A Bumpy Flight? Many Different Factors Cause Turbulence

Weather Talk
Friday, January 10, 2014 - 12:26pm

No Frequent Flyer Is a Stranger to Turbulence. But What Causes It, and How Dangerous Is It?

I remember flying back to Las Cruces from Colorado years ago in a small 19 seat airplane, when the plane dropped what I estimated was 1,000 feet or so in a matter of seconds. It jolted me out of my half awake state. When I stepped off the plane about 15 minutes later, my girlfriend who traveled with me laughed and said “ I have never seen you so white!” All the color had disappeared from my face, I quickly walked down the “air stairs” and kissed the ground.
First let us take a brief look on how a plane “flies”.

Aerodynamics tends to be a lengthy subject to explain, but one condensed statement sums up the basic principle of flight: “An airplane stays up because its wings push the air down” This is called “lift.”
An airplane generates lift only when it is moving. An airplane flies only when it builds up enough speed in the take-off run. At take-off, the wings have enough airspeed to “push down” hard enough on the air to overcome the airplane’s weight.

I used to always think that an airplane’s ability to fly had to do with the need for an engine to propel it through the air. We always think about gliders that can stay aloft for hours riding rising air currents, but if a glider is towed aloft and finds the air not good for sailing, it turns around and glides back down to the airport. The principle here is this: Altitude can always be “traded in” for airspeed. The same thing is true for regular airplanes. Even with all the engines stopped an airplane can glide back down. Of course, it won’t glide as well as a sailplane, and it can’t climb in an updraft, but it won’t fall like a rock either. Its altitude will be traded for airspeed, and the airspeed will generate enough lift to fly it back down to the ground for a safe landing

Turbulence is the random, swirling motion of air, caused by changes in air currents. When you are inside a flying airplane, it can range from minor bumpiness that can just sake you a bit to strong, sudden jolts that can cause structurally damage the plane and cause injury to the passengers. Always a great, safe idea to keep you seatbelt loosely fastened at all times.
Each year, pilots report about 65,000 accounts of moderate or greater turbulence and 5,500 accounts of severe turbulence. Turbulence is responsible for roughly 75 percent of all weather-related accidents and incidents, according to the National Transportation Safety Board.
All modern planes are tough, and built to hold up even against severe turbulence. Turbulence extreme enough to damage a commercial airplane is extremely rare, and pilots have many methods of both handling and avoiding it.
You can understand turbulence by visualizing a boat. As the boat goes through water, it causes ripples, waves and eddies. Air is the same way. Air currents, weather patterns and even other planes can make the air rough and bumpy. Pilots are taught to slow down when they encounter turbulence.
I thought I would list a few cause of aircraft turbulence.

Wind Shear
A majority of wind shears occur in the upper atmosphere and it is primarily vertical. Wind shears have a tendency to become horizontal as a plane is landing or taking off and is close to the runway. These horizontal winds produce small swirls or eddies which in turn create air turbulence. Horizontal wind shears can create eddies or swirls, of air that causes turbulence. This can quickly push or tilt the wings dangerously when near the ground.

Thunderstorm Turbulence
Even in an innocent looking puffy cloud on a calm summer day the air inside can be traveling as fast as 80 ft/sec up and 80 ft/sec down. This is called convective-induced turbulence. Thunderstorms are even more violent. Thankfully, there are many warning systems for pilots. Airplane radar, ground radar, air traffic control and other pilot reports will all warn a pilot about the location of thunderstorms. Thunderstorm turbulence is produced the storms by pulling large amounts of air in and sending it upwards very rapidly. Once this air cools, it has to come down, as it is heavier than the surrounding air. When it does, it can create micro burst and very turbulent conditions. The latest technology radars can also show areas of turbulence. Pilots know to keep their distance from storms and different airlines have different mandatory distances.

Wake Turbulence
Similar to a boat or Jet Ski creating eddies and waves in the water, rapidly spinning air currents can develop off the wing tips of an aircraft. Wake turbulence happens when an aircraft leaves a trail of swirling, disturbed air behind it. This wake turbulence is greater when the plane flying slowly during take-off or landing. The turbulence is a natural phenomenon that does not endanger the aircraft, but any other aircraft following too closely behind does have the chance of losing control flying into the eddies of strong swirling air. This is the main reason why air traffic controllers maintain strict limits of spacing between aircraft, both on arrival and departure. This safety precaution causes delays in take offs and landings, but the safety advantage is well worth the wait.

Mountain Wave
Upper level winds that blow across the mountain tops form waves as the air is forced to sweep across the mountain peaks. The air as we know, behaves like water, so this oscillation is similar to waves breaking on the ocean. Mountain Wave Turbulence can range from just be being bumpy to extreme enough to cause airplane damage. These waves can extend hundreds of miles well above the highest mountain peaks, into the stratosphere and over 100 miles from the down slope of a mountain. Aircraft can rise or drop as far as 1,000 feet. There is no visual indicator which makes mountain waves especially challenging and just like ocean waves it is tough to predict where they will break.

Thermal Induced Turbulence
Heat caused or convective currents, happen the most during our hot summer afternoons, and are one of the most common causes of turbulence at low altitudes impacting planes during their take-off or landing. The air that is heated near the ground rises, but since different surfaces have a hotter surface area than others i.e.. pavement heats up more than a grass covered field. Unevenly heated air produces different hot spots which abruptly changes air speed that can be dangerous when you are close to the ground. Places like El Paso or Phoenix with a lot of intense surface area heating especially late in the day, making this type of turbulence much more common.
Clear-air Turbulence

High altitude “Clean-air Turbulence is difficult to predict since it's invisible to weather radar, which can only see inside of clouds. This type of turbulence is usually caused by shifting jet streams. Jet streams are fast moving rivers of air way in the upper atmosphere. “Below and above these rivers are wind shears, or rapid changes in wind speed. Where there's a jet stream, there's shear, and where there's shear there's turbulence’, according to the National Center for Atmospheric Research (NCAR). "

The majority of the turbulence we should not be afraid of. Airplanes make hundreds of safe landings and takeoffs every day in bad and challenging weather every day. Airline commercial pilots have hundreds if not thousands of hours of training and flying experience flying in a variety of weather conditions. Plane crashes and accidents are the exceptions, not the rule. Airlines and airports will delay or divert flights if the weather is too risky to take off or land in. Now don’t you feel better about flying? I know I do after researching the reasons behind the “fasten your seatbelts” warnings and bumpy rides.
 

Chuck DeBroder, Chief Meteorologist
KTSM, NewsChannel 9, NBC, El Paso, TX
cdebroder@ktsm.com
www.facebook.com/pages/Charles-DeBroder/
www.twitter.com/ Chuck DeBroder NC9 @wxchuckNC9

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