Preliminary data from the deadliest U.S. aviation accident in nearly 25 years showed conflicting readings about the altitudes of an airliner and Army helicopter when they collided near Reagan National Airport in Washington, killing everyone aboard both aircraft, investigators said Saturday. Investigators also said that about a second before impact, the jet’s flight recorder showed a change in its pitch. Data from the jet’s flight recorder showed its altitude as 325 feet (99 meters), plus or minus 25 feet (7.6 meters), when the crash happened Wednesday night, National Transportation Safety Board officials told reporters.