Traffic Alert and Collision Avoidance Systems (TCAS)

Traffic Alert and Collision Avoidance Systems (TCAS): This tech detects when two aircraft are about to converge and gives pilots a warning. The alerts are limited at low altitudes, though, to prevent risky maneuvers. That’s why it couldn’t help the jetliner and military helicopter in last week’s crash in Washington, D.C., which killed 67 people (paywall link). The jet and copter were flying somewhere between 200 feet and 400 feet above surface level. So sad.