Originally Posted by
vihai
Cosa intendi con "cutout della barra"? Intendi i trim switch switch o i cutout (sul pedestal)?
Perché a me risulta che i cutout propriamente detti disattivano anche l'azione dell'MCAS, no?
Da quel che ho capito, entrambi disattivano l’azione dell’ MCAS; il cut-out switch lo fa in maniera permanente, il trim elettrico solo momentaneamente quando utilizzato e fino a 5’ dal rilascio ...
È presente un interruttore nella barra che se mossa in senso opposto al trim, a quest'ultimo viene disattivato il trim elettrico. L'MCAS però bypassa questo interruttore perché deve buttare il muso giù.
Per quanto riguarda MCAS vs Trim runaway, qui i dettagli:
The early design of MCAS allowed a maximum stabilizer movement of 0.6°, but it was later revised and extended to 2.5°. Boeing reasoned that unintended MCAS activation due to erroneous AOA input was able to be managed by using elevator alone, electric stabilizer trim or by stabilizer trim cutout switches. During manual flight, stabilizer manual electric trim is normally used to offload control column forces during mis-trim conditions. Without the awareness of the MCAS function, the flight crew would possibly recognize an MCAS activation as Speed Trim System (STS) input. MCAS behaves differently than the STS, it moves the horizontal stabilizer at a faster rate.
Following an erroneous MCAS activation, insufficient manual electric trim inputs result in the stabilizer not fully returning to its original trimmed position and gradually moving the stabilizer to greater mis-trim.
Any out of trim condition which is not properly corrected would lead the flight crew into a situation that makes it more difficult for them to maintain desired attitude of the aircraft. The flight crews in both the accident flight and the previous flight had difficulty maintaining flight path during repetitive MCAS activations.
Per Boeing, stabilizer trim cutouts switches were available but not required to counter MCAS activations. The only procedure that directs selecting the stabilizer cutout switches is the Runaway Stabilizer non-normal checklist (NNC). This NNS is used to stop un-commanded stabilizer trim wheel movement, which would stop MCAS-commanded stabilizer trim movement.
However,erroneous MCAS activation does not look like a typical stabilizer runaway, which is continuous un-commanded (runaway) movement of the stabilizer. During the accident flight, the stabilizer movement was not continuous; the MCAS commands were bounded by the MCAS authority (up to 2.5°); the pilots were able to counter the nose-down movement using opposing manual electric trim inputs; and after the pilots released the manual electric input and MCAS was reset, there was not another MCAS command for 5 seconds.
To incorporate MCAS, the basic column cutout function had to be inhibited during the MCAS activation. Pulling back on the column normally interrupts any electric stabilizer aircraft nose-down command, but for the MAX with MCAS operating, that control column cutout function is disabled.
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