Following several recent incidents involving dislodged in-pavement airport runway light fixtures, a comprehensive engineering assessment was performed in order to mitigate future light fixture issues. The engineering assessment consisted of an immediate root cause evaluation, followed by phases that addressed both short-term and long-term corrective actions.
Root cause analysis of the incident light fixtures revealed the bolts affixing the fixtures to the light bases fractured due to fatigue under cyclic loading. To determine the contributing factors to the fatigue failures (e.g., aircraft loading, installation requirements, maintenance practices) further evaluation included a sampling program to ascertain the current state of in-service light fixtures, finite element analysis of light fixture loading scenarios, light fixture bolt torque testing, and data acquisition of instrumented runway light fixture assemblies.
The primary findings from the ongoing assessment indicate aircraft loading, light fixture installation, and maintenance all play a role in the mechanical performance of the fixture assemblies. Current light fixture bolt torqueing (pre-loading) practices are not sufficient to withstand larger, modern aircraft loading, and bolt pre-load levels should be increased. In addition, design and use of the light fixtures should take into account the finding that the fixture assemblies and pavement act as a system when reacting to aircraft loading, such that light fixtures sustain cyclic loading even without direct aircraft contact. LPI’s Julia Grogan presented these findings at the 2015 Technology Meeting of the Illuminating Engineering Society Aviation Lighting Committee.
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