Have been using this aircraft for the past 12 months with no issues at all.

 

Today following take off I engage LNAV and VNAV,as usual,and then CMD autopilot.

 

However,I have difficulty in the Autopilot engaging and when it does VNAV disengages and when VNAV engages again the autopilot goes out again making the aircraft useless.

 

Could anyone throw any light as to the possible cause of this problem.

 

Many thanks.

 

Michael

Hi,

 

Do you have 'realistic autopilot engagement' engaged? (FMC > Menu > Simulation(?) )

This means the AP will not engage when your controls aren't centered (out of trim). That could be the first problem.

 

Does your CDU gives any message when you're trying to engage VNAV?

 

Richy