Pilot Debrief

SCHWEIZER 269C-1 near Allentown, PA — 2014-06-17

Final reportERA14LA293
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Date
2014-06-17
Location
Allentown, PA, USA
Airport
ABE
Aircraft
SCHWEIZER 269C-1
Registration
N152CC
Category
Helicopter
Highest injury
Minor
Fatalities
0
Phase of flight
Landing

Probable cause

Inadequate inspection and maintenance of the helicopter’s landing gear dampers, which resulted in ground resonance during helicopter shutdown.

NTSB narrative

The student pilot landed the helicopter after a 40-minute flight and started the engine shut down procedures. She stated that she applied the collective friction and started the timer, running the engine at 2,500 rpm for a cool-down period. She turned off the fuel boost pump and radios and referred to the checklist to ensure she had completed the proper items. She then engaged the collective friction and was tightening the cyclic friction at the cyclic base when the helicopter developed ground resonance. The student pilot could not get the helicopter airborne with the collective friction engaged, so she rolled the throttle to idle. The resonance continued to increase and, "in a matter of seconds, the helicopter shook itself apart." The helicopter had four poppet-type, nitrogen-charged hydraulic units (dampers) in the landing gear assembly to reduce landing shock and help prevent ground resonance. The four dampers were removed from the helicopter and pressure tested; all four failed to meet manufacturer's specifications. Without the airframe protection provided by the dampers, oscillations occurred that resulted in the helicopter rocking on its landing gear and the tailboom twisting toward the right side of the helicopter where it joined the main structure. Maintenance instructions noted that the landing gear dampers would experience a decrease in pressure with helicopter usage and required that they be extension-checked during each 100-hour inspection or every 6 months, whichever occurred first. The helicopter's most recent 100-hour inspection occurred about 2 months before the accident, and it had been operated 58 hours since the inspection. Review of maintenance records for the most recent 100-hour inspection and about 800 flight hours before the accident revealed no mention of any maintenance actions involving the dampers.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Inspection of landing gear dampers prior to flight could have prevented ground resonance.

NTSB coding

Evidence available

  • Photos
  • 11 docket documents
View NTSB final reportView NTSB docket

Docket documents11

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