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When the wind blows against the direction in which the aircraft moves it is called headwind.
In aerodynamics, flying against the wind at a certain speed is equivallent to flying in calm air at an increased airspeed and reduced groundspeed.
Impact on Operations
Headwinds impact all phases of the flight:
- During take off and landing, headwind increases the airflow, hence the necessary lift is achieved earlier and at lower speeds (the wind speed is added to the aircraft speed). As a result, less runway is required to perform a safe take off or landing. Therefore, headwind is more favourable for these phases of the flight.
- A climb or descent in headwind conditions results in an increase of the gradient (i.e. the level change over the distance travelled) even though the rate of climb or descent (i.e. the level change over time) remains the same. As a result, aircraft reach their cleared levels earlier compared to the calm wind scenario.
- In the cruise phase, having headwind means increased fuel burn (due to the increased drag) and increased flight time (due to the reduction in groundspeed). Operators try to avoid flying in headwind conditions whenever practicable by e.g. choosing an alternative route (which can be a bit longer but with less or no headwind) or choosing a different (normally lower) cruising level if the predicted windspeed is more favourable.
While headwinds are beneficial during the take off and the landing phase, underestimating them during the cruise can lead to increased fuel consumption which may e.g. lead to the need to divert or reduce the available holding time. In extreme cases, fuel exhaustion may occur resulting in forced landing or ditching.
Accidents and Incidents
This section contains examples of occurrences where strong headwinds were considered a contributor.
- WW24, vicinity Norfolk Island South Pacific, 2009 (On 18 November 2009, an IAI Westwind on a medevac mission failed to make a planned night landing at Norfolk Island in unanticipated adverse weather and was intentionally ditched offshore because of insufficient fuel to reach the nearest alternate. The fuselage broke in two on water contact but all six occupants escaped from the rapidly sinking wreckage and were eventually rescued. The Investigation initially completed in 2012 was reopened after concerns about its conduct and a new Final Report in 2017 confirmed that the direct cause was flawed crew decision-making but also highlighted ineffective regulatory oversight and inadequate Operator procedures.)