Indonesian aircraft missing off Jakarta

[wiedehopf]

Originally Posted by gums

Question rom a "light" pilot.

I am having a hard time with the procedure for runaway trim in the matter under discussion.

The AD and such indicate that manual trim using the switches on the yoke will work, but then the system runs the trim again unless the whole trim sytem is turned off. So if the stab is fully trimmed and the crew tuens off the trim, then all they have is basic elevator, right?

Jez asking...
Gums

Check the video posted a few posts above.
You can see the trim wheel in action. It can be turned by hand and even has a crank that is not used on the video (not sure why)
(This is the video in question https://tinyurl.com/ycah3ww)
A picture of the trim wheel with handle extended:

[tdracer]

Originally Posted by A Squared

I don't know. I'm just saying that Boeing's words in the AD seems to indicate that moving the switches to "CUTOUT" is not a 100% guaranteed clean kill on stabilizer trimming. Why that is, or how it happens, I can only speculate. I have a hard time imagining designing a system that moves your flight control surfaces, and you can't turn off completely. Perhaps Boeing is alluding to the possibility that the contacts in a STAB TRIM switch become welded and don't open the circuit. I'm grasping at straws here.

There are several failures that can cause a stab trim runaway - and not all are solved by turning the system 'OFF". In addition to welded switch contacts, the motor can fail in such a way that you can't turn it off. These failures are rare, but not impossible - the only way to 100% disable the system is to pull the circuit breaker(s) (and that's not something they like to tell the pilots to do).

[gums]

Thanks TDracer and others,

My poor copy of the 737 manual is not all that clear about the mechanical connection of the trim wheel with the stab. Looks to me like it still uses some electrical thing and does not physically rotate the jackscrew or have gears and such. So a frozen/welded electrical component might result in frozen stab angle and all that it entails.

After all this great discussion, I have a feeling that the Rostov crash investigation may not be over. Go around, steep climb and decreasing speed, push over and then can't recover. That is the scariest video I have ever seen other than ......

I then place myself in the cockpit of this plane and short time after gear gear up we get the nose down upset and finally recover and continue on up to 5,000 feet. And then we have ten minutes of porpoising and I wonder if it was MCAS cycles and the main electric trim switches were still not turned off simply because every time the pilot stopped using the yoke switch the damned plane started nosing over again.

later, Gums wonders....

[A0283]

Hard to keep up gents. Wonder if this description has been posted before. Pity there is no source and date on it.

The MCAS (Maneuvering Characteristics Augmentation System) is implemented on the 737 MAX to enhance pitch characteristics with flaps UP and at elevated AOA. The MCAS function commands nose down stabilizer to enhance pitch characteristics during steep turns with elevated load factors, and during flaps up flight at airspeeds approaching stall.

MCAS is activated without pilot input and only operates in manual, flaps up flight. The system is designed to allow the flight crew to use column trim switch or stabilizer aislestand cutout switches to override MCAS input. The function is commanded by the Flight Control Computer using input data from sensors and other airplane systems.

The MCAS function becomes active when the AOA exceeds a threshold based on airspeed and altitude. Stabilizer incremental commands are limited to 2.5 deg's and are provided at a rate of 0.27 deg's per second. The magnitude of the stabilizer input is lower at high Mach number, and greater at low Mach numbers. The function is reset once the AOA falls below the AOA threshold, or if manual stabilizer commands are provided by the flight crew. If the original elevated AOA condition persists, the MCAS function commands another incremental stabilizer nose down command according to current aircraft Mach number at actuation.

[CONSO]

RE GUMS 1233 cable/mechanical connection of trim wheel with styab ..
This SLF happend via google to find this link FWIW re 737 NG

https://www.slideshare.net/theoryce/...light-controls
Which in part says ( emphasis added )

• 4. Fully powered rudder Hydraulic systems A-B and Stby. No tab Power assisted Elevators Hydraulic systems A and B Manual reversion Aerodynamic balance tab. Power assisted Ailerons. Hydraulic systems A and B. Manual reversion Aerodynamic balance tab. Primary Flight Controls
• 5. Movable horizontal stabiliser powered by an electric motor for manual trim or by the Autopilot. Manual via cables from the trim wheels in the cockpit. Four flight spoilers on each wing symmetrical pairs powered by hydraulic systems A and B Secondary Flight Controls Inboard and outboard double slotted T.E Flaps Normally Hydraulic system B Alternate Electric motor Outboard and Inboard spoilers Ground only Hydraulic system A 4 slats on each wing . Hydraulic system B Normal Standby Hydraulic Alternate 2 Krueger flaps On each wing inboard of the engines move with the slats

[svhar]

I wonder why they did not make a 757 MAX instead of a 737. The 737 has lots of flaws and the MAX label has not changed anything. I don't remember any flaws on the 757.

[SLFstu]

Was MCAS certified?

Non-flyer here, sticking my neck out.

I note that tdracer and DaveReidUK provided clout about certification methodology in recent posts.

My source docs,
* B737 TC - an FAA doc actually named “Type Certificate Data Sheet A16WE” (page with link originally provided by Gysbreght in post #1187)
* Section 25.672 of Part 25 Airworthiness Standards (FAA)

Firstly, note that the B737 MAX-8 and -9 have both been methodically added to the B737 TC, as shown on the current B737 Type Certificate Data Sheet. Application for MAX-8 certification was first put to the FAA in June, 2012; design was finalized mid 2013; and its specific TC was issued in March 2017, (10 weeks before being flown by the first operator). In doing so, these new MAX a/c append in time sequence to a long list of all previous 737 variants that the TC Data Sheet covers. There are 2 more of the 737 MAX family to come yet.

So, digging into the TC, towards the end where 737-8 and 737-9 certification is summarized. On page 74 of the doc we find that in the CONTROL SYSTEMS section, the included item Part 25.672 Stability Augmentation and Automatic and Power-Operated Systems (an FAA named item) gets its first and only mention. This in a certification data sheet which includes every model since the very first 737, so logically the item applies only to the MAX-8 and -9. Apparently none of the prior B737 variants were certified for this.

Is it too much to conclude that this is MCAS first seeing the regulatory light of day?

If so, in the second source doc above, the FAA sets out the regulatory requirements for systems having this class of functionality. If Boeing had the MCAS in mind in citing this section for certification, there may be some pertinent questions to be answered.

[tdracer]

Originally Posted by DaveReidUK

The 737 MAX 8 was certificated (as the "737-8") in Revision 58 of the Boeing 737 Type Certificate (A44WE) on 8th March 2017.

While there are indeed a handful of STCs (16 in fact) that are applicable to the MAX 8, they do not form part of the TC.

Yes. I stand corrected - I'm going to claim a senior moment Mulligan . I was using the term STC in that post, I should have been using ATC (Amended Type Cert) - STC is different (although related). I'll edit it accordingly to avoid the most serious confusion.

[WillFlyForCheese]

Originally Posted by gums

Question rom a "light" pilot.

I am having a hard time with the procedure for runaway trim in the matter under discussion.

The AD and such indicate that manual trim using the switches on the yoke will work, but then the system runs the trim again unless the whole trim sytem is turned off. So if the stab is fully trimmed and the crew tuens off the trim, then all they have is basic elevator, right?

Jez asking...
Gums

Here ya go . . . all you wanted to know about spinning wheels . . .

Watch Videos Online Aircraft trim system, 737-200 Veoh.com

[LDRA]

Originally Posted by SLFstu

Firstly, note that the B737 MAX-8 and -9 have both been methodically added to the B737 TC, as shown on the current B737 Type Certificate Data Sheet. Application for MAX-8 certification was first put to the FAA in June, 2012; design was finalized mid 2013; and its specific TC was issued in March 2017, (10 weeks before being flown by the first operator). In doing so, these new MAX a/c append in time sequence to a long list of all previous 737 variants that the TC Data Sheet covers. There are 2 more of the 737 MAX family to come yet.

So, digging into the TC, towards the end where 737-8 and 737-9 certification is summarized. On page 74 of the doc we find that in the CONTROL SYSTEMS section, the included item Part 25.672 Stability Augmentation and Automatic and Power-Operated Systems (an FAA named item) gets its first and only mention. This in a certification data sheet which includes every model since the very first 737, so logically the item applies only to the MAX-8 and -9. Apparently none of the prior B737 variants were certified for this.

Is it too much to conclude that this is MCAS first seeing the regulatory light of day?

If so, in the second source doc above, the FAA sets out the regulatory requirements for systems having this class of functionality. If Boeing had the MCAS in mind in citing this section for certification, there may be some pertinent questions to be answered.

Good find

I just read through section 25.672, if MCAS falls under this section, Boeing is in deep trouble. MCAS fails every.single.clause in this section! There wouldn't be simple fix...

[Gipsy Queen]

Originally Posted by DaveReidUK

That's true, though of course most wings, being cambered, do still produce some lift at 0° AoA.

Actually, depending upon design, a wing can produce a lot of lift at 0deg AoA, certainly more than AoA alone with a conventional wing profile. But I thought we had agreed to leave Bernoulli out of it!

[George Glass]

It has been noted by others that differences training from B737-800 to B737-8 does not require emphasis on the MCAS.Boeing wants to keep it simple. If you get a hold of the Runaway Stabilizer Non Normal Checklist you can see why.If correctly followed it CAN resolve the issue. But like all non-normals it requires a well trained Pilot and the correct response to the condition. Having personally experienced an Airspeed Unreliable event in-flight I can only say that the startle factor is massive.Simultaneous stall and overspeed warnings is a challenge to say the least. You dont have long to make the right call.Same for runaway stab.Still the most likely cause is incorrect response to the condition.Having said that I have great sympathy for the crew.Very easy to play monday morning quarterback.Why the aircraft was cleared to line after 3 sectors with a know problems is another question.

[Capn Bloggs]

Originally Posted by Gums

So if the stab is fully trimmed and the crew tuens off the trim, then all they have is basic elevator, right?

You can trim it by manually turning the trim wheel.

Originally Posted by George

Having personally experienced an Airspeed Unreliable event in-flight I can only say that the startle factor is massive.Simultaneous stall and overspeed warnings is a challenge to say the least.

And then you're supposed to notice the trim quietly winding itself full nose down...

It should be one or the other. As mentioned previously, if there is a chance that the trim will runaway during a Unreliable Airspeed scenario, then "Stab Trim OFF" must be one of the memory items.

[Loose rivets]

CONSO's link has an interesting item on page 52. (Quick access via strip on top edge of black bar.)

Cam switches under the flight-deck floor disable the trim when the control column is moved in the opposite direction to the stabilizer trim direction. I'd struggling to cope with the technical issues, but if this has been mentioned, I missed it.

https://www.slideshare.net/theoryce/...light-controls

[neville_nobody]

If correctly followed it CAN resolve the issue. But like all non-normals it requires a well trained Pilot and the correct response to the condition.

Additional to this you need to identify the problem. I could imagine this being quite a difficult task if you had unreliable airspeed announciations additional to stick shakers going off, even hearing the trim running may not be possible. The only way to confirm would be to look down but not sure who would be doing that when you are under the impression the aircraft is stalled.

[jimtx]

Originally Posted by WillFlyForCheese

Here ya go . . . all you wanted to know about spinning wheels . . .

I can't post the OP's video

That mechanical stab trim brake system was changed to some type of column activated electrical cutout system some time in the later models. The brake release knob on aft pedestal normally used to secure the garbage bag on the 727 and, I guess the 737, was replaced by a switch to override the stab trim cutout system. If the Max still has the latest cutout system they must have made a bypass around it for the MCAS. When I was a 727 plumber we checked the brake, as seen on the video, on first flight of the day. 737 drivers please chime in on whether this system is checked/installed on your aircraft.

[megan]

Article on AVweb. Closing para,

I don’t often speculate on such things but if I were a betting man—and I’ve been known to dabble at the tables—my bet is that the accident investigation will once again revisit a familiar theme: automation bias. In the name of safety shaped by consistent procedures driven by automation in the cockpit, pilots are increasingly losing their basic feel for putting hands on controls and throttles and actually flying a flyable airplane. A second focus will be the utter perversity of how pilots now have to be trained to keep the automation that’s supposed to help them from killing them instead.

https://www.avweb.com/eletter/archiv...4190-full.html

[b1lanc]

There are a number of questions surrounding the certification process which as far as I can tell revolve around what documentation and/or training of a 'new' flight control automation capability was not documented to airlines let alone crew by the manufacturer. But, do we even know;
1) If the sensor was faulty or was there a problem further down the line, AoA sensor was replaced (1 or 2 sensors depending upon source cited) and it either didn't fix one "symptom" (airspeed disagree) or make matters a whole lot worse, but still allowed the next segment to complete, albeit more harrowing then the prior 2 segments (that may have been pilot skill - refer back to Golden Rivit's post #956 and listen to Capt VanderBurgh's last 10 minutes, including China Airlines 140 and the Delta L-1011 San Diego incident? Ok you can argue whether the unfortunate toga press caused 140, but I'd suggest that happened because of stab trim gone rogue.)
2) Was the correct part installed correctly?

Interesting read on why MCAS allegedly was created for the MAX - https://theaircurrent.com/aviation-s...em-mcas-jt610/. Take it for what it is worth as the site content was written by a media type.

[mnttech]

Originally Posted by DaveReidUK

The 737 MAX 8 was certificated (as the "737-8") in Revision 58 of the Boeing 737 Type Certificate (A44WE) on 8th March 2017.

I'm confused, A44WE is not the FAA TCDS, comes up as not a valid number, A16WE is, or at least per the FAA RGL.EASA number?
14 CFR 25.672 came out with Amdt. 25-23, Eff. 5/8/70, so it shows up (somewhat) in Type Certification Basis, (737-300 Series Airplanes), Type Certification Basis, (737-400 and 737-500 Series Airplanes),
*Applicable only to new or major modified structure or to new systems and components unique to the 737-400, and 737-500 series airplane with respect to the existing Model 737-200 Series airplane.
737-600, -700, -800 (Cont’d.) Certification Basis: A. 14 CFR Part 25 of the Federal Aviation Regulations as amended by Amendments 25-1 through 25-77 with the exceptions listed below
So for those aircraft it is a valid rule

[tdracer]

A bit surprised this hasn't been posted previously - it's from the Monday Seattle Times:
https://www.seattletimes.com/busines...ion-air-crash/

A former Boeing executive, speaking on condition of anonymity because discussion of accident investigations is supposed to be closely held, said that Boeing engineers didn’t introduce the change to the flight-control system arbitrarily.
He said it was done primarily because the much bigger engines on the MAX changed the aerodynamics of the jet and shifted the conditions under which a stall could happen. That required further stall protection be implemented to certify the jet as safe.

Side note - I'm a bit surprised even a 'former' Boeing exec was willing to talk about this to the press - this sort of information release during an active investigation could get them in some serious hot water...