On May 1, 1999, a Glaser-dirks DG-400 (registration N400FJ) was involved in an aviation accident near New Milford, CT. Investigators recorded the probable cause as: The manufacturer's use of inadequate adhesive material which resulted in the de-bonding and subsequent failure of the wing spar pin-lock assembly. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A glider broke up in flight after a loud bang and left wing displacement; examination revealed adhesive bond failure between the spar pin-lock assembly and fiberglass skin.
Incident Overview
During a flight at an indicated airspeed of 60 knots, the pilot of a glider heard a loud bang and the gear warning alarm activated. Looking to the left, the pilot observed the left wing displaced approximately 20 degrees upward from its normal position. The glider subsequently began to descend, and control inputs by the pilot were unresponsive. As the glider's speed increased during the descent, the pilot elected to egress from the glider. The glider then broke apart in flight and descended to the ground.
Examination Findings
A piece of the glider's fiberglass skin was recovered and examined. The interior surface of the skin contained a residue of an adhesive. This adhesive area would have attached the spar pin-lock assembly, which secured the wing spar pins. The surface of the epoxy layer on the skin featured impression marks similar to a cross-weave pattern found on the surface of fiberglass. The cross-weave pattern on the epoxy surface was consistent with a fracture that traveled between the UD-glass fabric tape and the epoxy layer. This separation was characterized as an adhesive separation. Additionally, the epoxy layer surface contained exposed voids; no bonding between the epoxy and UD-glass fabric tape was observed in the void areas.
Summary
The investigation found that the in-flight wing displacement and subsequent breakup were associated with a failure of the adhesive bond that secured the spar pin-lock assembly to the fiberglass skin.
