Pilot Debrief

SCHEMPP-HIRTH DISCUS CS near Woodstock, VA — 2022-10-08

Final reportERA23LA013
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Date
2022-10-08
Location
Woodstock, VA, USA
Airport
VG55
Aircraft
SCHEMPP-HIRTH DISCUS CS
Registration
N520RJ
Category
Glider
Highest injury
None
Fatalities
0

Probable cause

Improper repair of a crack by maintenance personnel, which resulted in a subsequent failure of the glider canopy.

NTSB narrative

The pilot reported that the glider was at 3,700 ft mean sea level when the canopy suddenly, without warning, separated from the glider. He subsequently landed uneventfully at his intended destination airport. Review of maintenance records revealed that about 2 years before the accident, a maintenance facility stop-drilled a hole to correct a canopy crack at the rear hinge along the glide frame. Metallurgical examination revealed that the drilled hole appeared to halt progression of the original crack along its initial propagation direction. However, both the new primary separation crack and a secondary crack propagated from the hole in diametrically opposite directions, which suggests they likely developed due to a stress state along the same plane. Additionally, both cracks propagated from internal surface corners of the hole, indicating the corners likely acted as stress risers that facilitated crack initiation. There was no approved method from the glider manufacturer to stop-drill a hole in plexiglass; however, manufacturer approval was not required as the glider was registered in the experimental category. The glider manufacturer stated that it was common practice for cracks in the plexiglass to be drilled-out to stop the crack progression as a temporary solution; however, for a proper repair, the canopy must be removed and re-glued. The presence of multiple cracks propagating out of the same stress riser of the internal hole corner indicated that the specific hole drilled did not prevent subsequent progression of further cracking and the eventual separation of the canopy.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Proper repair of the canopy should have been performed instead of temporary drilling.

NTSB coding

Evidence available

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

Docket documents7

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