5 ms·

Ah, I was not aware of that. But surely the pilots were under the impression that such a warning message existed?

• nraynaud 8y ago
  So there a weird thing about angle of attack: the autopilot uses it, but civilian pilots don’t use it (they use airspeed and descent angle). It’s used in the military, and airlines who recruit a lot of military pilots tend to buy the angle of attack option to get them comfortable. Ignoring the little MCAS issue, it was a fine reasoning, the autopilot can detect a disagree (I guess they just drop out, but I don’t know about cat 3 landings), ex-military pilots need a disagree because they read it, and other pilots don’t need to know.
  • yaur 8y ago
    In “the complete private pilot” they definitely talk about AoA in the context of stalls. I’m pretty surprised to hear that civilian pilots don’t use it.
    • cjbprime 8y ago
      Civilian planes (Cessnas etc) don't even have AoA indicators, so civilian pilots couldn't use them even if they wanted to. They have started to add them just in the last few years. But of course that means they're still not in the planes most private pilots are flying.
    • nraynaud 8y ago
      it's a very important concept, but it's a far cry from having a (redundant) gage and introducing it into the scanning pattern. Air speed is generally a very good indicator of how far you're from stall, unless you're in the army doing crazy attitudes very close to the ground. I'm pretty sure that small aerobatic planes don't have an angle of attack indicator, while the pilot would know everything there is to know about attitude control, having a number is not useful.
      • nraynaud 8y ago
        I would add an analogy: wing loading is an extremely important concept, and there is absolutely zero plane with a direct force reading on the wing spars.
  • lqet 8y ago
    But how can you even diagnose a failing AoA sensor, if there is no warning message but you expect it to be indicated by one? Is there any testing done on ground by the engineers after each flight?
    • nraynaud 8y ago
      The more I learn about the story and the more I realize the bureaucracy that is airplane flying. The boeing line is that they had to use the runaway trim checklist and that’s it. They missed the auto throttle item on the list so it’s their fault. I feel like it’s all about reading documents and never trying to use their brain. A lot of my bubble about diagnosing things and connecting information together has been bursted.
    • salawat 8y ago
      That's the rub. Let's plan a theoretical test case. At a minimum, you'd need two maintenance guys, maybe one and a pair of tools. One guy to tweak the sensor outside (as several hundred mile per hour airstreams aren't exactly in plentiful supply, or easy and trivial to reconfigure in a hangar near you), and a guy in the cockpit, reading off the measurement on the computer against some sort of calibration chart. The "tweaking" part would probably be done with some sort of precision test mount (that I doubt they even build into the plane.) Also, odds are, you'd only detect very specific types of disagrees on the ground. Bad springs should be trivially deducible from the forces required to create measurable deflections. Bad potentiometer connections should be deduceable from checking output voltage against the component spec sheet while deflecting. Unfortunately, this dive into Electrical Engineering won't stop until you've taken into account every length of wire and eventually, every circuit board and line of code between that sensor and the avionics suite. If some FOD for instance, was slowly wearing through the wiring and insulation leading from the sensor to the computer, or an inductive cross-talk event occurred, or something shorted. Etc, etc. And all of this work and diagnostics would need to be done by someone whose documentation told them the AoA sensor was a non-critical component so the manufacturer could cut corners. Oh yes. <double facepalm> Been here before. Way. Too. Many. Times. Not in safety critical systems , mind, but oh the web's I've seen woven.
  • inferiorhuman 8y ago
    Military or not you should know about the AoA disagree and the presence of MCAS as the combination can be quite deadly. Knowing the actual angle of attack could be useful, but knowing what sort of cascading failures to expect is critically important.
    • nraynaud 8y ago
      I am trying to explain Boeing’s point of view before the accident, you’re busting an open door.
  • inflatableDodo 8y ago
    I found it amazing that civilian pilots don't use angle of attack so went looking and found this article about the debate on installing angle of attack indicators on commercial aircraft, which cleared up for me why this would be the case. But not in the most reassuring manner. https://apstraining.com/the-angle-of-attack-debate/ https://apstraining.com/the-angle-of-attack-debate/ >"From day one, pilots should be—and in most cases are—taught that stall occurs when the critical angle of attack is exceeded. They are then told to memorize the stall speeds in various configurations. By the time they have become proficient, they relate stall to a certain airspeed, and don’t really relate it to an AOA anymore."
    • wnkrshm 8y ago
      Air France 447 immediately comes to mind, where the crew (or maybe specifically the copilot who kept pitching up for minutes) lost their airspeed indication and thought the stall warning was frivolous despite falling vertically at terminal velocity for minutes.
      • danaliv 8y ago
        Critically in that case, the stall warning stopped when the nose was pulled up even further, because the computers rejected the indication as too large to be correct. So every time the nose was lowered, the stall warning activated.
        • inflatableDodo 8y ago
          Fucking hell. That is a fucker of a dark UX pattern.
          • danaliv 8y ago
            Indeed. And it goes to show that rejecting “impossible” values is a dangerous strategy.
            • 8y ago
• phire 8y ago
  Yes. An in the aftermath of the Lion Air crash, Boeing were telling pilots that this warning message would alert them to that kind of problem before takeoff.
  • inferiorhuman 8y ago
    Boeing were telling pilots that this warning message would alert them to that kind of problem before takeoff. I doubt that, the alpha vanes aren't particularly useful until the plane is actually moving at a fairly decent clip.
    • AnssiH 8y ago
      Yes, it does not work. According to the OP article, Boeing said to American Airlines pilots in November that the warning would work on the ground, but later said it in fact does not.
    • phire 8y ago
      By before takeoff, I assume that means "during the takeoff roll" And I hope that also means "before V1". I know the DC 8 couldn't do it's elevator check until it was moving quite fast, as there was no direct connection between the pilots controls and the elevator and it couldn't respond without airflow.
    • danaliv 8y ago
      What speed is that? I don’t know about 737s in particular but some AoA sensors work at speeds as low as 20 knots—far less than V1 on any runway a 73 is going to use.
    • Maxious 8y ago
      So if you were to get a value that doesn't make sense on the ground when you aren't moving, that would be a assuring sign that you have correctly detected a fault.
      • sokoloff 8y ago
        The angle of attack of a wing that has zero airspeed is undefined. You could take two traditional weathervanes and put them inside your house and they wouldn't tell you the direction of the wind outside.
• briandear 8y ago
  If that annunciator isn’t in the checklist, you wouldn’t think about it being there or not. It wouldn’t be part of your scan.