5 ms·
The "light" is just a warning text that appears on the flight display, so the "no light installed" and "light installed but off" states are not distinguishable
by inferiorhuman 8y ago
The "light" is just a warning text that appears on the flight display, so the "no light installed" and "light installed but off" states are not distinguishable (as far as I have understood it).
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.
- cryptonector 8y agoReminds me of that Red Dwarf episode where Rimmer wants to go to red alert and Kryten asks "are you SURE sir? it does mean changing the bulb!".
- MaxBarraclough 8y agoReminds me of a different Red Dwarf moment. Any damage? I don't know, the damage-report machine's been damaged. Apparently they played the same gag twice: https://youtu.be/1KEHSOPSvhc https://youtu.be/1KEHSOPSvhc https://youtu.be/R49IKBWznOM?t=19 https://youtu.be/R49IKBWznOM?t=19
- cryptonector 8y agoGood one!
- blackflame7000 8y agoIf you see two AoA sensors that aren't in agreement then you can safely assume either one sensor has failed or physics itself has.
- phire 8y agoThe 737 has AoA sensors by default, the autopilot uses them and the flight computer corrects the flight speed based on the AoA and issues stalling warnings based on the values. 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.
- acqq 8y ago> 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. 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.
- dmix 8y agoThat's certainly not how the information is presented. But if you read closely you can see how they set it up carefully in the first half. 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).
- phire 8y agoOn both the Lion Air and Ethiopian Air crashes, the AoA sensor had failed before takeoff. 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.
- bitexploder 8y agoSerious tangent, but the idea of physics failing amuses me. One night we had an Earthquake in an area that basically almost never has them. Gentle shaking. It woke me and my wife up. I remember looking out my window for some sign of nuclear weapons going off or something. Nothing. I blurted out “Earthquake” all in about 10 seconds of processing. Rolled over. Went back to sleep. My wife was anxious the rest of the night and could not sleep from “what if” scenarios. One of her concerns was “what if physics was broken”?!
- bobsil1 8y agoWhat if the moon’s too bright? https://en.wikipedia.org/wiki/Inconstant_Moon https://en.wikipedia.org/wiki/Inconstant_Moon
- vidanay 8y agoDamn...I read that link as "Incontinent Moon"
- selimthegrim 8y agoWhat if it’s only there when someone looks? https://www.quora.com/Is-the-moon-there-when-nobody-looks-If-Bells-inequality-has-been-experimentally-violated-by-subatomic-particles-like-photons-why-is-it-not-violated-by-objects-like-the-moon https://www.quora.com/Is-the-moon-there-when-nobody-looks-If...
- touisteur 8y agoThat's kind of the plot of 'Ravages' (https://en.m.wikipedia.org/wiki/Ashes,_Ashes https://en.m.wikipedia.org/wiki/Ashes,_Ashes) a French SF novel by Barjavel. Electricity suddenly stops working.
- Haga 8y agoSo neurons stop working?
- 8y ago
- FabHK 8y agoSure. Problem is, if you can see the two disagreeing AoA indications, then you will get the "AoA disagreement" warning light/message, even though you don't need it. 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.
- sowbug 8y agoIf they're on either side of the fuselage and you're slipping, it seems like they'd give different readings. Pitots can give misleading readings if you slip away from the side they're on. I've never flown a plane with an angle of attack indicator.
- dreamcompiler 8y agoMost of the time when you're slipping close to the ground you're going to also have flaps deployed, in which case the MCAS is inoperative. Your AOA sensors will definitely disagree, but at least the MCAS won't act on them because it doesn't act when flaps are deployed. 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.
- bigiain 8y agoI'm now imagining a 737MAX8 in a flat spin... (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...)
- inferiorhuman 8y agoIf they're on either side of the fuselage and you're slipping, it seems like they'd give different readings. Which is why there's a threshold that much be crossed (IIRC ten degrees) before the disagree warning appears.
- rosser 8y agoWhile that's (partly) true, it's also pretty irrelevant to whether one can reasonably infer "AoA sensors agree" from the lack of an error notification indicating they don't, when the system that should be providing that notification is, in fact, disabled, because the airline one works for opted not to purchase some premium feature.
- pdonis 8y agoOr the sensors are on different sides of the plane and the plane is slipping or banking. Which happens routinely during normal flight.
- SomeHacker44 8y agoLooking at the mechanism of a vaned AoA sensor, I am guessing a fast enough roll would induce disagreement. Probably insufficient in degree to be material, though.
- spectre256 8y agoI'm a pilot, and absolutely this is a crucial difference. 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.
- segmondy 8y agoMost people experience the same when using DB, NULL in a database is hard to distinguish from, data never stored or data don't exist.
- kbenson 8y agoDo you mind explaining what you mean? To my knowledge, inspecting the number of rows returned eliminates this problem.
- RHSeeger 8y agoI think he's referring to something like a row with First, Middle, and Last name fields. If the Middle name field is null, does it mean "we don't known this value" or "this value is <nothing> (the person doesn't have a middle name)". For most database schemas, there is no way to tell the difference between the two states.
- fegu 8y agoThe latter case, no middle name, should be stored as an empty string. In practice, not enough care is devoted to the difference between Null and empty string for text fields.
- no-s 8y ago"First not null, Middle null, Last not null" represents an a priori assumption that everyone has a First, Middle, and Last - but sometimes we don't know what the Middle is. Allowing a zero length string in any of those attributes implies that some rows in a table have First, Middle, or Last represented by a zero length string. What a zero-length string actually means is subject to interpretation and thus beyond the data model. 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.
- lostlogin 8y agoI think you’re misinterpreting. The parent means that by design the plane makes the states indistinguishable.