Black Hawk Battled Bad Altitude Data Before Washington Crash (4)

Safety investigators probing January’s midair collision between an American Airlines Group Inc. regional jet and a US Army Black Hawk near Washington found a key instrument on the helicopter was displaying inaccurate altitude data that could have led the pilots to think they were flying lower than they actually were.

The US National Transportation Safety Board on Wednesday kicked off a three-day hearing to pore over findings in its investigation into the crash, which killed 67 people in the worst US civil aviation disaster in decades.

“There is a possibility that what the crew saw was very different than what ...