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Statistical Methods
Data for all statistics were obtained from the Federal Aviation
Administration, the NTSB, and the U.S. Department of Transportation.
Since some airlines fly much more often than others, a raw count of
accidents, incidents, and near mid-air collisions would not give an
accurate picture of how safe one airline is compared to another.
Therefore all statistics are reported as a number per
1,000,000 takeoffs. For example, if an airline flew
5,000,000 takeoffs during the year and had 10 accidents it would be
reported as having 2 accidents per 1,000,000 takeoffs. Again,
if another airline flew only 500,000 takeoffs during the same year
and had the same number of accidents (10 accidents) they would be
reported as having 20 accidents per 1,000,000 takeoffs.
Clearly the second airline is less safe than the first (even though
they both had the same number of accidents during the year).
The limitation on the
timeliness of the data provided in the tables is due to the fact
that it may take several months for an aviation event to be
recorded in the government's databases. Reliable data will
therefore be several months old.
The NTSB classifies an
"Aircraft accident" as "an occurrence associated with the
operation of an aircraft which takes place between the time any
person boards the aircraft with the intention of flight and all
such persons have disembarked, and in which any person suffers
death or serious injury, or in which the aircraft receives
substantial damage." An "Incident" is defined by the NTSB
as "an occurrence other than an accident, associated with the
operation of an aircraft, which affects or could affect the
safety of operations."
A "Near Mid-Air Collision" is defined as "an
incident associated with the operation of an aircraft in which a
possibility of a collision occurs as a result of proximity of
less than 500 feet to another aircraft, or a report is received
from a pilot or flight crew member stating that a collision
hazard existed between two or more aircraft."
An important thing to keep in
mind when interpreting the statistics is that the level of
variation between airlines will generally increase as the actual
number of flights becomes lower. For example, you will
notice that the variation among airlines is greater in the "One
Year Average" table than it is in the "Five Year Average" table.
This is because each airline flew more flights during five years
than it did during any particular year. During longer
periods of time the numbers tend to settle down to a more narrow
range in values. For this reason, it is best to not
directly compare the numbers in the Five Year table to the
numbers in the One Year table; rather you should compare
airlines to each other
within the Five Year table and then compare those same
airlines to each other within the One Year table.
This will give you a more accurate picture of an airline's
safety history. It's also important to remember that the
accuracy of the data reported in these tables can only be as
good as the accuracy of the data reported by the Federal
government. If there are errors in the data provided by
the FAA, NTSB, or the U.S. Department of Transportation, those
errors will be reflected in our tables as well.
Reference
in this web site to any specific commercial products, processes,
or services, or the use of any trade, firm or corporation name,
is for the information of the public, and in no manner
constitutes endorsement or recommendation by Airline-Safety-Records.com.
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