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19960703020029A

Accident · Substantial damage
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FAA accident report · Hiller OH23G · Marathon, FL · July 3, 1996

FAA Aviation Safety Information Portal

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Date
July 3, 1996 · 20:15 local
Place
Marathon, FL
Airport
Marathon Airport
Phase of flight
Pwr Off Vert Land/Autorotate
Operating rules
General operating rules (Part 91)
Damage
Substantial damage
Aircraft
N301CH
NTSB investigation
NTSBMIA96LA176
Reported as
Hiller OH23G
Reported engine
Franklin 6V335B
Fatal injuries
0
Pilot’s flight hours
5,961 total30 in this make and model

From the FAA’s Accident/Incident Data System (AIDS), through its Aviation Safety Information Portal, as reported. The NTSB investigates accidents separately, and its record of an accident is the fuller one. The aircraft is matched to the registry by N-number and event date, checked against the reported make and model; the registry’s history has gaps, so older matches can be wrong. Compare the reported make and model.

What happened

The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.

(.4)During a previous flight, the helicopter was reported to have excessive vertical vibration and to require excessive collective forces during flight. Mechanics worked on the main rotor blades to correct the problem, then the helicopter was flown on a maintenance test flight. During the test flight, the pilot noted that the vertical vibration had 'gone away,' but before landing, the vertical vibration returned. Shortly thereafter, the pilot heard a loud 'pop'. As he flared for landing, the blue main rotor blade separated and the helicopter crashed. Examination of the separated blade showed the wood in the area of the blade grip had failed, allowing the blade to separate. Evidence of a previous repair was present in this area, which lacked adequate adhesive between some of the mating surfaces. Also, an unapproved sealant had been used over the repaired area, and oil had contaminated the wood in this area. There was no evidence of dry rot in the failed area. The logbook records did not show the previous blade repair.

As the FAA filed it

(.4)DURING A PREVIOUS FLIGHT, THE HELICOPTER WAS REPORTED TO HAVE EXCESSIVE VERTICAL VIBRATION AND TO REQUIRE EXCESSIVE COLLECTIVE FORCES DURING FLIGHT. MECHANICS WORKED ON THE MAIN ROTOR BLADES TO CORRECT THE PROBLEM, THEN THE HELICOPTER WAS FLOWN ON A MAINTENANCE TEST FLIGHT. DURING THE TEST FLIGHT, THE PILOT NOTED THAT THE VERTICAL VIBRATION HAD 'GONE AWAY,' BUT BEFORE LANDING, THE VERTICAL VIBRATION RETURNED. SHORTLY THEREAFTER, THE PILOT HEARD A LOUD 'POP'. AS HE FLARED FOR LANDING, THE BLUE MAIN ROTOR BLADE SEPARATED AND THE HELICOPTER CRASHED. EXAMINATION OF THE SEPARATED BLADE SHOWED THE WOOD IN THE AREA OF THE BLADE GRIP HAD FAILED, ALLOWING THE BLADE TO SEPARATE. EVIDENCE OF A PREVIOUS REPAIR WAS PRESENT IN THIS AREA, WHICH LACKED ADEQUATE ADHESIVE BETWEEN SOME OF THE MATING SURFACES. ALSO, AN UNAPPROVED SEALANT HAD BEEN USED OVER THE REPAIRED AREA, AND OIL HAD CONTAMINATED THE WOOD IN THIS AREA. THERE WAS NO EVIDENCE OF DRY ROT IN THE FAILED AREA. THE LOGBOOK RECORDS DID NOT SHOW THE PREVIOUS BLADE REPAIR.

NTSB investigation

The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.

NTSB MIA96LA176Accident · Minor injuriesLimited investigationFinal reportMarathon, FLImproper repair of a previous crack in the blue main rotor blade by unknown persons; improper inspection of the main rotor blades by maintenance personnel, following a reported vibration problem; and subsequent failure of the main rotor blade, which resulted…Jul 4, 1996 · Substantial damage