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Guest Diego Martinez

LVL Change

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Guest Diego Martinez

HI Folksjust a very quick question on LVL Change. I have been reading a lot on descent on this forum but I seem to have missed something.The question I have is at what V/S does the plane descend when you hit LVL Change. Is is always fix or does it follow certain guidelines and accomodates to follow speed restrictions or speed mode. In this last case I may miss an altitude restricion given by an ATC and need to revert to V/S command?ThksDiego

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As I understand it, under LVL Change the aircraft constantly adjusts V/S via pitch/attidude to maintain a certain speed (the speed which is insert in the speed/mach settings) and a certain power setting (N1).In opposite to climbing or decending with fixed V/S, when N1 is adjusted to maintain a given speed. Experts pleae confirm/correct me.Wolfgang

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Diego,No, its not a fixed VS and it does not follow any speed or altitude constraints in the FMC, It only follows speed and altitude set on the MCP. Look at the Flight Mode Annunciation (FMA) on just above the attitude display on the PFD. AT mode is on the left, ROLL mode is in the middle and the PITCH mode is on the right. When the LVL CHG button is selected, the PITCH mode will engage in MCP SPD during descent and hold whatever speed is set in the Mode Control Panel (MCP) speed window. Therefore whatever VS results will be dependent on this speed. The faster the MCP speed the greater the VS. The slower the MCP speed, the less VS. The AT mode will show ARM because LVL CHG is a idle thrust descent and uses pitch to maintain MCP speed.Floyd


John Floyd

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