http://www.boeing.com/resources/boeingdotcom/commercial/737m...
They're absolutely different. If you're a pilot and you expect to see an error message when the two alpha vanes disagree, you'll be lulled into a false sense of security when that text never appears even in the case of a failure.
A pilot needs to be able to trust all of the instruments in the plane.
It also reminds me of a time years ago when a team I was on had to extend a Memcache client library, as it couldn't differentiate between the following two conditions:
- "I tried to retrieve a key from cache but was unsuccessful (due to connection error, etc)"
- "I tried to retrieve a key from cache but determined conclusively that key does not exist in the cache"
If it was important for a caching layer on our silly social game, the same thing is clearly important in aviation.
https://www.hl7.org/implement/standards/product_brief.cfm?pr...
in the real world it turns out not to be useful to require that people have names just in order to keep data about them...nor does a name particularly distinguish one person from another.
But the display which displays raw AoA readings to the pilots is an optional extra, only 20% of 737 maxes ship with it enabled. Normally pilots (or at least commercial pilots) are trained to fly without referencing the AoA by staying well within the safety margins.
So, if the AoA isn't shown anywhere in the default configuration, there is no way for the pilots to crosscheck them and see the fault. Which is why you need the AoA disagree warning message.
Unfortunately, Boeing messed up and the AoA disagree warning was only enabled on the planes with the AoA display option enabled.
But the article buried the lede!
There is much bigger problem reported now in this article:
The warning wouldn't have helped even when flying with those companies that paid extra for it!
Note:
"“We were told that if the A.O.A. vane, like on Lion Air, was in a massive difference, we would receive an alert on the ground and therefore not even take off,” said Dennis Tajer, a spokesman for the union representing American Airlines pilots. “That gave us additional confidence in continuing to fly that aircraft.”
But in the last several weeks, Boeing has been saying something different. Mr. Tajer said the company recently told American pilots that the system would not alert pilots about any sensor disagreement until the aircraft is 400 feet above the ground."
Note what happens then: at the moment you are above the ground, and the MCAS activates, we already know that if you "just follow the procedure" the forces against pilot corrections could be too big to do anything. That's what can be concluded from the analysis of the Ethiopian crash.
That means the plane from the "20%" with "paid option" would still eventually crash as soon as AoA vanes fail, just there would be one more of many alerts in the cockpit for some short time before everybody dies.
The sense of "security" Boeing gave the American pilots flying for the companies who paid for that additional feature was completely false. They would have been doomed too as soon as a single AoA vane that the MCAS depended on failed: The warning worked only at the moment it was completely useless.
The U.S. MAX planes were grounded the last, yet they were in the same danger as the other planes.
This is about adding to the narrative of Boeing's "general mismanagement" of the aircraft. Not about adding to the particular 737-800 crash investigation story (directly).
So the warning message could have potentially prevented both crashes and anything like it (assuming it activated during the takeoff roll, before V1 and the pilots were trained to abort take off when it happened)
Though you are right, if the AoA sensor had failed halfway though a flight, they still would have had problems.
Are you sure? The AvHerald narrative for the Ethiopian Airlines flight:
"The takeoff run was entirely normal, both AoA sensors were in agreement. Shortly after becoming airborne the left AoA sensor however began to deviate and reached a position of about 85 degrees nose up, which obviously triggered the left hand stick shaker motor (and provides a very noisy and distracting cockpit environment), which in turn, different to the 737 NG behaviour (where the AoA does NOT correct the pitot data), also caused the IAS and ALT data to differ from the right hand system, in particular the left IAS became 12 knots higher than the right hand IAS (the preliminary report does not mention that the IAS DISAGREE warning activated however, which would invoke the unreliable airspeed procedures). The captain was pilot flying and focussed to keep the aircraft on track (via the flight director) due to terrain around while at the same time trying to understand why the stick shaker activated. Several required callouts by the first officer did not occur (e.g. speed, ...), as result the crew lost speed as well as thrust control completely out of sight."
As I said somewhere below, I don't think the AoA disagree indication would have made much of a difference here.
"We were told that if the A.O.A. vane, like on Lion Air, was in a massive difference, we would receive an alert on the ground" ...
"But in the last several weeks, Boeing has been saying something different. Mr. Tajer said the company recently told American pilots that the system would not alert pilots about any sensor disagreement until the aircraft is 400 feet above the ground."
[0] https://en.wikipedia.org/wiki/Ground_effect_(aerodynamics)
No. A wing will stall at a consistent critical angle of attack. Ground effect works by increasing the lift available for a given angle of attack, not by allowing a larger angle of attack to develop.
Parent comment was asking about the need for minimum airspeed to set the AoA sensors into a reliable state such that they could be checked at the gate, though, which is unrelated to ground effect.
Granted, btw, that AoA readings on the ground may be unreliable - the question remains whether AoA disagree could be detected reliably before takeoff.
An abort just prior to V1 is a no-joke exercise from a safety standpoint. MCAS operation is suppressed with any flaps deployed, so taking an airplane with a failed AoA sensor into the air and troubleshooting/returning to the departure airport if needed or simply flying with an INOP MCAS may very well be safer than a high-speed abort.
Conversely, if your airline has not ordered the optional AoA indicators, and you'd really want the "AoA disagreement" warning light/message, you don't get it.
https://www.quora.com/Is-the-moon-there-when-nobody-looks-If...
I think this is the wish of very a many physicist as they drink their morning tea and contemplate the day.
Electricity suddenly stops working.
Which is why there's a threshold that much be crossed (IIRC ten degrees) before the disagree warning appears.
If you're slipping without flaps I guess it could still be a problem if the disagreement is outside the epsilon spec. I'm not sure if [normal] slip could ever cause that much disagreement.
(I've had the controls of a 172 and a Tiger Moth briefly, but have never _really_ flown a "real plane". I have flat spinned many many rc planes, mostly recovered fine, but also to their occasional doom...)
As a UXer I would _assume_ error messages would be in a consistent section of UI real estate. However, even if this is not the case I would expect both experience and training to mitigate the "can't find the error message among all das blinkenlights"
The pilot flying has eyes on the PFD continuously, only looking away for a few seconds at a time if handling other systems. Essentially when flying instruments you "scan" the 4 primary pieces of information in the middle of that screen every few seconds.
On top of that there is an audible reminder when a new failure annunciator appears, so even if they were on autopilot and not paying attention (rare so early after takeoff) they would hear it and look.
I'd expect building safe, efficient, high quality planes to be the answer. Whereas in their minds it's probably generate record profits by maximising ROI on past investments, protecting profit margin at all times having priority over things that might improve quality. Oh and with a complete spaghetti monster of responsibility layers.
I just keep getting more and more disgusted they are getting away with manslaughter.
- "We planned for, and certified, an MCAS operating within certain boundaries, but then delivered a plane that exceeds these limitations multiple times."
- "To save money, we built a plane whose handling characteristics are so crappy that we could not certify it, unless we put in an extra system interfering with primary flight controls, but let's not tell anyone about it."
- "We've added this powerful system interfering with primary flight controls, and it depends crucially on AoA data, which we receive from two sensors. Well, let's just pick one of them and ignore the other one. It'll be fine."
Managerial marvel? I assume you're not sarcastic, so what do you mean?
It's a managerial "marvel" because they managed to certify and deliver that mutant flying turd adding billions to their bottom-line, earning their bonus while spending Boeing's good name and capitalize their decades-long "investment" on FAA.
That's top-notch management right there...
Glad to hear :-)
If a pilot knows or believes it's installed, then they might discount a theory because the instrument appears to disagree.
To me, more dangerous, is that some safety systems are considered optional. Surely the plane either needs a safety feature or not, and it shouldn't be down to someone at an airline to make a decision on?
Who should make the decision whether an airplane is "safe enough"? Should it be the buyer who wants the safest plane? If you did that then rich airlines could keep out new competition by specifying safety features that make airplanes more expensive than they need to be. Should it be the country where the airline is based? But different airlines are based in different countries. Should there be options so that one country can specify higher standards than others?
Basically, that's how you get where we are I think. I'm not sure how you avoid that.
How about these guys? https://en.wikipedia.org/wiki/International_Aviation_Safety_...
I think that changes the calculus of "Do you pay 10x the price of an aircraft to reduce the chances a problem so that it goes from happening once every 100 years to once every 1000 years"
They had already invested the money to develop the feature. Delivering a plane with or without it to a customer had the same cost. If the customer paid more, they got the safety feature turned on, the end.
Not exactly, surely. The ongoing/recurring costs to Boeing would be increased with the feature enabled - it's another thing that can go wrong and must be monitored, it changes support requirements and the overall software runtime complexity. I assume that would get factored in, somehow...
People should have paid for the "warning when auto-crash enabled" option and I'm sure Boeing advertised their plane as absolutly unsafe without it...
Someone being pitched 30 different $1 million safety options?
In manuals that Boeing gave to Southwest Airlines — the biggest operator of both the MAX and 737s in general — the warning light was depicted as a standard feature just as it is on older 737s, according to Southwest spokeswoman Brandy King.
After the Lion Air crash, Ms King said, Boeing notified Southwest that it had discovered the lights did not work without the optional angle-of-attack indicators, so Southwest began adding the optional feature too.
(quotes from https://www.abc.net.au/news/2019-05-06/boeing-knew-737-probl... )
For example, airbags on your car may be mandatory but automatic emergency braking not so much.
Given that thanks to Boeing, the Lion Air crew didn’t even know the MCAS subsystem existed, and that MCAS would continue to rely on the single faulty sensor however many extra redundancies were installed, the decision not to buy seems kind of irrelevant.
This is the part I was trying to clarify. I don't know Boeing's internal processes, but there certainly could be options that are safety-critical but still optional because they are ranked low enough on the severity/probability/detectability scale.
I agree that it's wrong to blame Lion Air as the consumer. The fault seems to be in Boeing misapplying the risk categorization.
You're the one who made the factual statement. I'm not the one that's obliged to back that up.
Wikipedia lists the customers, and the number of aircraft delivered to US airlines is a good match for the 20% of aircraft that are said to have that feature. However, that assumption implies that 0% of leasing companies ordered it, that 0% of Canadian customers did, that the American airlines bought all their aircraft and didn't lease any, etc. Might all be true but you can see why I asked for a citation.
https://en.wikipedia.org/wiki/List_of_Boeing_737_MAX_orders_...
Does everyone know this delicious skit? "Clarke and Dawe - The Front Fell Off"
https://www.seattletimes.com/business/boeing-aerospace/faile...
Fuel loads, critical airspeeds, and maneuvering characteristics are indeed governed by weight and balance. That has nothing to do with AoA reading mismatch indicators.
Was there a separate question about automatic weight and balance measurement as a feature?
To you own the safest car that is available?
However, I'm not transporting passengers for money and accepting liability for passengers' lives; airlines do, so their financial calculation should be very different from Joe Blow private car buyer.
Finally, if I understand correctly, these extra safety features were software only, meaning they don't cost the manufacturer anything to add on, so there's no excuse to not make them standard. On cars, the extra safety features require expensive sensors, so they really do add to the BOM cost of the car, and putting them on an economy car really could push the price too high for buyers to afford, so carmakers put them in higher-cost models to help make them more commonplace and then move them into lower-cost models as the volumes increase and economies of scale make costs lower.
I would describe it as extreme criminal negligence with wanton disregard for human life.
Edit (as seeing downvote due to the possible tone of the comment): What I am saying is basically this should have been flagged by the FAA during the certification process. Maybe that was not part of the process but making sure to check which optional features offered are safety related could be absolutely critical for air safety.
Edit 2: I meant ON-OFF Light here
I don't think a light (rather than annunciator) can be a very serious safety feature in any case, simply because in an emergency pilots aren't going to be looking at random places throughout the cockpit to see which small lights are on. They're going to be looking at the central EICAS display, which is what they're trained to do.
I guess I shouldn't be surprised, this makes sense as a money-maker, and is how software is (necessarily) sold. When you have to pay extra for certain software features, whether or not they were actually included in the binary you have as a lesser-payer, it could have been, software is intangible and has no extra per-unit cost to include the "mechanism" once developed. This makes sense as a business model for selling software, in that that's how software works.
But yeah, I hadn't realized planes were sold that way. When we're talking about "features" that are pilot dashboard indicators... it really doesn't seem wise. Are there any pilot dashboard indicators that would be sold as add-ons that wouldn't increase safety were they there? I mean, what's a dashboard indicator for if not making it easier for the pilot to fly the plane? If you have to pay extra for some actual physical device, that's one thing, the physical device has to be installed. But when they're just holding back safety features with no extra per-unit cost that could simply be switched on if you paid... does not make me feel great about flying.
Is this some kind of airplane DLC and can I get the season pass for less money?
If I am to read this correctly, the angle-of-attack disagree light is installed on all Boeing 737-MAX aircraft. For customers who did not buy on optional additional indicator, the angle-of-attack disagree light was always off, even if there is a disagreement between to sensors of the angle of attack of the aircraft.
Doesn't this seem dangerous in-and-of itself? If a pilot assumes that the light is off because there is not a disagreement, instead of because there is no information available, she is acting on incorrect information, and might try to address problems unrelated to the actual problem.
Also, pilot may switch aircraft and expect the same functionality of safety features and may make incorrect assumptions about the functioning of this light.