I want to know why it is that the auto-pilot is not capturing the localizer. The auto-pilot is engaged and I have the mode selected to NAV/LOC. The manual says that when the NAV/LOC is selected and the HDG switch is engaged, the HDG switch automatically switches off when the LOC is captured, but it is NOT doing that. When the LOC needle moves to the center, the HDG switch does not switch off. It just maintains the same heading rather than capturing the LOC. What is the problem?

Ken.