Authorities continue to investigate the circumstances surrounding a helicopter crash in Houston on Sunday evening that killed four people on board and sparked a massive flame within sight of homes.

A helicopter that crashed into a Houston radio tower, killing all four people aboard and starting a fire below, was on an air tour flight at the time, authorities said.

Officials surveying the aftermath of a deadly helicopter crash in Houston on Sunday are looking into the possibility that the aircraft struck a radio tower because its warning lights were not working.