Hello, 

I was on approach to EPKK ILS 25 when I was established on the localiser I pressed the approach mode button. But when I did that the thrust randomly increased and the plane didn't descend. I pressed it when the glideslope diamond was centred in the middle. When do I press the APP button. What position does the pink diamond on the PFD need to be at when I press the APP button. 

Thanks

3 hours ago, Zaakit said:

When do I press the APP button.

Unless you have specific reasons not to, press it when you are currently pressing LOC. LOC is needed to capture LOC only, and is a mode used in a case in which you want to capture the LOC only.

...but in this case don't ask yourself "well when would I want to jump straight to APP?" Ask yourself "do I have any reason not to use APP?"

 

I'm guessing you use VNAV 99% of the time instead of using V/S, for example. Why? Likely because you're answering the latter type of question with "I have no reason not to."

3 hours ago, Zaakit said:

What position does the pink diamond on the PFD need to be at when I press the APP button.

You ideally want to be below the path, so anywhere above the middle line.