I'm using the FMC LNAV , but when I tried to activate the VNA it wrote me:"UNABLE CRZ ALT"I typed my crz alt FL190.What is wrong.Can someone guide me step by step to use VNAV?Raam123

Mr Raam123,When programming a flight into the FMC, you have to do everything right to make it work correctly. To fill in the weights(masses) in the performance-menu is one of the initial and most important steps. If you enter too high numbers on the masses (especially ZFM), the FMS will "think" that the aircraft isn't able to climb as steep as it really could with its actual (and lower) mass. So, if the flight in question is on a short leg, perhaps FL190 is too high for the mass you entered in the Performance-menu of the FMC.My suggestion to you is to try lower flightlevels and especially read the FMS-manual.Good luck!/Bj

Sir- Please sign your posts with your real name in this forum, thank you. You are choosing a CRZ ALT that is too high for your particular flight plan. Try a lower atitude for CRZ.[h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-5/196432/winglets_lg.jpg