The findings were revealed during the first day of National Transportation Safety Board hearings on the crash, which killed 67 people, including several skaters at the Skating Club of Boston

Horrific, newly released video shows the moment a passenger jet and a US Army Black Hawk helicopter collided in Washington, DC, early this year, as it was revealed that the chopper was receiving incorrect altitude readings in the seconds before the worst US air disaster in more than two decades.

It showed how the helicopter flew above the 200 feet (61 metres) altitude limit on the helicopter route along the Potomac River before colliding with the plane. Investigators said the flight data recorder showed the helicopter was actually 80 to 100 feet higher than the barometric altimeter the pilots relied upon showed they were flying.