On October 11, 2012, about 1330 eastern daylight time, a Diamond DA-42 Twinstar, N607PA, was substantially damaged following a hard landing at Flagler County Airport (XFL), Palm Coast, Florida. The designated pilot examiner (DPE) and private pilot were uninjured. The airplane was registered to and operated by Phoenix East Aviation under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed and no flight plan was filed. The flight departed from Daytona Beach International Airport (DAB), Daytona Beach, Florida at 1000. According to the DPE and the pilot, the purpose of the flight was to complete a multi-engine check ride. During an approach, the pilot was instructed to demonstrate a short field landing. While on short final, the pilot reduced power and slowed the airspeed. As the airplane crossed the runway threshold, the airplane descended rapidly and landed hard on the runway. Both pilots reported no flight control anomalies or mechanical malfunctions that would have precluded normal operation. A post-accident examination by a Federal Aviation Administration inspector revealed that the composite wing spar fractured at the fuselage bulkhead. A review of the Phoenix East Aviation's training manual revealed that the procedures for short-field approach to landing required the pilot to obtain 82 knots indicated airspeed (KIAS). A review of the Diamond Aircraft normal operating procedures revealed that the minimum airspeed with flaps applied for landing is 84 KIAS. There is not a published short field landing procedure in the Diamond Aircraft DA-42 operations manual. During the approach to land the DPE stated that the airspeed was approximately between 75-80 KIAS and indicated 67 knots before touchdown.