Air Force officials are still trying to determine why a JDAM bomb killed three American soldiers and several Afghan allies. While two possibilities (incorrect position coordinates entered, jammed fins on the guidance system) have been discussed, there are two others. Dropping a GPS-guided bomb into a deep valley can result in the weapon passing out of sight of GPS satellites, which causes the guidance system to stop trying to correct its impact point. The other possibility is that the weapon was aimed for a target high on a mountain, but that the elevation was not correctly calculated. When the bomb reached the three-dimensional coordinates for its target, there was nothing there but empty space and the guidance system froze. The bomb would then have continued its ballistic path and might have gone thousands of feet down the side of the mountain before impacting on the ground.--Stephen V Cole