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.

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