Approach Switch

[Tomcat61]

Hi all, I am having probs with the Approach switch on my 737.
I am on full AP, and about 10nm from the runway, I have ILS frequency set, and I am established with the ILS, I then hit Approach, but nothing happens, it either strays way off course, or it won't lower altitude, which by the way is held at around 3000ft.
Should I disengage Alt Hold before hitting Approach?
Or should Approach switch that off automatically?
Thanks again....Tomcat61

[zcottovision]

Have you made sure the NAV/GPS switch is set to NAV?

[microlight]

I'm assuming that:
- you have the autopilot and probably the autothrottle engaged.
- you're approaching the ILS heading using the 'HDG' hold and the 'ALT' hold, which are both engaged.
- you clicked the 'approach' switch after you picked up the localizer and the glideslope.

Under these conditions, the autopilot should turn off the 'hdg' and 'alt' switches, and pick up the localizer and glideslope. If you are doing multiple approaches sequentially on the same saved flight, the AP plays tricks with the 'approach' function, so it's best to start each new flight from scratch, if you want the 'approach' function to work properly.

Hope this helps.