I have recently started to work on ILS landings, and have come across a problem. I have set everything up right with Nav1 frequency in my radio stack and have activated the NAV hold and the plane lines up with the runway fine. However once the plane is lined up and I press the APP hold button, the plane does nothing. The ALT hold button does not switch off like it should. What could be the problem? I activate the APP hold while still below the GS.
I'm using a B737-800 if that makes a difference.
Thanks for your help.