The pilot reported that he had made a good approach, but had flared high. The aircraft landed heavily on the mainwheels then nosewheel. Buckling of the firewall and undersurface of the fuselage was discovered after the aircraft had been shut down in the parking area. Prior to the accident, the pilot had occasional difficulties in the landing phase. The airspeed indicator was found to be overreading by five knots at threshold speeds. This reduced the margin above the aircraft stall and is likely to have increased the pilot`s handling difficulties.
