MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

[Takwis]

From the Lemme article,

Stabilizer trim is susceptible to runaway without MCAS as a factor. Boeing has provided measures to limit the stabilizer mistrim in a runaway to ensure that the elevator remains effective.

The aft column cutout and the forward column cutout are switches that automatically stop the stabilizer from trimming in opposition to the column.

If the stabilizer is running away by trimming the airplane nose down, the pilot flying will respond with aft column travel to command sufficient airplane nose up elevator to exactly offset the stabilizer mistrim.

At the point the aft column cutout is reached, the stabilizer trimming is stopped, to which the level of mistrim is now prescribed by the rigging of the aft column cutout switch. If the switch is rigged at 50% travel, then the pilot still has the remaining 50% of travel available. It does not matter what type of runaway, when the pilot responds with column travel, the trim will stop with the same level of mistrim.

Boeing assumed that a pilot will take one second to recognize the runaway malfunction (by noting the nose starting to drop), and then three seconds to respond to the malfunction, which in this case is by pulling back on the column sufficiently to trip the aft column cutout.
. . .

The aft column cutout switch performs two functions.

1. Stop the stabilizer from running away
2. Limiting the level of mistrim to preserve elevator effectiveness.

Boeing has used the aft and forward column cutout switches starting with the 707 and then including 727, 737, 747, 757, and 767. In all those airplanes, over all those years, the column cutout switches performed exactly as designed.

What Lemme does NOT mention (unless I have missed it somehow), nor does anyone else mention (that I have seen), is that the MAX FRM still tells the pilots reading it that the control column switches still function exactly like they did in the 737NG, and the Classics, and the -200s, all the way back to the 707.

But it they don’t. The pilots have been (are still being) lied to.

Control column actuated stabilizer trim cutout switches stop operation of the main electric and autopilot trim when the control column movement opposes trim direction.