I don't know anything about Boeing's argument. I also don't know anyone who's suggesting the accidents/incidents happened during takeoff. They happened during the climb out not during takeoff. Takeoff finishes when the wheels leave the ground. Both planes had a completely normal takeoff
However the MCAS was not designed for that purpose. It is designed to make a stall recovery possible when the pilots controls become less able to correct a stall situation. It is turned off during takeoff while the flaps are extended and only becomes operational after the flaps are retracted during the climb out after takeoff.
It was required because if the airspeed drops low enough to get near enough to the stall point the natural and trained reaction is to increase power to increase airspeed and in many other planes this is an uneventful procedure. However with the Max due to the position, size and power of the new engines so that they will pull the nose of the plane up when increasing power, if this were not countered this would make the stall worse as the normal control surfaces will not be sufficient to counter the effect. Thus the trim function had to be linked and MCAS adjusts the trim to counter the tendency for the engines to pull the nose up and put a recoverable stall into a catastrophic stall.
The tail trim can, and unfortunately did, override all the other control surfaces.
I would suggest watching the Mentor Pilot's video for an overview of the need for MCAS and the way it works. He exclusively talks about MCAS in flight and nothing about takeoff, that is where my assumptions come from.
Boeing quote on MCAS design and usage
Further readingto compensate for some unique aircraft handling characteristics during it’s (sic) Part 25 certification” and help pilots bring the nose down in the event the jet’s angle of attack drifted too high when flying manually, putting the aircraft at risk of stalling,
https://www.nytimes.com/2019/02/03/worl ... ule=inline
So when the flaps are down MCAS is disabled.According to Boeing, MCAS does not control the plane during normal flight but "improves the behavior of the airplane" during "non-normal" situations.
These could be steep turns or after takeoff when a plane is climbing with flaps up at speeds that are close to stall speed.
Read more at: https://phys.org/news/2019-03-ethiopian ... 1.html#jCp
One pilot's comment on flap retraction in 777s
This ties in with the problems happening after the flaps would have been retracted.Below is sample screen of a Boeing 777's Primary Flight Display. See those flaps marks on the speed tape?Here's the thing: you don't want to retract the flaps from 5 to 1 when you're slower than the stall speed at flaps 1. So in terms of flaps retraction schedule, you'll:
Accelerate to (at least) the minimum speed for flaps 5 in the takeoff roll.
Pitch up really high (e.g. 12.5 degrees)
Upon reaching acceleration altitude (a.k.a. flap retraction altitude), pitch down a bit (e.g. from 12.5 to 10 degrees) and let the aircraft accelerate.
When the speed passes the "1" mark on the speed tape, set flaps 1.
When the speed passes "up" on the speed tape, fully retract the flaps.
Acceleration altitude is usually 1,000 feet or 1,250 feet. So that really steep climb right after takeoff roll lasts only about 30 seconds.
Usage of flaps
Usually retracted by 3,000 feet
http://www.boeing.com/commercial/aeroma ... icle05.pdf