General aviation accidents decreased by 3 percent from the 1,908 accidents reported in calendar year 1996. Chart 1 shows a downward trend in the number of aircraft accidents since 1978. The overall accident rate decreased from 1996 to 1997, from 7.67 to 7.26 accidents per 100,000 hours flown. In-flight air quality has caused concern for pilots, flight attendants and passengers who fear that recirculated air may contribute to illness. Air is replaced 20 to 30 times an hour in modern jets.
Air then passes through cooling packs to a mixing chamber.
The recirculated air has passed through high efficiency air filters similar to those used in hospitals and is essentially sterile. This overhead air distribution network runs the length of the cabin. Air is then exhausted through return air grilles. About half of the air will exit the plane, and the other half will be reprocessed to sterile conditions. In-Flight Illnesses Being packed like sardines on some flights, travelers are exposed to more illnesses, especially so during the cold and flu season.