What is Turbulence?
Turbulence refers to the irregular and unpredictable motion of air in the atmosphere. It is caused by disturbances in the air flow, often due to weather events like thunderstorms, jet streams, or strong winds over mountains. Turbulence can range from minor bumps to violent jolts and rolls that can toss passengers and crew around an aircraft cabin. While turbulence is normal and unavoidable, severe turbulence can damage aircraft and injure passengers and crew.
Types of Turbulence
There are several main types of turbulence that aircraft may encounter:
Clear Air Turbulence
Clear air turbulence (CAT) occurs in areas devoid of clouds or other visible weather events. It is caused by wind shear, mountain waves, jet streams, and other factors that disrupt smooth air flow. CAT can happen at high altitudes and is difficult to predict and detect.
Convective Turbulence
Associated with thunderstorms and cumulonimbus clouds, convective turbulence results from updrafts and downdrafts within the storm. It can be violently turbulent, with altitude changes of hundreds or thousands of feet.
Mechanical Turbulence
Caused by disruption of airflow around geographical features like mountains, mechanical turbulence can break aircraft apart if they fly too close to the obstruction.
Wake Turbulence
Generated by aircraft themselves, wake turbulence forms behind the wingtips in two counter-rotating vortices. It poses risks especially when a small aircraft takes off or lands behind a larger aircraft.
Low Level Wind Shear
Sudden changes in wind speed or direction near the ground can cause low level wind shear, resulting in turbulence during takeoff and landing.
Where Turbulence Occurs
Turbulence can happen at any point during a flight, but there are common areas it tends to occur:
– Near the jet stream – strong upper level winds
– Thunderstorms and cumulonimbus clouds
– Mountain waves – turbulence forms over mountains
– Heat from the ground – causes bumpy rising air
– In the wake of other aircraft
– Clear air at high altitude
Takeoffs and landings are common turbulence points due to low level wind shear. Turbulence from thunderstorms is most common in the tropics near the Intertropical Convergence Zone where storm activity is high. Flights over mountains like the Rocky Mountains often result in turbulence. Strong upper level jet streams can create widespread areas of turbulence.
How Long Does Turbulence Last?
The duration of turbulence depends on the type and cause. Some common timeframes include:
Thunderstorm Turbulence
Turbulence connected to thunderstorms can last 15-30 minutes as the aircraft passes through the active storm. Sometimes planes need to travel 100 miles or more to exit a large storm system or cluster of storms, resulting in an hour or more of moderate to severe turbulence.
Clear Air Turbulence
CAT can occur suddenly without warning and may only last 1-10 minutes as the plane passes through the turbulent patch of air. However, CAT can also continue intermittently for hours if the aircraft remains in the vicinity of the atmospheric disturbance causing it.
Mountain Waves
Turbulence from mountain waves can persist for 10-30 minutes as an aircraft crosses over the mountain range. It is generally confined to a specific area around the mountains.
Wake Turbulence
Wake turbulence begins as soon as the generating aircraft creates rotating air currents behind its wings. For smaller single-engine aircraft, wake turbulence may last 2-3 minutes before dissipating. For larger aircraft like airliners, it can last 5 minutes or longer.
Wind Shear
Low level wind shear on takeoff or landing normally only causes significant turbulence for less than a minute. It takes time to climb out of the disturbed winds near the ground.
Jet Streams
Strong winds in the core of a jet stream can cause moderate choppiness and vibrations lasting 15-60 minutes as the aircraft cruises through it. Clear air turbulence around the jet stream may come and go throughout the flight.
Severity and Effects of Turbulence
Turbulence ranges from light to severe. Light turbulence results in minor changes in altitude and attitude and feels like small bumps or vibrations. It poses little hazard. Moderate turbulence is more pronounced but aircraft remain in control. Severe turbulence causes large, abrupt changes in altitude and attitude, along with high accelerations. It can cause injuries and aircraft stress.
The effect of turbulence depends on its severity, size of the aircraft, and aircraft speed. Larger planes like airliners better resist turbulence due to greater inertia. Slower speeds also reduce the impact. General aviation aircraft are most vulnerable to turbulence due to lower mass and airspeeds.
Turbulence is measured using the G-force, the force exerted relative to earth’s gravity. Additional Gs exert strain on the aircraft and passengers. Light turbulence is less than 0.5 Gs; moderate is 0.5 to 1.5 Gs; severe is 1.5 to 2.5 Gs; and extreme is greater than 2.5 Gs.
Forecasting and Reporting Turbulence
Aviation weather forecasts provide valuable information to pilots on expected turbulence. However, only thunderstorms and mountain wave turbulence can be directly forecast. Other turbulence indicators include:
– Position and strength of jet streams
– CAT probability areas and pilot reports
– Strong crosswinds along a flight path
– Clouds associated with vertical air movement
Pilots relay turbulence reports to air traffic control using the PIREPs system (Pilot Weather Reports). They include location, altitude, severity, type, and duration of turbulence. Dispatchers and air traffic control pass these reports on to other pilots to help identify turbulent areas.
New technology like onboard radar systems can also detect turbulence ahead of the aircraft. Satellite data and computational models are improving turbulence forecasting accuracy.
Avoiding and Minimizing Turbulence
The best ways pilots can avoid turbulence is to:
– Check all weather and turbulence forecasts pre-flight
– Alter course and altitude to avoid known turbulence areas
– Slow aircraft speed if possible in turbulent conditions
– Keep seat belts fastened when expecting turbulence
– Delay takeoff or landing if intense low level wind shear is present
Communication with dispatch and air traffic control allows pilots to strategically plan routes and altitudes to avoid turbulence hot spots. Radar and satellite imagery also help identify developing storms and other hazards.
However, total turbulence avoidance is not always possible. Safety requires frequent turbulence training for pilots to maintain aircraft control in upset conditions. Aircraft designers also incorporate turbulence tolerance through features like wing flex, which dampens the force.
Turbulence Flying Procedures
Pilots follow set procedures to prepare for and manage turbulence:
– Turn on seat belt sign early if turbulence expected
– Slow aircraft below maximum speed if possible
– Gradually reduce altitude in mountain waves
– Increase distance behind wake-generating aircraft
– Maintain wings level with aileron and pitch +1 or -1 G with elevator
– Make smooth control inputs to avoid overstressing aircraft
– Hold heading using rudder and bank angle with aileron
– Inform ATC immediately if need to divert or declare emergency
Following procedures ensures the aircraft stays under control, reduces chances of passenger injuries, and prevents excessive structural loads.
Turbulence Safety Precautions for Passengers
To stay safe in turbulent conditions, passengers should:
– Keep seat belts fastened when seated
– Stow loose items like bags and laptops
– Stay seated – don’t try moving about the cabin
– Follow flight attendant instructions
– Keep head back against seat with hands in lap
– Avoid holding drinks/food until turbulence passes
– Remain calm and avoid sudden movements
– Do not interfere with crew operations
Proper pre-flight safety briefings instruct passengers on preparing for and reacting to turbulence. Following crew instructions is vital, along with personal precautions like using seat belts. Injuries typically result from being thrown about or hit by unsecured objects.
Turbulence Injuries
Most turbulence results in zero injuries, but severe cases can cause:
– Broken bones/fractures from falls or being thrown
– Blunt force trauma from impacts with interior surfaces
– Lacerations from sharp objects becoming projectiles
– Burns from hot coffee/food spilling
– Concussions from heads striking overhead bins or bulkheads
The most common injuries are to the head, neck, shoulders, and hips as they slam into solid objects and contact points have minimal cushioning. Lap held infants are especially vulnerable without restraints.
Severe turbulence has directly caused 3-4 deaths on airliners since 1980, with occasional indirect contributions to other crashes. Hundreds of serious injuries happen annually, usually among flight attendants.
Mitigating Passenger Injuries
Key actions to reduce turbulence related injuries include:
– Keeping seat belts fastened
– Securing loose items and cargo
– Following all crew safety procedures
– Making PA announcements about unexpected turbulence
– Ensuring passengers are seated as much as possible
– Training crew in proper response techniques
– Tracking locations of crew members
– Reporting turbulence encounters to aid other pilots
New technologies like turbulence detection and prediction radar also help crews avoid and prepare for rough air. More widespread adoption enhances safety margins.
| Turbulence Type | Duration |
|---|---|
| Thunderstorm | 15-60+ minutes |
| Clear Air | 1-10+ minutes |
| Mountain Wave | 10-30+ minutes |
| Wake | 2-5+ minutes |
| Wind Shear | Under 1 minute |
| Jet Stream | 15-60+ minutes |
Key Takeaways on Turbulence Duration
– Thunderstorm turbulence can last over an hour, especially in large storm clusters
– Clear air and mountain wave turbulence is often confined to specific areas and may last under 30 minutes
– Wake turbulence dissipates after several minutes but is most dangerous near airports
– Wind shear only causes significant turbulence below 1500 feet during takeoff and landing
– Jet stream turbulence depends on how long the aircraft remains in strong winds
Conclusion
Turbulence duration is highly variable from just seconds to over an hour depending on the cause and size of the disturbance. Thunderstorms, mountain waves, and jet streams can result in prolonged moderate to severe turbulence while wind shear and wake turbulence are generally short-lived phenomena. Advanced knowledge of areas with high probability of turbulence allows pilots to alter altitude and routing to avoid the roughest conditions when possible or ensure passengers are prepared well in advance. New detection and forecasting methods continue to improve turbulence anticipation and reduce risks for future flights.
