Other mistake: When the plane takes off in Alex's vision, the plane begins to go into a nosedive, and the entire left fuselage is blown apart, sucking many people out of the plane. The plane then explodes completely, but in reality, the plane just takes off, and explodes almost instantly afterwards. No struggling with the plane is shown in reality, nor is the plane going into a nosedive. This is also proven in FD5, which is a prequel. The jet engine explodes, leaving a flaming tail, and the plane spinning out of control. The plane just simply "explodes" without any signs of struggle.M0vi3
Other mistake: When Carter is basically trying to kill himself with the remaining "survivors" in his car, Billy makes a comment saying that when he saw Alex leaving Mrs. Lewton's place, Alex's shoe prints were in her blood and his prints were on the knife. All good and fine but there's just one thing that doesn't make much sense. Her house blew up right after he ran out, so could anyone still pull off any prints from the knife that killed her, and see footprints by her body? Wouldn't that evidence be gone in the explosion?