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> Original MCAS system used only 1 AOA sensor and switched back and forth between the two after every flight. Who the fuck thought that was a good idea??? Let
by ilogik 7y ago
> Original MCAS system used only 1 AOA sensor and switched back and forth between the two after every flight.
Who the fuck thought that was a good idea???
Let's make it 10x more difficult to detect that there is a problem.
- 6nf 7y agoJust to explain a bit more: It uses the main pilot side AOA sensor, and pilots switch seats every flight.
- amelius 7y agoSo switching seats during the flight would have solved the problem?
- philpem 7y agoThat sounds so unlikely that most people would dismiss it as silly... I'm not a pilot, but if the controls are linked -- why would the plane need to know where the pilot is sitting (or even have a switch for it)? (Any 747 pilots reading? Can you please fill in the gaps for me?)
- cjbprime 7y agoNot a pilot either. Perhaps to show different information to the pilot flying vs. assisting? E.g. only the pilot assisting needs to see checklists?
- tellak 7y agoNot a 747 pilot (not sure why that matters here)... but a pilot. The flight positions are equal. The plane is designed to be flown the same from either flight position and this is routinely done. The guy saying otherwise is talking out their ass.
- philpem 7y agoThanks for the details :) I said 747 because I was thinking Boeing at the time, and that was the first of their aircraft I could think of! I was also thinking something smaller like a Cessna might not have the same setup because they're used for very different things (the air travel equivalent of a bus vs. a car).
- bronco21016 7y agoI can’t speak to foreign operators but in the US that most certainly does not happen. The captain flies in the left seat and the first officer flies in the right seat. Turns are taken on who is flying and the automation is selected to the side of whichever pilot is deemed the pilot flying.
- 6nf 7y ago> Turns are taken on who is flying That's what I meant yes
- l31g 7y agoEach side of the airplane has a set of sensors. The ones on the left (while sitting on the plate) are named Captain <sensor_name> and the ones on the right are named First-Officer (F/O) <sensor_name>. The MCAS software would switch from Captain AoA vane to F/O AoA vane between flights. The location where the pilots are sitting doesn’t affect how the airplane is flying itself. The person flying the plane can be sitting on either of the two seats, but the most senior pilot usually sits on the left.
- chipsa 7y agoIt's not that the MCAS software would switch. It's that the sensors feed into two different flight control computers (Captain and F/O). And which FCC is primary would switch after each flight. Both FCCs run the same software, but with different inputs from the different sensors.
- cjbprime 7y agoDoes it switch automatically after each landing somehow, or because the pilots tell the plane which FCC is going to be primary for the flight?
- IMTDb 7y ago> Let's make it 10x more difficult to detect that there is a problem. A problem no one can detect is a problem you don't need to fix ! /s
- ddalex 7y agoIf you're looking from an engineering PoV that's absurd. If you're looking from a regulatory compliance PoV towards optimising sales - that's actually desired behaviour - if it's overly complex to diagnose it's less likely that somebody understands and point fingers back at us. You know, basically what happened after the Lion Air crash - Boeing being all over "it's not us, it's them"
- aivisol 7y agoI was wondering the same. What is the logic behind this setup? That basically means that it is no better than having one sensor. Because if any one of them breaks, you have broken sensor active on next or following flight. Also I recall there was something said about Lion Air crash that the crew on the day before experienced some flight control problems which was not communicated to the crew involved in crash? Did they use other sensor on the day before and that was faulty too, or isn't that is how it actually worked?
- Scarblac 7y agoIt's worse than having one sensor, the chance that one of two breaks is larger than that just a single one breaks. And by alternating you ensure that the broken sensor will be used.
- phkahler 7y agoWas talking to my flight instructor about twin engine planes. He was adamant that they were LESS safe than single engines because 1) you are twice as likely to have an engine failure and 2) the statistics indicate (non-intuitively) that an engine-out in a twin is more likely to lead to fatalities. He said the insurance companies used to think twins were safer but they have adjusted their rates after looking at actual data. I was fully on-board with point #1, but #2 was a surprise to me. I suppose that's what Burt Rutan tried to address with the Boomerang design.
- ebg13 7y agoTo your second point, my assumption as a non-pilot is that a symmetrically balanced glide is more controllable than lopsided thrust that could put you into a spin?
- mcguire 7y agoLoss of one engine at low speed will leave a twin uncontrollable. See Vmc (https://en.wikipedia.org/wiki/V_speeds?wprov=sfla1 https://en.wikipedia.org/wiki/V_speeds?wprov=sfla1).
- treis 7y agoA busted AOA sensor is going to set off a whole bunch of alarms since it's used in air speed and stall calculations. It's not something that is going to be missed with or without MCAS.
- arbitrage 7y agoUnreliable hardware fails unreliably. It's entirely possible to have all your checks in place, and still not be able to detect that the sensor is faulty. Independent comparable sensor input is invaluable and irreplaceable.
- treis 7y agoThe plane might not be able to identify that the AoA sensor is wrong, but the pilots will surely know something is wrong. They will be getting stall warnings and airspeed warnings. Again, maybe they can't say it's the AoA sensor but they will definitely know something is wrong.
- ceejayoz 7y agoYou're assuming all failures are detectable by a computer. That's not necessarily the case.
- cwilkes 7y agoWell if you have two sensors you never know which one is right.
- weaksauce 7y agoYou either trust both when they are nearly in agreement or disengage any autopilot type system like the mcas. The engineering solution is three sensors voting on agreement and disregarding the one that is out of agreement with the other two.