Basics For Air Traffic Control - Wake Turbulence PDF

BASICS FOR AIR TRAFFIC CONTROL – WAKE TURBULENCE INTRODUCTION As noise is the by-product of thrust, wake turbulence is the by-product of lift. Additionally, wake turbulence is invisible to the eye. To effectively provide wake turbulence separation, you must first understand wake turbulence and it...

BASICS FOR AIR TRAFFIC CONTROL – WAKE TURBULENCE INTRODUCTION As noise is the by-product of thrust, wake turbulence is the by-product of lift. Additionally, wake turbulence is invisible to the eye. To effectively provide wake turbulence separation, you must first understand wake turbulence and its causes and effects. The purpose of this module is to identify wake turbulence and associated characteristics, and explain the effects wake turbulence has on Air Traffic Control (ATC). WAKE TURBULENCE Purpose: This lesson explains the components and basic characteristics of wake turbulence. Objectives: Define wake turbulence Identify factors affecting wake turbulence intensity Describe wingtip vortices Identify hazards associated with an induced roll Describe helicopter downwash and vortices Identify the impact of wake turbulence on Air Traffic Control (ATC) References for this lesson are as follows: FAA Order JO 7110.65, Air Traffic Control FAA-H-8083-25, Pilot’s Handbook of Aeronautical Knowledge Aeronautical Information Manual (AIM) BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 1 Wake Turbulence Wake turbulence is a phenomenon resulting from the passage of an aircraft through the atmosphere. The term includes vortices, thrust stream turbulence, jet blast, jet wash, propeller wash, and rotor wash both on the ground and in the air. Vortices Vortices are circular patterns of air created by the movement of an airfoil through the air when generating lift. Vortices are a by-product of wing lift and are the most predominant factor contributing to aircraft wake turbulence As an airfoil moves through the atmosphere in sustained flight, an area of low pressure is created above it The air flowing from the high pressure area to the low pressure area around and about the tips of the airfoil tends to roll up into two rapidly rotating vortices, cylindrical in shape The vortices from large, heavy, and/or super aircraft can be extremely high velocity and hazardous to smaller aircraft Factors Affecting Wake Turbulence Intensity Vortex Strength The strength of a vortex (rotational force) is governed by three factors: Weight of the generating aircraft Shape of the wing (wing configuration) This determines wing loading, or how many pounds per square foot the wing is required to support Speed of the generating aircraft The greatest vortex strength is generated when the aircraft is heavy, clean, and slow. Some of the most intense vortices have been recorded at rotation speeds exceeding 300 feet per second (174 knots (kts)). BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 2 The strength of these vortices will diminish with time and distance. Note: The term “clean” refers to an aircraft’s configuration when it has its gear up, no flaps extended, or any other type of wing extensions; e.g., air brakes. Weight The weight of the aircraft is by far the greatest factor that affects the intensity of wake turbulence. Proportionately, the intensity and strength of the wake turbulence increase with the weight of the aircraft A heavier aircraft wing needs to support more weight, which results in greater wake turbulence Every airplane and helicopter generates wake turbulence in flight regardless of its size. Examples Shape of Wing and Configuration The intensity of the vortex can be changed when the flaps are extended. Clean configuration Dirty configuration A clean configured wing allows for a stronger vortex A dirty configuration wing increases the total wing to be generated because, without flaps, the wing has area and decreases the wing loading. The flaps also a smaller area and wing loading is therefore greater disrupt the airflow over the wing and break down the per square foot. formation of the vortex. BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 3 Speed The slower the speed, the greater the chance for the At higher speeds, the air flow over the wingtips is wake to take form. spread out and does not have as much of an opportunity to take form. This is especially critical for aircraft on approach to an airport A good example of this would be aircraft flying en route at flight levels Aircraft at Slower Speed (On Approach) Aircraft at Higher Speed (en route at Flight Levels) Knowledge Check A REVIEW what you have learned so far about wake turbulence and facts that affect wake turbulence. ANSWER the questions listed below. The greatest wake turbulence is associated with which aircraft configuration? (Select the correct answer.)  Heavy, clean, fast  Heavy, dirty, slow  Heavy, clean, slow Assuming similar aircraft, which aircraft would create a greater wake turbulence effect? (Select the correct answer.)  Aircraft cruising en route  Aircraft on approach to the airport  Aircraft on takeoff from airport Which one of these has the greatest impact on wake turbulence? (Select the correct answer.)  Speed  Weight  Configuration BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 4 Wingtip Vortices Lift is generated by the creation of pressure differential over the wing surface. Lowest pressure above the wing Highest pressure below the wing Pressure differential triggers a rollup of airflow. This results in a swirling air mass off of the wingtips trailing behind the aircraft This is often known as ‘wake vortex’ or ‘wingtip vortices’ Vortex Circulation When viewing aircraft from behind, vortex circulation off the wingtip is counterclockwise off right wing, clockwise off left wing. Both vortices will drift outward. Vortex Behavior and Generation Because vortices have certain behavioral characteristics, pilots can: Visualize the wake location Take precautions to avoid it Vortices are generated at the moment the aircraft Vortices discontinue at the moment the aircraft stops generates lift. generating lift. Normally, this is when the nose wheel leaves Normally, this is when all landing gear has touched ground down BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 5 Vortex Sink Rate Vortices from larger aircraft: Sink several hundred feet per minute, Slowly move outward from their track approximately 300 to 500 feet per minute Diminish in strength with time Normally level off 500 to 1,000 feet below the flight path Sink Rate = 300 to 500 Feet Per Minute Under certain conditions, vortices may descend at a slower rate or may even climb slightly. A temperature inversion may slow the descent Light updrafts may cause the vortices to climb Note: You will be taught wake turbulence separation in the next stage of training. Separation is now based on time and/or distance. Vortex Movement at the Ground with No Wind When close to the ground and there is zero wind, vortices from larger aircraft will move laterally. Note: Vortices move outward, away from the body of the aircraft because lift forms first at the root of the wing and then develops toward the wingtip. The associated vortices created as a result of this lift also move in the same 6 manner and continue moving outward after spilling over the tips of the wings. BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE Vortex Movement at the Ground with Crosswinds Crosswinds of 1 to 5 knots will decrease or stall the movement of one vortex while increasing the movement of another vortex. This increase could hasten the vortex arrival to another parallel runway. Ground Effect with a Tailwind Tailwinds can move vortices into the landing zones of aircraft that were originally trying to avoid the wake. Pilots and controllers should be aware of the presence of larger aircraft upwind from the approach or takeoff paths of smaller aircraft. BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 7  Knowledge Check B REVIEW what you have learned so far about wake turbulence and facts that affect wake turbulence. ANSWER the questions listed below. What is/are the name(s) given to the circular patterns created by wake turbulence? (Select all correct answers that apply.)  Wake vortex  Crosswinds  Wingtip vortices When do vortices begin for a fixed-wing aircraft? (Select the correct answer.)  During approach while landing  As soon as engines have begun  At rotation or when lift begins When observing an aircraft from behind, the circulation of vortices off the right wingtip is __________ and __________ off the left wingtip. (Select the correct answer.)  Counterclockwise, clockwise  Clockwise, counterclockwise  Down, outward Vortices from larger aircraft will sink approximately 300 to 500 feet per minute and level off approximately __________ feet below the flight path. (Select the correct answer.)  100 to 300  500 to 1000  1000 to 2000 With no wind, vortices within 100 to 200 feet of the ground will move ____________knots laterally across the ground. (Select the correct answer.)  10 to 30  5 to 10  2 to 3 Induced Roll Induced Roll is the mechanical force a wake vortex has on an aircraft. With no counter control (roll control), the aircraft would roll completely, spinning on its longitudinal axis until the vortex sufficiently weakened. BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 8 Hazards In some rare cases, a wake turbulence encounter could cause inflight structural damage of catastrophic proportions The usual hazard is when the induced roll exceeds the level of roll control of the aircraft Roll control is the ability of an aircraft to move around the longitudinal axis Serious and even fatal accidents induced by wake vortices do occur The heavier the aircraft, the more separation that must be given (or exist) for smaller aircraft when in trail (or following in trail) Vortex Roll Counter Control In experiments, it was shown that the ability of an An aircraft with a larger wingspan that extends beyond aircraft to counteract the effects of the roll (counter the outer edges of a vortex is better able to counter control) is based on two things: the roll effects of the vortex than a smaller aircraft The wingspan of the aircraft whose wingspan is completely engulfed within a The counter control capability of the aircraft vortex. Knowledge Check C REVIEW what you have learned so far about wake turbulence and facts that affect wake turbulence. ANSWER the questions listed below. Why would extra spacing be necessary when smaller aircraft are following larger aircraft at a terminal environment? (Select the correct answer.)  To prevent obstructed sight of the runway  To avoid the aircraft’s wake turbulence vortices  To clear a path for larger aircraft to maneuver Counter control is most effective and roll is minimal when the wingspan and the ailerons extend beyond the __________ of the vortex. (Select the correct answer.)  End of vortex  Inside edges  Outer edges BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 9 Helicopter Downwash In a slow hover taxi or a stationary hover, a helicopter will generate a downwash from its main rotors. This downwash produces a high-speed outward vortex as it reaches the ground These vortices spread outward to a distance of approximately 3 times the diameter of the rotor The downwash circulation is outward, upward, around, and away from the main rotors in all directions Pilots should avoid operating within three rotor diameters of any helicopter that is in any type of hover. Example Slow Hover Taxi or Stationary Hover: Avoid Operations Within Distances of 3 Times Rotor Diameter Helicopter Vortices Helicopters will generate a pair of wingtip vortices when in forward flight. These vortices are strong, high-speed trailing vortices that are similar to wingtip vortices produced by larger fixed-wing aircraft Pilots of smaller aircraft should use extreme caution when operating directly behind a helicopter in forward motion. Jet Blast and Hazards Jet blast is jet engine exhaust (thrust stream turbulence). BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 10 Hazards Jet blast is normally experienced during ground operations and during initial takeoff roll prior to lift. It can cause damage and upsets if encountered at close range Light aircraft need to maintain adequate distance Pilots of larger aircraft should consider the effects of their jet blast on smaller aircraft or ground vehicles around them The Impact of Wake Turbulence on ATC Wake turbulence can be encountered in flight or on the ground Because wake turbulence is unpredictable, the controller is not responsible for anticipating its existence or effects Although not mandatory, when issuing a cautionary advisory during ground operations, controllers may use the following terms in lieu of the term “wake turbulence”: Jet blast Prop wash Rotor wash General Impact of Wake Turbulence The greatest impact wake turbulence has on ATC is increased separation for: Tower operations, both ground and airborne Radar operations for both approach and en route environments Delays may occur due to increased separation, resulting in a lower airport acceptance rate. Note: The subject of “Wake Turbulence Separation” will be discussed in complete detail when you enter the next level of your training. An incident involving an Airbus (A380) and a Challenger (CL60) vividly illustrates the potential hazard of wake turbulence. The A380 passed 1000’ above the CL60, causing it to roll 3 to 5 times and lose 10,000’ feet in altitude. The CL60 was forced to make an emergency landing where stress fractures and popped rivets were discovered in the fuselage. Several passengers suffered injuries and the aircraft was damaged beyond repair. Incidents such as these have prompted the FAA to increase separation standards for the A380. BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 11  Knowledge Check D REVIEW what you have learned so far about wake turbulence and facts that affect wake turbulence. ANSWER the questions listed below. A hovering helicopter creates a downwash from its main rotors that can travel how far? (Select the correct answer.)  Five times the diameter of its rotors  Three times the diameter of its rotors  Two times the diameter of its rotors When do helicopters generate wingtip vortices? (Select the correct answer.)  Must be in forward flight  While parked on a helipad  In a stationary hover Why is the controller NOT responsible for anticipating the existence or effects of wake turbulence? (Select the correct answer.)  Increased separation and delays  Resources and staffing  Because it is unpredictable Wake turbulence has the greatest impact on ATC in the areas of __________. (Select the correct answer.)  Damage and money  Resources and delays  Increased separation and traffic delays Wake Turbulence Summary Because wake turbulence is unpredictable, air traffic controllers are not responsible for anticipating its existence or effects of wake turbulence, but they must be knowledgeable of the phenomenon to effectively respond to hazardous situations generated by wake turbulence. BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 12 SUMMARY Because wake turbulence is unpredictable, air traffic controllers are not responsible for anticipating its existence or effects of wake turbulence, but they must be knowledgeable of the phenomenon to effectively respond to hazardous situations generated by wake turbulence. In accordance with FAA Order JO 7110.65, Air Traffic Control; FAA-H-8083-25, Pilot’s Handbook of Aeronautical Knowledge; and the AIM, you should now be able to: Define wake turbulence Identify factors affecting wake turbulence intensity Describe wingtip vortices Identify hazards associated with an induced roll Describe helicopter downwash and vortices Identify the impact of wake turbulence on ATC KNOWLEDGE CHECK ANSWERS Knowledge Check A 1. Heavy, clean, slow; 2. Aircraft on approach to the airport; 3. Weight Knowledge Check B 1. Wake vortex, Wingtip vortices; 2. At rotation or when lift begins; 3. Counterclockwise, clockwise; 4. 500 to 1000; 5. 2 to 3 Knowledge Check C 1. To avoid the aircraft’s wake turbulence vortices; 2. Outer edges Knowledge Check D 1. Three times the diameter of its rotors; 2. Must be in forward flight; 3. Because it is unpredictable; 4. Increased separation and traffic delays BASICS FOR AIR TRAFFIC CONTROL | WAKE TURBULENCE 13