On the plane issue: the producers of Lost went to a used plane lot and bought the plane used on the show. So if they can buy an old plane and stage a crash scene on a beach that looks believable, why can't a super powerful shady organization have an old plane at their disposal and sink it deep deep deep into the ocean?

And you can't eject from a helicopter, that would send you up into the blades and they move around quite fast I am told You jump down from the chopper, like Ashton Kutcher in 'The Guardian'. It makes more sense to me that she jumped from high up (considering her gear) from a plane and steered herself to the island.

When Michael was leaving the island he was given specific coordinates or directions or whatever. Like you can only get to/leave or SEE the island from a certain angle, like a rainbow