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 maneuver might have taken the helicopter out of the direct path of a passenger jet as it was trying to land at Reagan Airport on Jan. 29.

A National Transportation Safety Board hearing revealed that the U.S. Army was aware of altitude discrepancies on Black Hawk helicopters.