Wake turbulence Cpl. Mario ŠAFÁRIK University of defence 22-3LP-ŘLP 04/04/2014

Dictionary Angle of attack – úhel náběhu Clean configuration - external equipment is retracted to minimize drag (flaps, landing gear retracted) To curl – vinout se Most severe – nejvážnější, nejvíc kritický Path of least resistance – cesta nejmenšího odporu Upwind – proti větru, po návětrné straně Vortex (pl. -texes/-tices) – vír Wake – the region of recirculating flow immediately behind a moving or stationary solid body, caused by the flow of surrounding fluid around the body = úplav Wingspan – rozpětí křídel 2

What is Wake Turbulence? During flight : o Lowest air pressure - above the wing o Highest air pressure - below the wing Air tends to flow towards the area of lower pressure -> air below the wing will try to flow upwards The fuselage blocks the flow - path of least resistance = towards the wingtips 3

What is Wake Turbulence? The vortex o produced always when the airplane is creating lift o usually not visible ! The largest wake is produced when the angle of attack is highest (aircraft is heavy or slow) 4

Vortex behavior The vortex of the aircraft trails behind the aircraft. The vortex will normally move downward at rates of ft/min. The vortex travels with the wind and stops 500 – 900 ft below the aircraft. From larger aircraft, the speed of the air inside the core can be up to 100 m/s Wake vortices can persist for three minutes (or longer, exceptionally) 5

Effects of Wake Turbulence The most dangerous situation is for small aircraft to fly directly into wake of a larger aircraft Greatest hazard – induced roll and yaw Aircrafts with short wingspan are most affected by wake turbulence Mildest form – slight rocking of wings Most severe form – complete loss of control of the aircraft 6

Intensity Strongest vortices produced by heavy aircraft flying slowly in a clean configuration at high angles of attack Considerable vortices also generated by manoeuvring aircraft (e.g. aerobatics) Aircraft with smaller wingspans generate more intense vortices than aircraft with equivalent weights and longer wingspans Helicopter wakes may be significantly stronger than those from fixed-wing aircraft of similar weight – they are strongest while operating at lower speeds (20 – 50 kts) 7

Wake Turbulence Category (WTC) For the purpose of assessing wake turbulence separation, aircraft are divided into the following categories by their Maximum Certificated Takeoff Weight (MCTOW): H (Heavy) aircraft types of kg ( lb) or more; M (Medium) aircraft types less than kg ( lb) and more than kg ( lb); L (Light) aircraft types of kg ( lb) or less. Super Heavy for Airbus A380 with a maximum take-off mass in the order of kg. 8

Wake turbulence avoidance The best way to avoid the wake of a preceding aircraft is to stay well behind and above the wake. 9

Wake turbulence avoidance 10

Summary Wake turbulence affects aircraft of all sizes and therefore all pilots (and ATCs) need to be aware of it. 11

Sources turbulence-after-the-first-lady%E2%80%99s-go-around- incident/ turbulence-after-the-first-lady%E2%80%99s-go-around- incident/ _Category _Category pdf pdf

Takeoff Strong wake turbulence will occur from the rotation point and during the climb as the preceding aircraft is flying slowly at a high angle of attack (also present right up until the touchdown point of a landing aircraft) During takeoff, plan to liftoff before the rotation point of the preceding aircraft(stay upwind of the touchdown point of the landing aircraft) If not possible, separation standards (Table 1,2,3) are used 13

Climb After takeoff; if you cannot out-climb the preceding aircraft’s flight path, turn off the extended centreline as soon as possible. If you cannot deviate significantly from the preceding aircraft’s flight path, track slightly upwind and parallel its course. 14

Crossing Avoid headings that cause you to cross behind and below a preceding aircraft. If you must cross behind, cross above its flight path, and if you can’t do that and with terrain permitting, cross at least 1000 feet below. Following Head On Stay either on or above the preceding aircraft’s flight path. If that is not possible, use one of the methods above; either stay slightly upwind and parallel its course or with terrain permitting, stay at least 1000 feet below and well behind. If approaching a heavier aircraft that is less than 1000 feet above you, alter course to the upwind side to avoid the wake turbulence. 15

Approach Most wake turbulence accidents occur in visual meteorological conditions. When flying a visual approach, do not assume the aircraft you are following is on the same or lower flight path. If practicable stay away from the localizer centreline, the larger aircraft are likely to be following it, offset your flight path slightly to the upwind side. VFR pilots of slower light aircraft need to be especially wary of wake turbulence when landing at busy aerodromes with heavier aircraft on the approach. 16

Landing Land well before a departing aircraft’s rotation point. When landing behind another aircraft stay above its flight path and if possible, land beyond its landing point. Research has identified that wake vortices in ground effect do not necessarily move laterally away from the runway, but can rebound after reaching the ground, to the height of twice the wingspan of the aircraft. Be wary of this possibility when passing over the previous aircraft’s landing point. 17

Crossing Runways When landing behind another aircraft on a crossing runway aim to avoid their wake by either landing over the portion affecting your runway, or by landing well before it. 18

Crosswinds Crosswinds may affect the position of wake vortices and can be very dangerous during parallel runway operations. Adjust takeoff and landing points accordingly. 19