Pilot Debrief

MCDONNELL DOUGLAS HELICOPTER 500N near Santa Monica, CA — 2014-04-18

Final reportWPR14LA253
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Date
2014-04-18
Location
Santa Monica, CA, USA
Airport
SMO
Aircraft
MCDONNELL DOUGLAS HELICOPTER 500N
Registration
N522GS
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Landing

Probable cause

The fracture of the right aft landing gear strut due to undetected fatigue cracking in an inboard rivet hole.

NTSB narrative

The private pilot/owner of the helicopter was conducting a local personal flight. The pilot reported that, upon landing, he slowly sat the helicopter down on a landing pad and then felt it "drastically" slip to the right. He then lifted the helicopter off the pad, at which time a passenger verified that the right aft landing gear strut was broken. A passenger reported that, upon touchdown, he heard a "loud pop." The Federal Aviation Administration (FAA) had previously issued an airworthiness directive (AD) applicable to the accident helicopter make and model to detect cracks that could result in the failure of the strut and subsequent loss of helicopter control during landing. The AD required modifications to the landing gear strut rivet holes and fairings and subsequent initial dye penetrant inspections followed by continuing 10x magnified visual inspections at intervals not to exceed every 100 hours time in service or during each annual inspection. According to the FAA, the AD was complied with at an airframe total time of 2,248.3 hours. At the time of the accident, the total airframe time was 2,274 hours. Examination of the right aft landing gear strut revealed that it had fractured due to undetected fatigue cracking in an inboard rivet hole. The fatigue cracks were very small, and given their size, they likely would not have been detectible by the existing required visual inspections. The cracks initiated after the rivet hole diameter was increased; therefore, they initiated after the initial penetrant inspection. Although it is possible that the fatigue cracks were the result of a degradation in material properties or, more likely, due to greater loads from a previous hard landing or normal landing on primarily the right skid, the investigation was not able to determine the origin of the fatigue cracks based on the available information.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Performing thorough inspections as per AD requirements could have prevented strut failure.

NTSB coding

Evidence available

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

Docket documents7

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