OPA-LOCKA, FL, USA
N95AF
SCHWEIZER 269C
THE HELICOPTER WAS INVOLVED IN A PREVIOUS ACCIDENT INVOLVING A TAIL ROTOR STRIKE. AS A RESULT, IN PART, THE 4 LANDING GEAR DAMPERS WERE SERVICED. THE HELICOPTER WAS REPAIRED, INSPECTED, AND SIGNED OFF FOR RETURN TO SERVICE. TESTS OF THE MAIN ROTOR TRACK AND BALANCE WERE PERFORMED WITH NO DISCREPANCIES NOTED. THE PILOT REPORTED THAT AS HE LANDED FROM A HOVER, THE HELICOPTER BEGAN TO OSCILLATE FORE AND AFT (APPARENT GROUND RESONANCE). AT THE TIME, FULL POWER WAS APPLIED AND THE COLLECTIVE CONTROL WAS DOWN. REPORTEDLY, THE PILOT DID NOT RAISE THE COLLECTIVE. SUBSEQUENTLY, THE LEFT SKID FAILED, AND THE HELICOPTER ROLLED ONTO ITS LEFT SIDE. THREE OF THE 4 LANDING GEAR DAMPERS WERE DETERMINED TO BE IMPROPERLY SERVICED. THE MAIN ROTOR BLADE DAMPERS WERE TESTED AND WERE FOUND TO BE FREE OF PREIMPACT FAILURE OR MALFUNCTION.
On October 6, 1993, about 1030 eastern daylight time, a Schweizer 269C, N95AF, registered to Helicopter Training Academy, Inc., was substantially damaged after touchdown during a maintenance test flight at the Opa-Locka Airport, Opa-Locka, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed. The commercial-rated pilot and one passenger were not injured. The flight originated about 5 minutes earlier. The pilot provided a written statement which indicates that the purpose of the flight was to track the main rotor blades. After landing from a hover, the helicopter began to oscillate fore and aft. At that time full power was applied and the collective control was down. The pilot did not raise the collective control and the helicopter rolled onto its left side. He further stated that there were no discrepancies found during the track and balance procedure. The pilot initially told an FAA inspector that the helicopter landed hard on the left skid but denied this when questioned. Review of FAA records revealed that the helicopter was substantially damaged in an accident on August 18, 1993, which was investigated by the NTSB. Review of the helicopter maintenance records revealed that the helicopter was repaired following the accident including, in part, servicing of the four landing gear dampners. Two mechanics each serviced two dampners; however, the records do not indicate which dampners by serial number were serviced by whom. The four landing gear dampners were removed from the helicopter and sent to the manufacturer for Load-Stroke testing which was performed in the presence of an FAA inspector. Load- Stroke testing of the four dampners revealed that the left front "exhibited a significant overcharged condition." The right front dampner was "slightly overcharged." The left rear dampner was determined to be serviced in the proper range, and the right rear dampner was serviced "slightly low." According to a warning listed in the Service Information section, improper pressure will deteriorate the damping capabilities of the landing gear dampners. These conditions may result in ground resonance and destruction of the helicopter. The main rotor blade dampners were also removed and sent to the manufacturer for examination in the presence of an FAA inspector. Examination of the dampners revealed no evidence of preimpact failure or malfunction.
IMPROPER SERVICING OF THREE OF THE FOUR MAIN LANDING GEAR DAMPERS BY COMPANY MAINTENANCE PERSONNEL, AND INNADEQUATE REMEDIAL ACTION BY THE PILOT AS GROUND RESONANCE BEGAN.
Source: NTSB Aviation Accident Database
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