Sir - Although not always accepted by the flying establishment, the danger of the "down-wind-turn" phenomenon is accepted by pilots of light aircraft and gliders. The effect may be seen, as birds circle in windy conditions, when the rapid loss of height as the bird turns down-wind, becomes obvious.

The loss of the Edgeley Optica some years ago, when its slow-flying surveillance ability was being demonstrated, is an example. The wind speed with respect to the ground was significant compared with the upwind airspeed before the start of the turn. The phenomenon is related to the sum of the potential and kinetic energy and the wind speed is a vital component of the latter.

The phenomenon must apply equally to large commercial aircraft. How many low-level accidents attributed to pilot error would more properly be described as being caused by lack of essential data to enable the pilot to take corrective action before it was too late?

Commercial-aircraft builders, operators and statutory bodies have been approached with this theory and the outline of a means of forewarning the pilot of this potentially dangerous situation. The response has varied from full acceptance (in a few cases) through indifference and dismissiveness, to open derision - but not one negative response has contained a reasoned rejection of this simple theory.

Source: Flight International