2011 was an active year for turbulence-related aviation injuries. Several major airlines operated flights that were affected by turbulence categorized as “moderate” or worse, with multiple events sending passengers and crew to the emergency room.
Turbulence is a disturbance in air movements that typically cannot be seen. Turbulence can occur as a result of any number of conditions, including proximity to the jet stream, mountain waves, or convective activity such as thunderstorms or frontal systems.
The culprit in most injury-causing encounters with turbulence is Clear Air Turbulence, (CAT). This type of turbulence is usually encountered at the higher Flight Levels utilized by airliners, (18,000 feet and above) and is especially dangerous because it is undetectable.
A fairly recent advancement is the “Turbulence Analysis Chart”, an example of which is shown in Figure 1. These charts show the areas with the highest probability of a turbulence encounter as well as the maximum forecast winds at various altitudes. Avoiding the colored areas depicted on the chart is recommended however doing so is no guarantee that the pilot will prevent the aircraft from encountering turbulence. The inability to accurately and precisely forecast CAT remains one of the biggest challenges in flight planning.
Figure 1. Turbulence Analysis Chart
White-knuckled flyers often cite turbulence as their greatest fear, wrongly believing a bumpy ride will make the wings fall off or cause the pilots to lose control. The fact is aircraft can withstand loads that far exceed those ever imposed by turbulence. During initial certification, airframe manufacturers are required to demonstrate a “limit load” test, with the final data point corresponding to the actual destruction of the aircraft wing. Engineers increase the wing loading at 10% increments up to 100% limit load, which is defined as the maximum in-service limit load the aircraft is ever expected to see. At 100% limit load, the test continues at 10% increments up to 130% limit load and beyond, to gather additional engineering data such as the actual load and location of structural failure. The Boeing 777 wing was pulled 24 feet above its normal position and remained intact until 154% of design limit load.
Passengers who later recount turbulence events often state that the aircraft hit an “air pocket” or that the plane “suddenly dropped thousands of feet.” In reality, air doesn’t disappear; however it does experience density changes and/or shear, which is a large change in speed or direction over a short distance. In response to these phenomena, the aircraft moves, usually up and down, causing the occupants to experience rapid changes in vertical acceleration. This is what causes the sensation of the aircraft “dropping”. Actual altitude changes during turbulence are typically less than 50 feet, except in rare cases of severe turbulence, where an altitude change might reach 200-300 feet. These changes pose no threat to a seated passenger whose seat belt is fastened.
The data acquired annually by the FAA demonstrates that turbulence-related injuries do not coincide with structural damage to the aircraft. Most injuries occur when standing occupants fall or when seated passengers not wearing seat belts are thrust up into the ceiling. According to the FAA, no airline pilot has been seriously injured by turbulence since 1962, when the regulation requiring pilots to fasten their seat belts while in their seats took effect. This is why the initial cockpit-to-cabin announcement will state something to the effect of, “…for your safety and the safety of those around you, please keep your seat belts fastened when you are in your seats as we do up here in the cockpit…”
Consider the following data from FAA.gov:
In nonfatal accidents, in-flight turbulence is the leading cause of injuries to airline passengers and flight attendants.
Each year, approximately 58 people in the United States are injured by turbulence while not wearing their seat belts.
From 1980 through 2008, U.S. air carriers had 234 turbulence accidents, resulting in 298 serious injuries and three fatalities.
At least two of the three fatalities involved passengers who were not wearing their seat belts while the seat belt sign was illuminated.
Generally, two-thirds of turbulence-related accidents occur at or above 30,000 feet.
In-flight turbulence is often unavoidable; your preparation for it and your adherence to flight crew instructions is key – not only to your enjoyment of the flight but, more importantly, to avoiding an in-flight injury.
Have a safe flight!!