A partial loss of engine power shortly after takeoff for reasons that could not be determined because postaccident examination did not reveal any anomalies that would have precluded normal operation and the pilot’s failure to maintain airplane control during the unsuccessful attempt to return for landing on the airport. Contributing to the accident was the pilot’s decision to conduct his second takeoff using less than the full runway length available and the airline’s lack of guidance regarding how to respond to engine failures at low altitudes.