In terms of the Overhead Contact System (OCS) mechanism of failure, the OCS wire failed as a result of necking, which was not detected in scheduled OCS inspections. In addition, post-incident inspections of the Green Line indicate necking at eight other locations of the Green Line. Also, the current inspection regime does not identify Cupric Oxide as a precursor to necking. As a result, the RAIU make the following safety recommendation:
Recommendation
Transdev, along with S2M, should conduct a full review of their inspection processes for Overhead Contact System (OCS) wires to ensure pre-cursors, likely location and faults with the OCS are referenced.