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FAA statistics show that 98 percent of the reported injuries were sustained by passengers who were not wearing seatbelts.  A majority of these injuries occurred to passengers who were not wearing their seat belts despite the seat belt sign being illuminated.  Turbulence is often associated with convective storm systems which can be seen by pilots or detected by radar, and hence enough warning time often exists for the flight crew to instruct passengers and cabin crew to be seated or to divert the aircraft around the suspected turbulent regions.  Approaches to reducing injuries associated with non-compliance to the seat belt sign are being handled through modified operating procedures and public education.  For example, in June 1995 the FAA issued a public advisory urging the use of seat belts at all times when seated and started a public education initiative to inform the flying public of the importance of wearing seat belts when turbulence was expected [http://www.faa.gov/apa/TURB/TURBHOME/Frturb.htm].  Many airlines also strictly enforce compliance to the seat belt sign.
However, approximately a third of the injuries occurred because of CAT for which there are few visible warning signs and hence not enough time to even instruct passengers and flight attendants to get safely seated.  In the current operational environment, CAT is not directly measured and forecasts are unreliable.  Hence, the main ways of avoiding CAT are to heed recent pilot reports (PIREPs) of CAT exposure by avoiding the region from which the reports originated.  Although this reduces the number of aircraft potentially exposed to the turbulence, a reporting aircraft still experiences the turbulence without warning and there is no visible evidence to indicate when the CAT has disappeared.  Because of this strategy, large numbers of aircraft may be diverted away from the region unnecessarily, adding to controller and pilot workload and reducing the efficiency of the airspace.
To address these problems, several efforts are under way to improve the remote sensing of CAT.  A promising technology involves developing airborne remote sensing systems to provide flight crew with warnings of the presence and severity of CAT.  Current technology employs sophisticated laser-based systems such as LIght Detection And Ranging (LIDAR), which detect aerosols affected by CAT using the principles shown in Figure III-1, and then warn the flight crew via a cockpit display.
 

 
(Source: NASA)
Figure III-1  Detection of Clear-Air Turbulence Using Lasers
 
Depending on the amount of advance warning afforded by a CAT sensor, the flight crew could respond in a number of ways.  If the warning time is too short, there may not be enough time to get passengers or cabin crew seated and therefore the situation may not be helped by the presence of the sensor.  With somewhat longer warning times, passengers and cabin crew could be seated before encountering CAT, thereby reducing the number of unrestrained people experiencing dangerous CAT relative to the no-sensor case.  With still longer warning times, the flight crew could divert around a region of CAT, avoiding potential injury and ride discomfort but adding to workload, fuel burn, and flight time, thus potentially reducing overall system efficiency.
Clearly, the mitigation of the impact of CAT is a pressing safety issue which also has a direct impact on system-wide operation, whether as a result of diversions due to the presence of injured parties after exposure or due to requested diversions to avoid exposure.  Determination of the required sensor characteristics to enable pilots to be warned of the presence of CAT with sufficient time to be effective is therefore an important area of research.  For these reasons, plus the need to model significant pilot/controller interactions, a CAT scenario was chosen to act as a focus for the simulation study.  The effect of sensors with various look-ahead times was chosen as the primary independent variable of interest with the intent of providing useful safety and efficiency measures to the CAT sensor development programs being undertaken by NASA and others.
　
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