WASHINGTON, Jan 30 (Reuters) - The National Security

Transportation Board will leave no stone unturned as it probes

the fatal collision of a regional jet and an army helicopter,

NTSB Chair Jennifer Homendy told a press conference on Thursday.

Homendy said the agency had almost 50 people on the scene.

She said she was not able to give initial details of why the jet

crashed with a U.S. Army helicopter at a Washington airport late

on Wednesday, killing 67 people.