London's Air Ambulance flew in to Harlington yesterday (Thursday, July 10) to pick up a male patient with a head injury.
It landed at around 4.30pm in a field near Manor Lane where the man was transferred from an ambulance to the helicopter.
Eyewitness Christine Taylor said: "Police appeared to be entering a house at the end of the road on the corner nearest the fence.
"A white male taken away in the ambulance.
"Medical staff spent a long time with the man in the ambulance so the helicopter may have been in the field for as long as 45 minutes.
"The ambulance travelled down Sipson Lane with an escort of vehicles and entered the field so that the transfer could be made safely - otherwise the man would have needed to be passed through a gap in the fence and over a deep ditch."
A London Ambulance Service spokesman said: "We were called at around 2.40pm yesterday afternoon to an an address in Manor Lane, Harlington.
"We sent two responders by car, an ambulance crew, a duty officer and London's Air Ambulance to the scene. We treated a man reported to be in his 50s for a head injury. He was taken as a priority by air ambulance to the Royal London Hospital."
His condition is unknown.