I’m concerned about Boeing aircraft safety design flaws because it is so disturbing to see so many lives lost in aircraft accidents. I’ve attempted to contact Boeing about this. But officially they can’t be bothered by public suggestions or questions. I also read that since a design flaw can expose Boeing to law suits, they hide such information by emphasizing an alternate reason for a crash such as that on the Indonesia flight JT610.

The fundamental design problem is that the aircraft can force the nose down without allowing the pilot to pull up (totally independent of pilot control). In response, Boeing claims that the pilot needs to read the instruction manual to correct this. But if the pilot is diving into the sea at 450MPH he really doesn’t have time to read the manual.

Lane control in a new Toyota Prius causes the car to be gently nudged back into a lane if the car deviates excessively. But if it totally took over steering control with a defective lane position sensor, the result would be catastrophic. Similarly, if the aircraft pitch control takes over by relinquishing pilot control, the same problem would occur.

A simple correction would eliminate this problem which should have been applied before carrying passengers as detailed below.

The horizontal stabilizer has a front jack screw and a rear fulcrum with the elevator hinged to the rear of the stabilizer. Moving the yoke back moves the elevator up (tail down, nose up). The stabilizer is then trimmed either manually or automatically to reduce yoke forces sensed by the pilot but incorrectly if the AOA sensor is defective.

If the stabilizer is too high as a result of erroneous AOA sensor input, the plane dives into the sea unless the pilot reads the manual (as claimed by Boeing).

To correct this major problem, can a switch be added which senses back yoke force so as to move the stabilizer down (nose up) independently of any other stabilizer inputs preventing the uncontrolled dive?


closed as primarily opinion-based by Ralph J, fooot, Gerry, SMS von der Tann, Sean Jan 12 at 3:45

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Have you seen the articles saying the pilots on the previous flight were able to turn off the control that caused the diving? The plane went into maintenance, the shop missed that the AOA sensor was not working. The next set of pilots then did not turn off the same control. Thus, lack of knowledge about the plane's controls did them in. $\endgroup$ – CrossRoads Jan 11 at 3:11
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    $\begingroup$ Closely related $\endgroup$ – Pondlife Jan 11 at 4:05
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    $\begingroup$ The point of the automatic nose down trim is to prevent the pilot from accidentally stalling the aircraft (i.e. pulling back too much - it happened on other accidents). If you add a switch which disables the system when the column is pulled back, it kind of defeats the sole purpose of the system. $\endgroup$ – Cpt Reynolds Jan 11 at 4:21
  • $\begingroup$ A much simpler fix would be to disable the MCAS if there's an AoA disagree. Not sure why it wasn't that way. They may have had a reason $\endgroup$ – TomMcW Jan 11 at 21:18
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    $\begingroup$ Is there a "Rant" tag that we can add to this question? The lack of understanding evidenced by the text of this question is too great to address in a single answer. $\endgroup$ – Ralph J Jan 11 at 21:34

Machines taking over the world is a common sci-fi theme for many entertaining movies, yet we continue to take control of our aircraft away from our pilots. Nothing can replace qualified and properly trained people. The most reliable way to correct a 1 in a million pilot error is to have another trained and qualified person working with them (co-pilot). Chances of both of them making the same error at the same time are now 1 in a trillion.

Older aircraft also had a flight engineer. The autopilot is the 4th. External information sources (Much better now with satellites and GPS) form yet another line of defense.

Taking pitch control away from the pilots simply does not make sense. Instrument data and warning lights or sounds certainly do. Sensible engineers need to draw the line as to where the technology should be applied and to where it is not needed.


The 737 does already have switches that prevents manual electric trim from moving in the opposite direction of the yoke position, called the "column cutout switches". If the yoke is pulled back of neutral, you can only trim nose up, and vice versa. The switches actually make an audible click when you pass through neutral, you can hear this on some videos. This is what you have suggested.

To aid stall recovery, the 737NG and later automatically trims nose down during a stall. The issue is, as I understand it, because of European certification requirements, automatic trim ignores the column position switches. This is so that the nose-down trim is applied even if the pilot inappropriately continues to pulls the yoke back during a stall.

Therefore, you can see that this system is designed this way on purpose due to prevent an identified unsafe condition. Unfortunately, it causes a new serious failure mode. If the auto trim system fails and keeps trimming the nose down, then the instinctive action of pulling back does not function. The trim cutout switches, which disable the entire electric trim system, operate properly, but due to human factors or training issues, the crew failed to action this.

In aviation accidents it rarely is a simple cause, but the interaction of a lot of disparate factors, almost always with a human component.

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    $\begingroup$ +1. Also, the pilots do not need to look up a manual to know what these switches do. It's instilled in training. The problem is recognizing the trim runaway, which the crew before the fatal flight could do, but for whataver reason this crew could not. $\endgroup$ – Ben Jan 11 at 3:33
  • $\begingroup$ Even worse is the pilot can not immediately override the condition. The design assumes both pilot and co-pilot a) will not recognize stall warning b) will continue pulling back on yoke. I would respectfully suggest that the high tech belongs in sensor reliability and redundancy, but the pilots should be flying the plane. $\endgroup$ – Robert DiGiovanni Jan 11 at 19:15
  • $\begingroup$ Noted that "trim cutout switches disable the entire electric trim system". Now how can they trim the airplane? $\endgroup$ – Robert DiGiovanni Jan 11 at 19:25
  • $\begingroup$ @RobertDiGiovanni Cranking the manual trim wheels. $\endgroup$ – user71659 Jan 12 at 0:47
  • $\begingroup$ Taking some bruises for this one, but please think about what a pilot does. Get info from eyes, ears, instruments, and operates yoke, rudderpetals, throttle. Also reaction time to trim failure, deactivating it, regaining control of aircraft. Not good near ground. $\endgroup$ – Robert DiGiovanni Jan 12 at 0:59

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