The Black Hawk that collided with an American Airlines jet in January may not have had accurate altitude readings, investigators said.

The National Transportation Safety Board is examining "bad data" the crew of an Army Black Hawk helicopter may have relied upon prior to their deadly crash with a passenger jet outside Washington D.C.

A Black Hawk helicopter crew may not have heard key instructions from air traffic control before it struck an American Airlines jet near Washington DC a fortnight ago, according to black box data.

National Transportation Safety Board officials said Friday that a key transmission from Reagan National Airport’s air traffic control tower may not have been heard by Army Black Hawk helicopter pilots just before they were collided with an American Airlines regional jet last month,