Another 737 MAX-8 down

originally posted by: Zaphod58
a reply to: KansasGirl

Because altitude is life. If you stall or have a pitch down at 1400 feet, you measure the time to react and correct it in seconds. The same thing at 14,000 and you're talking a minute plus.

To put it bluntly, that's basically what they get when remains are returned. When they say bodies are recovered, they're trying to be sympathetic to the families. In most crashes intact bodies are rare. In an impact like this, you're lucky to recover more than fragments.

Thanks for the info.

It seemed, from a comment from one of the family members, that they are expecting to eventually receive SOMETHING. He/she said they wouldn't be able to rest until they got the loved one's body or body parts. 😰😰. As hard as it is, seems like it would be better to tell them that they aren't likely to get even any body parts. At least then they aren't just waiting in vain. Awful any way you slice it though.

a reply to: KansasGirl

They'll get some remains, but they won't get much. There's enough left of the remains to DNA test. But 2 pounds is probably being generous for most families.

a reply to: Zaphod58

Oh FFS!
2 second research.
www.boeing.com...

Edit:

Correct. God forbid if you get a real stall, you have to pitch down 20 deg to regain flying speed and you do lose a lot of altitude

On another note, needless to say, I am petrified of flying as a pax, ever since I read about the AF 447 disaster
a reply to: Zaphod58

a reply to: Zaphod58

Thanks to you and Nelloh62. Forums at an airliner site was OK, as were discussions of European certification issues, but what I was curious about is whether Boeing itself published, if the material is not somehow classified, the syllabus for the flight test program for the Max aircraft, along with the results of data gathered.

It seems they tacked on the Max aircraft to the old original 737 type. Others are noting, and I tend to agree, that really the Max is so different from the original in so many ways that a new type would have been appropriate, with all the required test flying.

This MCAS system seems to have been hidden away somehow. Certainly it was not included in any training syllabus.

The Transportation Minister said this morning that "the data recorders show clear similarities to the Lion Air 610 crash", which we already knew. The preliminary report is due within 30 days.

Boeing’s safety analysis of the flight control system called MCAS (Maneuvering Characteristics Augmentation System) understated the power of this system, the Seattle Times said, citing current and former engineers at the U.S. Federal Aviation Administration (FAA). The FAA also did not delve into any detailed inquiries and followed a standard certification process on the MAX, the Seattle Times reported citing an FAA spokesman. The report also said both Boeing and the FAA were informed of the specifics of this story and were asked for responses 11 days ago, before the crash of an Ethiopian Airlines 737 MAX last Sunday, killing all 157 people on board. The same model flown by Lion Air crashed off the coast of Indonesia in October, killing all 189 on board

www.reuters.com...

Just spotted this on Reuters twitter feed.

a reply to: solidshot

I still say that while there appears to be a definite software problem, this is something else.

Ethiopian now says the F/O had 350 hours.

Boeing expects to have the software update and additional pilot training finalized within the next 10 days.

www.yahoo.com...

a reply to: Zaphod58

Here's a quick question, (ignorant at that).

From what I have been reading, the problem seems two-fold. One, the upgrade engins are heavier and push the center of gravity forward, forcing a nose up cruising angle. They attempted to solve this with a software upgrade to the autopilot which also forces the nose down to prevent stall.

Question: why not just fly the plane without the auto-pilot? Assuming the pilot is "awake", who needs auto-pilot anyway?

a reply to: TonyS

It gets tiring after awhile. The autopilot holds altitude and airspeed, making for less work on the crew. The way MCAS is designed though, is that it's only supposed to operate with the autopilot disengaged, and the flaps fully retracted.

That's why we know there's a different software issue. There are several reports that as soon as the autopilot was engaged, as they were climbing, the aircraft pitched down.

a reply to: TonyS

One, the upgrade engins are heavier and push the center of gravity forward, forcing a nose up cruising angle.

Moving the CoG forward would cause a nose-down pitch, not pitch up. The issue is that higher AOA, the nacelles produce an upforce (generically: lift) which is forward of the CoG. This is what causes the pitch up.

why not just fly the plane without the auto-pilot? 

It is designed to be disengaged when the auto-pilot is on. So it isn't. But the basis of your question still basically applies: Why automate the nose-over instead of relying on the stick-shaker? The answer is to alleviate crew load and make the plane easier to fly -- but I'm not sure how overriding manual pilot trim inputs after 3 seconds results in a plane that is easier to fly. Pilots have to manually switch it off to prevent the MCAS from engaging, and (at least in the first incident) seemed unaware.
It sounds like user error. I'd be willing to bet most MAX flights are by US, Canadian, Australian, European operators, and that isn't where the problems are occurring.
Boeing still has some responsibility to make their airplane as idiot-proof as possible. I'm not sure MCAS is doing that. It sounds like they got a little too cute with their flight control laws, and automated something users are not intrinsically aware of.

Also possible they have another problem that is showing up when the MCAS is engaged, which would be its own nightmare.

a reply to: RadioRobert

If you read the pilot incident reports, three jump out. In all three the aircraft pitched down immediately after autopilot was engaged. One pilot even stated that they double checked everything, to ensure they hadn't inadvertently caused it, and verified everything was set right. Immediately after engaging the autopilot, the aircraft began to pitch down.

a reply to: Zaphod58


Is it normal to engage the Autopilot while climbing after take off? I also assumed that the autopilot was only engaged after they leveled off.

a reply to: Guyfriday

They usually engage it somewhere during climb. The Max pilots started waiting longer, because of the pitch down, but as soon as they had a comfortable altitude under them it's active.

originally posted by: Zaphod58
a reply to: Willtell

In this one case it appears that they didn't. The system is only a real issue if you're flying by hand, and have either a runaway stabilizer or bad AoA data. Normally pilots are climbing out on autopilot, and a runaway stabilizer situation is so rare it's not funny. The AoA system is normally pretty bulletproof. The system was put into the operations and flight manual, but wasn't taught directly to the pilots during transition training.

Part 1
I’ve been researching this for the last few days, and I think the situation is a bit more complicated than I originally thought when I suggested that the crashes might have been simple departure stalls. It’s possible there’s a kind of stabilizer runaway involved, although not the usual one.

First, some background for general information. I ‘m pretty sure Zaph knows this, but others on this thread may not. When the 737 was first designed in the 1960s it was intended for operation out of relatively unimproved airports. That required the fuselage to be located relatively low to the ground so that passengers could enter and exit without need for jetways and so that cargo could be loaded by hand. The first generation was powered by relatively small diameter turbojets, so ground clearance on the engines was not a problem. In later generations, after they introduced the CFM56 turbofans, they had to put the engine nacelles on pylons out in front of the wing and also flatten them a little on the bottom to maintain ground clearance. On the 737 MAX series, they went to the bigger and longer LEAP-1 engines which had to be moved even higher and further forward. Static weight balance is not intrinsically a problem with this because it is possible to move other mass elements rearward to maintain the aircraft center of mass at the ideal point for stability (forward of the 25% of the wing Mean Aerodynamic Chord position.

The problem is that the front of a turbofan nacelle is basically a circular airfoil; that means that when the nacelle has some angle of attack (AOA)--either positive or negative--it becomes a lifting body (up or down). At low wing AOA typical of high speed cruise flight, the incidence angle of the nacelle is chosen to put it at or near zero lift condition. At high AOA typical of the initial climb after takeoff, the nacelle generates significant amounts of lift, along with the wing. Since the center of lift of the nacelle is ahead of the wing, that moves the overall center of lift forward and closer to the center of mass (CM) of the aircraft. Moving the center of lift closer to the CM reduces the pitch stability of the aircraft. In other words, going to the bigger engine nacelles made the pitch stability of the aircraft worse especially during the initial takeoff climb. I think the AOA sensor input to the flight computer was introduced on the MAX series in order to compensate for the reduced intrinsic stability of the aircraft by trying to make sure that the AOA never exceeds some critical level (which, of course, is most likely to occur just after takeoff).

I read a discussion on a pilot’s blogsite about how the system works on the 737 MAX. When the autopilot (AP) is engaged and the flight computer decides that the AOA is too high, the fast control loop in the computer first uses the elevator to pitch the nose down. It does that by applying a force to the control yoke, causing the yoke to physically move forward. The pilot can counteract the AP by manually applying an opposite force greater than about 25 pounds, and pull the yoke back. However, if the elevator stays deflected for more than a short time in what the AP considers is the wrong direction, a slow loop in the controller will move the stabilizer in the direction required to regain its desired state (i.e., nose down), using the trim wheel. If the AOA sensor keeps wanting to force the nose down, and the pilot keeps pulling the nose up with the elevator, the stabilizer trim will eventually get to a point where the elevator has reached its maximum deflection and the pilot can no longer counteract the stabilizer with the elevator. At that point, the AP would have won the fight with the human pilot and the aircraft would keep descending unless the pilot did something else. The obvious “something else” to do is to turn off the AP. However, if you turn off the AP and do nothing else, the aircraft immediately goes into the MCAS mode. In the MCAS mode, the flight computer still tries to lower the nose if it thinks the AOA is too high, but it does that by controlling the stabilizer only, since it no longer has authority over the elevator. The pilot would experience this as the forward pressure on the yoke being removed— the control yoke would no longer be “fighting” the pilot.

However, the stabilizer would still be in the position it was in when the AP was switched off—presumably in a definite nose down condition—and the pilot would still not have enough control authority with the elevator to overcome that condition. And the flight computer could keep driving the stabilizer to a still deeper nose down condition, if it thought the AOA was still too high. The only way for the pilot to get out of that situation would be to disengage the automatic trim control and manually spin the trim wheel back to a more nose up position, where the elevator would become effective again.

Part 2
Someone watching this scenario from the outside would see an initial pitch down maneuver (commanded by the AP), followed by a recovery into a pitch up condition (commanded by the human pilot), followed by subsequent pitch downs and recoveries, until the elevator reached the limit of its travel. At that point, the aircraft would continue downward and into the ground (or water) under power unless the pilot disengaged both the AP and the automatic trim wheel. Even if he/she did, they would still have to manually trim the aircraft back into a neutral condition quickly enough to allow sufficient altitude to recover. Of course, as the aircraft is alternatively nosing down and up, the airspeed would also be increasing and decreasing. This scenario sounds pretty close to what the flight recorders, GPS, and (I guess) radar data showed.

In fact, there are some pilot reports in the NASA safety reporting data base where US trained pilots successfully avoided this scenario by reacting to a sudden nose down command from the AP right after takeoff by quickly disabling both the AP and the automatic trim and then hand flying the aircraft through a normal departure climb out. Quickly identifying the problem and taking the correct actions is the key. If you simply try to fight the AP by pulling back on the yoke, the nose down control forces from the stabilizer will eventually win out. If you react quickly by disabling both the AP and the automatic trim, then the stabilizer will never get far from its initial (and presumably correct) position, the elevator will still be effective, and a normal climb can be accomplished.

In order for the first scenario to have been implicated in the two crashes so far, the combination of the AOA sensors and flight computer would have to have thought that the AOA was too high for an extended period of time, even though the aircraft pitch angle and fight speed were both continually changing by large amounts. I can think of two ways that could happen. One way is if the AOA sensors/flight computer have a glitch (either hardware or software) such that once a high AOA is detected (typically during takeoff and climb out), that high AOA reading erroneously remains in the autopilot controller, even after the true AOA returns to normal levels. The flight controller would be trying to compensate for a high AOA reading that does not exist in external reality. Another, more exotic (and probably more speculative) possibility is that when the high AOA reading is first detected by the flight computer and the elevator is suddenly commanded to a nose down position, the aircraft enters into a Phugoid oscillation. It’s an interesting fact that in a Phugoid oscillation, the pitch angle and the airspeed are continuously varying as the aircraft porpoises up and down, but the AOA remains constant. So, if an aircraft entered a phugoid oscillation with a high AOA, and the sensors were functioning perfectly, that high AOA would presumably remain high throughout the oscillations. I consider this a remote possibility, but someone should probably look into it.

What I find most instructive, is the fact that the aircrews who promptly disconnected the AP and automatic trim immediately after the flight computer reported a dangerously high AOA (and therefore pitched the nose down) were nevertheless able to execute a perfectly normal climb out when flying by eyeballs and seats of the pants. That suggests that the actual AOA of the aircraft was not really very close to either stall or stability divergence even though the flight computer thought it was. If flight data could be recovered from some of those flights that survived even after the AP commanded a nose down maneuver based on high AOA readings, it might show whether or not those AOA readings were erroneous and/or remained so.

If this does prove to be implicated in the accidents, an obvious solution would be to just turn the damn AP and automatic trim control off during climb outs.
a reply to: 1947boomer

looks like the inducer of the engines during climb is somehow causing the AoA indicator to give erroneous signal about AoA being higher than allowed
a reply to: RadioRobert

The FAA, citing lack of funding and resources, has over the years delegated increasing authority to Boeing to take on more of the work of certifying the safety of its own airplanes.

Flawed analysis, failed oversight

No wonder they are falling out of the sky.

Lol even before airbus first introduced the auto trim, I had suggested the auto trim in one of my ground school classes
a reply to: 1947boomer