Versuche mal auf FL380 zu steigen, also auf der CRZ-Page im FMC FL380 auswählen, danach im MCP FL380 auswählen und dann versuch mal, VNAV zu aktivieren:
Zitat1- Cruise Altitude: The cruise altitude entered on the PERF INIT page is displayed here. To change the cruise altitude, enter an altitude into the scratchpad followed by pressing the 1L LSK. Valid entries for altitude are XXX, XXXX, XXXXX, and FLXXX. The altitude is displayed in feet when below the TRANS ALT and as flight levels when above. Changes to the cruise altitude on this page are carried over to all other pages that display CRZ ALT.
After reaching the cruise altitude in VNAV, all enroute changes in altitude prior to the T/D are initiated by changing the cruise altitude on the CRZ page. Type the new cruise altitude into the scratchpad and press the 1L LSK to change the CRZ ALT. Then, select the new target altitude on the AFDS MCP. This initiates a VNAV cruise climb or descent to the new altitude. If both altitudes (FMC and MCP) are not changed, VNAV continues in cruise at the previously programmed altitude.