Flight Sequence
A certified flight instructor (CFI) and a student pilot were conducting a training flight at Homestead General Airport. According to the CFI, after departure the flight proceeded to the airport where the lesson was to include "running landing" and "running takeoff" maneuvers previously practiced. The flight entered the traffic pattern for runway 36. On short final approach, at approximately 5 feet above ground level (AGL) and 25 knots indicated airspeed, the helicopter contacted the runway with its skids parallel to the centerline. The CFI allowed the helicopter to slide along the runway.
Subsequently, the CFI announced the lesson would conclude with a running takeoff. As the helicopter lifted off at 35 knots indicated airspeed, the CFI detected a vibration from the main rotor system. Rotor rpm began decreasing, and he touched down again on the runway, after which the helicopter began to shake violently. The CFI recognized the phenomenon as ground resonance. He noted insufficient main rotor rpm to lift off and stabilize the vibrating rotor system. He lowered the collective but felt a force opposing his reduction of throttle input, which he attributed to the student pilot applying throttle. At that point, the CFI was struck in the head, lost consciousness, and later regained it in the hospital.
The student pilot told a Federal Aviation Administration (FAA) inspector that during the approach, when the helicopter was approximately 30 feet AGL before the running landing, the CFI took control. While the helicopter was sliding on the runway, the CFI began screaming and froze on the controls. The student pilot then braced for impact.
Post-Accident Examination
Following recovery, the landing gear and main rotor dampers were removed for examination at the manufacturer's facility under FAA oversight. Inspection of the main rotor blade dampers revealed all three exhibited damage consistent with lead-lag motions encountered in ground resonance. Examination of the four landing gear dampers, which had been installed at manufacture, showed all tested out of limits for charge pressure, being low.
Maintenance Background
The helicopter had last undergone a 100-Hour inspection on August 11, 2003, and had accumulated 87.9 hours since that inspection at the time of the incident. Review of the 100-Hour inspection guide indicated that landing gear dampers are required to be inspected for operation and condition, and for damper extension with a full fuel tank. Section 12 of the Basic Handbook of Maintenance Instructions manual notes that landing gear dampers experience a decrease in pressure with subsequent use, and they should be extension checked during a 100-Hour inspection, or every six months, whichever occurs first.
Additionally, a memorandum from the Director of Flight Training to all flight instructors, dated August 25, 2003, prohibited the demonstration and practice of running landings within the Dominican Republic Flight Training Program until further notice.