Originally Posted by
flyingfalcon16
I posted this in the Ethopian thread but perhaps it is more suited to this thread:
Can I ask a question about MCAS?
It's my understanding applying nose down trim, will produce the effect of adding negative pitch attitude. So MCAS when activated is literally pushing the nose down. MCAS is sending nose down trim to bring the nose downward. Is this a completely correct statement from an engineering perspective? Is there any reason to think of MCAS another way? Does trim effect pitch attitude directly or is it providing column force so the pilot changes pitch? Would MCAS ever not be trying to bring the nose down? Is it inaccurate to say MCAS uses nose down trim commands to apply negative pitch attitude to the plane? In other words, does adding nose down trim add negative pitch attitude? Would MCAS ever be active adding trim in a scenario of high AoA and the plane has negative pitch attitude? Is MCAS literally part of the trim system?
Sorry about all the questions. I've been trying to understand this system and it seems to be described a few different ways.
from seattle times
If the final safety analysis document was updated in parts, it certainly still contained the 0.6 limit in some places and the update was not widely communicated within the FAA technical evaluation team.“None of the engineers were aware of a higher limit,” said a second current FAA engineer.The discrepancy over this number is magnified by another element in the System Safety Analysis: The limit of the system’s authority to move the tail applies each time MCAS is triggered. And it can be triggered multiple times, as it was on the Lion Air flight.One current FAA safety engineer said that every time the pilots on the Lion Air flight reset the switches on their control columns to pull the nose back up, MCAS would have kicked in again and “allowed new increments of 2.5 degrees.” “So once they pushed a couple of times, they were at full stop,” meaning at the full extent of the tail swivel, he said.Peter Lemme, a former Boeing flight controls engineer who is now an avionics and satellite-communications consultant, said that because MCAS reset each time it was used, “it effectively has unlimited authority.”