PHILADELPHIA − Four people injured when an air ambulance plummeted into a neighborhood here last week remained hospitalized Monday, and the investigation into the tragedy remains "fluid and active," Mayor Cherelle Parker said.

Some have suggested that it stems from Hussenot's device, because it used film and "ran continuously in a light-tight box, hence the name 'black box,'" according to Airbus, which noted that orange was the box's chosen color from the beginning to make it easy to find.

Sixty-seven people died in a collision between a Bombardier CRJ700 regional jet operated by PSA Airlines and a military Black Hawk helicopter.