Hi everyoneI am new to forum and am asking for help with a problem.I have installed the 'Queen' but have not been able to activate the VNAV.VNAV will not arm or activate following loading of FMC nor will it arm or activate during flight.LNAV is not a problem.When I try and arm VNAV it lists a message 'unable Cruz alt' and this occurs at any altitude set for cruise alt.What am I doing wrong?Peter MurfittNew Zealand

Peter,Have you set a higher altitude in the MCP window than what you are cruising at? In other words have you given it something to aim at? And is your Autopilot actually on?Gerry

Hi GerryThanks for your reply.Yes autopilot is on and an example would be that the initial MCP altitude set for FL10,000 with steps to FL31,000.I have also tried with MCP set to FL31,000.Tried setting at lower altitudes with still the same results, no arm or activation of VNAV. Autopilot is on. Flight plan executed. no problems at any other point that I am aware of.Peter

Did you turn on the F/D switch?Jeff p

If the SID you select has an at or above altitude constraint, the FMC will often give you the unable next altitude message. But, you should still get VNAV after clearing the message. In these cases, I have found that I can use LVL CHG once accelerated to the flaps up speed, the plane will always easily exceed the constraint and the pesky FMC is finally happy so I go back to VNAV for rest of climb.If it's not the SID, then I would suspect your preflight is not complete... not sure what, but something is missing.Edit: Sorry, just re-read that you get unable cruise... different problem. A max load may not make it to 31000, try 29000.

Thanks for the feedback.Yes FD is on AP is on MCP set and V2+10.Have tried different Flight plans, databased stored company route and have followed the FMC to load to the letter.I feel that there is something I am missing and not completing the required information but I can not figure out what that may be.Peter