a For air carriers, the data were dampened, or smoothed, to reduce the month-to-month fluctuations. This dampening was performed using an exponential smoothing model, with a weight of 0.95. Departure data, and hence the denominator of the rates, are not strictly comparable between pre- and post- 1977 eras.
For large air carriers, fatalities resulting from the Sept. 11, 2001, terrorist attacks include only those persons onboard aircraft.
Source: Various sources, as cited in USDOT, Bureau of Transportation Statistics, National Transportation Statistics 2002 (Washington, DC: 2002).