What caused Delta Air Lines Boeing 717 landing incident?

A preliminary report into an incident in which a Delta Air Lines Boeing 717 was substantially damaged while landing without its nosewheel gear extended has attributed a cause According to the National Transportation Safety Board (NTSB), flight DL1092, operated by N955AT (c/n 55017), was descending through 2,000ft on approach to Charlotte/Douglas in North Carolina from Atlanta/Hartsfield in Georgia at around 0900hrs on June 28 when the “nosewheel unsafe condition light” illuminated in the cockpit after the gear handle was lowered