To me, it all comes down to to Boeing being able to self-certify their aircraft, and they knew they were sneaking the "fix" known as MCAS as a way to prevent loss of sales to A320. Super shady in my opinion.
The script required them to manually crank in the stabilizer, which wasn't possible. The script was manifestly not "working". That doesn't "remain to be seen" -- it's in the transcript of the cockpit
> At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working.
I guess the First-Officer must have been speculating...
Until someone sits down and calculates the torque needed to manually trim it's all just speculation.
They weren't
>the pilot is busy supplying maximum pull on the yoke,
Probably not true either
>and therefore likely unavailable to help crank a stiff trim wheel
Runaway trim should be a recoverable situation. If that's impossible then that means there is a distinct and major issue beyond MCAS.
> They weren't
They just took off, max height of the airplane was 1000 feet above the ground. That's a definely low altitude.
> Runaway trim should be a recoverable situation.
The trim pointed the nose down. The aerodynamic forces were so high on the elevator that the trim wheels could not be moved by a single person. This was confirmed in 737 simulator.
People thought that based on Flightaware data. But if you actually read the report you will see that it is incorrect and they reached about 7,000 feet.
>The trim pointed the nose down.
Incorrect. The plane was steadily gaining altitude until they re-enabled electric trim.
>I wouldn't feed the troll, but I don't want your misinformation to spread.
Try being right before throwing around personal insults.
which points clearly to MCAS applying maximum nose down, based on incorrect data from the left alpha sensor, both pilots pulling on their control sticks, and the aircraft failing to gain altitude even before final MCAS activation because the trim could not be manually reset by the F/O.
this report contradicts every element that you're pushing (plane reached altitude, pilots didn't pull on the column, the electric trim was not needed, MCAS did not intervene). did I missing anything ?
Screw Jack and effort force https://www.engineeringtoolbox.com/screw-jack-d_1308.html
Gearing: https://www.engineeringtoolbox.com/gears-d_1307.html
Here's some 737-800 dimensional analysis as a starting point.
https://holdingpoint.wordpress.com/2011/04/04/boeing-737-800...
Knock yourself out.
Or if you stick around long enough I may do it for gits and shiggles.
I'll need some schematic details of the actual manual trim wheel mechanism to figure out what the output forces on the jackscrew are... But hey, sounds like a fun mental exercise.
I'll see if I can find any details on it, but if anyone else just has it, reply to me, and let's see if we can get some delicious numbers going on here. Worst case scenario, I'll pull whatever design most makes sense to me out of my arse and theorycraft to get a feel for it.
737-800 has a 32.776m^2 horizontal stabilizer area. Let's double that to 65.556 to accomodate both airfoils.
Wing load is 1/2p(v^2)A Where A=65.556m^2 (352.8 ft^2) v=180.556m/s (350 knots) And we'll guess our air density around .95ish kg/m^3 given our altitude of 2334m (7625 ft plus change) asl
Barring any flawed fundamental assumptions, that gives us a wind load of 1015087 N (228200.636 pounds-force (lbf)), and a dynamic pressure of 15485 N/m^2
I'll leave this out there to offend any actual aerospace engineers that might be reading so they'll tell us I'm doing it all wrong while I try to work out whether I can use the screw jack equations and what we've calculated thusfar in the hopes of figuring out something that even remotely makes sense.
I have a feeling I'm oversimplifying or misapplying the wind load equation. But hey, it's the internet. I'm allowed to be wrong.
Dropping in the previously calculated wind load of 1015087 N, we end up with an effort force of 3182 N, which through a 6 in pulley would be 485Nm (357 ft-lbs) of torque,
Note, we're in automobile engine levels of torque output to actuate this screw jack against the wind load on the horizontal stabilizer.
Give me a bit to come up with some estimates on the trim wheel and play around with some gear trains to see if I can come up with an arrangement that does the trick.
It should be doable, but with the gear ratios I'm thinking will be required to generate the requisite torque, the actual rate of actuation is going to be pretty slow.
Your responses have been incredibly selective about which parts of the report you take as gospel and which you handwave away as "speculation".
From where I'm sitting it appears you've started out by picking a contrarian conclusion you like ("the plane was safe once STAB CUTOUT was set cutout, and the crew could have maintained altitude indefinitely at that point, but fatally fucked up by re-engaging electronic trim to try to trim the stabilizer"), and to maintain that a priori conclusion you've consistently ignored the data and parts of the transcript that indicate that was very likely impossible.
Where is that data in the report?
> At 05:41:30, the Captain requested the First-Officer to pitch up with him and the First-Officer acknowledged.
> At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough.
Take a look at the chart of control column position deflections. They're jolting around like crazy at +10 to +15 aft starting immediately at the first big MCAS trim event through to the end of the recording. That's because the stabilizer mis-trim is exerting considerable force on the elevator. The captain wasn't calling for aid on the column for shits and giggles.
okay
https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-ra...
05:41:30 - PIC requests SIC to pitch up with him
05:41:46, 05:41:54 manual trim not working, that is absolutely a trim wheel hand crank attempt; fairly clear (to me) but not stated is that both pilots were not simultaneously cranking on the trim wheel, there's plenty of anecdotal evidence that this exact configuration puts to much upward force on the jackscrew that it is difficult to impossible to turn.
05:43:04, PIC asks SIC to pitch up together says pitch is not enough
As for the noisiness of the control column position data, it could be partly the stick shaker, it could be light turbulence, the accel vert row at the bottom shows it's a bumpy flight, and pitch and roll attitude is also variable but less so than vertical accelerate. And accel vert gets noticably more perturbed as airspeed increases. I think it's light to moderate turbulence, but I'm not certain. A search for PIREPs and weather reports at the time could corroborate it.
Right, and my point is that until someone actually does that calculation we don't know how high that force was.
This isn't consistent with any coherent reading of the transcript:
> At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually.
They've already hit the stab cutout at this point. Now maybe they're think this is like the older 737s and the cutout cut the autopilot and not the full electrical, BUT if you think the question he was asking was whether or not he could try the thumb switch, what exactly would he have been trying prior to that that "wasn't working"?
There is no other trim to try before the thumb switches such that you'd refer to the thumb switches as "trying it manually" when $OTHER_THING was not working. In the transcript, given what's being said, it's clearly the wheel crank that's meant. It doesn't even make sense otherwise.
From the report:
At 05:38:44, shortly after liftoff, the left and right recorded AOA values deviated. Left AOA decreased to 11.1° then increased to 35.7° while value of right AOA indicated 14.94°. Then after, the left AOA value reached 74.5° in ¾ seconds while the right AOA reached a maximum value of 15.3°. At this time, the left stick shaker activated and remained active until near the end of the recording. Also, the airspeed, altitude and flight director pitch bar values from the left side noted deviating from the corresponding right side values. The left side values were lower than the right side values until near the end of the recording.
...
At 05:39:06, the Captain advised the First-Officer to contact radar and First Officer reported SHALA 2A departure crossing 8400 ft and climbing FL 320.
...
At 05:39:42, Level Change mode was engaged. The selected altitude was 32000 ft. Shortly after the mode change, the selected airspeed was set to 238 kt.
At 05:39:45, Captain requested flaps up and First-Officer acknowledged. One second later, flap handle moved from 5 to 0 degrees and flaps retraction began.
Bear in mind stick shaker and divergent instrument readings all this time.
Why not just return and land, leave the flaps configuration alone (which would have inhibited MCAS), especially since this is exactly how the Lion Air flight started.
I know this is easy to critique from the comfort of my chair, and the pilots are not here to defend themselves, but some things in this narrative just don't make sense.
Experience sounds like a good thing on the face of it, but it also adds noise where all of these indications sound familiar enough, and yet nothing in particular stands out and tells you to leave flaps alone. That suggestion isn't even in the emergency airworthiness directive. And still at the time of this event there's no simulator that can be configured for MCAS upset so that pilots can experience it in various phases of flight.
Also, the priority in a flight control problem is to fly the plane, get it stabilized, understand the problem, and turning back to the airport is inconsistent with that. Fly runway heading is the proper thing to do, it's less complicated. A turn increases angle of attack, increases drag, it makes a high angle of attack situation worse, and if you're trying to climb it reduces your rate of climb.
But check Boeing's MCAS bulletin, which is the only official information pilots received about MCAS at the time of the flight.
http://www.b737.org.uk/images/aoa-bulletin.jpg
It makes zero mention of flaps. It doesn't recommend avoiding retracting them or trying to land as soon as possible.
Trying to land as fast as possible is typicality a bad idea. Planes which have just taken off are almost always over their maximum landing weight. Even if you ignore that, the extra stress of trying to land as soon as possible could cause the pilots to make more errors.
Procedures for issues on take off are typically focused on continuing to climb to gain as much altitude as possible to give the pilots time and space to assess the problem before dumping fuel and landing. The more altitude you have the more time you have to recover.
And unfortunately, climbing through 5000 feet requires retracting the flaps.
I don't know the most likely consequence of flying with flaps 5 above Vfe. Maybe flaps would (asynchronously) depart the airplane, or induce flutter at a much lower than usual airspeed. Either of those is an extremely high risk of losing the aircraft.
MCAS should be disabled at this time and this is confirmed further in the report.
> At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance of AND automatic trim command occurred without any corresponding motion of the stabilizer, which is consistent with the stabilizer trim cutout switches were in the ‘’cutout’’ position
the crash happens full three minutes later.