Third Pilots' Union Raises Concern About Boeing 737 Max Jet(bloomberg.com) |
Third Pilots' Union Raises Concern About Boeing 737 Max Jet(bloomberg.com) |
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...
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.
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.
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.
edit: of course with the downvotes for an honest question. this site can be ridiculous.
Now, that doesn't mean I didn't double check the aircraft types for some upcoming flights flights...
Was that three previous flights of the same aircraft? And if so, why was it still in service?
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'.
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!
Because jumping to conclusions is not helpful. Let the NTSB do their job and find out what went wrong.
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:
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.
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'.
>> 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.
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...
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.
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.
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.
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.
If you're at a low altitude and managing other problems will you have enough time to even recognize the problem and then wind the cranks and recover before you hit the ground?
> Also the full range of mechanical motion is only available via the trim wheel, the electronic trim doesn't drive it to either extreme (although it can move it back to the centre from an extreme).
Can MCAS drive the trim full down? What I've read suggests that if you give it time, it can.
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.
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.
To be clear: you're suggesting that grounding an entire type of aircraft, either worldwide or even just within US airspace, is a common response to accidents?
I ask because the last general grounding of a type was in 2013 to remedy the 787 battery issues. Prior to that, the last such grounding was the DC-10 in 1979.
Anyway the question still stands, who and how decides if we should ground some airplanes?
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.
It's still worthwhile to warn the pilots about uncommanded movement and reiterate what to do about it. At this point I doubt any 737 pilot doesn't know about this.
To add to your summation, I'd expect the mechanism's inability to detect a faulty angle-of-attack sensor needs addressing.
Grounding the plane is exactly the opposite of jumping to a conclusion. It's declaring "we can't conclude that this plane is safe".
For example, in 1991 a Boeing 737-200 crashed in Colorado with the loss of all lives on board. In 1994 there was another crash of a 737, in Pennsylvania, again killing everyone on board. In both accidents the investigation pointed to unexpected movement of the rudder.
Several other cases were identified where pilots claimed the rudder was moving unexpectedly, but they were able to land safely.
The follow-up took several years of investigative work, and eventually identified a situation where a servo could jam and deflect the rudder.
Despite two severe crashes and many other suspected non-fatal incidents, that generation of 737s was not grounded; the remedy, once the cause had been determined, was an order from the FAA to replace the servos, with a timeline by which the replacement had to be completed.
My suspicion is that it would probably have required a well drilled crew to have handled the problem correctly. But I don't think we're up there with the extraordinary levels of piloting which we've seen demonstrated previously e.g. Flight 1549 (the miracle on the Hudson).
> Can MCAS drive the trim full down? What I've read suggests that if you give it time, it can.
I'd be surprised if it can drive it outside the normal range of electronic motion. There aren't really enough details out there for me to be sure though.
Although it may simply turn out that the MAX is a much more delicate plane to fly, something along the lines of DC-10 vs MD-11.
> I'd be surprised if it can drive it outside the normal range of electronic motion. There aren't really enough details out there for me to be sure though.
Yep. There are a lot of questions (at least in my mind) including why the Brazilians and Europeans (LOT, TUI) knew about MCAS and the Americans (US + Canada) and Indonesians did not.
Ha, yes that it possible.
Out of interest, where are you from and what do you do? If you find yourself in London at some point let me know. I'm sure it would be interesting to have a coffee or a pint. My email is in my profile.
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