Simultaneous death is a problem of inheritance which occurs when two people, at least one of whom is entitled to part or all of the other’s estate on their death (usually a husband and wife) die at the same time. This is usually the result of an accident, but in some cases may occur as a result of homicide (such as the families aboard the airplanes used in the September 11, 2001 terrorist attacks). Under the common law, if there was any evidence whatsoever that one party had survived the other, even by a few moments, then the estates would be distributed in that order, though the decedents could write (or have written) a clause in the will that requires their property to be distributed as though each had predeceased the other.
In order to alleviate problems of proving simultaneous death, many states in the United States have enacted the Uniform Simultaneous Death Act, which provides that each spouse will be treated as though they predeceased the other if they die within 120 hours of one another.
Some wills now include Titanic clauses (named for the RMS Titanic, which caused many simultaneous deaths among testators and executors). These clauses lay out explicit instructions for dealing with simultaneous death.