Investigators testifying at a hearing into the January's mid-air crash in Washington DC suggest faulty altitude data may have led to a miscalculation.

The head of the National Transportation Safety Board sharply criticized U.S. officials for failing to act before the January 29 collision of a U.S. Army helicopter with an American Airlines regional jet in Washington that killed 67 people.

The pilots of a Black Hawk helicopter that collided with a passenger jet near Washington Reagan National Airport in January likely didn’t know how high they were flying or how close they were to an airliner before the deadly crash,