The army helicopter that crashed into a passenger jet over Washington DC was flying too high, investigators have concluded.

An investigative hearing into a deadly mid-air collision of a US Army helicopter and a passenger plane that killed 67 people in Washington has revealed a discrepancy in the chopper's altitude displays.

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.