8 ms·

I urge people to read the discussion by pilots regarding the 737 MAX. https://www.airlinepilotforums.com/safety/120514-ethiopian-737-max-8-crash.html https://w

• Someone1234 8y ago
  Pilots have been pushing back hard on the narrative that this was simply pilot error. The crux is that safety agencies never mandated training on these new systems, and new procedures weren't created with them in mind. Worse still procedures from older models of the same aircraft (such as automatic overriding of auto-trim) were removed without re-training on that either. Lion Air had to repair the AOA sensor multiple times (replace, then flush), but a single sensor failure should not bring down an aircraft; and if the AOA sensor is that safety critical then why did Boeing put two of them instead of three (i.e. for cross-checking readings)? Either it wasn't safety critical and Lion Air's actions are reasonable, or it was and Boeing cut costs on safety. So the justifications blaming either the pilots (who didn't get training, because safety agencies told them it wasn't needed) or maintenance (who were repairing a non-critical sensor that turns out to be safety critical) are weak.
  • deleted 8y ago
    [deleted]
  • linuxftw 8y ago
    > Either it wasn't safety critical and Lion Air's actions are reasonable, or it was and Boeing cut costs on safety. This is an excellent point. Boeing can't have it both ways.
  • rocqua 8y ago
    I recall reading on HN that a second AOA sensor was an option.
    • Someone1234 8y ago
      If the AOA sensor is safety critical they need three, rather than two. The inherent problem with two is if one is feeding false data, you don't know which one, whereas if you have three (or more; but an odd number) you can cross-check the data and drop the faulty one. It is a very common strategy already for commercial aviation and is called "voting logic." > A more reliable form of voting logic involves an odd number of three devices or more. All perform identical functions and the outputs are compared by the voting logic. The voting logic establishes a majority when there is a disagreement, and the majority will act to deactivate the output from other device(s) that disagree. A single fault will not interrupt normal operation. This technique is used with avionics systems, such as those responsible for operation of the Space Shuttle. But the real crux here is: Is the AOA sensor safety critical or not? If it can fail-safe then they can likely continue as it is currently designed. But if its failure state can cause an aircraft crash, then it becomes a safety critical component.
• sokoloff 8y ago
  Almost every (or perhaps every?) swept wing jet has active/positive anti-stall systems, at least a shaker and often a pusher. The wings need to be swept for efficient travel much over Mach 0.6 and these aero aids are needed for swept wings. At this point, pushers and shakers are well-accepted fixes for aero that is not inherently recoverable.
  • VBprogrammer 8y ago
    Stick pushers go all the way down to the PC12 (a single engine turboprop). Honestly there is no putting that genie back in the bottle. Getting benign stall behaviour out of a highly efficient wing is very difficult.
• easytiger 8y ago
  All in the name of band aid environmental pandering.
  • odorousrex 8y ago
    Try the fact that the fuel efficiency saves the airline lots of $$$ on fuel, but yet they haven't reduced fares any. Go figure.
    • jcoffland 8y ago
      Since airlines have an oligopoly, fares are not based on the cost to the airline but on the price on the supply and demand curve that yields maximum profit. In other words, the maximum price that enough people are willing to pay. If there were more competition in the market the price would be closer to the airline's actual cost.
    • sokoloff 8y ago
      Haven’t they? Domestic and long-haul flights seem much cheaper to me than ever.
    • alexis_fr 8y ago
      Reduced fuel is done with an upfront investment. Which always makes me wonder, since every penny of the investment money goes to researchers, facilities and material which themselves aren’t more economic in emissions than fuel itself, then does it really save on emissions...
    • joshe 8y ago
      Nope, airfares bounce around and have been going down for the last 8 years. https://fred.stlouisfed.org/series/CUSR0000SETG01 https://fred.stlouisfed.org/series/CUSR0000SETG01 Partly as fuel prices go down: https://fred.stlouisfed.org/graph/?g=eaB3 https://fred.stlouisfed.org/graph/?g=eaB3
      • dmix 8y ago
        That's a very useful website. Nice work St Louis Fed.
• AWildC182 8y ago
  It's a bit more complicated than that even. The 737 was originally designed for a very different mission than it's being used for right now. If you find pictures of the original 737-200s they look very different from the MAX line of today. It was built in an era when it was assumed that 707 and soon after 747 class airliners would serve the hubs and then smaller 737s would serve the small regional airports. As such the 737 was designed with VERY low ground clearance such that it could offload without a ramp and generally be serviceable at these types of low infrastructure airports, hence the lack of wheel doors, the ovoid engine inlets and the generally low stance. Fast forward to today where airport infrastructure is much more developed and these small/medium size airliners are being pressed into front line service including intercontinental routes. The aircraft has changed drastically to accommodate these changes through the years, enough that it may be time for a clean sheet design. They've changed just about everything on the air-frame from the fuel load/cabin length/wing to the avionics to make this all work. Now, the other side of that coin is with systems. In theory this should be fine, but obviously isn't. It's hard to differentiate bandaids from regular systems and if either fails then safety is compromised. Obviously the amount of unnecessary systems should be minimized but as time goes on more systems WILL be added to gain the rewards of automation, which is a good thing. As such, we need to educate pilots on ALL of the systems, and rigorously test them before they enter service. Additionally, if you do as the pilots want and achieve very high aerodynamic stability through the air-frame instead of stability control systems (fly by wire essentially) it reduces the aerodynamic efficiency of the airliner, particularly with current conventional designs.
  • zanmat0 8y ago
    >if you do as the pilots want and achieve very high aerodynamic stability through the air-frame instead of stability control systems (fly by wire essentially) it reduces the aerodynamic efficiency of the airliner It's crazy to me that that would be an acceptable compromise.
    • AWildC182 8y ago
      How so? When I say stability control, we're not generally talking about unstable or "relaxed stability" airframes where the system failing would cause a pitching moment to accelerate rather than converge and the aircraft would tumble and disintegrate. From an efficiency and handling standpoint, this would be ideal, but it's only used in tactical military aircraft where the crew can bail if there's a problem. In most cases, we're talking about preventing stall in a swept wing aircraft. Swept wings are necessary to cruise efficiently beyond ~300mph at high altitude so they have to stay obviously, however they have VERY poor stall characteristics. As such, we have to do some things to prevent the aircraft from stalling such as playing with trim, using a stick pusher, etc.
• jostmey 8y ago
  I interpret this as an indication that the United States policy and law is run by Wall street and is corrupted. Boeing didn't want to develop a new airplane, cut costs, and doesn't want to lose money, so the FAA is not allowed to ban the plane
• dukoid 8y ago
  When I see cockpit videos, the pilots tell each other what they do / run checklists together... Does the MCAS do the same, i.e. announce "stall risk detected, increasing stabilizer trim by 2.5 degree to xx degree"?
  • erokar 8y ago
    No, but the pilots will hear/see the trim wheel moving.
    • metanoia 8y ago
      Inattention to autopilot modes has killed before. So much focus is put on pilots recognizing and confirming flight mode annunciator mode changes (such as change of autopilot or autothrottle state) has been put into place to stop that kind of accident. The lack of feedback from the MCAS system is probably the killer here. How am I supposed to know that MCAS is operating, and how do I know when to hit trim cutoff switches to override it? You don't want to ever be asking "what the heck is the airplane doing now?". Watching the trim wheel to check if it's spinning nose down all the time isn't going to work.
      • erokar 8y ago
        The Lion Air pilots were not even aware of the existence of the MCAS system, because Boeing at the time did not include any information about it in its manuals. The behavior would be similar to runaway stabilizers, though, for which B737 pilots have memory items to perform (turn off the trim). This would have solved that problem. However, several other warnings and alerts, like stick shaker, might have been going off at the same time, making the situation chaotic and problems hard to diagnose.
      • consp 8y ago
        An additional problem is that if it fails (the MCAS) the airplane is low, in full thrust during take-off and the pilots have zero room for error as the airplane is trying to dive into the ground (as in the LionAir flight).
• jakelarkin 8y ago
  "the plane should never have gotten the green light to fly." this is an overstatement. airframe fuel efficiency is a undoubtable good thing vis a vis climate change, costs, etc. Obviously they've reached a point were the aerodynamic profile of a modern, efficient airframe is difficult to control via manual pilot input alone in some scenarios. This was the case for stealth technology with fighter/bomber designs.. the B2 for example has no vertical stabilizer and would not be controllable at all without fly-by-wire. Of course pilots will lament complexity and the loss of manual input. Regardless, the FAA wanted MCAS in the 737Max. Augmenting human input in the face of instrument failure and possible human failure is an extremely hard problem and uncharted territory for the industry. Doesn't at all mean its a not a worthy goal or that the designers or regulators had ill intent or negligence.
  • erokar 8y ago
    That's not really the problem with the B737 MAX though. It's not inherently unstable like e.g. a fighter. The issue is that they had to fit the engines in front of the wings, and this will create a significant pitch-up if thrust is added abruptly, e.g. in a go-around. To counteract this they introduced the MCAS system. They would not have needed this if they hadn't "retrofitted" big engines on an old airplane design, but instead started from scratch. The B737 MAX is not really a modern aircraft, but a heavily modded old design.
    • calf 8y ago
      That's interesting to know, I think the 737 Max looks very kitbash because of the way the engines dangle in front of the wings.
  • usrusr 8y ago
    An aerodynamically sound redesign to accommodate the high bypass engines would have been just as fuel efficient as the version with confusing software band-aids. If it is cheaper to invent something like MCAS than to properly adapt the airframe, then maybe the processes that would be used for the latter are ripe for some efficiency optimization.
  • deleted 8y ago
• craftyguy 8y ago
  Reading the posts there is a lot like listenning to 'retired generals' on <insert entertainment "news" network here> who haven't seen action/training in decades talk about modern tactics, equipment, and situations as if they magically have been informed by companies/players in the field they left (hint: they haven't). I'd rather wait for formal investigations (e.g. NTSB-style) before jumping to any conclusions.