Val
It could be programmed in such a way that it could make a series of climbs or a descents but not both (other than the final descent after the fuel runs out!!)
If the aircraft is flown in VNAV (vertical flight path) and is at say 37000 and a way point altitude of 6000 feet is entered at some point down line then the aircraft will descend to reach 6000 feet point in flight idle descent PROVIDED that 6000 has been entered in to the MCP altitude window, the reverse (climb) is true, but unless some one makes a further amendment to the MCP target it won't climb or descend again.
If you were at 37000 feet and selected 43000 at some point down line (even if this was above the aircrafts CRZ capability at that mass) and entered that in the MCP window, then the aircraft would attempt to make that climb, the speed would slowly decline until just above the min speed and VNAV would likely revert to level change with near zero rate of climb, it shouldn't stall, VNAV would not re engage without human input.
In other words it will not leave any FL or altitude in VNAV unless the MCP window is set to a different value, if the FMC constraint was FL100 and you selected 100ft in the MCP it would only descend to FL100, not 100 feet.
You could program multiple climbs or descents, but not both, so starting at 370 you could set WP 1 to 350, WP2 to 300, WP 3 to 270 and so on, BUT the MCP would have to equal the lowest programmed value for it to achieve that, ditto the reverse in the climb, so stepped climbs or descents are of course possible (creating the illusion that someone is in control?) but not up and down without someone in control !!
This flight went where (ever?) it did because someone made it so, not a Li on battery fire or cockpit 02 fire.
The and only saving grace in this event (from an industry point of view) is that it wasn't a dream liner, that could well have resulted in a fleet wide grounding, even if not justified by the facts, but after the previous battery problems one could understand why
Last edited by LNIDA; 5th May 2014 at 14:47.
Reason: after thought