Pop quiz: When must you file an alternate? Thats an easy one, we all know the rule about needing 2000-3 one hour before and after the ETA. Next question: When do you file an alternate? Probably the most common answer is, I always file an alternate. Fair enough, its never a bad idea. Now, regulations aside, why do you file an alternate? Naturally the response is: In the event the weathers gone down too low at the destination and we need somewhere else to go. Right up there is an unexpected loss of equipment or a navaid required for an approach. And while the regs are also designed to provide a backup for lost communications, this often serves as a distant third, cause these days were just not all that worried about that.