I don't know what I have installed recently cause I keep on adding stuff (I mean quite a bit) everyday. However, since the day before yesterday, I have to press Clt-E to start the engines whereas previously the planes started with engines running on the runway.

Anybody know what happened and how to fix it?

I suspect you changed your default flight. You can always change it back or create a new one. Set up the flight exactly how you want it - aircraft, airport, gate or runway, engine running, weather etc. Then click Flights > Save Flight on the menu bar. Give your flight a suitable name & tick the box to make it the default flight before saving it.

Oops. Sorry Sean.