Seven people died and nearly two dozen more were injured when a medical jet crashed in northeast Philadelphia on Friday night.

The plane had been on a medical transportation mission to Mexico, carrying a child patient, her mother and four crew members.

Fatal crashes of commercial aircraft in the U.S. have become a rarity. The deadliest recent crash was in 2009 near Buffalo, N.Y. All 45 passengers and the four crew members were killed when the Bombardier DHC-8 propeller plane crashed into a house. One person on the ground also was killed.