The Federal Aviation Administration and New Jersey State Police are investigating the fatal plunge of a skydiver from Michigan who crashed near the Alexandria Field airport on Friday. State Troopers responded to a call for medical assistance around 2:30 p.m. at the airport, located in Alexandria Township in Hunterdon County. The skydiver, identified as Brandon M. Jackson, 37, of Troy, Michigan, was reported to be lying in a field near the airport runway when first responders arrived. He was pronounced dead at the scene, New Jersey State Police said. State Police did not release the name of the…