More MAX information

[Toad]

That method haven been in the manuals for the 737 for a very long time afaik and isnt anything pilots are trained on today.
10- 15 seconds after take off the normal power setting isnt 60%. You have to remember that they where very low, <1000 ft of the ground with mountains around them. 60% thrust and 2 degree pitch would have killed them even faster...

This is what hasn't changed: If you hold full aft stick it's difficult to manually trim the stab. The push/pull technique still works.

Secondly, you have to remember that pitch + power = performance. If they had held 2-3 degrees nose up and 60% N1, they would have been in a slow climb at a safe airspeed. Exactly what Mr. Bjorn recommends.

You should also realize that 340kts at low altitude with the nose down just makes bad things happen faster.

I see Busher pointed this out as well.

[Toad]

This is obviously not helpful in the case of ET302

If you have a graph of stick position throughout the flight of ET302, I'd love to see it.

Do you actually know where the stick was when they were trying to manually trim? Was it full aft? Was it mid position? Was it forward?

[Zimme83]

If you have a graph of stick position throughout the flight of ET302, I'd love to see it.

Do you actually know where the stick was when they were trying to manually trim? Was it full aft? Was it mid position? Was it forward?

Yes its in the Preliminary report. https://leehamnews.com/wp-content/uploads/2019/04/Preliminary-Report-B737-800MAX-ET-AVJ.pdf
page 26

[Toad]

The graph shows the stick pulled aft at about 9 degrees from 5:40:30 until about 5:43:25 -ish. Can we assume that the roughly 9 degrees is about as far aft as the crew was able to pull it? Seems reasonable as it essentially doesn't change.

When the SIC tries to trim manually at 5:41:46 - 5:41:54, the stick is pretty much in the same position, about 8-9 degrees aft. Looks to me like it is still full aft. Which, as has been pointed out, makes it extremely difficult to trim the stab manually.

From the graph it looks like they were Vmo+ from 5:40:30 thru 5:43:30. Again, Vmo would make it difficult to trim the stab manually, especially with the stick held as far back as possible.

Again, this calls into question the 94% (takeoff) power setting. From 5:40:30 - 5:43:30 they are climbing from about 9000 to ~14000 with the overspeed clacker sounding. Climbing at 340kts (+ ?) in overspeed for about 3 minutes, gaining 5000 feet. With the stick probably as far aft as they could get it.

To people that do this stuff for a living those printouts raise more questions about the crew than the aircraft.

[Puma44]

To people that do this stuff for a living those printouts raise more questions about the crew than the aircraft.

Exactly!  Appears the jet was flying the crew. 

Haven’t looked at the graph yet but, did climb power ever get called for and set?

[Toad]

Exactly!  Appears the jet was flying the crew. 

Haven’t looked at the graph yet but, did climb power ever get called for and set?

Nope.

From the Prelim:

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.

But takeoff power, 340kts +, overspeed clacker clacking and a ~1600 fpm climb rate is all normal procedure right?

Another thing on the graph:

From the Prelim:

At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds.

That would be the re-engagement of the Stab Trim Cutout switches. Funny the Prelim doesn't mention that.

Looking at the graph, 05:43:30 is where the terminal dive begins. It would suggest that the re-engagement of the Stab Trim Cutouts, an action step in total disagreement with the Runaway Stab NNC, was pretty much the last link in the accident chain.

[Busher]

Pages 10 and 11 of the report outlining the time line of the accident, make at least 2 references to significant airspeed differences between the Captain and the FO. One reference mentions a huge altimeter difference at the time of the crash.
I don't have any idea why their investigation seems not to care about these disagreements but its clear to me that there was a lot more going on than just an aggressive MCAS.
I may be beating a dead horse but the Pitot-Static issues on this airplane could affect all the other systems which are seen as the primary cause.
Has anyone heard if Boeing or any other interested party is looking into whether this type may have a propensity to Pitot-Static faults? (much like the A330)

[Puma44]

Nope.

But takeoff power, 340kts +, overspeed clacker clacking and a ~1600 fpm climb rate is all normal procedure right?

Another thing on the graph:

That would be the re-engagement of the Stab Trim Cutout switches. Funny the Prelim doesn't mention that.

Looking at the graph, 05:43:30 is where the terminal dive begins. It would suggest that the re-engagement of the Stab Trim Cutouts, an action step in total disagreement with the Runaway Stab NNC, was pretty much the last link in the accident chain.

This is looking more and more like a relatively simple mechanical malfunction that surprised the crew so much, and with their relatively low time in the 737, caused them to get so far behind the situation, there was no chance of recovery.

Pages 10 and 11 of the report outlining the time line of the accident, make at least 2 references to significant airspeed differences between the Captain and the FO. One reference mentions a huge altimeter difference at the time of the crash.
I don't have any idea why their investigation seems not to care about these disagreements but its clear to me that there was a lot more going on than just an aggressive MCAS.
I may be beating a dead horse but the Pitot-Static issues on this airplane could affect all the other systems which are seen as the primary cause.
Has anyone heard if Boeing or any other interested party is looking into whether this type may have a propensity to Pitot-Static faults? (much like the A330)

Agree.  Seems the malfunction(s) caused enough confusion to distract the crew away from the primary goal of maintaining aircraft control. 

[Busher]

This is looking more and more like a relatively simple mechanical malfunction that surprised the crew so much, and with their relatively low time in the 737, caused them to get so far behind the situation, there was no chance of recovery.

Agree.  Seems the malfunction(s) caused enough confusion to distract the crew away from the primary goal of maintaining aircraft control.

Then sadly have we not come full circle? That a terribly inexperienced crew were presented with series of failures that they were not equipped to handle.

[Puma44]

Then sadly have we not come full circle? That a terribly inexperienced crew were presented with series of failures that they were not equipped to handle.

Yep.

[Puma44]

Since there’s been some discussion about the Stab Trim Cutout Switches with regard to the MCAS, here are a couple of pictures.

These are the early versions found on -1/2/3/500s:

These are the later versions found on some -300s and subsequent NGs:

[Busher]

A very disappointing element of these tragedies will be, in my opinion, the ultimate failure of the 737-Max. Legs were broken jumping to conclusions about this airplane and these accidents, and well beyond the scope of this forum.
If I were still flying and had bid "the Max", I would have no concerns about flying this airplane but in my former employer, even so called professional flight attendants were refusing to work on them.
The Media who knows nothing about aviation, sews the seed, the Politicians who know even less, react. Public panic is now well fueled, so all 737 series will likely invoke a reaction to some degree.
It seems that seeking the truth for the benefit of aviation safety is subordinated now to innuendo, speculation and possibly even political image.
I'll read the details of the final report when its published in the hope it will be un-biased and not tainted. Until then I really have nothing more to add to this discussion.

[Toad]

I'm not quite ready to let this go. There's chatter around the US safety establishment that the Ethiopians are....um....not being totally forthcoming about that accident.

Now that the know-nothing MSM talking heads have moved on, some interesting FACTS are starting to come out in aviation related and aviation experienced press.

This is a long post; sorry about that. The whole article is definitely worth reading.

Aviation week:  https://aviationweek.com/commercial-aviation/ethiopian-crash-data-analysis-points-vane-detachment

...sources close to the probe say flight data recorder (FDR) data firmly supports the supposition that the aircraft’s left angle-of-attack (AOA) sensor vane detached seconds after take-off and that, contrary to statements from the airline, suggests the crew did not follow all the steps for the correct procedure for a runaway stabilizer....

...This is indicated by approximately 8-sec of nose-down stabilizer movement, which was followed by the use of manual trim on the control column. However, with the MCAS having moved the stabilizer trim by 2.5 units,the amount of manual nose-up trim applied to counteract the movement was around 0.5 units, or roughly only 20% of the amount required to correctly re-trim the aircraft

Because of the way the aircraft’s flight control computer P11.1 software worked, the use of manual trim also reset the MCAS timer, and 5 sec. later, its logic having not sensed any correction to an appropriate AOA, the MCAS activated again. The second input was enough to put in the full nose-down trim amount. The crew again manually counteracted with nose-up trim, this time offsetting the full amount of mis-trim applied by the latest MCAS activation.

By then, some 80% of the initial MCAS-applied nose down trim was still in place, leaving the aircraft incorrectly trimmed. The crew then activated the stabilizer trim cutoff switches, a fact the flight data recorder indicates by showing that, despite the MCAS issuing a further command, there was no corresponding stabilizer motion. The aircraft was flying at about 2,000 ft. above ground level, and climbing.

The crew apparently attempted to manually trim the aircraft, using the center-console mounted control trim wheels, but could not. The cut-out switches were then turned back on, and manual trim briefly applied twice in quick succession. This reset the MCAS and resulted in the triggering of a third nose-down trim activation lasting around 6 sec.

The source says the residual forces from the mis-trim would be locked into the control system when the stabilizer cut-off switches were thrown. This would have resulted in column forces of up to around 50 lb. when the system was switched back on.

Although this could have been reduced by manually trimming the aircraft, this did not occur, and the third MCAS activation placed the aircraft in a steep nose-down attitude. This occurred with the aircraft near its peak altitude on the flight—about 6,000 ft. The engines remained at full take-off power throughout the flight, imposing high aerodynamic loads on the elevators as the crew attempted to pull back on the columns. [/b] 

The reason they couldn't manually trim is that the left the power at 94% and were going faster than Vmo. That power setting and that airspeed means you have incredibly high loads on the stab. They probably could have trimmed it if they had kept the speed in the normal range, 250-300.

[Toad]

So, two 737 Max crashes; let's review.

Lion Air: Lion Air sends out an aircraft that is not airworthy (bad AOA) on Oct 28 and Oct 29. On Oct 28, the bad AOA generates a MCAS event and the jump seat pilot saves the day by telling the crew to use the Stab Trim cutout switches. Same aircraft gets sent out Oct 29, same bad AOA, same generation of a MCAS event and the crew does not use the Stab Trim cutout switches or reference the Runaway Stabilizer Trim NNC in their QRH and the plane crashes.

Ethiopian: Highly probably FOD event on AOA triggering a stick shaker shortly after takeoff. This is a semi routine simulator training event. Crew leaves power at takeoff setting, failing to realize they are NOT stalling (cross check power/pitch/airspeed). After cleanup, bad/missing AOA generates a MCAS event. Crew partially counteracts MCAS stab position using yoke electric trim switches, resetting MCAS timer. Second MCAS event from bad/missing AOA which crew counters with yoke electric trim switches, removing all MCAS stab input from second event. Still incorrectly at takeoff power, now going Vmo+. Finally use Stab Trim Cutout switches but because they are going way too fast and aerodynamically overloading the stab; they are unable to trim manually. They reset MCAS and enter terminal dive, exceeding 500 kts.

Somehow, these accidents are Boeing's fault?

In both, there are links in the accident chain that were EASY for the crew to break. No one needed to die, neither airplane was doomed from the start to crash.

Solely blaming Boeing is a huge mistake that is going to cause more heartache in the future. Boeing may have been lax in writing their systems description. They might have added a line to the Runaway Stab NNC, pointing out it works for bad MCAS too. They could have made MCAS require dual AOA confirmation, although I've pointed out very many manufactures trigger stall warning/stall protection off of the first (single) AOA to sense a stall. Yep, I go along with all of that.

However, ignoring the failure of the two crews to 1. Maintain Aircraft Control   2. Analyse The Situation  3. Take Proper Action is overlooking the training/experience issue in airline cockpits. There needs to be some deep soul searching about what qualifications are going to be required for these jobs. There needs to be serious evaluation of simulator profiles. The continual urge to cut training costs needs to be addressed and rectified.

YMMV.

[Vraciu]

I told you so...