Course 6 - Section 17 - Wake Turbulence

Question 1

Wake Turbulence Definition

Answer 1

Wake turbulence is a disturbance in the atmosphere that forms behind an aircraft as it passes through the air. It is especially hazardous during takeoff or landing

Wake turbulence can be catastrophic

Question 2

List the causes of Wake Turbulence

Answer 2

Wing-tip vortices
Rotor-tip vortices
Jet engine thrust stream
Rotor downwash
Prop wash

Question 3

Wing tip vortices

Answer 3

Lift is generated by higher pressure underneath a wing

Wake turbulence is created as the air flows outward from the body of the aircraft to the wing tip. When the air reaches the wing tip, the high pressure undernearth rotates upwards towards the low pressure

This results in a twisting rotating vortex or air that continues in downward spiral

Question 4

Properties of wing tip vortices

Answer 4

• The strength of a wing tip vortex is governed by the shape of the wings and the weight and speed of the aircraft

-They show little dissipation within the first two minutes of being produced. After two minutes, the dissipation rate will vary depending on a variety of factors

-The vortices on each side of the aircraft are counter rotating and cylindrical in shape

Question 5

Rotor Tip Vortices

Answer 5

Rotor tip vortices are similar to wing-tip vortices but they’re created by the rotor blades of a helicopter

• The problems created by rotor-tip vortices are generally GREATER than those caused by fixed wing aircraft of a similar category. This is because the helicopter’s lower operating speed produce higher intensity wakes than fixed-wing aircraft; the size of the aircraft has LITTLE BEARING on the intensity of the vortex
• Departing or landing helicopters produce high-velocity vortices similar to wing-tip vortices

Question 6

Jet Engine Thrust Stream

Answer 6

Jet engines produce a great amount of thrust, and the area behind them can be very turbulent. The area of turbulence created behind an aircraft’s jet engines is called the jet engine thrust stream

This turbulence IS USUALLY EXTREME, BUT OF RELATIVELY SHORT DURATION. IT TENDS TO BE MORE DANGEROUS THE CLOSER YOU ARE TO THE AIRCRAFT

Jet engine thrust stream needs to be accounted for WHEN AIRCRAFT OR VEHICLES FOLLOW A JET IN ANY CAPACITY

JET ENGINE THRUST STREAM IS GREATEST WHEN POWER IS INCREASED TO MOVE THE AIRCRAFT FORWARD FROM A STOPPED POSITION

Caution should be exercised when aircraft or vehicles operate near active runways or taxiways

Also known as jet wash or jet blast

Question 7

Rotor Downwash

Answer 7

Rotor downwash is the downward turbulence created by helicopters hovering or in forward flight.

ROTOR DOWNWASH IS GREATEST IN HOVERING FLIGHT BECAUSE THE AIRSPEED IS PRACTICALLY ZERO

As the turbulence reaches the ground, it spreads out in all directions, causing severe buffeting to anything in close proximity

Question 8

Factors that affect the strength of the turbulence from rotor downwash (LIST)

Answer 8

• Weight of helicopter
• forward speed (highest turbulence at hovering)
• Air density
• Rotor length

Question 9

Prop wash

Answer 9

Prop wash is the turbulence created by any propeller driven aircraft

Prop wash is based on the same principle as jet engine thrust stream, but the effect is not as great. However, it can still be enough to warrant attention by pilots and ATS personnel

Question 10

Wing tip vortices: INDUCED ROLL

Answer 10

Aircraft flying directly into the core of a vortex will tend to roll with the vortex.

This uncommanded roll can range from a slight roll to a roll that causes inversion of the aircraft

THE SMALLER THE AIRCRAFT THAT FOLLOWS INTO THE VORTEXT IN RELATION TO THE PRECEEDING AIRCRAFT THAT CREATED IT, THE MORE PRONOUNCED THE EFFECT AND LESS LIKELY THE FOLLOWING AIRCRAFT IS TO CORRECT THE UNCOMMANDED ACTION

An aircraft’s capability to counteract the roll depends on its wingspan and responsiveness

Question 11

Induced Roll: Larger Aircraft (large wingspan)

Answer 11

When the wingspan and ailerons of a larger aircraft extend beyond the vortex, counter-roll control is usally effective and the effect of the induced roll can be minimized

Question 12

Induced Roll: Smaller Aircraft (Shorter wingspan)

Answer 12

Pilots of short wingspan aircraft must be especially alert to vortex situations even if the aircraft is of the high-performance type

Question 13

Wingtip vortices: GROUND EFFECT

Answer 13

Wing-tip vortices that are generated behind departing or arriving aircraft, or aircraft that descend to less than 100 feet above the runway, are subject to ground effect

• VORTICES BECOME SUBJECT TO GROUND EFFECT LESS THAN 100 FEET ABOVE THE RUNWAY

Question 14

Ground Effect: No wind

Answer 14

In a no wind situation, vortices that contact the ground tend to move laterally outward, at a speed of about 5 knots

Question 15

Ground Effect: With Wind

Answer 15

The wind has an impact on that speed (lateral 5 knots for no wind conditions) and moves the vortices accordingly

A crosswind moves the vortices sideways with the direction of the wind.

A tailwind or headwind can also change where the vortices begin or end in relation to the runway

Question 16

Wing tip vortices: Calm or Light Wind Conditions

Answer 16

Even in calm or light wind conditions, wing-tip vortices can do unexpected things:

They can

• Remain in the touchdown area
• Drift from aircraft operating on a nearby runway
• Sink into take-off or landing paths from a crossing runway
• Sink into the traffic pattern from other runway operations
• Sink into the flight path of VFR flights at 500 feet AGL and below

Question 17

The best way to avoid wake turbulence:

Answer 17

Avoid flying through the area where vortices exist

Question 18

Wake Turbulence: Pilot Responsibilities: On the ground

Answer 18

Question 19

Wake Turbulence: Pilot Responsibilities:
During Takeoff

Answer 19

Question 20

Wake Turbulence: Pilot Responsibilities:
When Landing

Answer 20

Question 21

Wake Turbulence: Pilot Responsibilities:
Enroute VFR Flight

Answer 21

• Avoid flying below and behind aircraft of a heavier weight category
• If this is not possible, adjust position laterally, preferably upwind

Question 22

Wake Turbulence: Pilot Responsibilities:
IFR Flight and Landing

Answer 22

• Responsibility for IFR wake turbulence separation lies with the IFR controller. Therefore, pilots need to follow the instructions and clearances they are given to avoid the turbulence
• ATC will separate aircraft. On landing, pilots follow a specific glide slope, as will the preceding aircraft

Question 23

The No Vortex Zone (When landing)

Answer 23

Question 24

Wake Turbulence: ATS Responsibilities. List the basic responsibilities

Answer 24

• Watch for wind conditions
• provide information
• apply separation standards
• be aware of changing flight paths

Question 25

Wake Turbulence: ATS Responsibilities
Watch for wind conditions

Answer 25

wind conditions can affect the dissipation rate or location of wake vortices. Watch out for

1) Calm winds and stable air
2) Crosswinds or tailwind that might hold a vortex on a runway or cause it to drift onto another runway

Wake turbulence can become complex with light winds combined with intersecting or parallel operations

Question 26

Wake Turbulence: ATS Responsibilities
Provide Information

Answer 26

All ATS personnel must provide information about wake turbulence.

For example, if a helicopter is hovering or airborne while taxiing, that information must be passed along, and any vehicles and other aircraft must be kept clear of the area

ATS personnel communicate wake turbulence information and issue cautionary alerts when there is a possibility of an aircraft encountering wake turbulence

Question 27

Wake Turbulence: ATS Responsibilities
Apply Separation Standards

Answer 27

Controllers assume responsibility for wake turbulence separation of IFR aircraft, as these aircraft have to follow the specific route assigned by ATC

Wake turbulence can be minimized or negated through the application of separation standards, and controllers can also increase this standard, if necessary

Question 28

Wake Turbulence: ATS Responsibilities
Be aware of changing flight paths

Answer 28

All ATS personnel should be aware that a pilot may alter their flight path to avoid wake turbulence

For example, a pilot might decide to land farther down the runway to avoid vortices, and this could affect the timing and plan developed by ATS staff

Knowing what might happen can help you plan for these possibilities

Question 29

Weight Categories of Aircraft and the Overarching principle when applied to wake turbulence

Answer 29

Tests and studies have shown that aircraft within certain weight limitations create roughly equivalent vortices and react to these vortices in a similar manner

There are four categories of weight classification as defined by ICAO and recognized by NAV CANADA

Question 30

List the weight categories and their weights and give an example for each

Answer 30

Maximum take off weights

Light Aircraft: Max 7000 kg (15,500 lbs)
Cessna 172

Medium: More than 7000kg (15,500 lbs) but less than 136,000 KG (300,000 lbs)
Dash-8, 737, A320

Heavy: 136,000 KG (300,000 lbs) or more
777, 787, A340

Super: 136,000 KG (300,000 lbs) or more
A380

Question 31

What factors affect an aircraft’s ability to respond to wing tip vortices, counter act the roll

Answer 31

wingspan and responsiveness