Wake Turbulence Flashcards
Wake turbulence
● molecules from the high pressure region are able to go around the wing tips into the low pressure region and some trail off
● When seen from behind the aircraft, the left wing tip vortex turns clockwise and the right wing tip vortex turns counterclockwise.
● Both travel downwards, and both are partly responsible for induced drag
Identify the Dangers
● Wake turbulence is created whenever an aircraft is creating lift.
● It is most pronounced when we have an aircraft that is heavy, clean, (gear and flaps up) and slow.
● Another factor is air density.
○ Dense air will create more severe vortices.
○ That is to say, cold air creates more violent vortices.
● Vortices sink at 400 to 500 feet per minute and weaken as they descend
● Once within about 200 feet of the ground, vortices will move outward at about 5 knots
● Vortices drift with the wind and can be moved into touchdown zones as well as linger over the runway for quite some time. Crosswind can blow the vortices onto the runway
Avoidance techniques departures
● If possible, plan to rotate and climb out above the previous departing aircraft.
➢ After an overshooting aircraft, wait a couple of minutes to allow the turbulence to dissipate.
Arrival
➢ Plan an approach above that of the preceding aircraft and beyond its touchdown point
Separation Minima – Non Radar Departure
● Controllers will apply a 2 minute separation interval to any aircraft that takes off into the wake of a known heavy aircraft if
➢ The aircraft takes off from same runway.
➢ parallel runway that is less than 2 500 feet away
● NOTE: ATC does not apply this 2 minute spacing interval between a light following a medium aircraft, but will issue wake turbulence advisories to light aircraft
● Controllers will apply a 3 minute separation interval to any aircraft that takes off into the wake of a known heavy aircraft, or a light aircraft that takes off into the wake of a known medium aircraft if
➢ The following aircraft starts its takeoff roll from an intersection or from a point further along the runway than the preceding aircraft.
➢ The controller has reason to believe that the following aircraft will require more runway length for takeoff than the preceding aircraft
● ATC will also apply separation intervals of up to 3 minutes when the projected flight paths of any following aircraft will cross that of a preceding heavy aircraft
Pilot waivers
● Tower controllers are required to advise pilots whenever a takeoff clearance is denied solely because of wake turbulence requirements.
● The intention of this advisory is to make pilots aware of the reason for the clearance denial so that they may consider waiving the wake turbulence requirement.
● Pilots are reminded that there are some circumstances where wake turbulence separation cannot be waived
● Although controllers are not permitted to initiate waivers to wake turbulence separation minima, they will issue takeoff clearance to pilots who have waived, with the following exceptions:
➢ A light or medium aircraft taking off behind a heavy aircraft and takeoff is started from an intersection or a point significantly further along the runway, in the direction of takeoff.
➢ A light or medium aircraft departing after a heavy aircraft takes off or makes a low or missed approach in the same or opposite direction on the same runway
➢ Controllers are responsible for ensuring wake turbulence minima are met for IFR departures
Size of Wake Turbulence
● The vortex covers an area about 2 wingspans in width and 1 wingspan in depth.
● The vortices of a large heavy aircraft tend to settle below and behind the airplane at about 400 to 500 feet per minute.
● Within about 2 minutes they tend to level off at about 1 000 feet below the aircraft’s flight path.
● Vortices can trail the generating aircraft by 10 to 16 nm, depending on its speed
● The strength of a vortex remains relatively constant during the first 2 minutes and can last up to 5 minutes.
● They tend to break up more quickly with atmospheric turbulence and in calm conditions they last longer
