Hi there everyone,I'm having some trouble with the PMDG 747-400The problem seems to be that whenever I fly out from any airport, with the FMC correctly programmed and the VNAV and LNAV active, at some time during the flight, I will hear this horrible grinding noise and the VNAV switch deactivates and the FLCHG activates.Also during this occurrance, sometimes I can no longer activate the VNAV unless I reset the flight.I know it is an unusual problem and I can't quite put my finger on what is causing it.Please help!

I'm sorry to hear of your problem and am unable to help. Maybe try the PMDG forum (if you haven't already) as there may be more 'qualified' people there who can help. I'm not trying to be sarcastic, just helpful and friendly :-)Best regards!

That grinding noise sounds to me like the stick shaker which means you're stalling eg going too slow in climb. I think you need to set up your FMC properly and run through a tutorial to see what you're doing wrong. It's usually the silliest of things we overlook.