Pilots and flight attendants are aware of risks, but commercial aviation tragedies have been infrequent in the U.S. for years.

It has been nearly a week since a commercial jetliner and an Army helicopter collided in midair near Washington’s Ronald Reagan National Airport, killing 67 people in the deadliest U.S. air disaster since 2001. Even as salvage crews continue to haul the wreckage out of the Potomac River, investigators are seeking answers about what happened.

Salvage crews have recovered the bodies of all 67 people killed when a passenger plane and a US Army helicopter collided near Washington and plunged into the Potomac River, officials said Tuesday. All but one of the bodies have been identified,