Is it any related to the cause of the plane crash, i.e., magnetic interference?

What would have Desmond done originally if the flashes hadn't given him so specific a mission?

If Charlie was supposed to die why did he appear in Desmond's Vision where he was holding a parachute with them trying to rescue the person hanging from the tree ?

If Charlie had died would it have been Penny hanging from the line and not her?

What is the proper puzzle Desmond is supposed to complete. Is he preventing it by continuing to save Charlie's life?

__________________
Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for
you. Always. I love you, Pen

DESMOND: I love you, Penny. I've always loved you. I'm so sorry. I love you!
PENNY: I love you too.
DESMOND: I don't know where I am, but--
PENNY: I'll find you, Des--
DESMOND: --I promise--
PENNY: --no matter what--
DESMOND: --I'll come back to you--
PENNY: --I won't give up--
BOTH: I promise. I love you.