Former air traffic controller Michele Robson suggests the instructions from the air traffic tower could have been clearer, especially considering there was another plane, an Airbus A319, in the helicopter's line of sight.
At 8.47pm, with the plane at 600ft and preparing to cross over the river, an air traffic controller contacted the helicopter's pilot to tell them to pass behind the plane.
Asked if the plane was aware there was a helicopter in the area, Mr Duffy replied: "I would say the helicopter was aware that there was a plane in the area.".
Andrew Nicholson, chief executive of aviation security firm Osprey Flight Solutions, told Sky News that Black Hawk helicopters are typically very capable of avoiding obstacles in the sky, though a number of things could have gone wrong to cause the crash.
"In the dark in a city environment with lots of lights, and at that distance, I don't think the helicopter would have been able to tell what type [of plane] the Airbus was that far away, so may have just assumed.
