A person filming an air ambulance taking off was seriously injured after the gusts knocked her over, a report has revealed.

The woman was blown off her feet while videoing the helicopter outside her house in Southend-on-Sea in Essex on 28 February.

She was 30m (98ft) away and a hedgerow had blocked the pilot's view of her, the Air Accidents Investigation Branch (AAIB) found.

Essex & Herts Air Ambulance, which operated the aircraft, issued pilots with a reminder of the hazards associated with "downwash" after the incident.

The helicopter was taking off from a field next to London Southend Airport's car park at 18:08 GMT, having been just responded to a medical emergency.

The woman, who lived opposite the field in Southend Road, went outside to film its departure after hearing the engines switching on.

"About 50 seconds after the helicopter commenced its vertical climb, the observer that was outside her house was blown over by the helicopter's downwash and was seriously injured," the AAIB report read.

"Her relative quickly came to her aid and the injured person was subsequently taken to hospital."

The AAIB said other people had gathered to watch the take-off, but they were not affected.

The 47-year-old pilot, who had almost 4,000 flight hours, flew off unaware that anyone had been injured and later landed at North Weald Airfield.

Essex & Herts Air Ambulance was told what had happened four days later by the woman's relative.

When quizzed, the commander said he had not seen her but considered her distance to have been a safe one in hindsight.

The AAIB decided not to take any action against the air ambulance charity.

Investigators concluded: "The speed of the downwash may have been greater due to the funnel effect when it was affected by nearby buildings and a car."

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