATR) for Boeing 737 MAX

The FAA is establishing a Joint Authorities Technical Review (JATR). Chaired by former NTSB Chairman Chris Hart and comprised of a team of experts from the FAA, NASA and international aviation authorities, the JATR will conduct a comprehensive review of the certification of the automated flight control system on the Boeing 737 MAX aircraft. The JATR team will evaluate aspects of the 737 MAX automated flight control system, including its design and pilots’ interaction with the system, to determine its compliance with all applicable regulations and to identify future enhancements that might be needed.   


4/1/19 4:00pm Update

FAA Statement on Boeing 737 MAX Software Update

The FAA expects to receive Boeing’s final package of its software enhancement over the coming weeks for FAA approval. Time is needed for additional work by Boeing as the result of an ongoing review of the 737 MAX Flight Control System to ensure that Boeing has identified and appropriately addressed all pertinent issues. Upon receipt, the FAA will subject Boeing’s completed submission to a rigorous safety review. The FAA will not approve the software for installation until the agency is satisfied with the submission.


3/20/19 5:00pm Update

Update on FAA's Continued Operational Safety Activities Related to the Boeing 737 MAX Fleet

FAA issues new Continued Airworthiness Notification to the International Community (PDF) on Boeing 737 MAX.

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Interesting analysis from former NTSB investigator Greg Feith from his FB page......

 

"The Report is published and provides a lot of detail about the flight including the fact that the crew experienced errant AOA and airspeed issues immediately after takeoff. This corroborates the scenario in my previous post, but more importantly supports the fact that the AOA fault initially experienced by the crew did not activate the MCAS because the flaps and slats were deployed.

The report identifies a very good timeline of events, especially the flap retraction cycle, the operation of the stab trim and actions/inactions of the crew. In addition, the pilot engaged the autopilot which again would inhibit the MCAS.

At least the story is becoming clearer and contradicts some of the “conclusions” presented in the Ethiopian report. Here are their conclusions:

2 INITIAL FINDINGS

On the basis of the initial information gathered during the course of the investigation, the following facts have been determined:

* The Aircraft possessed a valid certificate of airworthiness;

*. The crew obtained the license and qualifications to conduct the flight;

*. The takeoff roll appeared normal, including normal values of left and right angle-of-attack
(AOA).

*. Shortly after liftoff, the value of the left angle of attack sensor deviated from the right one and reached 74.5 degrees while the right angle of attack sensor value was 15.3 degrees; then after; the stick shaker activated and remained active until near the end of the flight. [GAF: MCAS INHIBITED]

* After autopilot engagement, [GAF: MCAS INHIBITED] there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes; these oscillations also
continued after the autopilot disengaged.

* After the autopilot disengaged, the DFDR recorded an automatic aircraft nose down (AND)trim command four times without pilot’s input. As a result, three motions of the stabilizer trim were recorded. The FDR data also indicated that the crew utilized the electric manual trim to counter the automatic AND input. [GAF: ELECTRIC MANUAL INPUT WOULD ONLY INTERRUPT THE MCAS TRIM COMMAND FOR 5 SECONDS]

* The crew performed runaway stabilizer checklist and put the stab trim cutout switch to cutout position and confirmed that the manual trim operation was not working. [GAF: PROCEDURES DO NOT INSTRUCT REACTIVATING THE STAB TRIM]

There are many questions yet to be answered but the primary question is what caused the fault with the AOA immediately after liftoff. This is key because it caused other issues during various phases of the climb including improperly activating the MCAS.

Also the report does not address information about unreliable airspeed procedures which should be considered because they had erratic airspeed; and there is no information about the Autothrottle status - the FDR data appears to show the engines remained at a high power setting.

More to come."

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13 hours ago, Arctic Ace said:

"From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units. During this time, aft force was applied to the control columns which remained aft of neutral position."

Just a WAG but possibly air loads from the nose up elevator position caused the stabilizer to creep nose down.

No, probably not. It's a screwjack and can't easily be back-driven by stabilizer forces. Flaps driven by hydraulic cylinders, (vice motors) can blowback but not flaps driven by screwjacks.

Edit to add:

Quote

*. Shortly after liftoff, the value of the left angle of attack sensor deviated from the right one and reached 74.5 degrees while the right angle of attack sensor value was 15.3 degrees; then after; the stick shaker activated and remained active until near the end of the flight.

The AoA sensor is physically capable of reading +/- 20°, (AMM test procedure), so 1) the AoA was damaged on takeoff, (appears normal - trails to '0' - until liftoff), or 2) the AoA sensor is working correctly and the incorrect data is being generated downstream, possibly by the FCCs.

What, statisically, fits better, an errant AoA sensor or an errant box downstream? In the million-plus hours that have been flown by the MAX since 2017, why two incidents of incorrect AoA data within months of one another?

 

 

Edited by Don Hudson

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https://www.cnn.com/2019/04/04/us/boeing-sensor-investigation/index.html

Miramar, Florida (CNN)Aviation investigators are looking into two American companies that handled the sensor at the center of the Lion Air crash last year, according to multiple sources familiar with the case.

The sensor, a vane located on the front of the Boeing 737 Max model known as the angle-of-attack (AoA) sensor, fed incorrect data to the flight control system of the Lion Air plane, activating an anti-stall software on the aircraft that repeatedly pitched the plane downward before its crash into the Java Sea, killing 189 people, Indonesian authorities have said.
 
On Thursday, Ethiopian aviation authorities said that one of the AoA sensors on board the Ethiopian Airlines flight that crashed last month was also producing faulty data, activating the same automatic flight control system that pilots battled before that plane's crash, which killed 157 people.
 
The Indonesian and Ethiopian investigators have only both released preliminary reports, and they do not specify a cause for the crashes.
 
The sensor on the Lion Air flight had been repaired by Xtra Aerospace, a company in Miramar, Florida, in 2017, before it was returned to Lion Air and later installed on the doomed flight, according to Nurcahyo Utomo, an investigator with Indonesia's National Transportation Safety Committee.
 
The part sat in storage with the airline until it was put on the Lion Air plane the day before it crashed, Utomo said.
 
The US National Transportation Safety Board, which is assisting Indonesian authorities in the Lion Air investigation, is looking into work done on the sensor at the company in the aftermath of the crash at the request of the Indonesian aviation authority, according to Utomo.
 
In a statement, Xtra said that the part had "conformed to and passed all required and mandated tests" before it was delivered to Lion Air in November 2017, and that the company is cooperating with investigators.
 
"Our thoughts and condolences are with all those who have lost loved ones in the recent 737 Max 8 accidents," the company said. "Xtra is fully committed to supporting any investigations into this matter."
 
An airline that receives a refurbished part, like Lion Air, would be responsible for installing it in accordance with the aircraft maintenance manual and performing any required tests on it, according to aviation experts.
The manufacturer of the AoA sensor used on Boeing's 737 Max model, Rosemount Aerospace, was also visited by NTSB investigators after the Lion Air crash, according to a former engineer at the company who requested anonymity because he was not authorized to speak for the company.
 
A spokeswoman for United Technologies, which owns the Burnsville, Minnesota-based Rosemount, declined to comment.
 
Bloomberg first reported the involvement of the two companies in the AoA's development and maintenance.
 
It is routine for crash investigators to visit facilities that handled a part that could have played a role in an accident.
 
"The whole manufacturing and storage and installation of that component, the Angle of Attack sensor, is under investigation and that's what the NTSB guys are doing down there," said Dr. Alan Diehl, a former NTSB investigator, who is not working on this investigation and was speaking in general about his experience in crash investigations.
 
"That doesn't mean that there's anything wrong -- that's why they're investigating," Diehl said.
 
The NTSB declined to comment to CNN.
 
The former Rosemount engineer expressed astonishment that Boeing had originally designed the anti-stall software, known as the Maneuvering Characteristics Augmentation System, or MCAS, to draw from only one of two AoA sensors on the nose of the plane.
 
"How that got certified is something that's a mystery to us," he said.
 
The Justice Department is currently probing Boeing and the Federal Aviation Administration's certification and marketing of the plane, CNN has reported.
 
Boeing last week announced that they were updating MCAS to draw data from the two AoA sensors, adding a level of redundancy to the system.
 
Elements of plane design are classified by regulators for their risk of failure, which determines the level of redundancy needed. The higher the risk of failure, the more redundancy required.
 
Boeing officials have said that the software in its initial design had been classified at a level of risk of failure that, in line with industry standards, didn't require data from a second sensor.

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