Plane Engines and the 737 MAX 8 Accidents

[Tik-Tok]

This quote is hidden because you are ignoring this member. Show Quote

I really dont understand how an airplane of that size and price has only a single AOA sensor. Planes are full of failsafes but something that important is just simply overlooked?

Theres two, but only one is tied to MCAS, and the warning system to tell the pilots the two arent indicating the same was optional.

This quote is hidden because you are ignoring this member. Show Quote

So with stall warnings, and stick shakers, and all that... why is MCAS even necessary? No other version has it, so why don't they just delete the software and rely on pilots?

It was neccessary to pass a FAA certification because it was stalling during steep turns.

[Gman.45]

A couple friends of mine I've known for 20 years have posted about this on another board, one is a former F15E Strike Eagle pilot (among other types), the other is a long time airline pilot with a lot of fighter time, and even more flying the RC135/Rivet Joint spying on the Soviets during the cold war. I'll link the thread if anyone wants to read, a bunch of former Air Force/Navy and civilian pilot's discussing this.

Link to the entire thread - https://bbs.hitechcreations.com/smf/...96507.195.html

Here's where we differ: I DON'T think it's a significant problem.

Yes, the crews need to be aware of MCAS. The purpose, the "how" of what it does, what triggers it and, of course, knowing what to do if it malfunctions. The what to do is the standard, decades old Boeing Runaway Stab procedure.

Again, just about EVERY aircraft with electrical trim has just such a procedure. Potential Runaway Stab problems are not exclusive to Boeing.

However, I do think that they are going to 'have to make changes' to reassure the public due to all the misinformation spread around by pundits that don't know an aileron from spoiler panel. IMO, the MAX is not a 'dangerous' aircraft. It went through Part 25 certification and the FAA didn't find any problem with Boeing design during that process. Likely because of....wait for it...the decades old Runaway Stabilizer NNC.

As many here have pointed out, even after these changes there will continue to be 737 MAX crashes. And Airbus 320 crashes. And Embraer crashes. Crashes of all sorts of aircraft.

Because the REAL problem afflicting the airline industry world wide is a deepening shortage of highly qualified, well experienced aircrews. There's no easy fix for that so it will not be addressed. All IMO.

So while the MAX has 2 AOA sensors, the MCAS is wired to Flight Control Computer and the AOA currently in use.

The proposed Boeing fix, which is also in that link, would solve the problem of one bad AOA triggering MCAS along with a few other positive design changes.

None the less, even in the case of an MCAS runaway due to one bad AOA, there is now and always has been a procedure to successfully resolve the situation. The Runaway Stabilizer NNC.

In the end it comes down to FLY THE JET.

It sounds like they added high lift design features to the wing that also bumped up the drag curve, so that with the power at idle the airspeed bleed rate with the new wing features was higher than the pilots had gotten used to. A pilot used to ripping throttles to idle 5nm prior to the FAF and then casually dropping gear and flaps prior to bumping up the throttles to catch his 600ish fpm descent rate at the FAF might find himself getting VERY slow if he relied on his old pacing and habit patterns. "Slowing down faster" = higher airspeed bleed rate as the aircraft is configured.

Also, a pilot used to pulling the throttles back to idle at 50 ft prior to the roundout/flare in order to slow from approach speed to touchdown speed might find the increased airspeed bleed rate surprising, with the plane slowing below touchdown speed significantly higher than before. That would require a completely different power reduction profile when transitioning from approach to landing.

I can see how a complacent know-it-all pilot or a new guy relying on someone else's rule of thumb might get caught by this.

[BigDL]

This is what the stab trim on the 737 max sounds like and any 737 when it starts to trim. It is very hard to miss.

https://youtu.be/tCXPJkC7ZwI?t=625

[jonsey737]

This quote is hidden because you are ignoring this member. Show Quote

This is what the stab trim on the 737 max sounds like and any 737 when it starts to trim. It is very hard to miss.

https://youtu.be/tCXPJkC7ZwI?t=625

https://www.youtube.com/watch?v=TrjTUvhpBlE This is what the stick shaker sounds like on an NG (and I assume a MAX). That was going off the entire time so I could see how you might not hear the trim wheels spinning. You'd certainly feel the out of trim condition in the column force required though.

[HiTempguy1]

Based on the Bloomberg article I just read, it actually sounds like a big f'in problem GMan.

Especially if the pilots don't throttle down, it sounds almost impossible to control at a certain point.

This is clearly becoming a fuckup on Boeing's part.

[Misterman]

This quote is hidden because you are ignoring this member. Show Quote

I really dont understand how an airplane of that size and price has only a single AOA sensor. Planes are full of failsafes but something that important is just simply overlooked?

Yes, if you talk to anyone in this field of work that deals with control systems. You NEVER have a pivotal safety system rely on 1 of 1 voting. They have 2 sensors on these planes, there should be 2 out of 2 voting for something that can just crash your plane and kill everyone on board.

[rage2]

This quote is hidden because you are ignoring this member. Show Quote

Especially if the pilots don't throttle down, it sounds almost impossible to control at a certain point.

That's like saying there's a problem with your race car because it won't turn going twice the speed into a corner.

For whatever reason, the EI pilot didn't throttle down, and was going twice the normal speed at low altitudes, well beyond the plane's rated limits prior to the final dive (which picked up even more speed).

[HiTempguy1]

This quote is hidden because you are ignoring this member. Show Quote

That's like saying there's a problem with your race car because it won't turn going twice the speed into a corner.

For whatever reason, the EI pilot didn't throttle down, and was going twice the normal speed at low altitudes, well beyond the plane's rated limits prior to the final dive (which picked up even more speed).

Not really. A more accurate analogy would be that at a certain speed in a race car, your power steering failed because it didn't expect you to be going so fast for a given corner.

Its stupid design and stupid execution. The plane would be controllable at those speeds IF what I will describe as the "assisted power" controls were enabled.

Unfortunately, Boeing tied power assist to automated computer controls which is flat out fucking retarded.

[jonsey737]

This quote is hidden because you are ignoring this member. Show Quote

For whatever reason, the EI pilot didn't throttle down, and was going twice the normal speed at low altitudes, well beyond the plane's rated limits prior to the final dive (which picked up even more speed).

One thing to note about this, the underwing mounted engines on the 737 provide a huge nose up force with high thrust so reducing N1 could actually cause the plane to pitch down further which could have been on their minds. Reducing speed before the trim got out of hand might have helped in the recovery but it's also goes against all the training for what they initially encountered, unreliable airspeed and stick shaker activation.

[Mitsu3000gt]

I was reading on pilot forums and people seem to think another way to combat this would be to fly in a parabolic form and with every brief descent, manually crank the stab trim back into place each time pressure is taken off the stabilizer, making it much easier to accomplish. Also I can't seem to find if they even cut the stab power, which would have (presumably) been one of the most obvious first steps for a pilot. It looks more and more like an unfortunate/unexpected situation mixed with pilot error brought on by the failure of an AoA sensor.

Also from what rage said it seems they were going way too fast, which would have put huge pressure on the stabilizer and made it even more difficult to correct manually, especially without flying in a parabolic way.

And didn't someone buy a bunch of Boeing stock at like $380-385? Wouldn't want to be them right now.

[Gman.45]

Mitsu3000gt I'll cut paste again from the same link I put in above, with some new posts on that subject.

Also, here's a link to the PDF of the Aircraft Accident Investigation Prelim Report - https://leehamnews.com/wp-content/up...MAX-ET-AVJ.pdf

There's no excuse for 94% in this situation. None. Pitch + Power = Performance. Argue all you like. If you disagree with that, you are just wrong.

Mr. Bjorn says "And with Stick Shaker and IAS disagree you keep high thrust and fly a slow climb ". Actually, he's almost getting it. You use a KNOWN pitch and power setting that essentially emulates cruise pitch/power. Here's a clue: 94% is WAY too much power. WAY.

BTW, this works for flight with unreliable airspeed as well as a malfunctioning AOA. IIRC the 737-800 was about 2 degrees of pitch and 60% N1 for lower altitudes.

As for not being able to trim the stab manually, yeah, when you have the stick touching your spine, you can't trim manually too well. There's a procedure for that though. I recall Runaway Trim /manual trim demos in the RC-135 (B707-720) simulator. Both pilots pull back hard to get the nose up a bit then release back pressure and trim nose up like a madman using the trim handle (knee knocker). When the nose dropped again, both pull back hard, raise nose a bit, release back pressure, trim up like a madman, rinse, repeat, rinse, repeat. This resulted in a bit of an up and down rodeo but you would be surprised how fast you could get the aircraft back under control.

I'd bet money all the Boeings with the manual trim wheel/handle work the same way. I think I did this in the 727-200 and 737-200 sims a s well. I don't recall doing it in the -800 though. Too busy playing with the new HUD.

Oh...one other thing.... the pull back, trim madly procedure would not of course work if you left the engines at takeoff power while you rodeoed up and down.

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.

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.

Quote from: Puma44 on Yesterday at 01:11:27 PM

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.

Quote

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:

Quote

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.

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)

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.

Also some pics of the old 737 trim wheels/Stab trim cutout swithces and the MAX newer ones.

[sabad66]

how the fuck is everyone so knowledgeable about planes / flying them (besides from the guys who are pilots/aircraft tech)? i can hardly list 3 different models of planes off the top of my head let alone even try to make sense of what you guys are saying.

MS Flight Simulator back in the day?

[spikerS]

This quote is hidden because you are ignoring this member. Show Quote

how the fuck is everyone so knowledgeable about planes / flying them (besides from the guys who are pilots/aircraft tech)? i can hardly list 3 different models of planes off the top of my head let alone even try to make sense of what you guys are saying.

MS Flight Simulator back in the day?

I flew for 4 years when I was younger to get my pilots licence, and a lot of this is above my head, so I am surprised that there are that many people this "knowledgable" in this. I suppose with enough research you can understand how something works, but understanding=/=knowledge.

[Mitsu3000gt]

This quote is hidden because you are ignoring this member. Show Quote

how the fuck is everyone so knowledgeable about planes / flying them (besides from the guys who are pilots/aircraft tech)? i can hardly list 3 different models of planes off the top of my head let alone even try to make sense of what you guys are saying.

MS Flight Simulator back in the day?

There are channels on YouTube where actual pilots literally guide you through every imaginable control and step to flying a plane in real simulators or a real cockpit, just as one example. A lot of them are geared towards pilots in training. It's like anything, if you put in the time you can learn a lot about it. Also tons of people are interested in aviation, so the resources for anything and everything aviation related are extremely robust. There are communities of people who just go out plane-spotting at airports, track flights for fun, etc.

Also yeah flight simulators are pretty good these days and it's not hard to make them ultra-realistic at least on the software side.

I bet in 5 minutes you could easily learn the common commercial models from Boeing/Airbus - it's not complicated if its something you're interested in. I'm no expert but I find it all very interesting.

[Mitsu3000gt]

This quote is hidden because you are ignoring this member. Show Quote

Mitsu3000gt I'll cut paste again from the same link I put in above, with some new posts on that subject.

Yeah they seem to be describing the same action I was with the parabolic flying - lots seems to be pointing to pilot error at this point, at least in regard to their actions once they had an issue to deal with, and possibly digging themselves into a hole they couldn't get out of.

On the up side, when the MAX is back in service it will probably be the safest aircraft in the sky.

[Tik-Tok]

This quote is hidden because you are ignoring this member. Show Quote

how the fuck is everyone so knowledgeable about planes / flying them (besides from the guys who are pilots/aircraft tech)? i can hardly list 3 different models of planes off the top of my head let alone even try to make sense of what you guys are saying.

MS Flight Simulator back in the day?

Ever since Mayday/Air Crash Investigation/Air Disasters started on TV, everyone is an aviation expert.

[rage2]

As a kid I wanted to be a pilot. As a teen, I became interested in aerodynamics because F1. Then pilots forums came along and yea it’s not difficult to understand how it all works.

You only need to know 25% to be an internet expert.

[Gman.45]

They guys I'm quoting I've known since 1999 when we all started playing the same WW2 online flight simulator Aces High (the creator is responsible for both the name and the first code for Massively Multiplayer Online/MMO Games). They are all x USAF/USN fighter pilots, and current airline pilots with time on various 737 including the MAX.

For myself, my first real job after school in 1993 was as an air traffic controller for IFR/enroute centers (I was stationed at Winnipeg ACC initially, and it wasn't called that back then), back before NAV Canada was around, I worked for Transport Canada back then. I did my PPL, and have been interested in military flight sims since then - ran www.combatsim.com out of Calgary from 99 to the early 200s/dot.com crash, it was one of the largest gaming/sim sites in the world then, Nucleus's 2nd largest co-located server traffic wise (we did 40mil hits, 1 mil uniques, and had 250k forum registered users, and sold banner adds for 5 to 10k USD per month back then). I've kept in touch with a lot of pilots and guys working in the military and aerospace industry, Carl Norman is a good friend, he started Eagle Dynamics/Digital Combat Simulations, and now works for DARPA doing wizzy things. Just to give an example.

Regarding PC flight sims - the new F14 DCS simulation is very accurate, you can use the NATO NATOPS manual in fact to learn the game, and the guy who usually does the "guides" for players refuses to do the F14 one due to Iran having them, and the ITAR treaty being so aggressive that he's afraid he could lose his real job in defense/aerospace for violating that by creating a simple guide for DCS players, which Iran could use to train their new pilots on the F14. It's that accurate now.


I agree though, the level of knowledge is incredible here, Phil the CPS member's knowledge and posts surprised me, and of course beyond has a number of knowledgeable pilots that post here. Great thread IMO.

[Misterman]

This quote is hidden because you are ignoring this member. Show Quote

how the fuck is everyone so knowledgeable about planes / flying them (besides from the guys who are pilots/aircraft tech)? i can hardly list 3 different models of planes off the top of my head let alone even try to make sense of what you guys are saying.

MS Flight Simulator back in the day?

It's funny you mention MS Flight Simulator. That is a huge program still, not just back in the day. I worked with a guy who just had a general interest in flight. Just from his experience of doing the training on MS Fsim, I would feel confident that he could actually fly a real jet. That simulator covers basically every control in a real plane.

[95EagleAWD]

This quote is hidden because you are ignoring this member. Show Quote

It's funny you mention MS Flight Simulator. That is a huge program still, not just back in the day. I worked with a guy who just had a general interest in flight. Just from his experience of doing the training on MS Fsim, I would feel confident that he could actually fly a real jet. That simulator covers basically every control in a real plane.

Flight simulators are something else these days. I could hop into a real 737 and start it up, no problem. Or an F-14 these days haha...

Don't mind the VNAV on this one lol...