31–40 of 52 posts
> Pilots on the Lion Air flight were receiving erroneous speed readings, a problem that had occurred on three previous flights, according to the Indonesia National Transportation Safety Committee. They had radioed air-traffic controllers to say they intended to return to land. Was that three previous flights of the same aircraft? And if so, why was it still in service?
Earlier quoted context omitted.
Pulling back on the controls moves small control surfaces (elevators) on the horizontal stabilizer (the "tail wing"). The way the anti-stall measure works on the MAX (and many other planes, to be fair) is by adjusting the pitch trim. Adjusting the trim changes the angle of the entire horizontal stabilizer. https://en.wikipedia.org/wiki/Stabilizer_(aeronautics)#/medi... It's very possible for the effect of the extreme…
A 737 and a 737 MAX has big wheels in the cockpit that move as the stabilizer trim changes. This lets the pilots see what the autopilot is doing with the stabilizer, and/or override stabilizer changes by grabbing and holding the wheel or rotating it. You also have two switches to disallow control of the stabilizer, one for blocking other stabilizer controls in the cockpit, and one for blocking control by the autopilo…
https://www.youtube.com/watch?v=rxPa9A-k2xY
The issue for the Lion Air pilots was time. At 5,000 ft you don't have time to adjust the trim before you hit the ground. While I think that the stabilizer trim can be adjusted more quickly than the video shows you'd still be looking at somewhere around the order of 30 seconds end to end.
Earlier quoted context omitted.
A 737 and a 737 MAX has big wheels in the cockpit that move as the stabilizer trim changes. This lets the pilots see what the autopilot is doing with the stabilizer, and/or override stabilizer changes by grabbing and holding the wheel or rotating it. You also have two switches to disallow control of the stabilizer, one for blocking other stabilizer controls in the cockpit, and one for blocking control by the autopilo…
> In theory then, solving the stabilizer problem that caused the crash is as simple as flipping both switches to cutoff, then using the wheel to set the stabilizer back to a sane value. https://www.youtube.com/watch?v=rxPa9A-k2xY The issue for the Lion Air pilots was time. At 5,000 ft you don't have time to adjust the trim before you hit the ground. While I think that the stabilizer trim can be adjusted more quickly…
Earlier quoted context omitted.
Pulling back on the controls moves small control surfaces (elevators) on the horizontal stabilizer (the "tail wing"). The way the anti-stall measure works on the MAX (and many other planes, to be fair) is by adjusting the pitch trim. Adjusting the trim changes the angle of the entire horizontal stabilizer. https://en.wikipedia.org/wiki/Stabilizer_(aeronautics)#/medi... It's very possible for the effect of the extreme…
A 737 and a 737 MAX has big wheels in the cockpit that move as the stabilizer trim changes. This lets the pilots see what the autopilot is doing with the stabilizer, and/or override stabilizer changes by grabbing and holding the wheel or rotating it. You also have two switches to disallow control of the stabilizer, one for blocking other stabilizer controls in the cockpit, and one for blocking control by the autopilo…
Exactly, and critically that "break" occurred during a very busy phase of flight, when they had a lot of stuff to think about even during "routine" operations. They didn't have a lot of attention to spare to notice the runaway trim condition.
> Pilots on the Lion Air flight were receiving erroneous speed readings, a problem that had occurred on three previous flights, according to the Indonesia National Transportation Safety Committee. They had radioed air-traffic controllers to say they intended to return to land. Was that three previous flights of the same aircraft? And if so, why was it still in service?
If the company knew about this issue, I doubt they would have authorized putting the aircraft in service.
Earlier quoted context omitted.
> In theory then, solving the stabilizer problem that caused the crash is as simple as flipping both switches to cutoff, then using the wheel to set the stabilizer back to a sane value. https://www.youtube.com/watch?v=rxPa9A-k2xY The issue for the Lion Air pilots was time. At 5,000 ft you don't have time to adjust the trim before you hit the ground. While I think that the stabilizer trim can be adjusted more quickly…
The elevators still have some authority, you don't have to wind it from end to end to regain control. Also, the full range of mechanical motion is only available via the trim wheel, the electronic trim doesn't drive it to either extreme (although it can move it back to the centre from an extreme).
If you're at a low altitude and managing other problems will you have enough time to even recognize the problem and then wind the cranks and recover before you hit the ground?
> Also the full range of mechanical motion is only available via the trim wheel, the electronic trim doesn't drive it to either extreme (although it can move it back to the centre from an extreme).
Can MCAS drive the trim full down? What I've read suggests that if you give it time, it can.
Would it be overly cautious to avoid flights on Boeing 737 MAXs? edit: of course with the downvotes for an honest question. this site can be ridiculous.
Yes. This is a very specific failure mode, and given the publicity of this event, it's not going to catch anyone else out. Now, that doesn't mean I didn't double check the aircraft types for some upcoming flights flights...
Earlier quoted context omitted.
I have less ire for Boeing than I do the FAA. There was an interesting comment on airliners.net that the USSR operated new airliners on freight services for several years before putting them on passenger services. So far I've confirmed that for the Tu-154 trijet, for example, which flew freight for two years before taking a revenue passenger. But in the West there has always been a tension between certificating for s…
> Why hasn't the 737Max been grounded pending investigation? Because jumping to conclusions is not helpful. Let the NTSB do their job and find out what went wrong.
Grounding the plane is exactly the opposite of jumping to a conclusion. It's declaring "we can't conclude that this plane is safe".
The pilots would have seen the nose down action as an uncommanded stabilizer trim movement. The solution is to shut off the power to the stab trim. This would work and would require no knowledge of the stall avoidance mechanism.
Exactly this. Following the existing memory items and QRH checklist items taught to every 737 pilot is (very, very likely) enough to overcome this contemplated scenario of a runaway trim from a flaw in the stability system. (It's remotely possible that the crew holds no blame in that they followed the checklist properly and the cutout switches were defective or the checklist response was otherwise insufficient.)
Earlier quoted context omitted.
Yes. This is a very specific failure mode, and given the publicity of this event, it's not going to catch anyone else out. Now, that doesn't mean I didn't double check the aircraft types for some upcoming flights flights...
I've got an upcoming flight on a 737-800, is it safe to assume that model isn't affected by this?