Complex sentence: Crew resource management formally began with a National Transportation Safety Board (NTSB) recommendation made during their investigation of the United Airlines Flight 173 crash, in which a DC-8 crew ran out of fuel over Portland, Oregon while troubleshooting a landing gear problem.
Split into simpler sentences: Crew resource management formally began with a National Transportation Safety Board (NTSB) recommendation made during their investigation of the United Airlines Flight 173 crash. There a DC-8 crew ran out of fuel over Portland, Oregon while troubleshooting a landing gear problem.