The plane used for this flight was a DeHavilland DH-114 Heron B2 airplane, registry #N554PR. Eighteen passengers and a crew of two were on board on the fateful day.
As the plane first approached Ponce's airport, the pilots decided to abort their first attempt at landing. The crew did not give the tower of control any explanations as to why they took that decision; as a matter of a fact, no reason for them to do that was ever found. During their second attempt at landing, the pilot over-rotated, causing the plane to crash, killing three passengers and both people in the cockpit.
FAA and NTSB investigators concluded that the crash of Prinair flight 191 was simply a case of pilot's error.