A flag test is a stop test required to be performed once a year by the FRA. It may be by fusee or by flag. The time of day (or night) is what determines which is used. The test is done to see if the Engineer is both paying attention and if he has the ability to stop his train. If he passes the flag he loses his engineer license on the spot. The same penalty is applied if the train passes a red signal even by one foot. There have been Amtrak passengers who sat in the middle of nowhere because the crew got pulled and there was no new crew or the crew had to be bussed from miles away. JP