I have noticed that the attitude hold in the apache will constantly shift to pitch up or down. For example, I can trim my heli for perfectly level flight turn on att hold, and watch my heli slowly pitch forward or backward until it crashes. With alt hold on it slowly speeds up/down. I had the alt hold on, and was cruising for about 10 mins hands-off. I turned on the attitude hold and about 3 minutes later the aircraft could no longer maintain altitude for the nose position.