Course 6 - Section 17 - Wake Turbulence Flashcards
Wake Turbulence Definition
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
List the causes of Wake Turbulence
Wing-tip vortices
Rotor-tip vortices
Jet engine thrust stream
Rotor downwash
Prop wash
Wing tip vortices
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
Properties of wing tip vortices
- 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
Rotor Tip Vortices
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
Jet Engine Thrust Stream
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
Rotor Downwash
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
Factors that affect the strength of the turbulence from rotor downwash (LIST)
- Weight of helicopter
- forward speed (highest turbulence at hovering)
- Air density
- Rotor length
Prop wash
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
Wing tip vortices: INDUCED ROLL
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
Induced Roll: Larger Aircraft (large wingspan)
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
Induced Roll: Smaller Aircraft (Shorter wingspan)
Pilots of short wingspan aircraft must be especially alert to vortex situations even if the aircraft is of the high-performance type
Wingtip vortices: GROUND EFFECT
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
Ground Effect: No wind
In a no wind situation, vortices that contact the ground tend to move laterally outward, at a speed of about 5 knots
Ground Effect: With Wind
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
Wing tip vortices: Calm or Light Wind Conditions
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
The best way to avoid wake turbulence:
Avoid flying through the area where vortices exist
Wake Turbulence: Pilot Responsibilities: On the ground
Wake Turbulence: Pilot Responsibilities:
During Takeoff
Wake Turbulence: Pilot Responsibilities:
When Landing
Wake Turbulence: Pilot Responsibilities:
Enroute VFR Flight
- Avoid flying below and behind aircraft of a heavier weight category
- If this is not possible, adjust position laterally, preferably upwind
Wake Turbulence: Pilot Responsibilities:
IFR Flight and Landing
- 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
The No Vortex Zone (When landing)
Wake Turbulence: ATS Responsibilities. List the basic responsibilities
- Watch for wind conditions
- provide information
- apply separation standards
- be aware of changing flight paths
Wake Turbulence: ATS Responsibilities
Watch for wind conditions
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
Wake Turbulence: ATS Responsibilities
Provide Information
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
Wake Turbulence: ATS Responsibilities
Apply Separation Standards
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
Wake Turbulence: ATS Responsibilities
Be aware of changing flight paths
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
Weight Categories of Aircraft and the Overarching principle when applied to wake turbulence
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
List the weight categories and their weights and give an example for each
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
What factors affect an aircraft’s ability to respond to wing tip vortices, counter act the roll
wingspan and responsiveness
