4 ms·

The 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 base

• 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 ago
    That'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 ago
    On 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.
    • acqq 8y ago
      The new information in the article (buried in the last part of it!) is that apparently the warning message just didn't work on the ground at all, even with the already non-functioning sensors, and even if that option was paid for; read it again: "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."
    • FabHK 8y ago
      > On both the Lion Air and Ethiopian Air crashes, the AoA sensor had failed before takeoff. 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. http://avherald.com/h?article=4c534c4a/0052&opt=0 http://avherald.com/h?article=4c534c4a/0052&opt=0