Factual error: In Sam's premonition, when Isaac is still in the bus when it is falling down to the water, he is at the front of the bus. In reality the falling force should be pushing him to the back of the bus.
Factual error: Olivia's death starts with her laser eye surgery going wrong. Why did she only have one doctor with her, and then he left her alone? In any sort of surgery, especially ones with expensive machinery she wouldn't have been left on her own, nor would the doctor be working on his own.
Answer: To answer your second question, Sam's death is not like any other death's from the first final destination movie. If you are talking about Alex, he was hit by a falling brick off-screen. To answer your first question, near the end, Peter though that Candice had deserved to live more then Molly, and attempts to kill her. Sam kills Peter before he has a chance to stab molly. The gun dropped by peter lands on the stove, and shoots off in the air. This is a sign that Sam saved Molly from dying, thus, putting her on Death's list, and making it all right to kill her on Flight 180.
This is in response to the answer. Your answer is dismissive to the nuance of premonition as depicted by the movie. This is extremely crucial: Premonition, as visioned by every protagonist, is the event that would have happened if the protagonist didn't intervene. Every events in premonition is supposed to be absolutely true. As such, in the premonition, Sam saves Molly. This means if the events weren't intervened by Sam, he would still have saved Molly, while the rest (Sam, Candice, Peter) would have died anyway. So Molly should be safe all along. It wouldn't even be wrong to say that 'death' hadn't even planned to kill Molly at the bridge. So your point about Molly being next in the list because Sam killed peter and death skipping Sam now to go on Molly isn't even valid. So if Molly was clean in death's perspectives all along, why did she die at the end? (because she didn't cheat the design, she wasn't even supposed to be in the list of death's order; as I mentioned earlier, it was never the intention of death to kill Molly as evidenced by the saving of Molly in Sam's premonition).
How did we see Sam and Molly on flight 180 if it's final destination 5.
But Molly didn't die in his vision so she wasn't on the list to begin with so how can he skip someone's death that's not on the list and he kill his friend so why did he still die on the plane with Molly?.