From a deleted question: by @ffejrekaburb
From an email from the author of the SeattleTimes article, Dominic Gates:
The description of MCAS provided by Boeing for regulators (FAA and foreign) during certification, is this:
MCAS “was added to address potential nose-up pitching moment at high angles of attack at high airspeeds outside the normal flight envelope.”
Elsewhere in the documents, it’s made clear that MCAS was expected to kick in when a MAX approached a “wind-up turn,” which is essentially a banked downward spiral. Of course a commercial jet would never in normal flight do such a maneuver. But in flight tests for certification, the test pilots are required to show that the plane can approach that and not lose lift on one wing and flip over.
Can you post that answer for me?
An article from the SeattleTimes published in March makes mention of a high speed stall. The SeatlleTimes article linked to in OP mentions that in a wind-up turn:
Pilots who pull back forcefully on the column — sometimes called the stick — might suddenly feel a slackening of resistance.
The lack of smooth feel was caused by the jet’s tendency to pitch up, influenced by shock waves that form over the wing at high speeds and the extra lift surface provided by the (engine) pods...
This indeed points to a stick-force-per-g test, as @Jimmy mentions in a comment. Since the B737 has a fully irreversible hydraulically actuated flight control system, with an artificial feel that is proportional to dynamic pressure but not to load factor, the obvious mechanism for "lack of smooth force feel" would be having to release the column to some extent due to extra nose-up moment that the aircraft generates.
It is very plausible that the added lifting surfaces from the engine pods create a larger pitch-up moment than the 737NG has in the same circumstances. I'm not really sure how the supercritical airflow over the MAX wing differs from that of the NG to create extra pitch-up.
All of that is the original limited cure for the stick-force-per-g tests. If this was the only thing that needed to be fixed, all would probably have remained well. But the second article also mentions:
The flight-test pilots had found another problem: The same lack of smooth stick forces was also occurring in certain low-speed flight conditions. To cover that issue too, engineers decided to expand the scope and power of MCAS.
As you can see, the SeattleTimes is my source of information as well...there is no additional information on what were the "certain low-speed flight conditions".