The original 737 had some early issues also. Tail rudder problems that resulted in crashes is one that comes to mind. They were fixed and now nobody thinks twice about flying them and their long-term safety record is excellent.
The tail’s controls inverted in freezing temperatures.
Anyone have any more info on this? It seems completely insane for flight control inputs to invert themselves, but only in certain temperatures. I'd love to see the incident report on that...
EDIT: Ah: https://en.wikipedia.org/wiki/USAir_Flight_427
I'm so sorry that happened to your wife's father.
The accident report is here: https://www.ntsb.gov/investigations/AccidentReports/Reports/...
Section 2.7.2 is interesting:
2.7.2 Unusual Attitude Training for Boeing 737 Pilots
At the time of the USAir flight 427 accident, no air carrier training programs were specifically aimed at training 737 pilots to recognize and address a rudder jam or reversal. The guidance available at that time from Boeing advised pilots, as a first consideration, to maintain or regain full control of the airplane. Specifically, the guidance advised pilots to counter unwanted roll tendencies from a malfunctioning rudder with the application of up to full aileron control inputs. However, the guidance did not advise pilots that, at some airspeeds, an uncommanded full rudder input could not be successfully opposed by full wheel (aileron and spoiler) inputs and that a reduction in the airplane’s angle-of-attack could improve the effectiveness of the roll controls relative to the effectiveness of the rudder. Boeing’s guidance for relieving a jammed rudder informed pilots only that they should use maximum force to overpower the jam and specifically warned pilots against turning off flight control switches “unless the faulty control was positively identified.” No additional guidance was provided about the effects of flight control switch selections on rudder jam conditions.
(Oh, by the way, I didn't mean to imply you were mistaken, or anything like that. I was just so shocked that a plane's controls could invert themselves in any conceivable circumstance. Currently digging through the accident report to try to figure out what happened.)
"the probable cause of the USAir flight 427 accident was a loss of control of the airplane resulting from the movement of the rudder surface to its blowdown limit. The rudder surface most likely deflected in a direction opposite to that commanded by the pilots as a result of a jam of the main rudder power control unit servo valve secondary slide to the servo valve housing offset from its neutral position and overtravel of the primary slide"
Unfortunately I don't know what most of these terms mean. It sounds like it might be saying "they moved the rudder to its limit, and then it jammed at the limit; so when they tried to command the rudder to go the other way, the rudder was pointed in the opposite direction of the control inputs." But I'm really not sure.
My recollection in researching this a decade ago was that the cold weather made the behavior of the rudder change (my term was invert, maybe that’s not accurate), and pilots were trying to pull up, but in fact putting the plane deeper into a nosedive. Some 25 seconds later they hit the ground at some 300-400 MPH and vaporized.
The only way to have saved the plane would have been to dump the hydraulics and/or switch to a manual fly by wire mode, neither of which were a logici thing to do in the 15 seconds they had to save the flight.
I’ve only flown for 20 hours in a Cessna so sorry if my terminology isn’t perfect!
The rudder controls yaw, not pitch. The rudder controls did invert: the pilot tries to turn slightly left, the plane turns right, so the pilot naturally tries turning harder left until the rudder is in the full right position, and they're in an uncoordinated turn. The wing on the inside of the turn starts to drop significantly or even stalls. The plane is then sideways and in a dive, and on top of that, the rudder is all the way over in the direction that makes the dive steeper. The planes quickly rolled over on their sides and went into steep dives.
My understanding is that a big break in the case came when a pilot figured out what was going on and successfully landed a plane with reversed rudder controls.
"Testing revealed that under certain circumstances, the Power Control Unit (PCU)'s dual servo valve could jam and deflect the rudder in the opposite direction of the pilots' input. Thermal shock testing revealed that the uncommanded rudder movement could be replicated by injecting a cold PCU with hot hydraulic fluid. Thermal shock resulted in the servo's secondary slide becoming jammed against the servo housing, and that when the secondary slide was jammed the primary slide could move to a position that resulted in rudder movement opposite of the pilot's commands"
Did the rudder actually move in opposition to the commands, or was it stuck at some limit value?
i.e. in that situation, if you command the rudder to go left, does it move even more in the wrong direction? Or is it simply frozen at whatever position it happened to get stuck in?
Thanks for the info!
In theory the problem was recoverable but the pilots had about 10 seconds to realize what was going on and react appropriately. Sounds familiar to the 737-MAX uncommanded trim issues.
You had corners cut to deliver a product that ended up killing people. There is no real room for doubt in that just from the material we have available.
So, what? What happens? What should happen? Everything go back to "normal"? Let the same people who ran things continue to profit off their wrongdoing? Accept that as long as you're one of only two rides in town that you have the security to deliver and recover from delivering a lethal product?
That's the issue. That's the reality we're taking out of this. It isn't even self-regulating anymore. There is no bankruptcy, no hammer, no reallocation of assets to those that can wield them more responsibly, no reset. Just a token gesture. The same Goliath just shrugs and moves on.
While I get that might be tenable or desirable to some, I'm not one of them. Realistic risk of falling flat on your face, being held to account, and not being able to just shrug it off and keep going keeps you honest.
Once you lose that, "What's a life here and there? Doesn't bother me. Can't make an onelette without cracking a few eggs."
The economy is not an omelette, and people are not eggs. Either we serve it, or it serves us. I know which side of that assertion I'm on.
Also, responsibility doesn't just like with Boeing; the FAA certified the 737 MAX, and the rules that allowed that to happen were written by lawmakers and bureaucrats over a period of decades. How do you hold all of them accountable? Many, if not most, of those people aren't even actively working any more.
> " collateral damage so cost of that outweighs the benefits"
Do we have a system a justice or do we not? You seem to suggest some people are above the law. Let's see, could that possibly lead to corruption and abuse of power?
I'm suggesting no such thing. I'm simply pointing out that "justice" is not as simple as you are making it sound.
And the obvious defense to that is that the FAA certified the plane. Then what?
And their obvious defense is that they were acting entirely in accordance with statutes passed by Congress and regulations approved by the statutory process for doing that.
Then what?
> MCAS was devised to fulfill an airworthiness certification condition in 14 CFR 25.173 and 14 CFR 25.175. In high angle-of-attack (AoA) flight configuration, it is required that stick force/g (the stick force necessary to produce (hold) an incremental normal acceleration of 1g) and stick movement/g (ditto mutatis mutandis) must increase (or at least not decrease) with an increase in AoA (thanks to Clive Leyman for this formulation). I understand that in flight test, in which “wind-up turns” were conducted (a turn with increasing angle of bank; an increasing angle of bank means ceteris paribus increasing AoA), this condition was not fulfilled.
-- https://abnormaldistribution.org/index.php/2019/04/30/ieee-s...
And also to stop the plane dropping out of the sky!
@HPsquared “.. The plane is perfectly stable without MCAS ..”
NO, no, no it isn't .. doesn't matter how many different ways you re-arrange the word salad. MCAS is a software kludge to compensate for an unstable airframe
The implementation is certainly not "elegant". It's like this random batch job that triggers when some conditions are satisfied and does its own thing without regard for anything else, sure. Not integrated with the auto-pilot, does not display anything in the panel.
We have plenty of aircraft (even though most are military) which are aerodynamically unstable, and require fly-by-wire software to even be flyable. We don't think those are kludges. That's not too far from what Boeing has to do.
It could have been either a fancier fly-by-wire software in the Airbus philosophy that wouldn't let pilots exceed parameters(retrofitting it might have been a challenge, and possibly even more dangerous). Or it could be this non-elegant solution that behaves like an old-school stick pusher. Both could have worked.
The problem is that they did this while trusting a single sensor. And not informed anyone.
Airbus had a crash because their fly by wire averaged the input from both yokes vs doing what Boeing does which is to allow both to feel that the other is pushing on the yoke and the pilots where not trained to understand that.
An interesting question is going to be as to what happens elsewhere in the world; I'd be intrigued to see if Boeing ends up certifying the 737 MAX with MCAS as an optional feature with additional difference training required, as some things mentioned suggest that it's not implausible that this will happen.