Helicopter crew in collision with plane may not have heard key instruction from tower, NTSB says
Investigators say the crew of the helicopter that collided midair with an American Airlines jet near Washington D.
NTSB: Night vision goggles, altitude readings may have contributed to deadly Potomac crash
NBC News' Erin McLaughlin summarizes key takeaways from Friday's briefing by the National Transportation Safety Board regarding last month's deadly plane crash over the Potomac River.