Authorities are combing the Potomac River for a second day in search of victims and more clues behind the deadliest U.S. air crash in over 20 years.

A commercial plane with 60 passengers and four crew members on board collided with a military helicopter with a crew of three near Washington, D.C., on Wednesday night.

The Wall Street Journal examined flight route and elevation data to show the moments before American Airlines Flight 5342 ...