The failure of inspectors to spot defective motor supports led to a subway derailment in Philadelphia last year that killed four people and injured 158, the National Transportation Safety Board says.

The Southeastern Pennsylvania Transportation Authority, or SEPTA, had an inadequate inspection and maintenance program, the board said in a report adopted after a hearing on the crash Wednesday.The subway car derailed at 8:21 a.m. on March 7, 1990. The motor under the third car of the six-car train had dropped and dragged along tracks. SEPTA said the motor support equipment failed.