What is downwash?

Helicopter downwash and outwash refers to the downward and outward flow of air generated by a helicopter’s main rotor blades. In order to produce lift, the main rotor system accelerates air downward. When this air reaches the ground, it spreads out in all directions, creating strong and unpredictable winds at ground level. The closer a helicopter is to the surface and the heavier it is, the more intense the downwash becomes. For aircraft such as air ambulances, which often operate at low altitudes and land in confined places, downwash is always an operational consideration.

Unfortunately, downwash can pose several hazardous effects to third parties as well as the helicopter itself. It can lift and propel loose objects such as stones, dust, snow, vegetation, debris or unsecured equipment. Some debris (such as plastic sacks and washing) can pose a hazard, and damage, to the helicopter itself through re-ingestion into the main and tail rotors. Downwash can also knock people over, move doors, damage  fences and tents and create dust or snow clouds, compounding the hazard that downwash might create  to passing vehicles.

Downwash is more significant on departure when the aircraft is heavier, slower and producing more lift, so just because the aircraft landed with little noticeable downwash it does not mean that it will not generate more, and at far greater range, during its departure.

Our crews are experts at mitigating downwash They use careful site selection, approach planning, onboard technology and crew coordination to identify the safest place to land. Our paramedics are trained as Technical Crew Members (TCMs) to assist our pilots to manoeuvre in landing sites and monitor downwash hazards. You may see the aircraft circling whilst the crew discuss the effects of landing in a chosen site. This is called the ‘recce’ and it is a vital safety procedure.

Once on the ground, our crews secure loose equipment, keep people at a safe distance and offer advice to the public on  staying safe when they see a helicopter landing and departing. Through these and many other safety measures, our air ambulance crews can safely access patients, provide essential care, and airlift them safely to hospital.

For more information on safety when you see an air ambulance nearby, read our article on “What to do if you see an air ambulance hovering nearby”.