While licensed drivers deal with pesky potholes in the streets, experienced pilots are also tasked with avoiding similar bumps in the sky. These bumps are known as turbulence, of which there are different types, causes, and severities. As turbulence impacts aircraft in a variety of ways, this blog will outline what you can do to ensure a smooth flight.
Under normal conditions, aircraft maintain straight, level, and controlled flight when air flowing over and around the wings is smooth and undisturbed. However, turbulence is the irregular motion of air resulting from eddies and vertical currents. The eddies and vertical air currents change the airflow, causing pitching about the lateral axis, rolling about the longitudinal axis, or yawing about the vertical axis. All of these shifts are determined by the direction and severity of the current shift.
Turbulence can be caused by many things including warm or cold weather fronts, wind shear, thunderstorms, the jet stream, air around mountains, and atmospheric pressure. As previously mentioned, there is more than one type of turbulence, each of which is named according to where it is encountered and what causes it. The main types of turbulence are clear air, frontal, mechanical, thermal, wake, and wind shear variations.
Clear Air Turbulence
Serving at the stealthiest and most unexpected type, clear air turbulence often catches pilots by surprise. Common during wintertime, it is generated by strong wind shears in the jet stream. Unlike other types, clean air turbulence takes place without warning and in clear, cloud-free air above 15,000 feet. To fly out of clear air turbulence, pilots can ascend or descend a few thousand feet.
When two air masses collide, the unstable air between the two fronts will most likely contain turbulence. Frontal turbulence is generally found alongside fast-moving cold fronts and in the moist air of a warm front, especially if the warm front is building into a thunderstorm. Additionally, this type of turbulence cannot be avoided easily as the updrafts and downdrafts can extend anywhere between 15 and 30 miles from severe thunderstorms.
Mechanical turbulence consists of rough air resulting from friction between the air and the ground, terrain features, or man-made structures. With surface winds over 20 knots, rough terrain and unstable air temperatures create the perfect conditions for turbulence to envelope. The most severe mechanical turbulence can be felt in the mountains where eddies known as mountain waves form up to several hundred miles downwind from the mountain ranges. These updrafts and downdrafts can make the aircraft lose or gain up to 5,000 feet of altitude per minute.
Thermal turbulence is often called convective turbulence because it is caused by the isolated convective currents of warm air rising and cooler air descending. As such, it is more common on hot summer days when dark colored rocky, sandy, and urban areas heat up quicker than lighter areas like bodies of water, grassy parks, and fields. These temperature differences result in fluctuating air currents, and the onset of this turbulence can be identified by distinctive cloud formations.
For pilots operating small aircraft, they always need to be extra careful when taking off behind, landing after, or crossing the path of bigger airplanes. The wingtip vortices generated by other aircraft can remain in the airspace for up to three minutes, affecting any surrounding aircraft with this turbulent air. The strongest wingtip vortices are created by heavy airliners like the Boeing 747. Wake Turbulence Recategorization, or Wake RECAT, is defined as the safe decrease in separation standards between certain aircraft.
Wind Shear Turbulence
Rapid changes in wind speed and/or direction over particular vertical or horizontal distances can cause wind shear. Wind shear is common around the jet stream, along troughs, lows, and in regions with temperature inversions.
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