why are we talking about modes of autopilot to change altitudes?
Because, as my fiirst post on this subject states:
https://au.news.yahoo.com/thewest/a/...-interference/
The disappearance of Malaysia Airlines Flight MH370 could have only involved human input, according to two aviation experts.
A senior Boeing 777 captain and a former crash investigator agreed that given the information outlined in the preliminary report issued late last week, "human input was essential" for the MH370 to end its flight in the Indian Ocean.
The objective is to prove or disprove that human intervention was only essential for a short period after the first loss of contact. If proven, the vast majority of the flight,
including any decreasing level changes, could have been entirely automatically flown, despite all souls on board being dead.
Other possibilities might then follow, but, if so, we should leave those until later, to avoid confused logic (sadly, all too easily generated on PPRuNe).