NEW YORK — Federal regulators, spurred by a deadly helicopter crash into a river, ordered a temporary nationwide ban on open-door flights that have tight seat restraints that could trap people during emergencies. The Federal Aviation Administration on Friday grounded the flights amid concerns that harnesses meant to kept passengers from tumbling out of their seats wound up preventing them from escaping when a helicopter plunged into the chilly East River on Sunday. The pilot got out, but all five passengers died. The parents of a man killed in the crash, 26-year-old Trevor Cadigan, called the helicopter’s harnesses a “death trap” in a lawsuit.