DANGER  of  VORTEX WAKE

One of the most dangerous things for aircraft especially in the take off and landing phase is Vortex Wake. Vortex Wake is caused when a wing creates lift. The pressure on the top of the wing is lower than the pressure underneath. The air on the top of the wing flows inwards and the air on the underside of the wing flows outwards. This causes a mass of rotating air behind the aircraft.. The bigger the aircraft the bigger the wing the bigger the Vortex Wake. Then add to that the need for the bigger the distance between aircraft landing and the bigger the time delay between aircraft taking off. If a light aircraft follows a big jet this could present a danger problem. Air Traffic Controller's will allow for this when positioning aircraft for landing. This can be a problem if an aircraft is landing on a cross runway. A pilot may have to abandon an approach. The area below and out to a 1000ft behind an aircraft should be avoided. the wake starts at the rotation point and ends at the touchdown point. Pilots of light aircraft if possible should therefore touchdown further down the runway if it is safe to do so or rotate earlier in the take off and climb or descend above the wake area of the aircraft in front. The wake will move with a crosswind near the ground. This should also be considered.

For working out wake categories aircraft are graded as follows.

UK Maximum Take off Weight.

If an aircraft taking off is a heavy then all other aircraft groups must have a two minute take off delay.  The final approach separation time interval is between 2 or 4 minutes. This is equal to a distance between 3 and 8 miles. ICAO standards are different from the UK ones. These figures are based on the UK.

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