The Super Constellation was approaching Manhattan runway 21 (VFR) with flaps at 100% and an airspeed of 120 knots. At a height of 170 feet agl the right wing dropped and the aircraft yawed right. Power was added to all four engines, but the plane didn’t recover and struck the ground 546 feet short of the runway. The Constellation struck a 3,5 feet high ridge of earth, shearing off the nose- and right main gear legs. It appeared that the no. 3 prop was in reverse pitch angle on impact; the threaded brake cage locking bolts were missing from the propeller and the cage was backed off 3 full threads from the normal setting. This excessive brake clearance thus obtained rendered the brake propeller control function incapable if normal operations. PROBABLE CAUSE: “The in-flight reversal of the no. 3 propeller due to a propeller power unit malfunction, resulting from improper maintenance practices and inspection procedures.”