7 ms·

The previous flight had exactly the same issue. This is what that pilot wrote in the logs; After parking, the PIC informed the engineer about the aircraft prob

• VBprogrammer 8y ago
  I haven't checked but I'd bet STS is speed trim system (Aka Mach trim). Interesting that he came up with a reasonable mental model of what was wrong even though Boeing hadn't given them any details.
• Someone1234 8y ago
  MCAS problems weren't a memory item for any pilot, the memory item is Runaway Stabilizer and exhibits different behaviour to MCAS. Which is to say that they'll be receiving sim training for Runaway Stabilizer, learn what to expect (wheel moves continuously, hard nose down, etc), and then in real life have MCAS cause the same issue but in a substantively different way (change, delay, change, delay, etc). Without the benefit of hindsight why not try the Memory Item: Engine Surge / Stall or Uncommanded Roll? Both of which could exhibit as an uncommanded nose down. The reality of the situation is that some pilots immediately went straight for Runaway Stabilizer whereas others did not. That's a problem. That's a TRAINING problem. The type rating should have included additional training against the Runaway Stabilizer Memory Item for MCAS so "I've seen this before" is second nature.
  • dmix 8y ago
    > That's a problem. That's a TRAINING problem. Isn't the root problem still related to the fact that the AoA sensors were returning wrong information and the MCAS was simply reacting to that in a dangerous and non-obvious way? I guess the pilots should be aware of this type of system reaction but still it seems like something that should be fixed at a higher level than training (indicators, backup AoA sensors, detecting dangerous descent after trigging nose down, etc).
    • Someone1234 8y ago
      There's problems at multiple distinct levels. Regulatory/oversight, unsafe design, lack of information/training, and potentially poor maintenance practices. If you'll excuse the expression, everyone is going to get poop on them after this one is over.
    • jandrese 8y ago
      There's never just one cause of an airline accident. That was one of the causes, but alone it wouldn't have been sufficient. Fixing the problems at all levels is how you achieve high reliability.
      • beamatronic 8y ago
        Exactly - Defense in depth.
      • itronitron 8y ago
        Seems like it would have been sufficient to cause the crash, or are you saying that if the pilots let MCAS do its thing that the plane would not have crashed?
        • jandrese 8y ago
          Crash causes: 1. Faulty MCAS 2. Insufficient pilot training 3. Boeing design changes (MCAS used to be disabled automatically if the pilot applied sufficient counter-input, this feature was removed in the -MAX series, requiring the pilot to explicitly disable the system using a separate button) Take away any 1 of those causes and the plane doesn't crash. They all had to happen at the same time for these two tragedies to occur.
• ams6110 8y ago
  One wonders, when the prior flight landed with the stab trim system switched off, who switched it back on before the next departure? And was there no question raised as to why it was off? It's not normal to have that system switched off at any time. There are even guards over the switches to ensure they are only operated deliberately.
  • Someone1234 8y ago
    Maintenance attempted a repair between those two flights. They flushed the AoA system after replacing it previously.
    • sgc 8y ago
      They should have given the incoming pilots a thorough briefing of: this is what went wrong, this is how the previous pilots worked around it, this is what we did to remedy.
      • Someone1234 8y ago
        That's what this comment chain is about, the log book. Maintenance would have added comments after the previous pilot's above.
• _s 8y ago
  It probably is a memory item, but it's not something they got to immediately, and I'm guessing here because runaway trim symptoms are slightly different to what MCAS was doing. This happened to me a while ago involving trim, and I'll try and go through my thought process and why it takes a little while in the cockpit to figure things out: - Autopilot is engaged, holding a heading of X, altitude of Y and I've got a power setting for speed Z - My hands are off the stick, and I'm planning the next 20 mins of the flight. - The nose has slowly started creeping downwards, I don't notice until I look up a few seconds later - I glance at the altimeter and see we're now Y-300ft, and descending at 500ft/min. - I check the altitude hold on the autopilot flight director; see yes, it is still set to Y, and am rather confused, as the stick is fairly pulled back to pull the airplane up (autopilot), so the pitch hasn't changed that much. - Airspeed is slow, and I'm even more confused - how are we both descending and slowing down. - Glance over to the passenger, she's fast asleep, a bit restless but not touching the yoke or rudder. - ATC comes over the radio asking if we're descending and what our intentions are. - It's only been about 30 seconds but we're now Y-900feet, at a decent rate of of -1400ft, the AoA indicator is starting to beep as we're now in the warning arc, speed is Z-20kts. - Unsure of what's actually happening, I push in full mix/throttle to keep our airspeed up. - I grab the stick (already fairly back) and attempt to get us level. - Tell ATC over the radio I'm having difficulties with the autopilot as I disengage it. - Feel an immediate / tremendous force on the stick pulling it forwards, have to use both hands to keep it back. - I'm now wondering if the elevator control is broken. - Try to start trimming it back (electronic trim), but a warning flashes on the instrument panel. - Electronic trim usage also immediately disables the autopilot completely, so the wings are now rocking too, giving a weird sensation as I feel like I'm fighting the controls. - Reach over to the trim wheel, realise the passengers knee is propped on it. - Move her leg out of the way, and start wheeling it back and feel pressure easing on the stick. - Keep trying to use the electronic trim and it kicks in, and I can see the trim position on the panel (set pretty far forward). - Aircraft is now finally level, airspeed is increasing. Elevators / pitch control feels normal. - Set airspeed for best rate of climb, and tell ATC I'll level off at my previous altitude. Put us into a climb. - Re-engage the autopilot and all seems well That was about a minute and a half. I went from 8500ft to around 6800ft in what felt like a few seconds, and it's only after I was in the climb that I realised her shuffling was knocking the trim wheel around. She had been probably doing it for the better part of an hour, and the autopilot had been opposing her inputs. I didn't pick up on the airspeed changes as we're a slow plane flying into a strong headwind so I expected to not be flying the usual speeds. I pored over the Pilot Operating Handbook that day, and also the Garmin G3X/GFC500 to figure out what was happening and to understand the systems. The trim wheel itself doesn't disengage the autopilot, only the electric trim control does. When the servo motors can't engage (too much force), the system just shows a red X on the instrument display where the control display would be. Etc etc. The 737MAX pilots don't have that luxury, as they're told it's just a 737 type. Go through the above scenario, but have no knowledge of the fact that theres something moving the trim. You do not have the luxury of altitude, nor airspeed. The sensors are providing weird inputs. Plus, everything is happening around 10x faster, not a slow build up. You reset the trim, all is well for a few seconds and bam, nose down again. Reset again, it happens again. If I don't know about the MCAS, the 5 sec delay etc, my immediate thought is a faulty computer and I'll try and restart it. And so forth.
• jcims 8y ago
  Are the logs you're referencing a public resource? Would be interesting to look at. >This implies it took almost three minutes for the previous crew to figure out the STAB TRIM needed to be CUT OUT after finding the trim is so wrong that they can’t hold the stick back. I've seen a number of references to difficulty that pilots encounter managing forces of the flight controls in airliners. It seems strange to me that modern aircraft of that size would be designed in a way that aerodynamic forces on control surfaces would be allowed to translate back to control inputs in a manner that could overpower a pilot. I would think there would be some kind of scaled assist mechanism (ala power steering) in scenarios where there is a mechanical/hydraulic link. I'm guessing fly by wire scenarios wouldn't have this problem?
  • bdamm 8y ago
    The scaled assistance you're referring to is the hydraulic system. Airplanes are supposed to be light-touch because you need very fine movement control to balance the aircraft while landing. Think of the work required to move a pencil. That's about the level of effort a plane is supposed to require. But with the trim working against the pilot, the control required could be more like lifting a 50lb sack. Yes, most pilots can lift a 50lb sack. Can you lift and hold a 50lb sack for, say, an hour? Not many people can. (Without hydraulics, the forces would simply toss the pilot's body around. No possibility of control.)
    • VBprogrammer 8y ago
      Also worth noting that the reason we don't simply scale the forces down to the point a pilot could easily handle them is that above manouvering speed an aircraft can be damaged by full control deflection.
      • bdamm 8y ago
        Good point. This is something I bet most non-pilots don't know. A pilot can actually damage or destroy an airplane through control inputs alone. In fact there was a case of a pilot intentionally destroying his airliner by rapidly slamming the rudder back and forth, but I can't find the flight reference now. And there are other examples, such as AA flight 587 where the large control inputs were causal in the crash that killed all aboard.
• arianvanp 8y ago
  You are confusing things here. This article is about the crash that happened 6 months ago. You are comparing one and the same crash here. The recent crash is by Ethiopian Arilines. NOT Lion Air.