Yeah. once your radars cover every large body of land, you will be able to spot anything that gets close. Generally i found that every once in a while a stupid UFO will get close to a base and you can damage it enough to kill it or allow your fighters to finish the job.
I wait until the UFO is near my base, then I launch multiple interceptors with long range weapons. That normally brings down even the biggest alien UFO, and it can be done on any difficulty level (cuz planes are cheaper lateron)
I am not happy with the helicopters, I think they arent as good as the planes...
My problem is that if so many aliens can survive getting shot down why can't PHALANX soldiers survive? Its kinda weird
Maybe cuz the UFOs are better structure and stuff, and can survive a crash impact more readily. But I agree insofar, that I think a 100% kill rate when a PHALANX plane crashes is a bit too much. A slight luck factor could be involved too to rescue a few soldiers maybe. After all they are supposed to have great equip, great stamina etc... and ... well 100% just seems too much