<P> Essex & Herts Air Ambulance Trust (EHAAT) is a Charity Air Ambulance service providing a free, life - saving Helicopter Emergency Medical Service (HEMS) for the critically ill and injured of Essex, Hertfordshire and surrounding areas . It is not funded by the NHS--only by charitable donations . </P> <P> The charity aims to save lives, reduce or prevent disability or suffering from critical illness and injury, by delivering a first class pre-hospital emergency medical service . </P> <P> Since fundraising began in 1997, Essex & Herts Air Ambulance has flown over 20,000 missions--being deployed, on average, four to five times per day . The helicopters and Rapid Response Vehicles (RRVs) are based at Earls Colne Airfield and North Weald Airfield . </P> <P> It costs £ 6 million every year to cover all charitable costs and aircraft operations . </P>

Where is essex and herts air ambulance based