Third Pilots' Union Raises Concern About Boeing 737 Max Jet
79 points by swznd 6 years ago | 49 comments- WalterBright 6 years agoThe pilots would have seen the nose down action as an uncommanded stabilizer trim movement. The solution is to shut off the power to the stab trim. This would work and would require no knowledge of the stall avoidance mechanism.
- sokoloff 6 years agoExactly this. Following the existing memory items and QRH checklist items taught to every 737 pilot is (very, very likely) enough to overcome this contemplated scenario of a runaway trim from a flaw in the stability system. (It's remotely possible that the crew holds no blame in that they followed the checklist properly and the cutout switches were defective or the checklist response was otherwise insufficient.)
- JshWright 6 years agoIt's also possible they were simply overloaded by a misbehaving aircraft in very busy phase of flight. Would it have been technically possible for them to recognize and correct that issue? Maybe (obviously we don't know enough to make that call), but even if that were the case, I think "blame" is pretty strong word to use in evaluating the pilots' actions in this accident.
- bronco21016 6 years agoWould runaway trim be the thing they were reacting to? It seems to me the trim was pitching down due to the design of the stall system. I’m imagining they were getting erroneous stall warnings due to the AOA sensor feeding bad data. If I’m in an aircraft and I’m getting stall warnings, stick shakers, and stick pushers I’m definitely not going to run runaway trim memory items.
- sokoloff 6 years agoIt's pretty likely that they weren't reacting to runaway trim; on that we agree.
The trim wheels are large, painted mostly black with alternating, offset white stripes (so the motion is quite visible), and have a very distinctive clacker on them. https://www.youtube.com/watch?v=cQirIH_DuAs
It's possible that the crew fought to keep the airplane in a basic attitude flying configuration for several minutes without ever noticing the trim in motion unexpectedly, but that seems unlikely, particularly when the act of holding the nose up to hold attitude was accompanied by increasing nose down trim.
Minor note: there is no stick pusher in the 73. Those tend to only be installed on T-tail aircraft. Synthetic elevator feel increases, but no pusher only a shaker.
- sokoloff 6 years ago
- JshWright 6 years ago
- WalterBright 6 years agoHere's a picture of the cockpit, showing the location of the power switches, trim switches, and the wheel that turns when the stab trim is running.
I find it hard to understand how the pilots would not know the stab trim was moving, and how to cut it off.
https://www.nytimes.com/interactive/2018/11/16/world/asia/li...
- augustz 6 years agoOne question I have: on Boeing how easy is it to just jump down to secondary law to give up some of the flight envelope protections. Can that be switched manually? How exactly does that look?
If you know computer is getting garbage data / plane acting in an unusual way, you can dial things back. These planes and their engines are so reliable and maintenance is usually so good that it seems you could fall back to closer to direct law flying (power setting / pitch / etc) and at least keep plane out of the drink / gain some altitude.
- sokoloff 6 years ago
- A2017U1 6 years agoThe preliminary investigation report is due out 29th Nov.
Boeing is already being sued.
A bit OT but how hasn't the cockpit voice recorder been found yet? It's been weeks while giving off a detectable ping and is in 30m of water, that's recreational level diving. You simply follow signal strength.
Given the big economic hit that occurred last time when Indonesian carriers were banned from Europe you have to wonder whether they actually want to find it.
- cyberferret 6 years agoI think I read somewhere that they are not getting the 'pings' from the Cockpit Voice Recorder like they did the Flight Data Recorder, which was recovered.
I believe the force of impact, which was almost vertically nose down at high speed just caused such a shattering of the airplane that it might have fatally destroyed the CVR, or else driven it under many feet of mud and silt.
Re: Your last point - I think this time around the CVR could vindicate the crew and point the blame at Boeing, so it may seem in their best interest to recover it and have extra proof for the court case. Then again, the level of corruption in Indonesia could affect what happens with the recovery process.
- userbinator 6 years agoThe CVR is mounted next to the FDR so they should search in approximately the same place, and it probably won't be damaged if the FDR wasn't. It's more likely to be buried, as you note.
- userbinator 6 years ago
- cyberferret 6 years ago
- capkutay 6 years agoWould it be overly cautious to avoid flights on Boeing 737 MAXs?
edit: of course with the downvotes for an honest question. this site can be ridiculous.
- JshWright 6 years agoYes. This is a very specific failure mode, and given the publicity of this event, it's not going to catch anyone else out.
Now, that doesn't mean I didn't double check the aircraft types for some upcoming flights flights...
- capkutay 6 years agoYeah I usually only double check airline types for comfort rather than safety. But I think you're right that these heavily publicized events actually create more scrutiny/cautiousness, especially from US airline pilots.
- SteveNuts 6 years agoI've got an upcoming flight on a 737-800, is it safe to assume that model isn't affected by this?
- JshWright 6 years agoCorrect, the 800 is a "Next Generation" series jet, not a MAX, and so it doesn't have the MCAS that is suspected to be related to this accident.
- JshWright 6 years ago
- capkutay 6 years ago
- JshWright 6 years ago
- gargravarr 6 years agoOkay, I've never sat in the cockpit of an aircraft, but the one thing I don't understand - if the nose of a plane suddenly drops, isn't the pilot's first instinct to pull back on the controls to raise it? From what I've read, in Boeing aircraft at least, the pilot's controls can always override the automatic systems.
- JshWright 6 years agoPulling back on the controls moves small control surfaces (elevators) on the horizontal stabilizer (the "tail wing"). The way the anti-stall measure works on the MAX (and many other planes, to be fair) is by adjusting the pitch trim. Adjusting the trim changes the angle of the entire horizontal stabilizer.
https://en.wikipedia.org/wiki/Stabilizer_(aeronautics)#/medi...
It's very possible for the effect of the extreme trim condition to be more than the elevators can overcome. The pilot can certainly override the trim setting, but the issue here is that they weren't expecting that to change, since they weren't trained on the fact that the plane might do it automatically (in those flight conditions).
Here's a good video explaining how trim works (in normal operation) on a (slightly older) 737:
- danielvf 6 years agoA 737 and a 737 MAX has big wheels in the cockpit that move as the stabilizer trim changes. This lets the pilots see what the autopilot is doing with the stabilizer, and/or override stabilizer changes by grabbing and holding the wheel or rotating it. You also have two switches to disallow control of the stabilizer, one for blocking other stabilizer controls in the cockpit, and one for blocking control by the autopilot.
In theory then, solving the stabilizer problem that caused the crash is as simple as flipping both switches to cutoff, then using the wheel to set the stabilizer back to a sane value. Handling a stabilizer runaway is a standard part of US 737 training, and the updated Emergency Airworthiness Directive just says to follow the stabilizer runaway checklist. Again, in theory, this should have been a no-brainer, "common" emergency, and following the usual checklist would have fixed the issue.
However, pilot's mental model of the aircraft has been broken. In the previous generation of 737's, there were exactly two things outside the wheel that could control the stabilizers - the cockpit trim switches, and the autopilot, and each had it's own cutoff switch. Now we have three systems that can control the stabilizer wheels, and the new one doesn't have a labeled switch, nor was anyone told it existed.
- VBprogrammer 6 years ago> In the previous generation of 737's, there were exactly two things outside the wheel that could control the stabilizers
It doesn't take anything away from what you've said really but there is at least one other system which can control pitch trim. The Mach trim system counteracts changes in the centre of pressure due to speed by making adjustment to the trim.
> Now we have three systems that can control the stabilizer wheels, and the new one doesn't have a labeled switch, nor was anyone told it existed.
Just to add to this point, I believe the reason this was done this way was an attempt to keep the control behaviours of the new aircraft as similar as possible to the old (despite having more powerful lower slung engines) for the sake of maintaining training consistency.
- inferiorhuman 6 years ago> In theory then, solving the stabilizer problem that caused the crash is as simple as flipping both switches to cutoff, then using the wheel to set the stabilizer back to a sane value.
https://www.youtube.com/watch?v=rxPa9A-k2xY
The issue for the Lion Air pilots was time. At 5,000 ft you don't have time to adjust the trim before you hit the ground. While I think that the stabilizer trim can be adjusted more quickly than the video shows you'd still be looking at somewhere around the order of 30 seconds end to end.
- JshWright 6 years ago> However, pilot's mental model of the aircraft has been broken.
Exactly, and critically that "break" occurred during a very busy phase of flight, when they had a lot of stuff to think about even during "routine" operations. They didn't have a lot of attention to spare to notice the runaway trim condition.
- VBprogrammer 6 years ago
- gargravarr 6 years agoThat's very informative, I didn't realise the whole horizontal stabiliser itself can be a moving part - I always thought they were fixed and trim was done using the elevator surface. Thanks for the links.
So essentially, trim changes the relative 'zero point' of the elevator, and if past a certain angle, even if the pilot applied full nose-up elevator, the altered airflow over the smaller control surface would be unable to counter the altered airflow by the stabiliser itself having been adjusted. I now see why recovery is so dependent on quickly disabling the trim system and resetting the stabiliser to 'true zero'.
- Steve44 6 years ago> That's very informative, I didn't realise the whole horizontal stabiliser itself can be a moving part
On most, if not all, supersonic aircraft they are like that. It was found that the traditional design didn't work well at supersonic speeds, there is debate as to who developed it but the Miles M52 is a likely candidate.
I've had a quick look for a decent video demonstrating it. This one shows it fairly clearly in the 5-10 second segment.
- Steve44 6 years ago
- danielvf 6 years ago
- mveety 6 years agoNo, my first instinct is to give it the beans and push the nose down more because more often then not you're in a stall if that happens. Also, as a general "rule", it's pretty common for American aircraft to provide easily accessible overrides to the envelope protection stuff. I've never seen the cockpit of an Airbus, but, from what my friends have said, it's much harder to do. I don't know if Boeing is going in that direction, but I doubt they would.
- laken 6 years agoYes, but this is where it gets a little complicated, and why this accident is so fascinating to many people in aviation...
>> if the nose of a plane suddenly drops, isn't the pilot's first instinct to pull back on the controls to raise it?
Not exactly, as the correct way to get out of a stall is pointing the nose down, in order to pick up airspeed to gain more lift. The stall horns were going off, so the pilots may have thought they were stalling. In addition, as others have mentioned, the yoke alone may be unable to beat out the trim by the autopilot.
>> From what I've read, in Boeing aircraft at least, the pilot's controls can always override the automatic systems.
Historically, you are exactly right. This is the _biggest_ reason pilots are pissed at Boeing right now. It's believed that the autopilot was turned off entirely when the plane started thinking it was stalling, and trying to point itself down. This is not present on any of the original 737 aircraft, only the MAX series, and Boeing didn't inform pilots of this.
- JshWright 6 years ago
- smaddox 6 years ago> Pilots on the Lion Air flight were receiving erroneous speed readings, a problem that had occurred on three previous flights, according to the Indonesia National Transportation Safety Committee. They had radioed air-traffic controllers to say they intended to return to land.
Was that three previous flights of the same aircraft? And if so, why was it still in service?
- StreamBright 6 years agoIf this is true I am going to lose all my confidence in Boeing.
- dingaling 6 years agoI have less ire for Boeing than I do the FAA.
There was an interesting comment on airliners.net that the USSR operated new airliners on freight services for several years before putting them on passenger services. So far I've confirmed that for the Tu-154 trijet, for example, which flew freight for two years before taking a revenue passenger.
But in the West there has always been a tension between certificating for safety versus commercial imperative. Why hasn't the 737Max been grounded pending investigation? Because that would lead to companies losing money. Why would the FAA care about that? Because it considers manufacturers and airlines as 'stakeholders'.
- matt4077 6 years agoThey have grounded aircraft before, so we know they aren't inherently opposed to that.
I would tend to trust the FAA, given the rather impressive track record of aviation. The difference from "Oh, the humanity!" to today, where North America and Europe have entire years without fatalities is astonishing. It's even more impressive considering passenger-miles/p.a. increased by something like 3 or 4 orders of magnitude.
So it would seem that the FAA is doing a rather good job with these decisions. And "not considering airlines as stakeholders" may sound sensible, but is actually a phrase devoid of meaning: If you want to consider safety only, you or I or the Russians could come up with the trivial (and only correct) solution, which is to ban air travel.
Having flown with regional carriers in Russia during my (and their) wild times in the 90s also makes your praise of their processes suspicious of being parody. I personally saw a pilot take a sip from a suspiciously small bottle of clear liquid. But my seat neighbour reassured me: If you think it's dangerous to fly with a drunk pilot, you should see the way he flies when he's sober!
- sokoloff 6 years ago> If you want to consider safety only, you or I or the Russians could come up with the trivial (and only correct) solution, which is to ban air travel.
This would be a safety failure. Banning air travel is overwhelmingly likely to increase transport fatalities. It would decrease air travel fatalities, but would not represent an increase in safety.
"The National Highway Traffic Safety Administration (NHTSA) supported the FAA's decision [to not require tickets for pax under 2 years old] based on current FAA and NHTSA studies that show a mandate could result in another 13 to 42 added family member fatalities over 10 years in highway accidents." - [0]
[0] - https://www.faa.gov/news/press_releases/news_story.cfm?conte...
- sokoloff 6 years ago
- WalterBright 6 years ago> Why hasn't the 737Max been grounded pending investigation?
Because jumping to conclusions is not helpful. Let the NTSB do their job and find out what went wrong.
- simion314 6 years ago>Because jumping to conclusions is not helpful. Let the NTSB do their job and find out what went wrong
We are used from previous cases that aircrafts will get grounded until we are sure the airplane is not at fault. So why in the past this happened before the investigation was complete but in this case the risk is considered t be minimal? I am not saying that it is right or wrong but I want to understand the algorithm that is used to decide what to do in this cases.
- VBprogrammer 6 years agoI'm almost certain that the solution in this case will be training. Almost exactly as you've said in another comment. The correct response to an commanded stabiliser movement is to set the stab trim switch to cutoff. Pilots will probably experience this failure mode in their next recurrent training.
The accident is more than likely to be attributed to a system being added without sufficient guidance being added to the PoH, some degree of maintenance failing on behalf of the airline and finally a failure of the pilots to identify an issue and take appropriate action.
It's unlikely that those particular holes in the cheese will line up again in the near term given the emergency AD. No reason to ground the fleet.
- gpm 6 years agoExactly, jumping to the conclusion that it is safe is not helpful.
Grounding the plane is exactly the opposite of jumping to a conclusion. It's declaring "we can't conclude that this plane is safe".
- simion314 6 years ago
- matt4077 6 years ago
- dingaling 6 years ago
- anticensor 6 years agoIs this third union of pilots or union of third pilots?
- isostatic 6 years agoIf it's Boeing, I 'aint going
- jsjohnst 6 years ago“I’d rather be hit by a bus than fly in an Airbus”
There’s versions of these type of statements for all aircraft manufacturers. Does it add anything to the conversation to state them? Not in my opinion.
- jsjohnst 6 years ago
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