2008 Nall Report - Aircraft Owners and Pilots Association

2008 NALL REPORT
*Includes dusk.
Light and Weather Conditions
Conditions All Accidents Fatal Accidents
Day VMC 1202 (86.8%) 168 (66.7%)
Night VMC* 112 (8.1%) 31 (12.3%)
Day IMC 44 (3.2%) 36 (14.3%)
Night IMC* 24 (1.7%) 17 (6.7%)
Not reported 3 (0.2%) 0
Figure 19
Flight Conditions
Flights conducted at night and/or in adverse weather
are more challenging than daytime and/or VMC
operations. In spite of this, far more accidents occurred
during the day than at night (1,246 vs. 136),
and far more occurred in VMC than IMC (1,314 vs.
68). Some of this seems likely to reflect underlying
patterns of aircraft use. However, changes in the
FAA’s methods for measuring overall exposure to
each of these conditions led to estimates for 2007
that differ dramatically from those for previous
years. The ASF’s estimation of accident rates within
light and weather categories has been postponed
pending resolution of this discrepancy. Figure 19
depicts 2007 accident data sorted by day vs. night
and VMC vs. IMC.
Though the total numbers are lower, accidents at
night are more than twice as likely to be deadly as
those during daylight. Those occurring in IMC increase
the chances of fatality by a factor of five. Only
16.4 percent of daytime accidents resulted in fatalities,
but over one-third (35.3 percent) of all night
accidents were fatal. Though only 15.1 percent of accidents
in VMC were fatal, more than three-quarters
of those in IMC (77.9 percent) claimed a life.
Looking at the combined factors, day VMC accidents
had the lowest fatal accident rate of any
light/weather condition, with 14.0 percent resulting
in death. Fatal accidents made up 81.8 percent of
those that occurred in day IMC. At night, just over
one-fourth of the accidents in VMC conditions
were fatal (27.7 percent) compared to nearly threequarters
of those in IMC (70.8 percent).
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